i

Fabrication of Biomaterials for orthopedic applications

Doctor of Philosophy

in

PHYSICS

by

Muhammad Ahsan Shafique

2012-PhD-Phy-33

DEPARTMENT OF PHYSICS

GC UNIVERSITY LAHORE

ii

Fabrication of Biomaterials for orthopedic applications

Submitted to GC University Lahore

In partial fulfillment the requirements

For the award of

DOCTOR OF PHILISOPHY

In

PHYSICS

by

Muhammad Ahsan Shafique

2012-PhD-Phy-33

DEPARTMENT OF PHYSICS

GC UNIVERSITY LAHORE

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Dedication

Dedicated to one of my favorite verse "My Lord!

Enrich me with knowledge...” (Quran, 20:114)

and

To the tolerance and consistent support of all my

teachers, family members and supervisor.

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Acknowledgement

“Sufficient for us is Allah, and he is the best disposer of affairs” Quran 3:173

All the praise and glory to God, for whom nothing is hard.

“There is no beauty better than the intellect”

Prophet Muhammad (PBUH)

I would like to express my deep gratitude to the kind and humble Prof. Dr. Riaz

Ahmad, as a supervisor, he gave me the opportunity to think out of the box for my

projects and different experiments, I am particularly thankful for his guidance regarding

my academic writing skill.

I am thankful to all my lab fellows Dr. G Murtaza, MrAtharNaeem, MrShahzadSaadat,

Mr Muhammad Shahnawaz and Mr. Muhammad Khalil for their support and

coordination regarding the experimentation in accelerator lab, they were always ready to

help. I must acknowledge the tolerance and patience of my family because they had

difficulties due to my busy schedule during PhD studies.

Last but not least I would like to acknowledge the financial support of HEC Pakistan and

the office of research of innovation (ORIC) GC University Lahore, for the financial

support.

Muhammad Ahsan Shafique

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Abstract

The surface properties of functional materials are often more important than the bulk

properties because of its varied applications. In case of biomaterials, the surface

properties become even more important because the surfaces of biomaterials are either in

close contact with the body or the surfaces are exposed to an in-vivo biological system.

Therefore it is highly desirable to tailor the surface properties of currently used and

potential candidate biomaterials. Surface properties of metallic biomaterials are improved

using two techniques; ion implantation by 2MV pelletron accelerator and by plasma

focus system. The experiments based upon ion implantation are presented in this

thesis. Currently Stainless steel and nearly equiatomic nickel-titanium alloy are selected

to study different mechanical and biomedical properties after ion implantation. Stainless

steel samples are selected to investigate for corrosion properties, hardness,

hydroxyapatite growth and cell viability likewise nickel-titanium alloy samples are tested

for toxic ion releases in the simulated body fluid, corrosion potential and hardness.

Stainless steel 306 is implanted with various doses of nitrogen ions using a 2MV

pelletron accelerator for the improvement of its biomedical surface properties biomedical.

Raman spectroscopy reveals incubation of hydroxyapatite (HA) on all the samples and it

is found that the growth of incubated HA is greater in higher ion dose samples. SEM

profiles depict uniform growth and greater spread of HA with higher ion implantation.

Human oral fibroblast response is also found consistent with Raman spectroscopy and

SEM results; the cell viability is found the maximum in the samples treated with the

highest (more than 300%) dose. XRD profiles signified greater peak intensity of HA with

ion implantation; a contact angle study revealed the hydrophilic behavior of all the

samples but the treated samples were found to be lesser hydrophilic compared to the

control samples. Nitrogen implantation yields greater bioactivity, improved surface

affinity for HA incubation and improved hardness of the surface.

The effect of hydrogen ion implantation on surface wettability and biocompatibility of

stainless steel is investigated. Hydrogen ions are implanted in the near-surface of

stainless steel to facilitate hydrogen bonding at different doses with constant energy of

500 KeV, which consequently improve the surface wettability. Treated and untreated

x

sample are characterized for surface wettability, incubation of hydroxyapatite and cell

viability. Contact angle (CA) study reveals that surface wettability increases with

increasing H-ion dose. Raman spectroscopy shows that precipitation of hydroxyapatite

over the surface increase with increasing dose of H-ions. Cell viability study using MTT

assay describes improved cell viability in treated samples as compared to the untreated

sample. It is found that low dose of H-ions is more effective for cell proliferation and the

cell count decreases with increasing ion dose. Our study demonstrates that H ion

implantation improves the surface wettability and biocompatibility of stainless steel.

Carbon ions are implanted on nickel titanium alloy (nitinol) and nickel ion release is

investigated along with affinity of calcium phosphate precipitation on nickel titanium

alloy. Four annealed samples are chosen for the present study; three samples with

oxidation layer and the fourth without oxidation layer. X-ray diffraction (XRD) spectra

reveal amorphization with ion implantation. Proton-induced X-ray emission (PIXE) result

shows an insignificant increase in Ni release in simulated body fluid (SBF) and calcium

phosphate precipitation up to 8 × 1013 ions/cm2. Then Nickel contents show a sharp

increase for greater ion doses. Corrosion potential decreases by increasing the dose but all

the samples passivate after the same interval of time and at the same level of VSCE in

Ringer lactate solution. The hardness of samples initially increases at a greater rate (up to

8 × 1013 ions/cm2 and then increases with the lesser rate. It is found that 8 ×

1013 ions/cm2 (≈1014) is a safer limit of implantation on nickel titanium alloy; this limit

gives us lesser ion release, better hardness and reasonable hydroxyapatite incubation

affinity.

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Table of Contents

Chapter 1 ............................................................................................................................. 2

Introduction ......................................................................................................................... 2

1.1 Synthetic Biomaterials .................................................................................................. 3

1.2 Metallic biomaterial ...................................................................................................... 4

1.2.1 Biodegradable metals ................................................................................................. 5

1.3 Biomedical properties of materials ............................................................................... 6

Mechanical Properties ......................................................................................................... 7

1.4 Biomaterial market........................................................................................................ 8

1.5 Three generations of biomaterials ................................................................................. 9

1.6 ASTM standard for materials...................................................................................... 10

1.7 Introduction to particle Accelerators .......................................................................... 10

1.71 Electrostatic Accelerators ......................................................................................... 11

1.8 Ion implantation using accelerator .............................................................................. 13

1.9 The motivation of this thesis ....................................................................................... 14

Thesis layout ..................................................................................................................... 15

References ......................................................................................................................... 17

2 Literature Review....................................................................................................................... 20

2.1 Surface modification by ion implantation using particle accelerator ..................................... 22

2.2 Surface modification by Plasma ................................................................................. 22

2.3 Stainless steel surface treatment for biomedical application. ..................................... 23

2.5 Processing of magnesium and magnesium alloys for biomedical applications. ......... 28

References ......................................................................................................................... 31

Chapter 3 ........................................................................................................................... 35

Experimental details and characterization techniques ...................................................... 35

3. Introduction to pelletron Accelerator ............................................................................ 35

3.1 Working principle of Pelletron accelerator ................................................................. 35

3.2. Working and different parts of Pelletron accelerator ................................................. 35

3.3Characterization techniques ......................................................................................... 43

3.3.1 X-ray diffractometer (XRD) .................................................................................... 44

3.3.2Scanning electron microscope (SEM) ...................................................................... 46

3.3.3Raman spectroscopy ................................................................................................. 49

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3.3.4Biocompatibility study .............................................................................................. 51

3.3.5 Bioactivity study ...................................................................................................... 52

3.4 Stopping range of ions in matter (SRIM) ................................................................... 53

Sample preparation ........................................................................................................... 56

References ......................................................................................................................... 57

Chapter 4 ....................................................................................................................................... 58

Results and Discussions .................................................................................................... 58

Ion implantation in stainless steel and nitinol ................................................................... 58

4.1 Effect of nitrogen ion implantation in stainless steel .................................................. 59

4.1.2 Earlier work ............................................................................................................. 60

4.1.3 Nitrogen Ion implantation ........................................................................................ 61

4.1.4 Immersion in simulated body fluid .......................................................................... 63

4.1.5 Results and Discussions ....................................................................................................... 63

4.1.5.1 Raman Spectroscopy profiles ........................................................................................... 63

4.1.5.2 XRD studies ...................................................................................................................... 65

4.1.5.2.1 Estimation of range of ions in material lattice (SRIM study) ............................ 66

4.1.5.3 SEM Results.......................................................................................................... 67

4.1.5.4 in- vitro Cell Viability Studies .............................................................................. 69

4.1.5.5 Contact Angle studies ........................................................................................... 71

4.1.5.6 Hardness Results ............................................................................................................... 72

4.2 Effect of Hydrogen ion implantation in stainless steel ............................................... 73

4.2.1 Introduction .............................................................................................................. 73

4.2.2 Ion implantation. ...................................................................................................... 74

4.2.3 Immersion in simulated body fluid .......................................................................... 74

4.2.4 Results and Discussions ........................................................................................... 75

4.2.4.1 Contact Angle Studies........................................................................................... 75

4.2.4.2 Raman Spectroscopy ............................................................................................. 76

4.2.4.3 Mass of incubated species ..................................................................................... 77

4.2.4.4 in- vitro Cell Viability Studies .............................................................................. 79

4.4 Effect of carbon ion implantation in nitinol lattice ................................................................. 80

4.4.2 Ion implantation and heat treatment of samples. ................................................................. 81

4.4.2.1 Immersion of samples in SBF and Sample Preparation for PIXE Analysis ..................... 82

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4.4.3 Results and Discussion ........................................................................................................ 82

4.4.3.1 XRD Analysis ................................................................................................................... 82

4.4.3.2 FTIR Analysis ................................................................................................................... 83

4.4. 3.3 PIXE Analysis .................................................................................................................. 83

4.4. 3.4 Corrosion potential and passivation time ............................................................. 85

4.4.3.5 Hardness Test ........................................................................................................ 87

Refrences........................................................................................................................... 88

Chapter 5 ........................................................................................................................... 93

5. Conclusion and future work .......................................................................................... 93

5.1 Conclusions ............................................................................................................................. 93

5.2 Future work ................................................................................................................. 94

List of Publications ........................................................................................................... 95

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2

Chapter 1

Introduction

Material science is a versatile field of research which actively caters the needs of almost

all fields of applied sciences such as spintronics, optoelectronics, mining, petroleum,

water purification, renewable energy automobile etc. The biomaterial research is an

important field of science. 100 years before Lane (1895) laid the foundation of this

discipline when he introduced metal plate inside the body for bone fracture fixation. The

biomaterials are such materials which come in close contact with body i.e. contact lenses

and dental implants etc. or the materials which are implanted inside the body to assist

and/or to repair a body organ i.e. heart valve, cardiovascular stents, pacemakers, hip and

knee prostheses etc. are formally known as biomaterials.

American National Institute of Health presented the most acceptable definition of

biomaterials which defines biomaterial as “any substance or combination of substances,

other than drugs, synthetic or natural in origin, which can be used for any period of time,

which augments or replaces partially or totally any tissue, organ or function of the body,

in order to maintain or improve the quality of life of the individual’’.

There are some essential requirements for biomaterials

Ideal biomaterial must possess appropriate stability

Ideal biomaterial must be compatible with tissue or organ of body

Ideal biomaterial should not trigger any unwanted body response

Ideal biomaterial must have set of suitable mechanical properties (strength,

tensile)

Ideal biomaterial must have high wear resistance

Biomaterials are broadly classified into two main types:

Natural biomaterials

Synthetic biomaterials

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Naturally, derived biomaterials include cellulose, chitin/chitosan, glucose

(polysaccharides based) and collagen, gelatin, silk (Protein based). The synthetic

biomaterials include metals, alloys, ceramics and polymers. There are some advantages

and disadvantages associated with each class of biomaterial.

1.1 Synthetic Biomaterials

Natural biomaterials are biologically recognized by the body and the introduction of these

materials inside the body does not trigger any unwanted biological response, while

synthetic biomaterial has some drawbacks: their structure, composition and mechanical

properties are not similar to the biological system. The synthetic biomaterials when

applied in-vivo are stranger to body therefore body immune system responses to these

materials which create complications. Metallic biomaterials corrode in-vivo and release

toxic ion e.g. Ni, Cr, etc.

Synthetics biomaterials do have benefits such as strength and durability. The synthetic

biomaterials are easy to manufacture and these materials can be given a desired shape.

Each type of synthetic biomaterial possesses its specific advantages and disadvantages.

Natural biomaterial

cellulose, chitin/chitosan,

glucose,collagen, gelatin, silk , etc.

biocompatible, does not trigger immune

responce, not hostile to body

synthetic biomaterials

metals, alloys, ceramics and

polymers

strong, resistant to fatigue, easy to

manufacture,can be stirlize easily

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1.2 Metallic biomaterial

Several medical purposes are being served with metallic materials e.g. titanium and

stainless steel has been used in cardiovascular stent fabrication and orthopedic implant

applications. Nickel-titanium shape memory alloy for orthodontics and stent applications.

Cobalt chromium and platinum chromium are also being utilized for stent applications

because of their strength. Some specific properties and applications of different are

described below [1].

Stainless steel

Stainless steel has been used during last few decades in orthopedics as bone implant, in

orthodontics as braces and as cardiovascular stent. Stainless steel is useful biomaterial

because of its supporting properties like biocompatibility, cost effectiveness, corrosion

resistance and suitable mechanical properties. But the mismatch of mechanical properties

with bone give rise stress shielding effect, release of carcinogenic ion i.e. Ni and Cr from

the surface of stainless steel into blood plasma and high density (greater mass to volume

ratio) hinders the use of stainless steel as perfect material [2, 3].

Nickel titanium Alloy

Nitinol is an alloy having a nearly equal atomic ratio of Ni and Ti elements

(approximately 50 each). This alloy contains wonder properties like shape memory

effect and super elasticity also the elastic modulus of nitinol is nearly equal to the elastic

modulus of human bone. The mentioned thee properties makes nitinol an exceptional

material to make novel surgical implants [4, 5]. Currently, nitinol is being used in

orthopedics for bone fixation, in orthodontics for teeth alignment and in cardiology for

stent application. Along with mentioned advantages, the higher Ni content makes this

material somehow less biocompatible.

Titanium

Titanium metal is very important biomedical material, some of its relevant supporting

properties are given below:

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Titanium metal is low density, biocompatible, good corrosion resistance, and suitable

mechanical properties and has a high strength to weight ratio. The fact that the

mechanical properties of titanium are similar to bone makes titanium a natural choice for

orthopedic implant application. Titanium and its alloys used in hard tissue replacement,

in dental implants, in artificial bone joints [6, 7].

Cobalt Chromium Alloy

Cobalt chromium is an important biomedical material. High corrosion resistance,

biocompatibility and formation of a passive film over the surface make this material a

promising candidate for biomedical application. Cobalt chromium alloy has mechanical

properties similar to that of stainless steel. This material is being widely used in dental

and orthopedic implant applications. Cobalt chromium alloy is also being employed for

cardiovascular stent application [8, 9].

1.2.1 Biodegradable metals

The biomedical implants are often needed inside the human body for a specific period

time, from six months to 12 months, after the healing the implant materials are no more

needed by the body, therefore a second surgery is needed to remove these materials from

the body. Biodegradable stents and orthopedic implants are being studied which could

leave the body after the healing of affected body part so that the second surgery may be

prevented. Iron and manganese are the biodegradable metallic materials, they are

biocompatible and possess excellent mechanical properties. Both the metals are tested in

the lab for degradation and other properties however magnesium showed rapid

degradation rate, rapid enough to degrade before sufficient healing while biodegradability

of iron is too slow. Researcher are making alloys of these metals with other elements to

tailor degradation rate of these metals [10-12].

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1.3 Biomedical properties of materials

The candidate material for biomedical applications should have an appropriate set of

mechanical and biomedical properties [13-15], some key properties of a candidate

biomaterial must possess are explained below.

Biocompatibility

Property of a biomaterial being compatible with the biological system. A biocompatible

material does not produce any toxicity and does not trigger an immunological response of

the biological system. According to ASTM (American Society for Testing and

Materials), definition biocompatibility is “Comparison of the tissue response produced

through the close association of the implanted candidate material to its implant site within

the host animal to that tissue response recognized and established as suitable with control

materials”

Corrosion resistance

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The resistance of a material to withstand unwanted chemical reaction with surrounding

elements, the reaction cause leakage of atoms from the material surface. Corrosion is the

loss of atom from the metal surface due to chemical reaction with an environment.

There are various types of corrosion

The electrochemical corrosion is the most common form of corrosion, this type of

corrosion occurs when electron transfers from surface atom to an electron acceptor

species through an electrolyte. Corrosion from localized depassivated small pits or

cavities is called, this is one of the most damaging form of corrosion.

When two metal are brought into electrical contact then one metal corrode faster than the

second one preferentially this type of corrosion is called galvanic corrosion.

Mechanical Properties

Hardness is an important mechanical property of a material, hardness can be defined as

the ability of a solid material to retain its shape against permanent shape changing or

deforming forces. There are various methods to measure the hardness e.g. Rockwell

Hardness Test, Brinell hardness Test and Vickers Hardness Test. Ductility is the ability

of a material to undergo permanent change i.e. elongation or bending without breaking.

The maximum amount of stress produced in a material just before plastic deformation or

this is the stress at which some plastic deformation is produced in a material. The

maximum pulling or stretching force which a material can bear before failure, in other

words, the ability of a material to resist failure under tensile stress. The ratio of applied

force to a material to resulting strain within elastic limit is called modulus of elasticity

Surface wettability

The surface wettability an important biomedical property, according to some reports cell

viability of a material is closely interconnected to surface wettability

(hydrophilicity). The tendency of a material surface to adhere a liquid is called surface

wettability. The drop of a liquid spread over the surface of wetting material while liquid

drop tends to have a spherical shape on the surface of a non-wetting material. Wettability

of a surface is usually measured by the contact angle of a liquid drop with the surface.

8

Lesser the contact angle greater is the wettability or in case of water drop word,

hydrophobicity is used. The contact angle is usually measured by different methods.

The static sessile drop method

The dynamic sessile drop method

The pendant drop method

The Wilhelmy balance method

The degree of Irregularity in the topography of a material is called surface roughness, or

surface roughness may be defined as “deviation in the direction of the normal vector of a

real surface from its normal form”. The surface roughness is also an important parameter

that sometimes determines the surface wettability and cell viability[16].

1.4 Biomaterial market

The global market for the biomaterials is growing very fast, due to the fact that almost all

the sections of biomedical sciences are looking for artificial material and/or devices for

the treatment of different disorders. It is estimated that the global market of biomaterial

will reach the value of $139 billion by 2022. It is predicted by some reports that the

metallic material contributes a momentous volume in future biomaterial market. Today a

large number of different biomaterials are being used, the number of different

biomaterials used per year is listed below:

The people of America are the big user of biomaterials, more than 50% of total produced

biomaterials are being used in the USA, then Germany, Japan and other parts of the

world. From given data it is clear that rich countries are proportionally big users of

biomaterial while economically developing countries share a relatively smaller portion of

biomaterial, therefore low cost and medically safer biomaterial are desired so low-income

group people can have equal advantages of biomaterials.

Table 1. Biomaterial being use per year.

Sr.No Type of Biomaterial Used per year

1. Catheters 300,000,000

2. Contact lenses 75,000,000

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3. Cardiovascular stents 2,000,000

4. Renal dialyzer 25,000,000

5. Hip and knee prosthesis 1.000,000

6. Dental implants 500,000

7. Intra ocular lenses 7,000,000

8. Heart valve 200,000

1.5 Three generations of biomaterials

First generation biomaterials

Biomaterial researchers were rather much contained initially as they were after simpler

requirements for biomedical applications. The goal of first generation biomaterial

research was to develop biomaterial having suitable physical and chemical properties

with the minimal toxic response of host body, it was desired as well that biomaterials

should not interact with a biological system. Therefore biologically inert materials were

chosen for the fabrication of first generation biomaterials in order to prevent the immune

response to foreign implanted material and leaked toxic ions from implant surface. By the

end of 1980, the researchers were able to develop more than 50 materials for implant

prosthesis from 40 different materials

Titanium and its alloys, stainless steel, cobalt-chromium are the examples of first

generation metallic biomaterials while the polymers and ceramic materials were Alumina

Al2O3, Zirconia ZrO2, silicone and acrylic resins etc.

Second generation biomaterials

First generation biomaterials were prohibited to interact with the biological system while

in second generation biomaterials the term bioactivity was introduced, bioactivity refers

to the ability of a biomaterial to interact with the biological system to improve body

response without triggering the immune system. Metallic materials are not biomaterial

but researchers opted two approaches to fabricate bioactive biomaterials, both the

methodologies depend upon surface modification of materials, the first approach relies

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upon coating of substrate material with bioactive ceramic material e.g. hydroxyapatite,

bio-glass while the second approach is to chemically modify the material surface to make

the material bioactive.

Examples of second generation biomaterials include ceramic (calcium phosphate,

bioglass, glass ceramics), polymers (polyglycolide, polylactide).

Third generation biomaterials

Currently, third generation biomedical materials are being considered: these materials are

being designed to stimulate a specific cellular response, the concept of bioactivity and

resorbability is converged. Researchers are trying to have both the properties in a

material, bioactive materials are being made resorbable and resorbable materials are

being made bioactive.

Some porous metallic and nonmetallic structures, artificial skin, some resorbable bone

repair cements etc. are the examples of third generation biomaterials [17, 18].

1.6 ASTM standard for materials

ASTM stands for American society for testing and materials. ASTM International is an

organization that develops and publish technical standards for a variety of materials,

systems and products. Moreover, ASTM provides protocols for different procedures, the

purpose is to provide a compendium for a particular method. ASTM does not enforce the

compliance of standards however the standards become mandatory when referenced by

some agency or government. ASTM standards have been adopted in many states of USA,

other governments also refer the ASTM standards. ASTM international was founded

in1898. The headquarter is situated in Pennsylvania, Philadelphia, USA. More than

12000 standards of ASTM operate worldwide.

1.7 Introduction to particle Accelerators

A particle accelerator is a device which accelerates charged particle to high energy, the

charged particles may be elementary particle electron, proton or ions of different

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elements e.g. Cu, Fe, Au etc. the energy that a particle accelerator imparts to charged

particles ranges from few KeV to 100s of GeV or TeV.

Accelerators accelerates the charged particles between two electrodes which are at

different potential

Particle accelerators are divided into two basic types:

Electrostatic Accelerator

Electromagnetic Accelerator/ electrodynamic Accelerators (oscillating field

accelerators)

1.71 Electrostatic Accelerators

Electrostatic accelerators are simpler in design as compare to oscillating field

accelerators, the first electrostatic accelerator was realized by Ernest Walton and John

Cockcroft. Electrostatic accelerators use the principle of electrostatic attraction and

repulsion to accelerate charged particles. The charged particles are accelerated in an

evacuated tube or high gas pressure tank between two oppositely charged plates. These

are the initial accelerator manufactured however these accelerators are still very popular

for low energy acceleration requirements because of their simple working principle and

design.

The main disadvantages of an electrostatic accelerator are the energy constraints: the

limited number of eVs can be provided to the charged particle with the help of these

accelerators because it is difficult to generate and maintain high electrostatic potential.

There are two types of electrostatic accelerator

I. Cockcroft Walton Accelerator

II. Van de Graaff Accelerator

Cockcroft Walton accelerator is a type of electrostatic linear accelerator, the first nuclear

disintegration was done by Cockcroft Walton accelerator when lithium atom was

bombarded with fast-moving proton:

P + Li 2 He

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Cockcroft Walton Accelerator uses an electrical circuit called voltage doubler circuit

which produces high DC voltage from low AC input voltage.

Van de Graaff accelerator is a type of electrostatic linear particle accelerator. It uses Van

de Graaff generator to develop high accelerating potential difference. The charges are

transported mechanically with the help of a moving belt from one point to other to

develop a high voltage, often two generators are used an in pair to double the applied

voltage, this type of accelerators are known as tandem accelerators.

Fig 1: schematic diagram of Van de graaf generator (source: http://helios.augustana.edu/~dr/203/van-de-

graaff.html)

Electrodynamic accelerators use periodically changing electric field, the changing electric

field imparts extremely high energy to charged particles. Electrodynamic acceleration can

arise from either of two mechanisms: non-resonant magnetic induction or resonant

circuits or cavities excited by oscillating RF fields. Some popular particle accelerators are

mentioned below.

Linac (Linear Accelerator)

The cyclotron

Betatron

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1.8 Ion implantation using accelerator

Ion implantation is a process by which energetic ions of different elements are created,

accelerated and then bombarded on the surface of a target material. The bombarded ions

produce different phenomenon in target lattice [19, 20]. Depending upon the energy of

and nature ions (atomic radius, charge state etc.) of bombarded ions, moreover, the

impact depends upon the nature of target material [21, 22]. The bombarded ions damage

the surface lattice by producing surface roughness, craters and other irregularities [23].

Incident ions cover some distance in target lattice, lose their energy by multiple

phenomena and get implanted. The incident ions sometimes they cross the target depth,

which is called ion irradiation. The incident energetic charged particle undergoes multiple

interactions in target lattice, it transfers energy to target atom and knock it down, the

knocked out atom is called primary knock down atom (PKA). The primary knock down

atom has ample of energy it further knocks down the lattice atoms while passing through

the lattice which are called secondary knock down atoms. In this way the energy of

incident ion gets distributed within a certain region of target lattice called displacement

cascade [24, 25]. The displaced lattice atoms travel through crystal system, collide with

the atoms in their way and displace these atoms from their original sites. The displaced

atoms contain energy they collide further and this is the way a collision cascade is

created. Finally, an equal number of displaced atoms and vacancies are created in the

crystal system. Thus defects are created as a result of ion implantation or irradiation

results if crystal defects, therefore, annealing is needed to restore the crystal

symmetry[26].

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Fig 2: Schematic of ion implantation process (source: Ion implantation Physical encyclopedia by A.M.

Prokhorov. 1990)

Ion implantation has various technological applications e.g. CMOS fabrication,

modification of compounds (TiO2), doping in a semiconducting material, surface

modification of materials and many more. The surface modification by ion implantation

is a useful phenomenon in material science. Surface amorphization, point annealing,

surface hardening surface functionalization by incorporation of implanted ion in the near-

surface region of a materials etc. are the examples of surface modification. The implanted

ion changes the chemical, electrical and mechanical properties of target material[27].

1.9 The motivation of this thesis

The aim of this thesis is to improve the biomedical properties of various currently used

biomaterials by accelerated ion implantation in near surface region. There are some

specific important issues with currently used metallic biomaterials which compromise the

safety of that material to be used in-vivo: Nickel titanium alloy (nitinol) is an important

biomedical material, it contains some wonderful mechanical and biomedical properties

18, therefore it is being widely in dentistry as orthodontic arch wires, in orthopedic

surgery as bone implant and in cardiovascular treatments as stent, but nitinol contains

approximately 50% nickel content which is a toxic material. The nickel titanium alloy

15

when implanted inside the body it experiences some chemical interactions with human

blood plasma, the human blood plasma is a corrosive fluid, therefore the toxic nickel ions

are released into blood plasma which consequently causes allergy 19, activates immune

response and some other disorders similar is the case with stainless steel, the stainless

steel also contains a considerable fraction nickel and other toxic ions these issues hinder

the safe use of these materials for in-vivo biomedical applications 20. Therefore the

biomaterial should be stable, the safer use of nitinol and stainless steel requires high

corrosion resistance and some other properties.

Various studies revealed that ion implantation in material lattice enhances the corrosion

resistance [28-30] produce amorphization and some other properties. It was hypothesized

that the chemical interaction of specific implanted ion in the material surface can improve

the bonding between material surface and bone (hydroxyapatite) which will consequently

lead to rapid healing of bone tissue. In first experiment nickel titanium alloy was

bombarded with C+ ions, the ion implanted samples were studied for nickel ion release,

surface amorphization, corrosion potential of prepared samples and incubation of

hydroxyapatite over the surface.

In the second experiment, the stainless steel was implanted with different doses of

nitrogen ions, the prepared samples were characterized for incubation of hydroxyapatite,

surface wettability, hardness and cytocompatibility.

In third experiment, the stainless steel surface was bombarded with different doses of

protons H+, the prepared samples were studied for surface wettability, incubation of

hydroxyapatite, and cytocompatibility.

Thesis layout

The thesis is divided into four chapters. Chapter 1 contains an introduction to

biomaterials, some major types and generations of biomaterials are also introduced.

Moreover, the essential properties of a candidate material are explained. Next sections of

chapter 1 describe the magnitude of the worldwide market of biomaterial and description

of the technique used for material modification.

16

Chapter2 (literature review) describes the current focus of researchers working in the

field biomaterials and related field. The section 2.1 and 2.2 describe different

experiments, their objectives, the techniques used and results of surface modification by

ion implantation and plasma treatment. Section 2.3 and 2.4 reveals the attempts made by

researchers to tailor the properties of stainless steel and nickel titanium alloy using

different techniques. Finally, the last section contains the literature review of

biodegradable magnesium and magnesium based alloys.

The experimental details and characterization techniques are explained in chapter 3. This

chapter describes pelletron accelerator and explains the functions of different parts of a

pelletron accelerator. The second part of chapter 2 describes the principles and working

of different techniques used for characterization.

The first part of chapter 4 explains the associated problems of potential biomaterials and

possible harmful effects of these materials .e. nickel titanium alloy and stainless steel,

when applied in physiological conditions. Section 4.1 reveals the detail of the first

experiment. Effect of nitrogen ion implantation in stainless steel, the experimental

parameters, results of characterization techniques and findings are mentions similarly the

4.2 and 4.3 contain the details of next two experiments.

17

References

[1] Niinomi M. Recent metallic materials for biomedical applications. Metallurgical and

Materials Transactions A 2002;33:477.

[2] Sundgren JE, Bodö P, Lundström I. Auger electron spectroscopic studies of the

interface between human tissue and implants of titanium and stainless steel. Journal of

Colloid and Interface Science 1986;110:9-20.

[3] Eschbachz JADaL. Stainless steel in bone surgery Injury, Int I Care Injured

2000;31:S-D2-4

[4] Ryhanen J, Niemi E, Serlo W, Niemela E, Sandvik P, Pernu H, et al. Biocompatibility

of nickel-titanium shape memory metal and its corrosion behavior in human cell cultures.

Journal of biomedical materials research 1997;35:451-7.

[5] D.J. Wever AGV, M.M. Sanders, J.M. Schakenraad, Horn aJRv. Cytotoxic, allergic

and genotoxic activity of a nickel-titanium alloy Biomoteri0ls

1997;18: 1115-20.

[6] Wen CE, Yamada Y, Shimojima K, Chino Y, Asahina T, Mabuchi M. Processing and

mechanical properties of autogenous titanium implant materials. Journal of Materials

Science: Materials in Medicine 2002;13:397-401.

[7] Long M, Rack HJ. Titanium alloys in total joint replacement—a materials science

perspective. Biomaterials 1998;19:1621-39.

[8] Jacobs JJ, Skipor AK, Doorn PF, Campbell P, Schmalzried TP, Black J, et al. Cobalt

and chromium concentrations in patients with metal on metal total hip replacements.

Clinical orthopaedics and related research 1996:S256-63.

[9] Lucchetti MC, Fratto G, Valeriani F, De Vittori E, Giampaoli S, Papetti P, et al.

Cobalt-chromium alloys in dentistry: An evaluation of metal ion release. The Journal of

Prosthetic Dentistry 2015;114:602-8.

[10] Moravej M, Mantovani D. Biodegradable Metals for Cardiovascular Stent

Application: Interests and New Opportunities. International Journal of Molecular

Sciences 2011;12:4250-70.

[11] Yun Y, Dong Z, Lee N, Liu Y, Xue D, Guo X, et al. Revolutionizing biodegradable

metals. Materials Today 2009;12:22-32.

18

[12] Hermawan H, Dubé D, Mantovani D. Developments in metallic biodegradable

stents. Acta biomaterialia 2010;6:1693-7.

[13] Katti KS. Biomaterials in total joint replacement. Colloids and Surfaces B:

Biointerfaces 2004;39:133-42.

[14] Wang RZ, Cui FZ, Lu HB, Wen HB, Ma CL, Li HD. Synthesis of nanophase

hydroxyapatite/collagen composite. Journal of Materials Science Letters 1995;14:490-2.

[15] Kokubo T, Kim HM, Kawashita M. Novel bioactive materials with different

mechanical properties. Biomaterials 2003;24:2161-75.

[16] Amjed J, Manish K, Seokyoung Y, Jung Heon L, Satomi T, Masaru H, et al. Role of

surface-electrical properties on the cell-viability of carbon thin films grown in

nanodomain morphology. Journal of Physics D: Applied Physics 2016;49:264001.

[17] Navarro M, Michiardi A, Castaño O, Planell JA. Biomaterials in orthopaedics.

Journal of the Royal Society Interface 2008;5:1137-58.

[18] Mousa HM, Tiwari AP, Kim J, Adhikari SP, Park CH, Kim CS. A novel in situ

deposition of hydroxyapatite nanoplates using anodization/hydrothermal process onto

magnesium alloy surface towards third generation biomaterials. Materials Letters

2016;164:144-7.

[19] Wei R, Wilbur PJ, Sampath WS, Williamson DL, Wang L. Effects of Ion

Implantation Conditions on the Tribology of Ferrous Surfaces. Journal of Tribology

1991;113:166-73.

[20] Wahl KJ, Dunn DN, Singer IL. Effects of ion implantation on microstructure,

endurance and wear behavior of IBAD MoS2. Wear 2000;237:1-11.

[21] Pope LE, Picraux ST, Follstaedt DM, Knapp JA, Yost FG. Effect of ion implantation

species on the tribological response of stainless steel surfaces. Journal of Materials for

Energy Systems 1985;7:27-37.

[22] Jin-Liang Z, Zhao-Min L, Zhen-Wen Y, Ye-Ping G, Zue-Teh M, Rui-Zhong B.

Effects of ion implantation on the electrical conductivity of polyaniline. Nuclear

Instruments and Methods in Physics Research Section B: Beam Interactions with

Materials and Atoms 1994;91:469-72.

[23] Krishnan M, Saraswathy S, Sukumaran K, Abraham KM. Effect of ion-implantation

on surface characteristics of nickel titanium and titanium molybdenum alloy arch wires.

19

Indian journal of dental research : official publication of Indian Society for Dental

Research 2013;24:411-7.

[24] Azarov AY, Kucheyev SO, Titov AI, Karaseov PA. Effect of the density of collision

cascades on ion implantation damage in ZnO. Journal of Applied Physics

2007;102:083547.

[25] Porte L, Villeneuve CHd, Phaner M. Scanning tunneling microscopy observation of

local damages induced on graphite surface by ion implantation. Journal of Vacuum

Science & Technology B: Microelectronics and Nanometer Structures Processing,

Measurement, and Phenomena 1991;9:1064-7.

[26]Hamm RWH, Marianne E. Industrial Accelerators and Their Applications. . World

Scientific 2012.

[27] Wilson IH, Zheng NJ, Knipping U, Tsong IST. Effects of isolated atomic collision

cascades on Si interfaces studied by scanning tunneling microscopy. Physical Review B

1988;38:8444-50

20

2 Literature Review

Researchers from various disciplines are struggling to modify the surface of materials

using different methods, the most frequently used method for surface modification is thin

film fabrication, thin film is applied over the surface of a material to serve some

purposes: primarily to protect underlying material from deteriorating hostile environment

or some times to separate one type of material from another type, this type of coating is

called protective coating, other types of coating includes optical coatings: the optical

coatings are used to tailor the interference, reflection of light and some other purposes.

Thin films are also deposited for the photovoltaic cell, for batteries, to induce some

magnetic and electrical properties in a material etc.

Along with film fabrication, ion implantation is also a very important technique for

surface modification of materials. The basic difference between ion implantation and thin

is the number density and energy of implanted ions, generally the number density of

implanted material is much more in case of thin film: therefore thin film covers the whole

surface of substrate while in case of ion implantation the number density is lesser and the

ions are more energetic, in case of ion implantation, the implanted ions penetrate in

substrate lattice, they don’t cover the whole surface, the ions are sprinkled on the surface

of a material.

2.1 Surface modification by ion implantation using particle accelerator

Surface modification of materials using particle accelerator is relatively less famous

technique as compare to some other techniques, although this technique is being used

from many decades for surface engineering[1-3], researchers have been using focused ion

beam for various purposes: Kant et al modified TiN thin film using nitrogen ions, they

found reduced oxygen contamination in N ion implanted coatings as compare to un-

implanted coatings, they also found significantly reduced hardness and ductile behavior

of TiN ion implanted coatings[3, 4]. Ensinger et al demonstrated that ion beam assisted

deposition is appropriate for adherent coating, they also found that these coatings are

suitable for long-term corrosion protection[5]. Natishan et al prepared Mo-Al surface

alloy using accelerated ion implantation and vapor deposition on aluminum substrate,

they studied pitting corrosion resistance in prepared samples, the studies reveal

approximately six time higher pitting potential of ion beam mixed Mo-Al surface alloy

than pure aluminum and ion implanted Mo-Al alloy[6].

Iwaki et al modified the surface of various organic materials by ion implantation: they

used substrates poly-tetra-fluoroethylene (PTFE), Silicone rubber, poly styrene (PS), poly

21

imide (PI), poly acetylene and different kind of protein for ion bombardment or ion

implantation, the substrates were bombarded with inert ions, chemically active ions and

metallic ions. They investigated surface wettability, cell adhesion, and electrical

conductivity of prepared samples, finally, they concluded that surface properties of

organic materials can be tailored by using certain ion implantation or bombardment[7].

Colli et. al. [8] implanted high dose (1015ions/cm2) of Phosphorous and Boron ions in

silicone nano wires (SiNW), they found only limited amount of amorphization and they

recovered fully crystalline structure after annealing as prepared samples at 800 0C, they

concluded the results by Raman spectroscopy and electrical transport properties

measurements.

Chu et.al. [9] studied cobalt implanted ZnO nano wires and heat treated cobalt doped

ZnO nanowires, they found a high degree of structural disorder in implanted samples as

compared to annealed samples using hard X-ray nano probe. They estimated the average

content of cobalt in nanowires using XRF analysis, they concluded structural distortion in

nano wires by ion implantation may affect the performance optoelectronics and

spintronics devices.

Since ion implantation is a versatile technique for a material scientist, it has been used for

diverse purposes, Ghicov et al fabricated TiO2 nano tubes by electrochemical self-

organized oxidation of titanium, and they implanted two doses of nitrogen ions in

prepared samples i.e. 1×1015 ions/cm2 and 1×1016 ions/cm2 . The ions were implanted in

both crystalline and amorphous phases, successful doping was confirmed using XRD,

SEM and photo-electrochemical measurements, they concluded that the crystalline tubes

were amorphized by ion implantation while the amorphous tube lost their morphological

integrity moreover they found decreased photo response in UV range in amorphized

tubes, and N-doping yield strong sub band-gap response[10].

22

2.2 Surface modification by Plasma

Plasma ion implantation is being used frequently to improve surface properties of

metallic, polymers and other materials, plasma film deposition is an effective and

economical method for surface modification. This technique allows depositing a thin film

of various compositions and thickness over different substrates. The deposited thin films

are used for various applications:

Han et al modified the surface of polymers by oxygen implantation, they evaluated the

wetting properties of untreated samples and oxygen implanted surface they found

contrasting results: the surface modified samples showed high degree of hydrophilicity as

compare to untreated samples, they also modified the surface by CF4 implantation: they

found this group of sample highly hydrophobic the contact angles exceeds 100 degrees,

they concluded that plasma ion implantation is highly effective technique for surface

modification [11].

Larisch et al nitrided four grades of stainless steel at different temperatures between

2500C to 5000C, they prepared nitrogen enriched surface layers. The nitrided samples

were found harder as compared to pristine samples, they also concluded that there are no

precipitations of CrN if the samples are treated at low temperature i.e. 4000 C[12].

Suh et al also performed a similar experiment on stainless steel, they carburized the

surface of AISI- 316 stainless steel using CH4/H2 to increase surface hardness. They

analyzed the carburized samples by scanning electron microscopy (SEM), micro hardness

tester, optical microscopy and Auger electronscopy, the hardness in prepared samples

found linearly increasing with carbon content. They divide the carburized surface into

three regions: the near surface named as white zone, they observed elongated carbon

structures and found carbon concentration about 4% by weight, the dark zone had carbon

concentration 1.5 to 4 % by weight and they found fine carbides in this zone, finally the

third one is the core in this zone the carbides were observed only at the grain

boundaries[13].

23

Jamesh et al modified the surface of magnesium alloy ZK-60 by plasma ion implantation

for biomedical application, the purpose of experiment was to tailor the corrosion behavior

of samples, they implanted Zr, O and both Zr and O ions in the surface of magnesium

alloy, the prepared samples were studied by electrochemical impedance spectroscopy

(EIS) after 30 hrs. of immersion. They observed 37 times decrease in corrosion current

(Icorr) and 62 times lesser Rp. they finally concluded that plasma ion implantation is an

effective method for modification of initial corrosion behavior[14].

Hosseni et al studied the corrosion behavior of plasma spray aluminum coated nickel-

titanium alloy (nitinol) modified. They investigated the prepared samples by X-ray

diffraction studies (XRD) and scanning electron microscopy (SEM) to investigate

morphology and microstructure of samples and electrochemical impedance spectroscopy

was used to study corrosion behavior of plasma coated and untreated samples. They

found slightly decreased corrosion resistance but the nickel release in simulated

biological fluid was significantly hindered, they concluded that the stability of coated

samples in simulated biological fluid was enhanced as compare to untreated samples [15]

2.3 Stainless steel surface treatment for biomedical application.

Stainless steel is an important material for various biomedical applications, the

conventional stainless steel alloy has been modified largely for biomedical application

during last few decades: initially, stainless steel contains vanadium but it was replaced

with nickel and chromium then molybdenum was added to reduce carbon content and to

achieve high corrosion resistance[16]. Stainless steel is a low cost, biocompatible and

corrosion resistant material. Typically stents, artificial valves, bone plates, artificial

joints, pins, screws orthodontic wires and any other applications are being catered with

stainless steel, therefore, researchers are working actively to tailor some properties of

stainless steel.

Qin et al fabricated silver nano particles of different sizes and distributions on the surface

of stainless steel by plasma ion immersion implantation (PIII), they treated the samples

for 0.5h and 1.5h respectively. The prepared samples were then evaluated by in-vivo and

24

in-vitro tests, they found enhanced antibacterial activity of stainless steel moreover they

observed improved osteogenic differentiation of human bone marrow stromal cells[17].

Braceras et al selected 316LVM austenitic stainless steel for their study, stainless steel

316 MVM is a potential choice for the temporal musculoskeletal implant. They aimed the

study to improve surface resistance of stainless steel to bacterial colonization, they

implanted 50KeV silicon ions (flounce 2.5-5 ×1016, at angle 45 to 900), and they found

decreased adhesion of bacterial species to the surface of medical grade stainless steel

without compromising the biocompatibility, they also concluded that bacterial adhesion

is dependent on implantation conditions[18].

Corrosion is an important biomedical property, appropriate corrosion resistance and

stability of biomedical implant are crucial for in-vivo application of the material. There

are several studies to improve the corrosion behavior.

Galvan et al also selected surgical stainless steel 316LVM and they implanted same ions

as Braceras et al did, but the aim of the study was different. They aimed the study to

investigate the effect if silicon ion implantation on short-term corrosion resistance and

ion release. They varied three parameters: ion doses, accelerating voltage and angle of

incidence. They carried out corrosion test using electrochemical impedance spectroscopy

(EIS), They demonstrated that at certain value to dose and voltage the corrosion

resistance is enhanced while they found worst contrasting results of corrosion resistance

in higher ion dose samples: they observed corrosion protection at ion dose equal to

1×1016 ions/ cm2 and accelerating voltage 50KV while at 1×1017 ions/ cm2 and

accelerating voltage 80KV they found worst corrosion resistance, they also concluded

that enhanced corrosion resistance yields reduced ion leakage from the surface of surgical

stainless steel [19].

Muthukumaran et al modified the surface of surgical AISI 316L stainless steel by ion

implantation: in their study they implanted 1×10 17 nitrogen and helium ions/ cm2 at

100KeV energy, they studied surface morphology and crystallographic orientations by

SEM and XRD respectively moreover they evaluated the corrosion behavior of fabricated

samples in 0.9% of NaCl solution using electrochemical test, the Tafel scan revealed that

25

the ion implanted samples are more corrosion resistant as compare to virgin samples, they

also observed improved micro hardness by Vickers method by varying load [20].

Zou et al investigated the mechanism of corrosion and wear improvement of stainless

steel 316 L by low energy and high current pulsed electron beam. They used

potentiodynamic polarization analysis and electrochemical impedance spectroscopy to

model the corrosion behavior of prepared samples. They concluded that corrosion

resistance was improved by 3 order of magnitude after sufficient pulses and the wear

resistance was also improved by sub surface work hardening (over 100 micrometer)[21].

Kheirkhah et al coated Nanostructured forsterite (Mg2SiO4) over the surface of AISI

316L stainless steel by the sol gel dip coating method, they utilized X-ray diffraction

(XRD, scanning electron microscope (SEM) and energy dispersive spectroscopy for

structural morphological and elemental composition analysis. Electrochemical corrosion

was studied in simulated body fluid (SBF) finally the in-vitro bioactivity was evaluated

by soaking the prepared samples in SBF. They observed lesser corrosion current density,

which shows improved corrosion resistance, the deposition of Calcium phosphate

products confirmed bioactivity of prepared samples, they concluded that deposition of

nano structured forsterite may be beneficial for dental and orthopedic implant

applications [22].

Shih et al passivated the surface of stainless steel 316L using different techniques for

improved corrosion resistance for, both in-vivo and in-vitro application. They used

different characterization techniques i.e. tunneling electron microscope (TEM), auger

electron spectroscopy (AES), X- ray photoelectron spectroscopy (XPS) and anodic

polarization test, their results showed that only amorphous oxidation improves the results,

all other techniques do not improve corrosion resistance, the author attributed the

improved results to the removal of plastically deformed oxide layer and development of

new layer, the author concluded that the properties of oxide layer determine the in-vitro

stability of prepared sample surfaces rather than the thickness of oxide films [23].

2.4 Surface treatment of nickel titanium alloy (nitinol)

26

Nitinol is nearly equi-atomic, super elastic shape memory alloy, this super elastic alloy of

nickel and titanium is being extensively studied for various biomedical applications,

along with some favorable mechanical properties there are also some potential drawbacks

e.g. toxic nickel ion release from the surface of nitinol is one of the major problems,

researchers are employing different techniques to tailor corrosion and some other related

biomedical properties of nitinol [24].

Gill et al applied magneto-electropolishing technique to alter surface characteristics of

nitinol, i.e. biocompatibility, surface wettability, roughness and corrosion resistance of

nickel titanium alloy, they motivated by the fact that magneto- electropolishing alter the

composition and morphology of surface films, which improves corrosion resistance on

nitinol. They observed improved mechanical properties by addition of alloying element.

Improved corrosion resistance and cell viability was observed by potentiodynamic

polarization test and endothelial cell response in magneto-electropolished samples [25].

Tape et al compared different surface modification approaches. They evaluated heparine,

aluminum and polyurethane coating, they found improved results in polyurethane coated

samples: coagulation and inflammation was improved compared to other designs [26].

Ghaley et al bombarded the surface of nitinol with three different doses of nitrogen ion,

they aimed the study to improve biological properties of alloy while preserving

mechanical properties. The prepared samples were investigated by the small angle x- ray

diffraction study to evaluate newly generated phases on the surface. Electrochemical

impedance spectroscopy and potentiodynamic polarization test in simulated body fluid

were applied to investigate the corrosion behavior of prepared samples, atomic absorption

spectroscopy was applied to estimate nickel ion release in simulated body fluid within the

period of two months. The ion implanted surfaces were also evaluated for cellular

response, the results showed improved cytocompatibility and corrosion protection in

modified samples, they found highest corrosion resistance and lowest nickel ion release

in simulated body fluid by the sample bombarded with 1.4×1018 ions/ cm2[27].

Sun et al utilized cathodic electrophoretic deposition (EPD) to deposit composite films on

the surface of NiTi shape memory alloy, they deposited chitosan-heparin films from the

solution of non-stoichiometric Chitosan–heparin, and they found that addition of anionic

27

heparin to the of chitosan yields a significant increase in film thickness. Their results

showed that ability of chitosan- heparin films to bind antithrombin was enhanced [28].

Poon et al proposed enhanced corrosion properties of Nickel titanium alloy by carbon

plasma immersion ion implantation (PIII), but the release of toxic nickel ions from the

surface of NiTi alloy into human body was a great concern. They deposited amorphous

hydrogenated carbon thin film and implanted carbon ion into NiTi target using plasma

immersion ion implantation and deposition (PIII&D) technique. They analyzed that

deposited carbon thin film has graded carbide interface which strengthens the film

adhesion. They found enhanced corrosion protection in both PIII treated and PIII&D

treated sets of samples. They observe implanted and carbide layer is mechanically

stronger than NiTi substrate, they concluded that PIII&D is an effective technique for

improving corrosion resistance, mechanical properties and cell viability of orthopedic

nickel titanium shape memory alloy[29].

Tan et al used plasma source ion implantation (PSII) technique to improve surface

properties of NiTi shape memory alloy, they implanted different doses of oxygen ions

5×1016, 1×1017 and 3×1017 ions/cm−2. They investigated the pitting and corrosion

behavior of prepared and untreated samples by cyclic potentiodynamic polarization test.

Their results revealed that corrosion resistance depends upon heat treatment and ion

implantation: they found maximum corrosion resistance in the sample implanted with

oxygen ion dose 1×1017ions/cm2 with Af = 21oC. They concluded that oxygen ion

implanted nickel-titanium samples possess better corrosion resistance in Hanks

solution[30].

There are some applications if nitinol other than as implant material: Lee et al assumed

that boron implanted Ni-Ti alloy has potential to develop better nitinol root canal

instrument for outstanding cutting properties, they modified the surface of nitinol with

boron ion beam of energy 110KeV, the ion dose was chosen 4.8×1017ions/cm2. They

found considerably enhanced surface hardness in boron implanted samples as compare to

untreated sample, they concluded that ion implanted nitinol is harder than stainless

steel[31].

28

Corrosion resistance and nickel ion leakage from the surface of nitinol is a matter of great

concern for biomedical applications, therefore a big fraction of researchers working on

nitinol tried to resolve corrosion and ion leakage issues by various methods: Saugo et al

tried anodisation of nickel titanium alloy to hinder ion leakage and to improve in-vivo

corrosion. They found that anodisation process considerably reduce the nickel ion

leakage and this process also enhances the titanium content in the outermost surface as

TiO2, which consequently improve anticorrosion performance in ringer lactate

solution[32].

Flamini et al also attempted to resolve the same problem of stability of nitinol in chloride

containing environment as human blood plasma contain high fraction of chlorine and

other corrosive species: Flemini et al modified the surface of nitinol by self-assembled

alkylsilane compounds (propyltrichlorosilane (C3H7SiCl3) and then the coating of doped

polypyrrole. They observed good adherence between polypyrrole and underlying

alkylsilane film, they concluded that organic coating is promising for anti-corrosive

protective treatment of Ni-Ti shape memory alloy[33].

2.5 Processing of magnesium and magnesium alloys for biomedical

applications.

Magnesium is a wonderful metal for biomedical application owing to excellent

biocompatibility and remarkable mechanical properties, moreover, biodegradability

provides an opportunity to avoid complications of second surgery for the removal of the

implant from the body. The young modulus of permanent implants is approximately 10

times greater than the bone i.e. 100-200 G Pa for permanent implant while 10-30G Pa for

bone, the mismatch of mechanical properties between implant material and adjacent bone

causes serious clinical issues[34]. Rapid biodegradability is one of the major issue

associated with magnesium, different allying and surface modification techniques are

being applied to tailor in-vivo degradation rate of magnesium.

29

Waksman et al planed a study to investigate safety and efficacy of biodegradable

magnesium stents, they randomly deployed magnesium alloy or stainless steel stents in

coronary arteries of domestic and mini pigs, and they sacrificed domestic pigs after two

days (on the third day) or 28 days, mini pigs were sacrificed after three months,

interesting results were obtained: they observed signs of degradation after 28 days, they

found no evidence of stent particle embolization, inflammation or thrombosis, at 28 days

and 3 months they observed significantly less neointimal area in comparison to stainless

steel stent area, they concluded that magnesium alloy stents are safe to use in-vivo [35].

Wang et al investigated degradation of magnesium alloy AZ 31 in simulated body fluid

(SBF) and Hanks solution, they found significantly reduced degradation rate of

magnesium alloy after mechanical processing, they specified that hot rolling yields

improved corrosion protection, while their subsequent treatment does not improve

corrosion resistance further [36].

Lock et al explored the application of magnesium alloy as ureteral stent: they investigated

the affectivity of magnesium and magnesium alloy as antibacterial and biodegradable

ureteral stent, they demonstrated the decreased viability of Escherichia colibacterial and

reduced colony forming units after 3 days of incubation in artificial solution. They

concluded that antibacterial properties coupled with biodegradation in artificial urine

present an alternative approach to design next generation ureteral stents [37].

A coating over the surface of magnesium and its alloys could be promising to reduce the

rate of biodegradation, fluoride coating is a conventional method for magnesium base

materials. Zhang et al treated cardiovascular Mg-Nd-Zn-Zr alloy by immersion in

hydrofluoric acid, they observed the formation of 1.5 micro meter thick layer of

magnesium fluoride after immersion. The surface roughness was increased and zeta

potential was found to shift more negative value, they also found more hydrophilicity

after surface treatment by static contact angle technique. Cell viability investigation

revealed that encouraging results [38].

Another attempt was made to improve corrosion properties of magnesium base material

using coating technique by Gu et al: they deposited silane coating on magnesium alloy by

electrodeposition, the fabricated samples were studied by various techniques i.e. scanning

30

electron microscopy, Fourier transformed infrared spectroscopy, contact angle study and

biocompatibility. They found the coatings deposited at -2.0 volts are more corrosion

resistant in comparison to other silane coatings, moreover the silane coatings produced

significantly increased biocompatibility as tested by cell viability test, reduced hemolysis

rate and platelet adhesion, they concluded that silane coating provides better corrosion

protection and other related biomedical properties [39].

Liu et al also attempted to fabricate corrosion resistant coating over the surface of the

magnesium based material, they fabricated Mg-Mn-Ce coating by simple one-step

electrodeposition method. They employed energy-dispersive X-ray spectroscopy (EDX)

Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR),

and X-ray photoelectron spectroscopy (XPS) techniques were employed to analyze the

surface properties of fabricated samples. The contact angle study revealed maximum

contact angle was 159.8o. Potentiodynamic polarization test and electrochemical

impedance spectroscopy revealed that the prepared surface more corrosion resistant in an

aqueous solution of NaCl, Na2SO4, NaClO3, and NaNO3.The authors concluded that

investigated method is effective rapid and low cost method for industrial fabrication of

super hydrophobic, anti-corrosive surfaces [40].

Another attempt was made to improve corrosion protection of magnesium based alloy as

the rapid corrosion is the major problem associated with orthopedic and cardiovascular

application of magnesium and its alloys. Huo et al applied chemical conversion treatment

and electroless Ni plating to improve corrosion properties of AZ 91D magnesium alloy.

They applied potentiodynamic polarization test to investigate the variation in corrosion

properties of prepared samples, they observed improved corrosion resistance of

magnesium alloy in 3.5 wt% of NaCl solution at pH 7.0, and scanning electron

microscopy indicated porous topographic structures which provide advantage adsorption

prior to electroless nickel coating. They concluded that corrosion resistance of untreated

samples was limited it improved by surface treatment of AZ 91D samples[41].

31

References

[1] B. Y. Tsaur ZLL, and J. W. Mayer. lon-beam-induced silicide formation. Appl Phys

Lett 1979;34:168-70.

[2] Jain IP, Agarwal G. Ion beam induced surface and interface engineering. Surface

Science Reports 2011;66:77-172.

[3] Surface modification of metallic biomaterials. New Mater Jpn 1998;37:853.

[4] Kant RA, Sartwell BD. Ion beam modification of TiN films during vapor deposition.

Materials Science and Engineering 1987;90:357-65.

[5] Ensinger W, Wolf GK. Ion-beam-assisted coatings for corrosion protection studies.

Materials Science and Engineering: A 1989;116:1-14.

[6] Natishan PM, McCafferty E, Hubler GK. Localized corrosion behavior of aluminum

surface alloys produced by ion implantation and ion beam mixing. Materials Science and

Engineering: A 1989;116:41-6.

[7] Iwaki M. Ion surface treatments on organic materials. Nuclear Instruments and

Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

2001;175:368-74.

[8] Colli A, Fasoli A, Ronning C, Pisana S, Piscanec S, Ferrari AC. Ion Beam Doping of

Silicon Nanowires. Nano Letters 2008;8:2188-93.

[9] Chu MH, Martínez-Criado G, Segura-Ruiz J, Geburt S, Ronning C. Local lattice

distortions in single Co-implanted ZnO nanowires. Applied Physics Letters

2013;103:141911.

[10] Ghicov A, Macak JM, Tsuchiya H, Kunze J, Haeublein V, Kleber S, et al. TiO2

nanotube layers: Dose effects during nitrogen doping by ion implantation. Chemical

Physics Letters 2006;419:426-9.

32

[11] Han S, Lee Y, Kim H, Kim G-h, Lee J, Yoon J-H, et al. Polymer surface

modification by plasma source ion implantation. Surface and Coatings Technology

1997;93:261-4.

[12] Larisch B, Brusky U, Spies HJ. Plasma nitriding of stainless steels at low

temperatures. Surface and Coatings Technology 1999;116:205-11.

[13] Suh B-S, Lee W-J. Surface hardening of AISI 316L stainless steel using plasma

carburizing. Thin Solid Films 1997;295:185-92.

[14] Jamesh MI, Wu G, Zhao Y, McKenzie DR, Bilek MMM, Chu PK. Effects of

zirconium and oxygen plasma ion implantation on the corrosion behavior of ZK60 Mg

alloy in simulated body fluids. Corrosion Science 2014;82:7-26.

[15] Hosseini SA, Akbarinia S, Mohammadyani D, Sadrnezhaad SK. Enhanced corrosion

resistance of porous NiTi with plasma sprayed alumina coating. Corrosion Engineering,

Science and Technology 2015;50:595-600.

[16] Jaganathan SK, Supriyanto E, Murugesan S, Balaji A, Asokan MK. Biomaterials in

Cardiovascular Research: Applications and Clinical Implications. BioMed Research

International 2014;2014:11.

[17] Qin H, Cao H, Zhao Y, Jin G, Cheng M, Wang J, et al. Antimicrobial and

Osteogenic Properties of Silver-Ion-Implanted Stainless Steel. ACS Applied Materials &

Interfaces 2015;7:10785-94.

[18] Braceras I, Pacha-Olivenza MA, Calzado-Martín A, Multigner M, Vera C, Broncano

LL, et al. Decrease of Staphylococcal adhesion on surgical stainless steel after Si ion

implantation. Applied Surface Science 2014;310:36-41.

[19] Galván JC, Larrea MT, Braceras I, Multigner M, González-Carrasco JL. In vitro

corrosion behaviour of surgical 316LVM stainless steel modified by Si+ ion implantation

– An electrochemical impedance spectroscopy study. Journal of Alloys and Compounds

2016;676:414-27.

[20] Muthukumaran V, Selladurai V, Nandhakumar S, Senthilkumar M. Experimental

investigation on corrosion and hardness of ion implanted AISI 316L stainless steel.

Materials & Design 2010;31:2813-7.

33

[21] Zou JX, Zhang KM, Hao SZ, Dong C, Grosdidier T. Mechanisms of hardening, wear

and corrosion improvement of 316L stainless steel by low energy high current pulsed

electron beam surface treatment. Thin Solid Films 2010;519:1404-15.

[22] Kheirkhah M, Fathi M, Salimijazi HR, Razavi M. Surface modification of stainless

steel implants using nanostructured forsterite (Mg2SiO4) coating for biomaterial

applications. Surface and Coatings Technology 2015;276:580-6.

[23] Shih C-C, Shih C-M, Su Y-Y, Su LHJ, Chang M-S, Lin S-J. Effect of surface oxide

properties on corrosion resistance of 316L stainless steel for biomedical applications.

Corrosion Science 2004;46:427-41.

[24] Shabalovskaya S, Anderegg J, Van Humbeeck J. Critical overview of Nitinol

surfaces and their modifications for medical applications. Acta Biomaterialia 2008;4:447-

67.

[25] Gill P, Musaramthota V, Munroe N, Datye A, Dua R, Haider W, et al. Surface

modification of Ni–Ti alloys for stent application after magnetoelectropolishing.

Materials Science and Engineering: C 2015;50:37-44.

[26] Tepe G, Schmehl J, P Wendel H, Schaffner S, Heller S, Gianotti M, et al. Reduced

thrombogenicity of nitinol stents—In vitro evaluation of different surface modifications

and coatings. Biomaterials 2006;27:643-50.

[27] Maleki-ghaleh HK-a, J; Sadeghpour-motlagh, M; Shakeri, M S; Masoudfar, S; et al.

Effect of surface modification by nitrogen ion implantation on the electrochemical and

cellular behaviors of super-elastic NiTi shape memory alloy. Journal of Materials Science

: Materials in Medicine; Dec 2014;25:2605-17.

[28] Sun F, Sask KN, Brash JL, Zhitomirsky I. Surface modifications of Nitinol for

biomedical applications. Colloids and Surfaces B: Biointerfaces 2008;67:132-9.

[29] Poon RWY, Yeung KWK, Liu XY, Chu PK, Chung CY, Lu WW, et al. Carbon

plasma immersion ion implantation of nickel–titanium shape memory alloys.

Biomaterials 2005;26:2265-72.

[30] Tan L, Dodd RA, Crone WC. Corrosion and wear-corrosion behavior of NiTi

modified by plasma source ion implantation. Biomaterials 2003;24:3931-9.

[31] Lee D-H, Park B, Saxena A, Serene TP. Enhanced surface hardness by boron

implantation in nitinol alloy. Journal of Endodontics 1996;22:543-6.

34

[32] Saugo M, Flamini DO, Zampieri G, Saidman SB. Corrosion resistance improvement

of nitinol by anodisation in the presence of molybdate ions. Materials Chemistry and

Physics 2017;190:136-45.

[33] Flamini DO, Saidman SB. Corrosion behaviour of Nitinol alloy coated with

alkylsilanes and polypyrrole. Materials Science and Engineering: C 2014;44:317-25.

[34] Guo MSaY. Biodegradable Orthopedic Magnesium-Calcium (MgCa) Alloys,

Processing, and Corrosion Performance. Materials 135-55.

[35] Waksman R, Pakala R, Kuchulakanti PK, Baffour R, Hellinga D, Seabron R, et al.

Safety and efficacy of bioabsorbable magnesium alloy stents in porcine coronary arteries.

Catheterization and Cardiovascular Interventions 2006;68:607-17.

[36] Wang H, Estrin Y, Zúberová Z. Bio-corrosion of a magnesium alloy with different

processing histories. Materials Letters 2008;62:2476-9.

[37] Lock JY, Wyatt E, Upadhyayula S, Whall A, Nuñez V, Vullev VI, et al. Degradation

and antibacterial properties of magnesium alloys in artificial urine for potential

resorbable ureteral stent applications. Journal of Biomedical Materials Research Part A

2014;102:781-92.

[38] Zhang JK, Ni; Niu, Jialin; Shi, Yongjuan; Li, Haiyan. Influence of fluoride treatment

on surface properties, biodegradation and cytocompatibility of Mg-Nd-Zn-Zr alloy.

ournal of Materials Science : Materials in Medicine 2014;25:9.

[39] Gu XN, Guo HM, Wang F, Lu Y, Lin WT, Li J, et al. Degradation, hemolysis, and

cytotoxicity of silane coatings on biodegradable magnesium alloy. Materials Letters

2017;193:266-9.

[40] Liu Q, Chen D, Kang Z. One-Step Electrodeposition Process To Fabricate

Corrosion-Resistant Superhydrophobic Surface on Magnesium Alloy. ACS Applied

Materials & Interfaces 2015;7:1859-67.

[41] Huo H, Li Y, Wang F. Corrosion of AZ91D magnesium alloy with a chemical

conversion coating and electroless nickel layer. Corrosion Science 2004;46:1467-77.

35

Chapter 3

Experimental details and characterization techniques

The experiments are performed using 2MV pelletron accelerator in Accelerator lab,

CASP GC University Lahore, different parameters e.g. energy, nature and charge states

of bombarded ions are chosen for the different experiment. The chosen parameters are

determined by nature of the hypothesized final product and its potential applications.

Sample characterization techniques are also determined by the potential applications and

presumed impact of different ion implantation [1-3]. This chapter contains the details of

the pelletron accelerator, sample preparation, and characterization techniques.

3. Introduction to pelletron Accelerator

Pelletron accelerator is a type of electrostatic accelerator, this type of accelerator is based

upon Van de Graf charging system, and it can have a terminal voltage ranges from

500KV to 25 MV, the corresponding energy of charged particles ranges from few MeV

to several hundred MeV.

3.1 Working principle of Pelletron accelerator

In pelletron accelerator pre accelerated (few KeV) charged particles are further

accelerated to very high energy (several hundred MeV) using an electrostatic field, the

high potential difference between the plates is developed by mechanical transportation of

charges from one plate to another. The charges are transported using chains repetitively

running from one end to other end, the charging belts pick charges from one plate and

accumulate the charges on other. The process does not involve the rubbing but the belt

picks the charges by induction (the detail is discussed in the section of charging system).

3.2. Working and different parts of Pelletron accelerator

The pelletron accelerator is made up of various essential components, some important

components are listed below.

Ion sources

36

Switching magnets

Faraday cups

Accelerating tank

Stripping system

focusing systems

Beam lines

End stations

Ion sources

There are several ion sources being used for production and injection of the ions to

accelerating system of an accelerator. The choice of ion source depends upon nature of

charge particle needed.

SNICS ion source

SNICS stands for the source of a negative ion by cesium sputtering, SNICS ion is used

when ions from solid state species are needed. This is a negative ion source based on

sputtering of the solid source by cesium. Cesium is heated in an oven, the heated cesium

vapors move from oven to area between the cathode and hot ionizing surface. Some

cesium ions condensed on cooled cathode while some Cs atoms get ionized by a hot

ionizing surface. The ionized Cs ions accelerate toward the cathode and sputter the

cathode material, the sputtered negative ions are then focused and pre-accelerated by the

potential between the cathode and ionizing surface.

37

Fig1: schematic diagram of SNICS ion source1.

Switching magnet and Faraday Cup

The switching magnets are electromagnets they inject the ions coming from source to

beamline, the magnetic field of switching magnet is controlled by coil current, the

magnetic field, in turn, determines the bending radius or bending angle.

The ion beam coming from ion source contains a variety of species e.g. sputtered ion may

have multiple charges, multiple clusters (bi atomic, triatomic etc.) and contamination,

therefore it is necessary to monitor the beam. The beam current is monitored by Faraday

cups. This is metallic cup it measures species of charged particle hitting it in the vacuum.

38

Fig2: Faraday Cup(NEC Model FC50)2

When a charged particle collides with the Faraday cup it gains a net charge the cup then

discharged to measure the current equivalent to incoming charged particles.

Accelerating tank

The accelerating tank is a major part of the electrostatic accelerator, multiple processes

including the main process of acceleration of charged particles take place in this part of

the accelerator. This part contains following components.

Charging system

Stripping system

Sulfur hexafluoride gas

In the electrostatic accelerator, a stable electrostatic field is provided to electrodes in

order to accelerate the charged particles. The high potential difference is developed inside

the accelerating tank with the help of charging chains. The charging chains are made up

of metallic pellets connected to each other with the help of insulating material like nylon.

The charging chains pick up charges from one end by induction process and leave the

charges to other end. Negatively charged inductor pushes electrons off by induction

process, the pellets are in contact with a grounded drive pulley, and therefore the

39

electrons are grounded. The positively charged metal pellets then move to the high

potential terminal there the pellets pass through the negatively biased suppressor, this

electrode prevents arcing. After the metallic pellets leave suppressor the negative charges

flow to pellets leaving a net positive charge on the pulley. This way a high potential is

developed between two ends by continues mechanical transportation of charges.

Fig3: charging chains (NEC pelletron accelerator)3

A gas stripping system is introduced in the way of charged particles to reverse the

polarity of incoming ions, the incoming negatively charged ions are twice accelerated by

same electrostatic field by stripping process, gaseous or solid state stripping is used to

strip some electrons from negative ions, after removal of few electrons, the negative ion

is converted into positive ion. The stripped ion after changing polarity once again gets an

electrostatic push, consequently doubling its energy. Gas stripping is normally done by

nitrogen or argon gas, in our experiments we used nitrogen gas for striping.

40

Fig4: schematic of the charging system in pelletron accelerator4

Sulfur hexafluoride gas is introduced in accelerating tank to prevent corona discharge,

this is an electrical discharge in surrounding gases due to high terminal voltage, although

the accelerating tank is vacuumed using turbomolecular pumps up to 10-8 pa the chances

of corona discharge are still there due to a high voltage about 2MaV.

41

Fig5: schematic diagram of accelerating tank5

Focusing system

A highly energetic beam of positively charged ions emerges from accelerating tank, the

ion beam needs to be focused. Quadrupole magnet is introduced in the way of the ion

beam to focus the beam line. Quadrupole magnet is also known as Q magnets, as the

speed of accelerated ions in an accelerator is very high, therefore magnetic deflection is

more effective than electrostatic deflection. Maxwell equations show that it is impossible

for a quadrupole magnet to focus the beam of charged particles in both the axes (x-

pinching and y-pinching) simultaneously.

F = E+ q (V×B) (Lorentz equation)

The quadrupole magnets are of two types: F quadrupole magnet, they focus the ion beam

in the x-axis (horizontally) while defocusing vertically. D quadrupole magnet focuses

vertically but defocuses horizontally.

42

Fig6: Schematic of quadrupole magnet

Fig7: magnetic field line of quadrupole magnet and direction of Lorentz forces6

43

Beam Lines

The ion beam is once again deflected to a specific beam line in the assembly of multiple

beam lines with the help switching magnets. The beam lines lead to the end station,

where the beam of charged particles is utilized, before the end station the beam is once

again monitored by the Faraday cup just before entering to end station chamber.

Fig8: diagram of pelletron accelerator

3.3Characterization techniques

The fabricated samples were characterized using following techniques

X-ray diffractometer (XRD)

Scanning electron microscope (SEM)

Raman spectroscopy

Contact angle study

Cell viability study

Hardness testing

Electrochemical corrosion study

Particle induced x-ray emission study (PIXE)

44

3.3.1 X-ray diffractometer (XRD)

The materials exhibit unique diffraction pattern, therefore diffraction pattern is the

fingerprint for material identification. English physicists W.H. Bragg developed a

relationship to explain why cleavage planes reflect the beam of X-rays when they are

incident at a specific angle.

2d sinθ = nλ (1)

Where d= interatomic layer

n= integer for constructive interference

λ= wavelength of incident X –ray beam

θ = scattering angle

Fig9: schematic of x-ray reflection from different crystal planes7

This is called Braggs law, this law is basic working principle of X-diffraction

identification of crystal system.

45

The XRD technique can reveal following information about an unknown crystal

Crystal system of a material

Interatomic spacing

Size and shape of crystallite

Internal stress of crystallite

Orientation of single crystal or grain.

Construction and working

A typical XRD contains following part

X-ray tube

This is an evacuated tube, contain a copper anode and an electron source usually a heated

filament, the emitted electrons are accelerated in an electrostatic field between the copper

anode and a cathode. Bremsstrahlung radiations are produced when accelerated electrons

are suddenly stopped by the metal target. The incident electron has sufficient energy to

eject the inner shell electron out from the target, consequently, the electron from outer

shells will jump to inner shell releasing energy in the form of X-rays. These x-rays are

then used for diffraction from unknown crystal system.

Transducers produce electrical signals when they are exposed to incoming radiation, the

transducers are used as a detector. They count the number of diffracted x-ray photon, the

number of counts is equal to the intensity of the diffracted beam of x-ray at a specific

angle.

Goniometer

X-ray goniometer is a device that is used to record the direction of x-rays after diffraction

from the specimen. An x-ray detector is mounted on goniometer such a way the

goniometer can move to a certain position where the necessary conditions of diffraction

are fulfilled.

46

Fig10: Schematic of a typical XRD operation8

3.3.2Scanning electron microscope (SEM)

SEM is an electron microscopy used to study the surfaces of objects. This microscopy

technique uses a beam of the focused electron to scan the surface of a material and to

produce an image of the scanned material.

Working of SEM

Electron gun produce beam of electrons, the beam of electrons is focused by using

electromagnetic lenses. High energy backscattered electrons and low energy secondary

electrons are ejected from the surface of the specimen, by the interaction of bombarded

electrons from the electron gun. The secondary and backscattered electrons reveal

information about the sample. The signal obtained from the specimen contains the details

of topography, size, and composition of the specimen under study. The diffracted

backscattered electrons contain the information about crystal system of the specimen.

Primary and secondary backscattered electrons carry the topographical information. The

47

x-rays emitted by the specimen after the interaction with incident electrons carry the

compositional evidence.

Fig11: different types of species emitted from sample carries different information9

Different part of SEM

A type SEM comprises of basic following parts

Electron gun

Electromagnetic lenses

Sample holder/ stage

Vacuum system

Detectors

Requirements for SEM operation

There are some requirements for accurate operation of SEM.

Vacuum system

Cooling system

48

Vibration free ground

Power supply

Advantages

Little or no sample preparation is required

It is a nondestructive technique

The image collection is rapid

A detailed three dimensional image is obtained

The magnification ranges from 20x to 30000x

The technique is user friendly: easy to operate and harmless

Very small and big samples up to 10cm can be analyzed

Disadvantages

Only solid samples can be analyzed.

Samples more than 40 mm thick cannot be studied.

The device operate in high vacuum 10-6 torr.

The only samples which are stable in vacuum chamber are possible to examine.

Wet samples are not likely to be examined

Samples needs to be electrically conducting, insulating samples are coated with

conducting material.

49

Fig12: Schematic diagram of SEM10

3.3.3Raman spectroscopy

Interaction of incident monochromatic light with molecules changes the frequency, every

molecule interact with incoming light differently, therefore by the shift of frequency the

nature of molecule can be determined

Fig13: schematic of typical Raman scattering by a molecule

There are two types of scattering

Elastic scattering

50

Elastic scattering also called Rayleigh scattering. In this type of scattering energy and

wavelength remain conserved only the direction changes. Elastic scattering also called

Raman scattering. In this type of scattering the scattered photon have

diminished/increased energy. Energy and wave length does not remain conserve.

Stokes and Anti-Stokes scattering

In stokes scattering, scattered photon have lesser energy than the incident photon. The

final state is higher in energy than the initial state. In case of anti-stokes scattering, the

scattered photon have higher energy than the incident photon. The final electronic state is

lower in energy.

Operation of Raman spectrometer

The sample is illuminated with a beam of monochromatic light. The incident light

scattered by the sample, a very small fraction of light scattered in-elastically (Raman

scattering), typically one part out of one million. The scattered light from the sample is

filtered and directed to the spectrometer, where it is analyzed. The molecules in the

sample absorb only a specific frequency of incoming laser light, which gives the

fingerprints of molecules. The Raman spectrum is plotted by varying frequency of

incident light and intensity of scattered light of a particular frequency.

Fig 14: schematic of Raman spectroscopy analysis11

51

3.3.4Biocompatibility study

Biocompatibility is the property of material being compatible with the biological system,

for a clinical implant material biocompatibility refers to the performance of implant

material inside a biological system such that it does not trigger immunological response

and does not release toxic materials. Biocompatibility is a general term in a broad sense a

biocompatible material does not harm the user. The implant materials and devices need to

be tested for their biocompatibility property. Biocompatibility of a candidate biomaterial

is measured by cell viability assay.

Fig15: lay out of cell culture hood12

Cell viability

Cell viability refers to no of living or dead cell in a particular sample or on the scale of a

total number of cells. Cell viability assay measures how healthy the cells are after

interaction with a particular chemical or a biomaterial. MTT assay is an authentic

indicator of cellular activities. The MTT assay is based upon the reduction of yellow

water-soluble tetrazonium dye.

52

Fig16: different steps involved in cell viability study13

Assay protocol

1. Separate the media from cultures.

2. Put 50 µL of serum-free media and 50 µL of MTT.

3. Incubate the plate at 37.5°C for 3 hrs.

4. Then add 150 µL of MTT solvent to each well.

5. Wrap plate in foil and shake it with shaker for about 15 min.

6. Read the plate before 1 hour.

3.3.5 Bioactivity study

Along with biocompatibility, another related biological property is bioactivity, bioactivity

of a biomedical implant refers to the activity of that material inside a biological system.

Bioactivity of an implant material is often evaluated by simulated body fluid (SBF). SBF

was first introduced by Kokubo and his colleague [4, 5]. The fabricated samples are

immersed in SBF for seven days usually, at 37 0C. The ionic species in SBF get

precipitated over the surface of the immersed sample to form a bone-like structure called

hydroxyapatite. The bone binding ability of an orthopedic implant material is also

53

assessed by its ability to form apatite layer over its surface while immersed in SBF under

physiological conditions.

Table1: Ionic concentrations of the simulated body fluid and human blood plasma

Ion Simulated body fluid

(SBF)

(mmol/dm3)

Human blood plasma

(mmol/dm3)

1 Na+ 142.0 142.0

2 K+ 5.0 5.0

3 Mg2+ 1.5 1.5

4 Ca2+ 2.5 2.5

5 Cl- 147.8 103.0

6 HCO3- 4.2 27.0

7 HPO42- 1.0 1.0

8 SO42- 0.5 0.5

3.4 Stopping range of ions in matter (SRIM)

The range of implanted ions in target lattice is an important parameter. It depends upon

multiple factors such as nature of target material, nature of incoming ions and energy of

ions. The incident atom performs multiple elastic collisions with the target atom. The

momentum is transferred from bombarded ion to target atoms during the process of

elastic collision. Sometimes the transferred energy is sufficient enough to overcome the

binding energy of target atom, then a surface atom may be ejected from target surface

called the sputtered atom.

The energy of incident ion is lost in the target lattice by two phenomena. Nuclear energy

loss and electronic energy loss, the equation for energy transferred is given below.

54

.

𝐸transferred = 4𝑀1𝑀2/(𝑀1

+ 𝑀2) 𝐸𝑡 𝑠𝑖𝑛2 𝛼/2 (2)

Where M1= mass of ion

M2 = the mass target atom

α = angle of deviation

Et= total energy of ion

The electronic energy loss takes place due to inelastic repulsive interactions between the

electrons of bombarded ions and the electrons of target atoms. The nuclear energy loss

takes place in discrete steps by elastic energy transfer. The range of bombarded ion may

be defined as the path length of the single atom in a target material.

𝑅𝑎𝑛𝑔𝑒 = ∫𝑑𝐸

𝑑𝐸/𝑑𝑥

𝐸0

𝐸𝑚𝑎𝑥 (3)

Schematic diagram of sputtering by ion matter interaction (Source: Nastasi et at., 1996)

SRIM is a software package to simulate the ion matter interaction. This package was first

introduced in 1985. TRIM (transport of ions in matter) is the core of SRIM package. This

package is helpful to ion implantation community, it helps the experimentalists and the

55

researchers of other disciplines in a number of ways[6]. The TRIM is based upon Monte

Carlo method of random sampling to obtain numerical outcomes. The software package

uses two basic approximations. Firstly it uses the analytical formula to obtain atom-atom

collision secondly it uses the concept of free flight path between the consecutive

collisions. Monte Carlo method has some advantages over the analytical methods which

are based upon transport theory. The. Monte Carlo method can be used for

comprehensive calculations of ion-atom interaction. The main limitation of Monte Carlo

method is that it is a time-consuming method. Therefore there is a divergence between

computer time and statistical precision. The issue is resolved considerably by sacrificing

little accuracy, the TRIM user has the option to bypass the approximation and calculate

the problem with the highest accuracy. The software package uses some specific

assumption for calculations. The ions are assumed to change their path during binary

collisions and follow straight free-flight-path. It is assumed that the ions losses their

energy as a result of nuclear and electronic scattering. The energy loss during nuclear

scattering is discrete and continuous energy loss by electronic interactions. The nuclear

and electronic energy losses are assumed to be independent of each other.

𝑑𝐸

𝑑𝑥= (

𝑑𝐸

𝑑𝑥)

𝑛𝑢𝑐𝑙𝑒𝑎𝑟+ (

𝑑𝐸

𝑑𝑥)

𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑖𝑐(4)

The target is assumed non-crystalline and the atoms are located at random positions,

therefore the anisotropic properties are ignored. This method allows a wide range of

energy calculation typically from 0.1keV/u to several MeV/u. Energy-dependent free-

flight-path is introduced to deal with the calculations that involve high energy particles.

The developed formulism is applicable to all ion-target combinations. The program

provides the information about penetration depth of ion in target lattice at a particular

energy, damage events, recoiled atoms, vacancies and interstitials etc.

Sample preparation

Cutting, grinding and polishing of stainless steel samples

The samples of stainless steel 306 are cut into cylindrical shape with the help of diamond

wheel cutter. The length of the samples was 1cm and the diameter of the samples was 1

56

cm. The samples were grinded with the help of different grits of silicon carbide paper

such as 320, 500, 1000, 1500, 2000, 2500 and 3000 respectively. We continuously

monitored the scratches of samples with the help of an optical microscope. Different

micron of diamond was used to have a mirror like shine, minimize surface scratches. The

samples were cleaned subsequently in an ultrasonic bath in de-ionized water and then

acetone.

Cutting, grinding and polishing of nitinol samples

Four NiTi wire (2 mm diameter)samples of 6cm each are polished using SiC paper of

1000 grit size, then polished using metal polish paste and are subsequently cleaned by

an ultrasonic bath in de-ionized water and acetone. Samples are annealed at 450oC for 2

hrs. This temperature is chosen from earlier studies which show more Ni release from the

samples annealed greater than this temperature [7].

References

[1] Roeder RK. Chapter 3 - Mechanical Characterization of Biomaterials A2 -

Bandyopadhyay, Amit. In: Bose S, editor. Characterization of Biomaterials. Oxford:

Academic Press; 2013. p. 49-104.

[2] Wang H, Chu PK. Chapter 4 - Surface Characterization of Biomaterials A2 -

Bandyopadhyay, Amit. In: Bose S, editor. Characterization of Biomaterials. Oxford:

Academic Press; 2013. p. 105-74.

57

[3] Morra M, Cassinelli C. Biomaterials surface characterization and modification. The

International journal of artificial organs 2006;29:824-33.

[4] Kokubo T, Takadama H. How useful is SBF in predicting in vivo bone bioactivity?

Biomaterials 2006;27:2907-15.

[5] Cho S-B, Nakanishi K, Kokubo T, Soga N, Ohtsuki C, Nakamura T, et al.

Dependence of Apatite Formation on Silica Gel on Its Structure: Effect of Heat

Treatment. Journal of the American Ceramic Society 1995;78:1769-74.

[6] Ziegler JF, Ziegler MD, Biersack JP. SRIM – The stopping and range of ions in

matter (2010). Nuclear Instruments and Methods in Physics Research Section B: Beam

Interactions with Materials and Atoms 2010;268:1818-23.

[7] Kokubo T, Kushitani H, Sakka S, Kitsugi T, Yamamuro T. Solutions able to

reproduce in vivo surface-structure changes in bioactive glass-ceramic A-W3. Journal of

biomedical materials research 1990;24:721-34.

References to figures

58

Chapter 4

Results and Discussions

4. Ion implantation in stainless steel and nitinol

Stainless steel and nickel-titanium alloys (nitinol) are important bio-material. These

materials are currently being used for various biomedical applications. The significance

and associated problems with these materials have been discussed in previous chapters

(section.1 and section. 2). Some major problems associated with stainless steel and

nitinol were considered to study, i.e. in-vivo stability (corrosion protection): these

materials often corrode in physiological environment and release toxic ions e.g. nickel,

chromium, etc.[1]. The leaked ions cause allergy, disorders in bone growth, cell death

and some other undesired effects. Therefore it is necessary to study the factor affecting

ion release and corrosion properties. The incubation of Hydroxyapatite (HA) over the

surface of candidate biomaterial is an important factor, this factor determines the in-vivo

behavior of implant material: An apatite layer gets deposited over the surface of implant

material inside the human body. This apatite layer bonds between implant material and

neighboring bones. In-vivo apatite forming-ability of a candidate biomaterial can be

evaluated in-vitro by using simulated body fluid (SBF). In-vitro incubation of apatite

layer determines bio-activity and bone bonding ability of material under investigation [2].

Cell viability of a candidate biomedical material is also an important concern: cell

viability of a material refers to the degree of survival and to increase in number of cells,

the interaction of material surface to alive cells may cause cell death which leads to a

decreased percentage of alive cells, which refers to decreased cell viability. Sometimes

the interaction does not cause cell death or very less fatality to cells, the interaction may

also lead to increase in the number of cells, which is called cell proliferation or increased

cell viability (more than 100%). Minimum and maximum cell viability of a material for

safe use is not defined. Threshold cell viability depends upon the application of material,

some researchers claim that good cell viability is more than 50%. In our experiments, we

have investigated the variation in cell viability in treated samples.

59

Some mechanical properties are also very important for orthopedic implant material, in

our experiments we investigated the variation of surface hardness after the treatment of

samples.

Surface wettability of a material is another important biomedical property. Some studies

claimed that biocompatibility of a material depends upon hydrophilicity (contact angle)

[3]. Researchers are attempting to study the relationship between surface wettability and

bio-compatibility [4, 5], in present work the relationship between hydrophilicity and bio-

compatibility hydrogen ion implanted samples is also studied.

4.1 Effect of nitrogen ion implantation in stainless steel

Stainless steel 316L is the most commonly used orthopedic material[6, 7]. Stainless steel

is chosen for orthopedic and some other applications e.g. artificial heart valve, medical

needles, medical syringes orthodontic wires, catheters etc. Because of its

biocompatibility, mechanical properties, and low cost. Nitrogen is a wonderful element it

is the fourth most abundant element in the human body and its compounds are basic

building blocks of biological system e.g. nitrogen is the major component of amino acid

and amino acid make up the proteins. Because of its biological importance, it is

hypothesized that nitrogen ions in the near-surface region of orthopedic implants may

yield suitable effects e.g. enhanced bonding ability, improved stability and cell response

to the surface. Literature also reports enhanced corrosion protection by nitrogen ion

implantation [8, 9]. The enhanced corrosion protection by N ion implantation is due to

the formation of nitrides and oxynitrides in ion implanted region. The oxynitride layer

prevents the exposure of surface to reactive ions (cl, O2 etc.). The metallic nitrides have

exceptional electrochemical properties, particularly chemical stability making metallic

nitride a potential candidate to be used as electrode in lithium-ion batteries [8, 10].

Stainless steel 306 is implanted with various doses of nitrogen ions using a 2MV

pelletron accelerator for the improvement of its surface biomedical properties. The

samples are characterized for mechanical, biomedical and chemical properties using

various techniques.

60

4.1.2 Earlier work

The metallic materials are being employed for diverse biomedical applications in various

fields of biomedical science. The examples of metallic materials as biomaterials includes;

the mesh of stainless steel or nickel alloy as coronary heart stent, stainless steel or cobalt

as artificial femoral head (artificial hip) for total hip replacement, stainless steel and

titanium as bone plates and screws etc. Therefore there is an earnest need to improve the

relevant properties of candidate biomaterials [11-14] . Stainless steel (SS) is an important

alloy for many biomedical applications because SS is stable (appropriate corrosion

resistant), bioactive and has good mechanical properties, but there are always some

associated deficiencies with every material. The deficiencies of SS includes toxic ion (Ni,

Cr) release from the surface and mismatch of mechanical properties with bone (hardness,

tensile) etc. [15-18]. Due to the mismatch of mechanical properties of bone and implant

material, an unwanted effect is produced, which is called stress shielding effect, due to

the effect the bone does not share the mechanical stress, consequently, leading to the

reduction in bone density. Some mechanical properties of femur bone and stainless steel

are tabulated below.

Table1: comparison of different properties of bone and stainless steel

Properties Femur bone Stainless steel

1 Density (g/cm3) 1.6-1.7 8

2 Tensile strength (M Pa) 90-130 680-750

3 Compressive strength (M Pa) 130-200 500

4 Hardness (vicker) 50-100 155

Biocompatibility and bioactivity are two different properties, for a material

biocompatibility refers to the degree of friendliness, being harmonious to body

functioning and not stimulating any unwanted in-vivo response, while the bioactivity

refers to being beneficial to biological system or triggering an in-vivo positive response.

The bioactivity and biocompatibility are two fundamental properties required to use a

material as a biomaterial. The bioactivity of a material surface is determined by cellular

response to the

61

surface, the cellular response to a particular surface is estimated by the exposure of the

surface to a specific type of cells. Size, shape and number of alive cells determine the

behavior of the surface to exposed surface after a specific time.

Different surface modification techniques are being employed to improve cellular

response to surface of metallic materials and some related properties [18, 19]. Metals and

alloys are being treated in variety of ways [20, 21] in order to tune some required surface

properties. Researchers are working to modify the material surfaces for improved

properties by plasma immersion ion implantation and thin film fabrication, nano pores or

micro/nano surface roughness fabrication etc [22-25].

Jiang et al. had shown uniform apatite growth on porous nitinol substrate [24, 26]. Kawai

et al prepared porous Ti metal treated with H2SO4/HCl mixed acid solution and/or given

heat treatment, they concluded maximum bone ingrowth on fully treated samples and it

was attributed to accumulation of positive charges on the surface. Kawai et al reported

similar results in another study where they produce micrometer surface roughness by

H2SO4/HCl and heat treatment at 600C, they also prepared nanometer roughness by

NaOH followed by HCl and then the samples were heat treated both of these sample

showed good apatite firming ability in SBF and in-vivo. These results were credited to

concentration of positive charges on the surface [27, 28].

The biocompatibility of an orthopedic implant can be evaluated by in-vitro exposure of

samples; SBF is a wonderful solution for the in-vitro test. Incubation and proliferation of

hydroxyapatite in SBF on a surface determines its biocompatibility and efficacy as

biomedical implant.

We have implanted nitrogen ions to produce roughness on the surface of stainless steel

samples. As a result of dual effects of surface roughness and presence of nitrogen ions on

the surface we observed significantly improved results.

62

4.1.3 Nitrogen Ion implantation

Nitrogen ions are produced in SNICS ion source by sputtering of nitrogen source. The

produced ions are pre accelerated in SNICS source then out of the cluster of many

species

(e.g. impurities, monoatomic, bi-atomic etc. ions of N and the species with different

charge state q=1, 2, 3 etc.) singly charged monoatomic nitrogen ions are chosen to

implant in target lattice. The remaining unwanted species are filtered out by deflecting

them to some angle using an electromagnet. The pre-accelerated chosen ions are further

accelerated in accelerating tank under an electrostatic field strength of 250 kV.

The energy corresponding to given voltage is estimated by the following equation.

E = (q+1) V

The selected ions are implanted on four stainless steel samples at a constant energy of

500keV and one sample is studied as the un-implanted sample. Mono-atomic singly

charged (q=1) nitrogen ions are implanted into stainless steel lattice at constant energy.

The number of implanted ions is varied in different samples. The detail of ion dose is

given in table1.

The ion dose was calculated using equation

Dose/sec = (I × 6.3 × 1018) ÷ beam size

Dose = [(I × 6.3 × 1018) ÷ beam size] × time of exposure

Where I = beam current

Beam size = 2cm × 2cm = 4cm2

Table 2: ion dose for four samples

Samples Dose (number of ions/cm2)

NSS1 3.6×1013

NSS2 2.3×1014

NSS3 4.5×1014

NSS 4 2.8×1015

63

4.1.4 Immersion in simulated body fluid

Four ion implanted samples and one untreated sample is immersed in Kokubos

simulated body fluid for 7days at 37.5 oC to incubate a layer of hydroxyapatite[29], the

extent of incubation of hydroxyapatite determines bioactivity of samples[23]. The

immersed samples were then analyzed by various techniques.

4.1.5 Results and Discussions

4.1.5.1 Raman Spectroscopy profiles Raman spectroscopy is employed to analyze the chemical nature of species incubated

over the surface of samples after immersion in SBF. Total of six samples are chosen for

Raman spectroscopy: four ion implanted samples after immersion in SBF, one un-

implanted sample after immersion in SBF and one un-implanted sample without

immersion in SBF.

Raman spectroscopy is performed using DXR Nicolet Thermo scientific. Raman Spectra

of HA over the surface of samples under investigation is shown in Fig: 1. each sample is

investigated by Raman spectroscopy from three different points. It is observed that

pristine sample (un-implanted without immersion in SBF) does not show any

representative peak of HA. The Raman peaks are observed in all the remaining five

samples but with different peak intensities. The Raman peak positions are compared with

literature [30, 31]. It is found that all the peak positions represents the composition of

HA. The peak positions from the literature are tabulated below.

Table3: different peak positions of HA groups

Sr.no Raman Peak position (cm−1 ) bond

1 422 to 454 υ2 (PO4)3-

2 568 to 617 υ 4 (PO4)3-

3 815 to 921 C-C stretching

4 957 to 962 υ 1 (PO4)3-

5 1003 to 1005, 1006 to1055 υ 3 (PO4)3

6 1065 to 1071 CO32-

7 3572–3575 O-H stretching

64

From the Raman spectra of different samples it is observed that all the finger prints of

HA are present in prepared samples, different modes of vibrations of (PO4)3- are observed

at peak positions 918 cm-1,410 cm-1, 1045cm-1 and 615cm-1 , the mentioned peak

positions represents υ1, υ2, υ3 and υ4 of (PO4)3- respectively. CO3 bond is observed at

1170 cm-1, amide III peak is also found at 1295 cm-1. A prominent peak is observed at

770cm-1, Hadrich et al attributed this peak to hexagonal structure of stoichiometric HA

[32]. Moreover the sharp and distinct peaks represents ordered and fine growth of HA.

From the spectra of different samples it is clear that HA has incubated in all the prepared

sample and untreated sample, but the magnitude of incubation is different in different

samples, the intensity of HA peaks characterizes the magnitude of incubated HA, the

spectrum shows increased incubation by increasing ion dose, as maximum peak intensity

is observed in maximum ion dose sample and minimum peak intensity is found in least

ion dose sample. Therefore it is concluded that presence of nitrogen ions in near surface

region of SS facilitate the growth of HA over the surface.

65

0 500 1000 1500 2000 2500 3000 3500

-100

0

100

200

300

400

500

600

Inte

nsity

Raman Shift(cm-1)

Sample4

Sample4

Sample3

Sample2

Sample1

UnEx

pristine

Pristine

Conterol10

12ion/cm

2

1013

ion/cm2

1014

ion/cm2

1015

ion/cm2

PO

-3 4v 2

PO

4-3v 4

PO

4-3v 1 P

O4-3

v 3C

O-2 3

amid

eIII C

H2w

ag

Fig1: Raman Spectra of incubated HA

4.1.5.2 XRD studies

XRD study of prepared samples is performed to analyze the nature of incubated

crystalline species over the surface of ion implanted and untreated SS samples and to

study the effect of N ion implantation on the crystallinity of incubated species. XRD

profiles are shown in Fig: 2.

The typical HA XRD peak positions are HA 210 at 2θ=28o, HA 211 at 2θ=32o, HA 300

at 2θ=35o HA 113 at 2θ=45o, HA 213 at 2θ=49o approximately [33-35].

The XRD patterns specify the presence of typical HA peaks in highest N ion implanted

sample [210], [211], [300] at 2θ position= 28o, 31.6o and 34.5o respectively the next two

peaks at 2θ position= 43o and 500 are common in both hydroxyapatite and stainless

steel[22, 36], these are the positions at which both hydroxyapatite and stainless steel

profile exhibits peaks.

66

The XRD profiles shows absence of hydroxyapatite peaks in control sample and low ion

dose samples (sample 1, 2 and 3) except the peak at [300] which gradually evolves with

increasing ion dose, and the maximum intensity of this peak can be observed for greatest

ion dose 1×1015. From the profiles we can also observe origination of [211] and [210]

peaks in greater ion dose samples [21].

The results suggests that the HA growth is proportional to number of N ions, maximum

growth is observed in highest (1015ions/cm2) ion dose sample and minimum or no growth

is found in controlled and minimum ion dose sample (sample1) while sample 2 and 3

exhibits evolutionary behavior between un-implanted and heavily implanted samples .

20 30 40 50 60 70 80

-200

0

200

400

600

800

1000

1200

1400

1600

1800

Inte

nsity

(a.u

)

(degree)

Unexposed

sample

NSS1

NSS2

NSS 3

NSS 4

HA(210)

HA(211)

HA [300]

SS (110)

HA (113)

SS (200)

HA (213)

Fig 2: XRD profiles of incubated HA

4.1.5.2.1 Estimation of range of ions in material lattice (SRIM study)

The nitrogen ions are implanted into stainless steel lattice at 500KeV energy. This

energy is chosen to force the ions to stay at the surface of samples so that the implanted

ions could interact chemically with ionic species present in SBF, the range of implanted

ions are estimated by SRIM shown in Fig 2a . Implanted nitrogen ion resides within 0.5

µm (500 nm) of target depth as calculated using SRIM. These ions produce porosity,

surface roughness and amorphization. The amorphous surfaces are more efficient for

67

hydroxyapatite settlement [37]. Liu et al [38] prepared hydrogenated amorphous surface

of silicon and they found improved bioactivity along with evolution of hydroxyapatite

peaks in XRD spectrum. They also established that the improved biocompatibility is not

only due to surface amorphization or hydrogen implantation only but this is due to

combined effect of Hydrogenated amorphous surface.

Fig2a: SRIM profile of depth of N ions in target substrate

4.1.5.3 SEM Results

Scanning electron microscopy study is performed to investigate topography of prepared

samples after immersion in SBF and variation in extent of growth of HA on sample

surface by varying N ion dose. Moreover the percentage of area covered by incubated

HA is also an interesting feature to study, it determines the response of modified surface

for bone growth.

SEM images of four prepared samples (sample1, sample2, sample3 and sample4) are

shown in Figures 3 and 4. Figure 3 shows the images of ion modified SS surface, while

Figure 4 shows the images of ion modified surfaces after immersion in SBF. The impact

of bombarded ions on the sample surface is visible in the form of holes, surface

roughness and other surface imperfections.

Fig 4 depicts the growth of hydroxyapatite in all the four samples, but the surface area in

sample 1 and sample 2 are found largely uncovered which indicates restricted growth of

hydroxyapatite, SEM micrograph of sample 1 shows discontinued, localized

precipitated hydroxyapatite at specific regions only, likewise SEM profile of sample 2

68

represents similar restricted growth of hydroxyapatite but the growth is found enhanced

as compare to sample1. SEM topography of Sample 3 shows that almost all the surface

area is covered with hydroxyapatite but the density of growth is different in different

regions.Finally, SEM profile of sample 4 shows fully covered surface area with a uniform

layer of hydroxyapatite.

This clearly confirms encouraging effects of N ion implantation for hydroxyapatite

growth on the surface. SEM results are consistent with XRD, Raman spectroscopy and

MTT study of as prepared samples.

Fig 3: SEM Micrographs before immersion in SBF

69

Fig 4: SEM Micrographs of NSS1, NSS2, NSS3 and NSS4 respectively after immersion

in SBF.

4.1.5.4 in- vitro Cell Viability Studies

Biocompatibility of all produced nitrogen implanted stainless steel samples is

investigated by using cultured human oral fibroblasts (P4) and cellular response is also

observed by using standard MTT assay protocol. Samples with 5 mm in height and 1cm

in diameter are prepared and sterilized by using autoclave (15 min at 121°C/ 15 psi).

Similarly, cells are cultured in DMEM (Dulbecco's Modified Eagle's Medium) media

supplemented with 10 % of FCF serum (dye for protein staining), 1% penicillin /

streptomycin, 1% glutamine (Sigma Aldrich UK). Moreover, cells are allowed to

confluent (100%) over the surface of tissue cultured plate and are detached by using

trypsin EDTA (Sigma Aldrich, UK). Cells are seeded into wells of 24 well plates

containing test sample seeding density of 1.25 x 104 cells / ml. A material and non-

material control (positive and negative) are introduced for the direct comparison

respectively. Both material and cells are incubated at 37°C in a 5 % CO2 atmosphere for

24 hrs.

However, for quantitative measurement MTT assay is performed individually on all

prepared samples. 0.1 ml of MTT solution are aseptically added to each well and are left

for incubation at 37°C for 4 hrs. Cells are than lysed with Isopropanol. The intensity of

colored solution is measured by using a photo spectrometer at a wavelength of 570 nm.

Fig: 6 shows percentage cell growth versus N ion dose in different samples.

70

0.0 2.0x1015

4.0x1015

6.0x1015

8.0x1015

1.0x1016

50

100

150

200

250

300

Ce

ll vi

ab

ility

%

Ion Dose (ions/cm2)

Fig 5: Cell viability VS ion dose graph

Fig 6: Histogram representation of Cell viability in different samples

Human oral fibroblasts (passage 4) are used to study in-vitro cellular response to the

sample surface by varying N ion dose. Cell growth versus ion dose is shown in Fig:6

Percentage cell viability, morphology and cell proliferation are studied in comparison of

a control sample (SS sample 1) after 24 hours of incubation at 37 o C; all the samples are

found positive as the minimum observed cell viability is 60% in sample 2. We observe

decreased cell viability in sample 1 and sample 2 as compared to unexposed sample

(Control SS sample) then a slight increase in sample 3, 95%, 60% and 83% respectively.

A drastic increase in cell growth approximately 300% is observed for ion dose of 1015

ions/cm2. Our quantitative result agrees with Rizwan et-al[39] up to the limit of their

maximum implanted ions 1014ions/cm2, they attributed reduced cytocompatibility to

surface roughness. It has been reported the effect of surface roughness on hydrophilicity

71

[40] and it is generally claimed the decrease in hydrophilicity with increasing roughness.

It is also well known from the literature that hydrophilicity is proportional to

bioactivity[41]. Our results support this assumption. Figure (a) and figure (b) shows

proportional variation in hydrophilicity and cell viability, which supports earlier

literature.

4.1.5.5 Contact Angle studies

Contact angle of all the samples are evaluated at three different points using Goniometer

Model 100-00 (220).UK. The average of three measurements is plotted in Fig 7 against

ion dose for each sample.

From the figure, we can conclude that contact angle of all the samples is less than 90o and

therefore all the samples are generally hydrophilic. It is observed that hydrophilicity

changes with ion doses. The ion bombardment on the surface produces roughness which

strongly affects the wetting property. The figure also indicates that the untreated sample

which is the smoothest is most hydrophilic. Contact angle increases in implanted samples

up to the sample 2 (ion dose=1013ion/cm2) which is the least wetting (this sample was

found to be least biocompatible as well in MTT study). After this dose limit the next dose

is 1014ion/cm2, this is the number of ions which is sufficient to create a mono atomic layer

on the surface of the material. The larger number tend to create bigger damage area (the

damage of multiple incoming ions combines to produce a single bigger damaged area as

seen in SEM profiles), the damage size after a certain limit is a local smoother region

which may reduce the hydrophobic effect

0.0 2.0x1014

4.0x1014

6.0x1014

8.0x1014

1.0x1015

73

74

75

76

77

78

79

cont

act a

ngle

(de

gree

)

ion dose (ion/cm2)

72

Fig 7: contact angle VS ion dose

Many authors reported that hydrophilicity can be affected by the roughness of the

surface, Kubiak et al demonstrated that contact angle was strongly correlated with surface

roughness [42] they plotted graphs between contact angle and surface roughness, the

graph

shows a hump like symmetry in which medium rough surfaces are least hydrophobic,

which was also reported by Bikerman in 1949, they reported that rough solids surfaces

are comparatively hydrophobic[41]. Kittu et al also reported that the surfaces become

more hydrophilic as roughness decreases [43].

4.1.5.6 Hardness Results Variation in micro-hardness by ion implantation is shown in Fig 8 against N ion dose.

Micro-hardness of samples is measured using Vickers hardness tester at a maximum load

of 200g. The figure shows that the least hard sample is the control sample while the

hardest among all the samples is sample 1. Sample 2 and sample 3 are less hard than the

sample 1, the hardness then increases in sample 4 as compared to sample 2 and sample 3.

It is known that ion implantation in substrate lattice generates defects and amorphization.

It is known that the amorphous surfaces are generally harder than ordered surfaces. The

hardness is increased due to the presence of the defects which are produced by ion

implantation which prevent further lattice movements and dislocations which is a cause

of surface hardening, another reason of improved hardness is the formation of nitride

phase which tends to harden the surface[44, 45].

73

0.0 2.0x1014

4.0x1014

6.0x1014

8.0x1014

1.0x1015

280

285

290

295

300

305

310

Hard

ness

(HV)

ion dose (ion/cm2)

Control

NSS1

NSS2

NSS3

NSS4

Fig 8: Hardness VS ion dose

4.2 Effect of Hydrogen ion implantation in stainless steel

Effect of hydrogen ion implantation is being investigated for various application:

researchers working in semiconductor field are trying to use H- ion beam for exfoliation,

the changing parameters of H ion implantation leads to different results. Hydrogen ion

implantation is also being applied for resistivity tailoring and to modify mechanical

properties. We have hypothesized that incorporation of H- ions in the surface of the

biomedical implant may yield improved hydrophilicity and biocompatibility due to

greater chances of H-bonding. The effect of hydrogen ion implantation on surface

wettability and biocompatibility of stainless steel is investigated. Hydrogen ions are

implanted in near surface of stainless steel to facilitate hydrogen bonding at different

doses with constant energy of 500KeV.

4.2.1 Introduction

Orthopedic biomaterials are important class of materials; because of their use in various

applications such as, bone plates for healing of broken bones, artificial hip joints for

replacement of damaged joints, intramedullary nails to maintain alignment and position

of bone and to share load of bone, bone defects filler, bone graft, spine, orthodontics

wires etc[46, 47].

74

An appropriate set of biological and mechanical properties is required for proper

functioning and safety of these materials to be used in the biological environment.

Existing materials and alloys do not cater the necessary requirement properly. Therefore

researchers are looking for new and/or modified material to exploit suitable properties

which would take care of human body requirements [48-50]. Stainless steel titanium and

its alloys, cobalt chromium alloys, nickel titanium alloy and some polymers are being

used at present [51-53], because of their unique properties but they have shortcoming for

desired purposes. Researchers are currently working on two approaches for achieving

desired properties. They are trying to fabricate new class of materials by alloying while

another class of material scientist harvesting unique interfacial properties.

In addition to suitable mechanical properties, appropriate biological properties are also

important. Surface wettability is an important property, it is believed that hydrophilic

materials are generally biocompatible [54, 55]. Surface hydrophilicity and hydroxyapatite

precipitation depend upon H-bonding due to partial electrostatic attractive forces between

less electronegative H and more electronegative OH group (as OH present is both water

molecule and HA molecules). Thus we assumed that H ion incorporation in the near-

surface region of an orthopedic implant will enhance the chances of H-bonding, thereby

improving hydrophilicity and hydroxyapatite precipitation.

We have implanted different doses of 500KeV H-ion on stainless steel and prepared

samples are then characterized for wettability, biocompatibility and bioactivity.

4.2.2 Ion implantation.

Stainless steel-306 samples are bombarded with H ion in evacuated target chamber of

2MV Pelletron accelerator (Accelerator Lab, CASP-GCU Lahore). Mono-atomic singly

charged (q=1) H ions are selected for experiment. The chosen ions are accelerated to 500

KeV of energy. According to SRIM calculation H ions of given energy may penetrate

within 2.48µm depth. These H ion are implanted in all samples for various ion doses

(1012, 1013, 1014 and 1015 ions/cm2) in HSS1, HSS2, HSS3 and HSS4 samples

respectively.

75

4.2.3 Immersion in simulated body fluid

Simulated body Fluid (SBF) is prepared according to Kokubos protocol [23]. The ion

implanted samples are cleaned with DI water and acetone. Then these are dried and are

immersed in 25ml of SBF at 37.50C for eight days. After eight days of immersion

samples are removed from SBF and then are oven dried to remove water contents.

4.2.4 Results and Discussions

4.2.4.1 Contact Angle Studies

Contact angle (CA) of all the samples are evaluated at three different points using

Goniometer Model 100-00 (220).UK. All the three readings of the same sample are

approximately equal with minor error is found to be ± 0.1 degree. The average of three

measurements is plotted in Figure 9 against ion dose.

It is assumed that greater H-bonding by H ion implantation will result smaller CA

consequently [56], the wettability profile of treated samples reveals variation in contact

angle as expected. The figure depicts an exponentially decreasing relation of contact

angle with respect to ion dose variation. Maximum CA is observed in untreated sample

which is 74o. Then it is decreased continuously with increasing number of ions/cm2,

(69.1o, 67.8o. 64.54o and 62o) for HSS1, HSS2, HSS3 and HSS4 samples respectively.

Impact of energetic H-ions with sample surface produces craters, surface roughness,

amorphization and other lattice imperfections. Surface roughness is also an important

parameter which impacts the surface wettability, as reported by some studies. Kubiak et-

al [57] measured variation in apparent contact angle with respect to average roughness

and they concluded that CA with stainless steel surface decreases up to a certain limit of

roughness, then it increases for more irregular surfaces. Kittu et al [43] performed

experiments on different materials and they also observed that the magnitude of contact

angle decreased by increasing surface roughness. More over their graphs demonstrated

that after a certain limit of surface roughness the contact angle increases, and they

showed concave up type of graphs in their study. In our experiment, the H ions are

smaller in size, and at energy 500 KeV they penetrate in the lattice without significantly

damaging the surface lattice, but if the ion dose is increased beyond a certain limit the

surface damage is profound [58] , because of ion recoiled ion and knocked out atoms.

76

Therefore along with chemical interactions of H- ions surface roughness is an additional

factor to improve surface hydrophilicity[59].

Fig:contact angle versus H+ ion dose

4.2.4.2 Raman Spectroscopy

In- vitro bioactivity of a material is usually evaluated by SBF [60]. Raman spectroscopy

is performed to investigate the nature of incubated species on prepared surfaces after 8

days of immersion of samples in SBF and to draw comparison between untreated sample

and (different doses of H) ion implanted samples and to have a quantitative assessment of

precipitated species. Raman spectroscopy is performed using DXR Nicolet Thermo

scientific as mentioned previously. Figure 10 shows Raman spectra of four treated

samples and one untreated sample. Raman profiles reveal the presence of all the

representative peaks of HA in untreated and prepared samples , υ1, υ2, υ3 and υ4 of PO4

group of HA are present at 910 cm-1,390 cm-1, 1050 cm-1 and 610 cm-1 respectively, CO3

bond is observed at 1170 cm-1 [30]. It is found that peak intensity of precipitated HA is

proportional to H ion dose given to the surface of sample. Growth of HA in untreated

sample is lowest while maximum growth in highest ion implanted sample HSS4 after the

same time of immersion in equal quantity of SBF. Improved growth of HA is attributed

0.0 2.0x1014

4.0x1014

6.0x1014

8.0x1014

1.0x1015

62

64

66

68

70

72

74

co

nta

ct a

ng

le (

de

gre

e)

H ion dose/cm2

Control Sample

HSS1

HSS2

HSS3

HSS4

77

to presence greater number of H ions in near surface region which enhances the chances

of H- bonding.

3600 3200 2800 2400 2000 1600 1200 800 400

-20

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

Inte

nsity(a

.u)

Raman Shift (cm-1)

Control

HSS1

HSS2

HSS3

HSS4

Fig 10: Raman spectroscopy of sample surfaces after immersion in SBF

4.2.4.3 Mass of incubated species

Effect of H rich surface on HA incubation is also determined by the mass of incubated

species. The samples are weighed before immersion and after immersion (after drying)

using Ohaus Analytical Plus instrument (reliability 0.01mg) to determine the mass gained

by sample surface after immersion in SBF. The measurements are mentioned in table and

mass of incubated species is plotted against H ion dose in Figure 12. The Fig shows

increase in mass of HA by H ion implantation. Figure 3a also shows a macroscopic view

of the enhanced growth of HA by H ion implantation.

Fig 11: Macroscopic view of sample surface after immersion in SBF

78

0.0 2.0x1015

4.0x1015

6.0x1015

8.0x1015

1.0x1016

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

ma

ss o

f in

cub

ate

d H

A(g

m)

Hydrogen ions (ion/cm2)

ControlHSS1

HSS2

HSS3

HSS4

Fig 12: Mass of incubated HA versus H+ ion dose

Table4: Mass of sample before and after immersion in SBF after drying

Sample mass of Sample

before immersion

(gm)

mass of Sample

after immersion

and subsequent

drying (gm)

Difference/ mass

of incubated

species(mg)

1 untreated Sample 3.0082 3.0082 0

2 HSS-1 2.1452 2.1452 0

3 HSS-2 2.3658 2.3660 0.2

4 HSS-3 2.2653 2.2657 0.4

5 HSS-4 2.5880 2.5885 0.5

4.2.4.4 in- vitro Cell Viability Studies

Biocompatibility of all ion implanted stainless steel samples is investigated by using

cultured human oral fibroblasts (passage 4) and cellular response is also observed by

using standard MTT assay protocol. Samples with 5mm in height and 1cm in diameter

are prepared and sterilized by using autoclave (15 min at 121°C/ 15 psi). Similarly, cells

are cultured in DMEM media supplemented with 5 % of FCF serum, 1% penicillin /

streptomycin, 1% glutamine and 0.2% amphotericin (Sigma Aldrich UK). Moreover,

cells are allowed to confluent (100%) over the surface of tissue cultured plate and

79

detached by using trypsin EDTA (Sigma Aldrich, UK). Cells are seeded into wells of 24

well plate containing test sample seeding density of 2.0 x 104 cells / ml. A material and

non-material control (positive) and (negative) are introduced for the direct comparison

respectively. The cells are incubated at 37°C in a 5 % CO2 atmosphere for 24 hrs.

However, for quantitative measurement MTT assay is performed individually on all

prepared samples. 1 ml of MTT solution is aseptically added to each well and left for

incubation at 37°C for 40 min. Cells are then lysed with Isopropanol. The intensity of

colored solution was measured by using a photo spectrometer at a wavelength of 570 nm.

Cell viability of untreated sample and hydrogen ions implanted samples is studied

quantitatively with standard MTT assay protocol. Fig 13 shows percentage cell growth

versus H implanted samples with respect to positive reference (100%). All the treated

samples show cell viability more than 100%, maximum cell viability is observed about

192% in HSS1 likewise HSS2 and HSS3 also exhibit comparable cell viability of 170%

and 177% respectively, the untreated sample exhibits cell viability 141%. Least cell

viability is observed for highest H ion dose (1015 ions/cm2) of HSS4 which is 122.2%. H

implantation in near surface region makes the surface friendlier for hydrogen bonding

which consequently enhances hydrophilicity, HA precipitation and cell viability. Some

studies suggests that appropriate hydrophilic surfaces are often biocompatible [40, 61]

Surface topography is an important factor which determine biomedical response of

surface. Many studies has been conducted to understand the relation of protein

absorbance, cyto- compatibility and other cell responses with surface roughness [62-64].

HSS4 contains roughest surface among the entire sample under observation because it is

most heavily bombarded with H ions. Zareidoost et al claimed higher surface roughness

produce lower cyto- toxicity and better biocompatibility [65], a typical spindle like shape

of oral fibroblasts in all the treated samples is observed and it is observed that in treated

samples the cells are able to grow relatively longer [66, 67].

80

Fig 13: Bar graph of cell growth in different samples

4.4 Effect of carbon ion implantation in nitinol lattice

Several studies reveals that carbon ion implantation in material lattice improves corrosion

resistance and some mechanical properties of material [68, 69], in the first experiment

carbon ions were implanted in nitinol, the main objective of experiment was to study

variation in ion leakage by varying implanted ion dose.

4.4.1 Overview

Nitinol has been admired for super elasticity and shape memory effects. These two

properties make this alloy useful for number of biomedical applications such as

vascular stent, dental implant and bone fixation plates in orthopedics. But there are

some serious issues with this material and one of them is in vivo corrosion and toxic

Nickel release [70]. The released nickel causes many undesired effects like allergy, in

vivo cell death and disordered bone growth [71]. Several experiments were performed to

passivate the surface of this alloy and to build a barrier to prevent Ni escape from the

surface. Liu et al[72] studied the effects of multilayered Ti/TiN or single layered TiN

films on corrosion resistance of NiTi alloy in artificial saliva. Yeung et al [73]

treated NiTi alloy with nitrogen and oxygen using plasma immersion ion

implantation(PII I) and they concluded that nitrided samples were better for orthopedics

because they observed better degree of cell proliferation and lesser nickel ion release

0

50

100

150

200

250

HSS 1 HSS 2 HSS 3 HSS 4 Positive

Cel

l gro

wth

in p

erce

nta

ge

Hydrogen Ions Implanted Stainless Steel Samples Cell Viability Results with MTT Assay

81

from the surface. Zhao at al [74] also selected PIII to fabricate graded surface layers

of TiN and TiC on NiTi alloy. They observed consistent hydrophilicity but improved

surface roughness, improved corrosion resistance and better cell adhesion and

proliferation. Pogrebnjak et al [75] studied the effect of high dose implantation on nitinol.

They found increase in wear resistance, nano-hardness and corrosion resistance. Bulk

properties like pseudo plasticity and shape memory effect remained invariant. Green et al

[76] amorphized the surface of nitinol by N+ ion implantation and by controlled shot

peening. They found N+ ion implanted Ni-Ti contained a TiN phase within the surface

which reduced wetting. Lee et al implanted nitinol surfaces with high dose of boron up to

1017ions/cm2, they concluded that surface hardness of boron implanted nitinol exceeds

the surface hardness of stainless steel[77].

In this paper both ion implantation and oxidation layer coating are employed to

modify the surface of NiTi alloy. The samples are then analyzed using Fourier

transformed infrared spectroscopy (FTIR),x-ray diffraction (XRD), proton induced x-

ray emission (PIXE), hardness test and electrochemical corrosion potential.

4.4.2 Ion implantation and heat treatment of samples.

An oxidation layer is developed on the samples after annealing in muffle furnace. Out of

four prepared samples oxidation layer of one sample is removed by polishing the sample

using metal polish paste and subsequent cleaning in acetone. Ions are implanted using

Pelletron accelerator, having terminal voltage capacity 2MV in accelerator lab of GC

University (CASP) Lahore. Pelletron accelerator facility (2MV) is used for ion

implantation. Four samples are exposed with a beam of C + ions having 0.75MeV energy

for different intervals of time. The dose of each sample is calculated by using current of

the beam and exposure time. Sample 1, sample 2, sample 3 and the sample without

oxidation layer exposed to 2.4×1012, 8×1013, 8.32×1013and 3.32×1014ions /cm2

respectively.

4.4.2.1 Immersion of samples in SBF and Sample Preparation for PIXE Analysis SBF is prepared as proposed by Kokubo and his colleagues[78]. C+ implanted NiTi wires

are immersed in SBF for 150 days in order to provide enough time for ion leakage.

82

Residue in the SBF is dried at 35oC. This powder is then analyzed for presence of Ni ions

and remaining number of Calcium and Phosphate ions.

4.4.3 Results and Discussion

4.4.3.1 XRD Analysis X-Ray diffraction studies are performed to study the impact of ion implantation and

oxidation layer on crystallinity of nitinol surface. XRD profiles of four fabricated

samples are shown in figure 14, starting from least dose (≈2.4×1012ion/cm2) to maximum

(≈3.3×1014ion/cm2) and a profile of nitinol wire without oxidation layer and implanted

with the same dose (≈3.3×1014ion/cm2).

Maximum crystallinity has shown by the sample with minimum ion dose and by the

sample without oxidation layer. Crystallinity decreases (amorphization) by increasing the

dose. The fourth sample which is without oxidation layer and treated with maximum dose

has crystallinity comparable to the sample with least dose. Amorphization produced in

samples is due to hammering effects of implanted ions[79].

20 30 40 50 60 70 80

0

100

200

300

400

500

inte

nsi

ty(a

u)

2theta(degree)

2.4*1012

ions/cm2

8*1013

ions/cm2

3.3*1014

ions/cm2

3.3*1014

ions/cm2

witout oxidation layer

Fig 14: XRD Spectra of four Samples with doses

We know that the atomic radius of carbon (≈70pm) is smaller than both Ni (≈124pm) and

Ti (≈170pm). Substitutional settlement of C+ ions cannot increase the unit cell volume.

As peak shifting in samples 2 and 3 toward left indicates the increased volume of unit cell

that is due to interstitial accumulation of C+ Invariant peak position of sample 4 is evident

83

of lesser penetration due to harder surface. Peak shift in samples 2 and 3 also shows the

presence of stresses in the lattice due to penetration of ions. Oxidation layer and

implanted C+ are responsible for surface amorphization.

4.4.3.2 FTIR Analysis FTIR Analysis Fourier transformed infrared (FTIR) analysis is performed to analyze the

nature of functional groups accumulated on the substrate. Fig 15 shows the FTIR profiles

of different samples. Samples 1, 2 and 3 show phosphate absorbance peaks at wave

number approximately of 1000cm-1[80]. The fourth sample without oxidation layer does

not carry any representative peak of hydroxyapatite. These results can be confirmed from

PIXE analysis as well[81], which is given in next section.

500 1000 1500 2000 2500 3000

98

100

102

104

106

108

110

112

Inte

nsi

ty (

a.u

)

Wave Number (cm�-1)

2.4*1012

ions/cm2

8*1013

ions/cm2

3.3*1014

ions/cm2

3.3*1014

ions/cm2

without oxidation layer

Fig 15: FTIR spectra of four samples, revealing hydroxyapatite incubation on three

sample except the one without oxidation layer.

4.4. 3.3 PIXE Analysis

Proton/Particle induced X-Ray emission (PIXE) analysis is performed to estimate the

number of nickel ion released in simulated body fluid (SBF) and to calculate the number

of phosphate and calcium radicals left in SBF after 150-day incubation of hydroxyapatite

on as prepared samples. Remaining calcium and phosphate ions in SBF can reveal the

deposited calcium and phosphate ions on prepared samples. Proton beam of 3.8MeV

energy is used for PIXE analysis. Fig 16 shows normalized nickel release in SBF with

respect to ions/cm2. Ions release from the sample 4 is maximum with the same dose of

84

ions as sample 3. Nickel release decreases by decreasing of implanted ion dose.

Implanted ions in nitinol produce dual effect on the surface of the substrate: firstly they

cause surface damage by producing void and channels resulting in an increased surface

area; secondly, the amorphization is also achieved by implanted ion. SRIM calculations

show that at 0.75MeV energy one C+ ion can produce about 722 vacancies in the lattice.

Damage produced on the surface provides additional degrees of freedom for ion leakage.

The competing factor surface amorphization can prevent ion escape from the lattice. Fig.

16 shows the competition of both mentioned factors compete up to a limit then the ion

escape factor becomes more dominant as the dose is increased from a certain limit

(9×1013ions/cm2), which results in a steeper graph. Other positive effects of C+

implantation and oxidation layer are clear from Fig. 6 that calcium and phosphate

incubation is greater on heavily implanted species. Least number of Ca and P species is

found in the solution in which sample 3 is immersed which conversely indicates

maximum deposition. Minimum apatite growth and maximum nickel release are

observed by the same sample without oxidation layer.

3.0x1013

6.0x1013

9.0x1013

1.2x1014

1.5x1014

0.00000

0.00001

0.00002

0.00003

0.00004

0.00005

0.00006

0.00007

no

rma

lize

d n

ickle

io

n r

ele

ase

ions/cm2

without oxidation layer

Fig16: PIXE study of Ni ion release, Normalized graph Nickel release versus ion/cm2

85

Fig17: PIXE spectra of four samples

0.0 3.0x1013

6.0x1013

9.0x1013

1.2x1014

1.5x1014

0.00

0.01

0.02

0.03

0.04

0.05

0.06

no

rma

lize

d r

em

ain

ing

co

nce

ntr

atio

n

of C

a a

nd

P s

pe

cie

sin

SB

F

ion/cm2

p

Ca

witout oxidation layer

Fig 18: PIXE study of Ca and P ions transferred from SBF to substrates, Normalized

graph between remaining Ca and P ions in SBF versus ion/cm2

4.4. 3.4 Corrosion potential and passivation time

Four samples are chosen to study the behavior of fabricated samples toward corrosion

tendency. Sample1 (dose=2.4×1012ions/cm2), sample 2 (dose=8×1013 ions/cm2), un-

annealed sample (dose=3.3×1013ions/cm2), and the sample without oxidation layer

(dose=3.3×1013ions/cm2). The corrosion potential versus time graph of these four

samples is shown in Fig 19 Sample 1with minimum implanted carbon ions has maximum

initial corrosion potential among all the other that is more than +6VSCE. The corrosion

potential then increases with time toward a saturation point that is approximately 12VSCE

86

for Sample 2 with greater number of implanted ions (8×1013ions/cm2) and

correspondingly has greater surface damage due to greater ion exposure. The sample is

initially more reactive in ringer lactate solution as compared to sample1.This is due to

larger exposed surface area. The surface area is increased due to voids and damages

produced on the surface by C+ ion bombardment and consequently greater local corrosion

on wider surface area. Similar initial behavior is observed for sample3 with maximum

number of implanted ions, maximum damage and largest number of voids resulting in

highest initial activity. Right after the initial activity on the surface the passivation starts

and all the samples attain the saturation point. These three samples show the same linear

behavior with time. The fourth sample whose oxidation layer is removed exhibits

peculiar behavior starting from +ve potential= +2VSCE and stays on the same value

throughout the observation. There is no increase in corrosion potential, no saturation

value and no passivation like sample1, Sample2 and sample 3. This shows that oxidation

layer in other three samples is responsible for initializing and catalyzing the passivation

and lesser damage depth in sample4.Three samples are initially active and the activity

decreases as the vacant sites (voids due to damage) seal themselves with oxidation

species resulting in greater corrosion potential. No oxidation layer in fourth sample and

lesser penetration depth due to harder surface which does not appreciate passivation [82].

Fig 19: Corrosion potential versus Time, graph showing passivation with time.

87

4.4.3.5 Hardness Test

Micro-hardness of samples is measured using Vickers hardness tester at a maximum load

of 200g. The hardness profile shows a linear increase in hardness by increasing

ions/cm2except the sample without oxidation layer. The slope of the graph is steeper

initially up to 9 x1013ions then the slop decreases. In other words, less increase in

hardness per unit ion occurs after 9 x1013 ions/cm2. Similar hardness behavior is also

reported by Naveed et al [45]. They found proton irradiated un-annealed nitinol gets

harder with greater rate per unit ion initially and then lesser increase for higher doses, that

is due to increased surface damage, wear and tear.

0.0 3.0x1013

6.0x1013

9.0x1013

1.2x1014

1.5x1014

200

220

240

260

280

300

320

340

360

380

400

420

440

ha

rdn

ess

ions/cm2

without oxidation layer

Fig 20: Hardness profile of fabricated samples (Hardness VS C+ ions/cm2)

Refrences

[1] Sansone V, Pagani D, Melato M. The effects on bone cells of metal ions released

from orthopaedic implants. A review. Clinical Cases in Mineral and Bone Metabolism

2013;10:34-40.

[2] Kokubo TaT, H. . Simulated Body Fluid (SBF) as a Standard Tool to Test the

Bioactivity of Implants, in Handbook of Biomineralization: Biological Aspects and

Structure Formation Wiley-VCH Verlag GmbH, Weinheim, Germany doi:

101002/9783527619443 (2007);Ch51.

[3] Kara L. Menzies aLJ. The Impact of Contact Angle on the Biocompatibility of

Biomaterials” Optometry and Vision Science 2010;Vol. 87.

[4] Majeed A, He J, Jiao L, Zhong X, Sheng Z. Surface properties and biocompatibility

of nanostructured TiO2 film deposited by RF magnetron sputtering. Nanoscale Research

Letters 2015;10:56.

[5] Belibel R, Avramoglou T, Garcia A, Barbaud C, Mora L. Effect of chemical

heterogeneity of biodegradable polymers on surface energy: A static contact angle

88

analysis of polyester model films. Materials Science and Engineering: C 2016;59:998-

1006.

[6] Saini M, Singh Y, Arora P, Arora V, Jain K. Implant biomaterials: A comprehensive

review. World Journal of Clinical Cases : WJCC 2015;3:52-7.

[7] Chen Q, A. Thouas G. Metallic implant biomaterials2015.

[8] Thair L, Mudali UK, Bhuvaneswaran N, Nair KGM, Asokamani R, Raj B. Nitrogen

ion implantation and in vitro corrosion behavior of as-cast Ti–6Al–7Nb alloy. Corrosion

Science 2002;44:2439-57.

[9] Krupa D, Baszkiewicz J, Jezierska E, Mizera J, Wierzchoń T, Barcz A, et al. Effect of

nitrogen-ion implantation on the corrosion resistance of OT-4-0 titanium alloy in 0.9%

NaCl environment. Surface and Coatings Technology 1999;111:86-91.

[10] Muhammad-Sadeeq Balogun WQ, a Wang Wang, Pingping Fang, Xihong Lu and

Yexiang Tong Recent advances in metal nitrides as high-performance electrode materials

for energy storage devices Journal of material chemistry A 2015:1364-87.

[11] Hendra Hermawan DRaJRPD. Metals for Biomedical Applications, Biomedical

Engineering - From Theory to Applications, .

. InTech, DOI: 105772/19033 2011;Prof. Reza Fazel (Ed.),.

[12] Kubies D, Himmlova L, Riedel T, Chanova E, Balik K, Douderova M, et al. The

interaction of osteoblasts with bone-implant materials: 1. The effect of physicochemical

surface properties of implant materials. Physiological research 2011;60:95-111.

[13] Plecko M, Sievert C, Andermatt D, Frigg R, Kronen P, Klein K, et al.

Osseointegration and biocompatibility of different metal implants - a comparative

experimental investigation in sheep. BMC Musculoskeletal Disorders 2012;13:32-.

[14] Simard T, Hibbert B, Ramirez FD, Froeschl M, Chen YX, O'Brien ER. The

evolution of coronary stents: a brief review. The Canadian journal of cardiology

2014;30:35-45.

[15] Chenglong Liu PKC, Guoqiang Lin, Dazhi Yang Effects of Ti/TiN multilayer on

corrosionresistance of nickel–titanium orthodontic bracketsin artificial saliva. Corrosion

Science 2007: 3783–96.

[16] de Groot K, Geesink R, Klein CP, Serekian P. Plasma sprayed coatings of

hydroxylapatite. Journal of biomedical materials research 1987;21:1375-81.

[17] Shabalovskaya S, Anderegg J, Van Humbeeck J. Critical overview of Nitinol

surfaces and their modifications for medical applications. Acta biomaterialia 2008;4:447-

67.

[18] Jabbari YSA, Fehrman J, Barnes AC, Zapf AM, Zinelis S, Berzins DW. Titanium

Nitride and Nitrogen Ion Implanted Coated Dental Materials. Coatings 2012;2:160.

[19] Li J, Zhou L, Li Z. Corrosion behaviors of a new titanium alloy TZNT for surgical

implant application in Ringer’s solution. Rare Metals 2010;29:37-44.

[20] Martinesi M, Bruni S, Stio M, Treves C, Bacci T, Borgioli F. Biocompatibility

evaluation of surface-treated AISI 316L austenitic stainless steel in human cell cultures.

Journal of biomedical materials research Part A 2007;80:131-45.

[21] David S, Serena MB. Production of zinc substituted hydroxyapatite using various

precipitation routes. Biomedical Materials 2013;8:025003.

[22] Camargo NHA, de Lima, S.A. and Gemelli, E. . Synthesis and Characterization of

Hydroxyapatite/TiO2n Nanocomposites for Bone Tissue Regeneration. American Journal

of Biomedical Engineering 2012;2:41-7.

89

[23] Kokubo T, Takadama H. How useful is SBF in predicting in vivo bone bioactivity?

Biomaterials 2006;27:2907-15.

[24] , Rapacz-Kmita AP, C.; Ślósarczyk, A.; Paszkiewicz, Z. FTIR and XRD

investigations on the thermal stability of hydroxyapatite during hot pressing and

pressureless sintering processes. Journal of Molecular Structure 2005;744:653-7.

[25] Rapacz-Kmita A, Paluszkiewicz C, Ślósarczyk A, Paszkiewicz Z. FTIR and XRD

investigations on the thermal stability of hydroxyapatite during hot pressing and

pressureless sintering processes. Journal of Molecular Structure 2005;744:653-6.

[26] Jiang HC, Rong LJ. Effect of hydroxyapatite coating on nickel release of the porous

NiTi shape memory alloy fabricated by SHS method. Surface and Coatings Technology

2006;201:1017-21.

[27] Kawai T, Takemoto M, Fujibayashi S, Akiyama H, Tanaka M, Yamaguchi S, et al.

Osteoinduction on Acid and Heat Treated Porous Ti Metal Samples in Canine Muscle.

PLOS ONE 2014;9:e88366.

[28] M.Lee MSMAP. Synthesis and Characterization of Hydroxyapatite Nanoparticles

and β-TCP

Particles 2nd International Conference on Biotechnology and Food Science

IPCBEE, IACSIT Press, Singapore 2011;7.

[29] Kokubo T, Kushitani H, Sakka S, Kitsugi T, Yamamuro T. Solutions able to

reproduce in vivo surface-structure changes in bioactive glass-ceramic A-W3. Journal of

biomedical materials research 1990;24:721-34.

[30] Khan AF, Awais M, Khan AS, Tabassum S, Chaudhry AA, Rehman IU. Raman

Spectroscopy of Natural Bone and Synthetic Apatites. Applied Spectroscopy Reviews

2013;48:329-55.

[31] Yilmaz B, Evis Z. Raman Spectroscopy Investigation of Nano Hydroxyapatite

Doped with Yttrium and Fluoride Ions. Spectroscopy Letters 2014;47:24-9.

[32] Hadrich A, Lautie A, Mhiri T. Vibrational study and fluorescence bands in the FT-

Raman spectra of Ca(10-x)Pb(x)(PO4)6(OH)2 compounds. Spectrochimica acta Part A,

Molecular and biomolecular spectroscopy 2001;57:1673-81.

[33] Sobczak-Kupiec A, Wzorek Z, Kijkowska R, Kowalski Z. Effect of calcination

conditions of pork bone sludge on behaviour of hydroxyapatite in simulated body

fluid2013.

[34] El Boujaady H, Mourabet M, Abdelhadi ER, Bennani-Ziatni M, El Hamri R,

Abderrahim T. Adsorption of a textile dye on synthesized calcium deficient

hydroxyapatite (CDHAp): Kinetic and thermodynamic studies2016.

[35] Mujahid M, Sarfraz S, Amin S. On the Formation of Hydroxyapatite Nano Crystals

Prepared Using Cationic Surfactant. Materials Research 2015;18:468-72.

[36] Maleki-Ghaleh H, Khalil-Allafi J, Khalili V, S. Shakeri and M, Javidi M. Effect of

hydroxyapatite coating fabricated by electrophoretic deposition method on corrosion

behavior and nickel release of NiTi shape memory alloy2014.

[37] Peitl Filho O, LaTorre GP, Hench LL. Effect of crystallization on apatite-layer

formation of bioactive glass 45S5. Journal of biomedical materials research 1996;30:509-

14.

[38] Liu X, Fu RK, Poon RW, Chen P, Chu PK, Ding C. Biomimetic growth of apatite on

hydrogen-implanted silicon. Biomaterials 2004;25:5575-81.

90

[39] Rizwan M, Ahmad A, Deen KM, Haider W. Electrochemical behavior and

biological response of Mesenchymal Stem Cells on cp-Ti after N-ions implantation.

Applied Surface Science 2014;320:718-24.

[40] Menzies KL, Jones L. The impact of contact angle on the biocompatibility of

biomaterials. Optometry and vision science : official publication of the American

Academy of Optometry 2010;87:387-99.

[41] BIKERMAS JJ. SURFACE ROUGHNESS AND CONTACT ANGLE. Research

Laboratories, Merck and company 1949.

[42] Moita As, Moreira ALN. Influence of surface properties on the dynamic behavior of

impacting droplets2017.

[43] Kittu Anjana T, Bulut R, Puckette J. Effects of Surface Roughness on Contact Angle

Measurements on a Limestone Aggregate.

[44] A. D. Pogrebnyak SNB, V. M. Beresnev, N. Levintant-Zayonts, . Shape memory

effect and superelasticity of titanium nickelide alloys implanted with high ion doses.

Russian Chem Reviews 2013;82: 1135–59

[45] Afzal N, Ghauri IM, Mubarik FE, Amin F. Mechanical response of proton beam

irradiated nitinol. Physica B: Condensed Matter 2011;406:8-11.

[46] Navarro M, Michiardi A, Castaño O, Planell JA. Biomaterials in orthopaedics.

Journal of the Royal Society Interface 2008;5:1137-58.

[47] Hallab NJ, Bundy KJ, O'Connor K, Moses RL, Jacobs JJ. Evaluation of metallic and

polymeric biomaterial surface energy and surface roughness characteristics for directed

cell adhesion. Tissue engineering 2001;7:55-71.

[48] Liu X, Chu PK, Ding C. Surface modification of titanium, titanium alloys, and

related materials for biomedical applications. Materials Science and Engineering: R:

Reports 2004;47:49-121.

[49] Zhang F, Kang ET, Neoh KG, Wang P, Tan KL. Surface modification of stainless

steel by grafting of poly(ethylene glycol) for reduction in protein adsorption.

Biomaterials 2001;22:1541-8.

[50] Ramakrishna S, Mayer J, Wintermantel E, Leong KW. Biomedical applications of

polymer-composite materials: a review. Composites Science and Technology

2001;61:1189-224.

[51] Niinomi M. Recent metallic materials for biomedical applications. Metallurgical and

Materials Transactions A 2002;33:477.

[52] El Feninat F, Laroche G, Fiset M, Mantovani D. Shape Memory Materials for

Biomedical Applications. Advanced Engineering Materials 2002;4:91-104.

[53] Scholz MS, Blanchfield JP, Bloom LD, Coburn BH, Elkington M, Fuller JD, et al.

The use of composite materials in modern orthopaedic medicine and prosthetic devices:

A review. Composites Science and Technology 2011;71:1791-803.

[54] Desai NP, Hubbell JA. Biological responses to polyethylene oxide modified

polyethylene terephthalate surfaces. Journal of biomedical materials research

1991;25:829-43.

[55] Han DK, Park KD, Ryu GH, Kim UY, Min BG, Kim YH. Plasma protein adsorption

to sulfonated poly(ethylene oxide)-grafted polyurethane surface. Journal of biomedical

materials research 1996;30:23-30.

[56] Good RJ, van Oss CJ. The Modern Theory of Contact Angles and the Hydrogen

Bond Components of Surface Energies. In: Schrader ME, Loeb GI, editors. Modern

91

Approaches to Wettability: Theory and Applications. Boston, MA: Springer US; 1992. p.

1-27.

[57] Kubiak K, Wilson M, Mathia T, Carval P. Wettability versus roughness of

engineering surfaces2009.

[58] Kang TJ, Kim J-G, Lee H-Y, Lee J-S, Lee J-H, Hahn J-H, et al. Modification of

optical and mechanical surface properties of sputter-deposited aluminum thin films

through ion implantation. International Journal of Precision Engineering and

Manufacturing 2014;15:889-94.

[59] Tian Y, Jiang L. Wetting: Intrinsically robust hydrophobicity. Nat Mater

2013;12:291-2.

[60] Muller L, Muller FA. Preparation of SBF with different HCO3- content and its

influence on the composition of biomimetic apatites. Acta biomaterialia 2006;2:181-9.

[61] Lincks J, Boyan BD, Blanchard CR, Lohmann CH, Liu Y, Cochran DL, et al.

Response of MG63 osteoblast-like cells to titanium and titanium alloy is dependent on

surface roughness and composition. Biomaterials 1998;19:2219-32.

[62] Boyan BD, Sylvia VL, Liu Y, Sagun R, Cochran DL, H. Lohmann C, et al. Surface

roughness mediates its effects on osteoblasts via protein kinase A and phospholipase A2.

Biomaterials 1999;20:2305-10.

[63] Deligianni DD, Katsala N, Ladas S, Sotiropoulou D, Amedee J, Missirlis YF. Effect

of surface roughness of the titanium alloy Ti-6Al-4V on human bone marrow cell

response and on protein adsorption. Biomaterials 2001;22:1241-51.

[64] Zareidoost A, Yousefpour M, Ghaseme B, Amanzadeh A. The relationship of

surface roughness and cell response of chemical surface modification of titanium. Journal

of materials science Materials in medicine 2012;23:1479-88.

[65] Citeau A, Guicheux J, Vinatier C, Layrolle P, Nguyen TP, Pilet P, et al. In vitro

biological effects of titanium rough surface obtained by calcium phosphate grid blasting.

Biomaterials 2005;26:157-65.

[66] Chung TW, Liu DZ, Wang SY, Wang SS. Enhancement of the growth of human

endothelial cells by surface roughness at nanometer scale. Biomaterials 2003;24:4655-61.

[67] Anselme K, Bigerelle M, Noel B, Dufresne E, Judas D, Iost A, et al. Qualitative and

quantitative study of human osteoblast adhesion on materials with various surface

roughnesses. Journal of biomedical materials research 2000;49:155-66.

[68] Krupa D, Jezierska E, Baszkiewicz J, Wierzchoń T, Barcz A, Gawlik G, et al. Effect

of carbon ion implantation on the structure and corrosion resistance of OT-4-0 titanium

alloy. Surface and Coatings Technology 1999;114:250-9.

[69] Poon RWY, Yeung KWK, Liu XY, Chu PK, Chung CY, Lu WW, et al. Carbon

plasma immersion ion implantation of nickel–titanium shape memory alloys.

Biomaterials 2005;26:2265-72.

[70] Heintz C, Riepe G, Birken L, Kaiser E, Chakfe N, Morlock M, et al. Corroded

nitinol wires in explanted aortic endografts: an important mechanism of failure? Journal

of endovascular therapy : an official journal of the International Society of Endovascular

Specialists 2001;8:248-53.

[71] Kao C-T, Ding S-J, He H, Chou MY, Huang T-H. Cytotoxicity of Orthodontic Wire

Corroded in Fluoride Solution In Vitro. The Angle Orthodontist 2007;77:349-54.

92

[72] Liu C, Chu PK, Lin G, Yang D. Effects of Ti/TiN multilayer on corrosion resistance

of nickel–titanium orthodontic brackets in artificial saliva. Corrosion Science

2007;49:3783-96.

[73] Yeung KWK, Chan RYL, Lam KO, Wu SL, Liu XM, Chung CY, et al. In vitro and

in vivo characterization of novel plasma treated nickel titanium shape memory alloy for

orthopedic implantation. Surface and Coatings Technology 2007;202:1247-51.

[74] Zhao Y, Wong SM, Wong HM, Wu S, Hu T, Yeung KWK, et al. Effects of Carbon

and Nitrogen Plasma Immersion Ion Implantation on In vitro and In vivo

Biocompatibility of Titanium Alloy. ACS Applied Materials & Interfaces 2013;5:1510-6.

[75] Pogrebnjak A, Bratushka S, Levintant-Zayonts N. High Dose Ion Implantation Into

NiTi for Improvement of Pseudoplasticity and Shape Memory Effect2013.

[76] Green SM, Grant DM, Wood JV. XPS characterisation of surface modified Ni-Ti

shape memory alloy. Materials Science and Engineering: A 1997;224:21-6.

[77] Lee D-H, Park B, Saxena A, Serene TP. Enhanced surface hardness by boron

implantation in nitinol alloy. Journal of Endodontics 1996;22:543-6.

[78] Kokubo T, Takadama H. How useful is SBF in predicting in vivo bone bioactivity?

Biomaterials 2006;27:2907-15.

[79] G. Dearnaley. Ion bombardment and implantation”. Prog Phys 1969; 32,:405-91.

[80] Wu S, Liu X, Chan YL, Ho JPY, Chung CY, Chu PK, et al. Nickel release behavior,

cytocompatibility, and superelasticity of oxidized porous single-phase NiTi. Journal of

Biomedical Materials Research Part A 2007;81A:948-55.

[81] REHMAN I, BONFIELD W. Characterization of hydroxyapatite and carbonated

apatite by photo acoustic FTIR spectroscopy. Journal of Materials Science: Materials in

Medicine 1997;8:1-4.

[82] Alzubaydi TL, Alameer SS, Ismaeel T, Alhijazi AY, Geetha M. In vivo studies of

the ceramic coated titanium alloy for enhanced osseointegration in dental applications.

Journal of materials science Materials in medicine 2009;20 Suppl 1:S35-42.

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Chapter 5

5. Conclusion and future work

Several experiments are performed to improve the performance of currently used,

conventional biomedical materials (stainless steel, nickel-titanium alloy) and potential

candidate materials (iron and magnesium) for future biodegradable implant application.

The modified materials are tested for their potential applications and related issues, such

as surface modified nickel titanium alloy is tested for nickel ion release in simulated body

fluid because the toxic ion escape from the surface of nickel titanium alloy is an issue.

The modified stainless steel samples are characterized corrosion, cell viability and

wettability properties because the stability and improved hydroxyapatite incubation is

desired for stainless steel.

Out of all the performed experiments only three experiments are reported in presented

thesis and to the international journals. Some of the experiments are in the pipeline

(under the process of write up and characterization), and many of the experiments are not

found suitable to report due to adverse effects of ion implantations.

5.1 Conclusions In the first experiment singly charged, monoatomic nitrogen ions are accelerated under

250 KV potential and implanted in stainless steel surface subsequently. The effect of

nitrogen ion implantation on the surface of stainless steel is investigated using different

techniques. XRD profiles show improved incubation of HA over the surface in higher ion

dose samples. Raman spectroscopy describes greater peak intensity of HA functional

groups by greater ion implantation, XRD and Raman spectroscopy results are confirmed

by SEM profiles, these profiles show greater surface area of samples is covered with HA

in greater ion implanted samples. Human oral fibroblasts response shows enhanced cell

viability by ion implantation. Therefore improved biomedical properties are observed in

prepared sample.

In the second experiment, stainless steel surfaces are modified using an energetic beam of

H ions with the help of particle accelerator by using various ion doses. The effect of

increasing ion dose is observed on different properties of stainless steel.

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It is observed that:

Hydrophilicity of surface is found increasing with H ion dose.

Greater HA incubation is observed on treated samples.

Treated surfaces are found more compatible for cell growth as observed in cell viability

profiles of samples.

Nickel titanium alloy was modified by accelerated carbon ion implantation. Singly

charged monoatomic carbon ions were accelerated under 0.375 MV of potential, 0.75

MeV ions are implanted in nickel titanium alloy. The prepared samples are evaluated for

stability (corrosion resistance), hydroxyapatite incubation, hardness and nickel ion

release in simulated body fluid. Hydroxyapatite incubation and passivation (increase

in corrosion potential VSCE) is not observed at all in the sample without oxidation

layer. Maximum nickel release is also observed from the same sample.

Increasing ion dose in the samples produces following effects

Lesser crystallinity and increased volume of the unit cell which is attributed to the

interstitial accumulation of C +ions in the lattice.

Greater initial reactivity in ringer lactate solution, but all the samples saturate at

same Level of corrosion potential (VSCE= 12V) after the same interval of time

(≈450seconds).

Ni release and calcium phosphate incubation increase insignificantly up to

8×1013ions/cm2 and then increase per unit ion

FTIR and PIXE analysis are in agreement to confirm no incubation of

hydroxyapatite in the sample without oxidation layer.

Hardness increases with greater rate up to 8×1013ions/cm2 and then lesser increase

/ion and hardness is maximum for the sample without oxidation layer.

5.2 Future work

Biodegradable materials both polymeric and metallic are being considered as potential

candidate for biomedical applications. The advantage to use biodegradable material is to

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avoid the second surgery, the second surgery is normally performed to remove implanted

material. The elimination of a surgery from the therapeutic process may potentially

reduce the risk, complications and cost of the process. Therefore biodegradable materials

may be considered for future studies.

Iron and magnesium are the favorite materials of researchers due to their generic property

of biodegradability. But there are issues with both iron and magnesium, the issues include

rapid degradability of magnesium and gentle degradability of magnesium, the problem

may be attempted to cater in different ways.

Some new materials may be searched for the purpose.

Some composites may be prepared to have desired set of properties.

Surface modification techniques may be applied to tailor the surface properties.

Ion implantation is a versatile technique to tailor the surface properties.

List of Publications

Muhammad Ahsan Shafique, G. Murtaza, Shahzad Saadat, Muhammad K H

Uddin & Riaz Ahmad. Improved cell viability and hydroxyapatite growth on

nitrogen ion-implanted surfaces.Radiation Effects and Defects in Solids 172, 7-8,

(2017)

Muhammad Ahsan Shafique, G Murtaza, S. Saadat, Z. ZAHEER, M.

Shahnawaz, M. KH UDDIN, RIAZ AHMAD.STUDY OF NICKEL ION

RELEASE IN SIMULATED BODY FLUID FROM C+-IMPLANTED NICKEL

TITANIUM ALLOY, Surface Review and Letters. 1650045(2016).

Muhammad A Shafique, R Ahmad, Ihtesham Ur Rehman: Study of wettability

and cell viability of H implanted stainless steel. Mater. Res. Express 5 036509

(2018).

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MA Shafique, SA Shah, M Nafees, K Rasheed, R Ahmad. Effect of doping

concentration on absorbance, structural, and magnetic properties of cobalt-doped

ZnO nano-crystallites. International Nano Letters 2 (1), 31.

SA Shah, A Majeed, MA Shafique, K Rashid, SU Awan. Cell viability study of

thermo-responsive core–shell superparamagnetic nanoparticles for multimodal

cancer therapy. Applied Nanoscience 4 (2), 227-232.

M Nafees, W Liaqut, S Ali, MA Shafique. Synthesis of ZnO/Al: ZnO

nanomaterial: structural and band gap variation in ZnO nanomaterial by Al

doping. Applied Nanoscience 3 (1), 49-55(2013).

M Nafees, S Ali, S Idrees, K Rashid, MA Shafique. A simple microwave assists

aqueous route to synthesis CuS nanoparticles and further aggregation to spherical

shape Applied Nanoscience 3 (2), 119-124 (2013).

G Murtaza, R Ahmad, MS Rashid, M Hassan, A Hussnain, MA.

Shafique.Structural and magnetic studies on Zr doped ZnO diluted magnetic

semiconductor. Current Applied Physics 14 (2), 176-181 (2014)

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