Titanium and Its Biomedical Uses

8/19/2019 Titanium and Its Biomedical Uses

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Titanium and itsbiomedical uses: TotalHip Arthroplasty (THA)

Danny FreitasChris Mah

Siavash Soltani


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Anatomy of hip [8]


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History of Total Hip Arthroplasty (THA)

1891: First THA design using Ivory

adhered with glue, proposed by

Themistocles Gluck1

1925: Mold arthroplasty proposed

by Marius Smith-Peterson, usingglass as a hollow shell to be fit

over the femoral head2.

1953: First instance of metal-

on-metal THA, proposed by

George McKee4.

1970s: Sir John C

THA design, usin

stem, polyethylen

component and a

1930s: Marius Smith-Peterson and

Phillip Wiles proposed the stainless

steel hip replacement, fitted to the

bone with bolts and screws3.


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History of Total Hip Arthroplasty (THA)

X-ray, total hip arthropIvory hip implant [1]

Titanium alloy hip implant w/ HA coating [2]


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PropertiesCommercially pure Ti and low interstitial Ti-6Al-4V are the two mo

Ti based implants

● Biologically inert

● No adverse reactions and are tolerated by human tissues

● No allergic reactions● Formation of passive oxide layer

● Low elastic modulus is achievable to avoid stress shielding


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Manufacturing Techniques● Traditional methods: casting and machining

Vs

● Advance techniques: injection molding and additive layer ma

Advantages: Design flexibility, cost saving, reduce waste, custom-

implants


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Injection Molding● Metal Injection Molding (MIM)

- A specialized form

of plastic injection molding

uses metal powder

mixed with some type of binder

- Four steps:

1) Feedstock preparation

2) Injection molding

3) Removing the binder

4) Sintering

Flow chart for Ti-PIM process [S4


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Injection Molding

A TGA test can confirm that debinding was successful:

Shorter period of time in Argon

Weight loss curves for PMMA at a heating rate of 5 ◦C/m

before and after thermal pyrolysis [S5]


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Injection Molding● Comparison of surface properties of machined and MIM Ti

Surface profiles coming from machined samples and sintered samples [S7]


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Additive Layer ManufacturingUsing a laser beam or electron

beam to melt the metal powder

to build complicated

components

http://www.youtube.com/watch?v=OSIImvwfNnshttp://www.youtube.com/watch?v=OSIImvwfNnshttp://www.youtube.com/watch?v=OSIImvwfNns


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Stress Shielding● Biomechanical mismatch of Ti-6Al-4V

- Outer cortical region of dense bone:

E=16 to 20 GPa

- Inner trabecular bone:

E= an order of magnitude less than cortical

- Elastic modulus for commercial Ti-6Al-4V

is about 105 to 110 GPa


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Additive Layer ManufacturingDiamond and hatch structures of Ti-6Al-4V manufactured by ALM

SEM image of Ti–6Al–4V diamond and hatched structure [S11]


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Additive Layer Manufacturingthe diamond structure exhibits properties comparable with trabe

whereas the hatched structure’s properties lie in between those o

and cortical bone

Mechanical properties of the untreated cellular Ti–6Al–4V structures tested in compression with the loading direction parallel a

direction of the specimens, where E is elastic modulus, σy0.2 is the yield strength, σmax is the maximum strength [S10]


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Corrosion● Corrosion - The tendency for a metal to dissolve in the presen

water, releasing metallic ions in the surrounding environmen● Dependant upon;

○ The mechanical and chemical properties of the metal.○ The environment you choose to observe.


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● In biological systems, the equilibrium between metal dissolut

metal redeposition is never reached, and corrosion is allowed

because of a cyclic redox reaction between the metal dissolu

(eq. 1) and biological reduction (cathode). (eq. 2)

Corrosion


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Passivation

● Formation of a protective oxide layer, the lowest energy state

can attain, that makes them less reactive with both air and w


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Passivation

Passivation and contamination of titanium over time [5] Active, Passive and Tra

electric potential [6]


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Corrosion Resistance

The electric potential at which the metalcan still dissolve to form metallic ions

The electric potential at which the metal

can still form an oxide layer

The electric potential at which the metal

will readily corrode in the body


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Regardless of material properties, the morphology and geometry or wear particles have been s


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THA using PE to reduce wear [7]


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Potential Solutions

● Anodising titanium in acid

● Flame, plasma and detonation gun sprayed co

● Nitride coating

● Conversion coating


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Alternative Materials● Stainless Steel

○ Fe-18-18Cr-14Ni-2.5Mo

■ 316L ASTM F138

● Cobalt Alloys○ Co-28Cr-6Mo

■ Cast CoCrMo ASTM F75

○ Co-35Ni-20Cr-10Mo

■ Wrought CoNiCrMo ASTM F562

● Alumina (not in clinical uses in the United States)○ ASTM F603

■ Compressive strength: 4000MPa

■ Flexural strength: 400MPa

■ Elastic Modulus: 380GPa

Properties 316L Ca

CoC

TensileStrength

(MPa)

862 655-

YieldStrength(MPa)

689 448-

Elastic

Modulus(GPa)

200 210

Mechanical properties of various materials used i

[C1][C2][C3]


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Stainless Steel 316L● Inexspensive

● Manufactured with common

methods

● Readily available

● High yield strength

● High tensile strengthStainless steel 316L rods [C4]

● Long term exposuenvironment resucorrosion and pitt

● Relatively low fatig(383MPa at 107 cyc

● High elastic modu

to bone

SEM imaging of SS316L showing pitting after accelerated

corrosion[C5]


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Cobalt Alloys● Most commonly used metals for hip

implants

● Cobalt not particularly biocompatible

○ Chromium addition creates a passivating

oxide film

■ Corrosion resistance an order of

magnitude better than SS316L

● High fatigue strength (793MPa for F562107 cycles)

● High wear resistance

Hip joint made of Co-Ni-Cr-Mo (ASTM

F562) [C2]

● Brittle

● Relatively poor bioco

● High elastic modulus

bone

B

(A


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Alumina● Very high compressive strength (4000MPa)

● Excellent corrosion resistance

● Bioinert● Exceptionally low friction coefficient and

wear rate

Friction and wear of alumina-alumina hip joint compared to a metal-PE prosthesis[C2]

Alumina-on-alumina bearing for hip replacemen

● Difficult manufacturin○ grain size under○ 99.7% purity○ 1700C sintering

● If loosely fitted, encapcan reach 100s of um

● Brittle● Extremely high elastic


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Advantages of Titanium

A comparison of orthopaedic metallic implant materials[C6]


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Advantages of Titanium

Elastic modulus values of orthopaedic alloys[C6]

● Lowest elastic modulus materials

● TiO2 passivating layer isgrown when Ti is expose○ Contributes to its r

corrosion resistanc● Mixing of hydroxyl functi

TiO2 layer allows for rela

osseointegration● Basis for further researc

○ Alloys○ Grain structuring○ Structure


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Advancements in Titanium-Alloys● -phase

○ TC

○ BCC - ductile○ Stabilizers

■ -isomorphous

● Mo,V,Nb,Ta● Most interest as

alloys give lowest

E■ -eutectoid

● Fe,W,Cr,Si,Ni,Co,

Mn,H

● (+) Ti Alloys

○ Provides higher YSfatigue strength○ Ti-6Al-4V, Ti-6Al-7

■ Fatigue Stres(MPa): 625, 6

● Ti Alloys○ Provides a lower e○ Lower notch sensit

and (+) Ti Allo○ Mo>10○ Ti-12Mo-6Zr-2Fe (

3Nb-0.3Si(21SRx)5.7Ta(TNZT)

○ Fatigue strength at

(MPa): 525, 490, 2


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Advancements in Titanium-Alloys

Properties of various titanium alloys[C6]


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Advancements in Titanium-Sever Plastic Def

● Alternative approach to alloying in order to get more favorab

mechanical properties and prevent potentially harmful ion re

● Efficient fabrication of bulk nanocrystalline titanium● High plastic strains, complex stress rates, hydrostatic pressu

strains break down coarse grains to ultrafine(100nm-1000nm

sized(under 100nm) grains

Chemical compositions of the 4 grades of Ti CP[C3]

Properties of the 4 grades of Ti CP[C3]


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Advancements in Titanium-Severe Plastic De● Equal Channel Angular Extrusion (ECAP):

○ Material pressed through a special die with two channels intersecting angle

○ Material can have multiple passes

● High Pressure Torsion (HPT)○ Small disk is placed between two anvils

○ High pressure is applied and one anvil is rotated

○ Pure shear stress● Accumulative Roll Bonding(ARB)

○ Sheets of material are ran through two rolls causing a severe reduction r

● Hydrostatic Extrusion(HE)○ Material surrounded by hydrolic fluid and pressed through die


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Advancements in Titanium-Severe Plastic De

Mechanical Properties of nanostructured titanium and Ti-based alloys produced with various SPD methods[C8]


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Advancements in Titanium-Structure● Decrease in elastic modul

compressive strength clos

● Porous gradient structureselastic modulus, but providcapabilities in comparison

porous material● Outer shell of porous grad

architecture mimicking tha○ porosity of 70% and

the range of 200-500● Allows for new bone tissue

(a) SEM imaging of the overall structure of porous titanium with a porosity gradient (b)

Enlarged SEM imaging of porous structure[C9]

Mechanical properties of sample with gradient porosity and uniform porosity[C9]

● Solid Ti rod - inner ● Ti powder - outer ● Ammonium bicarbonate -

● Mould, 200MPa pressure1200C (sinter)

● Mechanical Properties degrade with higher pore size

● Difficult to control pore structure


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Advancements in Titanium-Structure

● Titanium wire is rolled into coils, stretched,

woven, compressed at ~300MPa, andsintered

● Mg ingot melted under inert state, Ti is

immersed in molten form● Soaked in 10% HCl (volume)● Cleaned with acetone

● Controllable pore size: 58% porosity, 490um average

pore size● Can control depth of solid base with etching time

● Compressive strength: 110MPa● Elastic Modulus: 5GPa● Mechanical properties can be increased for various

uses by decreasing the etching time and increasingthe solid core diameter

(a)Schematic diagram showingraded porous Ti–Mg composi

(from left to right): porous Ti pr

composite, and graded porous


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Economic, Legal, and Ethical Issues


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Conclusion● Designs for fixed bearing THA

● Biocompatibility of titanium and its alloys

● Manufacturing techniques

● Alternative Materials

● Advancements in titanium

Documents

Titanium and Its Biomedical Uses