Diamond-like Carbon Coating for Bio-medical Implant Materials

Kwang-Ryeol Lee

Future Technology Research DivisionKorea Institute of Science and Technology

krlee@kist.re.krhttp://diamond.kist.re.kr/DLC

Acknowledgement

• Dr. R. Hauert (EMPA, Switzerland)for valuable discussion and providing me the presentation materials on this issue.

• Prof. Jeong-Ku Kim (SKKU, Korea)for corrosion test in body fluid condition

• Prof. In-Seop Lee (Yonsei Univ., Korea)for tribological test of DLC coated Ti alloys in body fluid

• Prof. Hyeonee Kim (SNU, Korea)for cell attachment and hemocompatbility test

• Prof. R. Wang (UBC, Canada)for mechanical stability test

• Mr. Sejun Park, Mr. Heon-Woong Choi and Ms. Youngjin Lee

• Financial Support from Ministry of Science and Technology of Korea

Requirements for Bioimplants1. Should not cause infections2. Prevent uncontrolled cell growth3. Maintain their integrity inside the body4. Interact in a controllable way with the

biological environment5. Avoid formation of debris

Requirements for Bioimplants1. Should not cause infections2. Prevent uncontrolled cell growth3. Maintain their integrity inside the body4. Interact in a controllable way with the

biological environment5. Avoid formation of debris

Surface PropertiesSurface Properties

Bioimplant Materials

Required Surface Properties

• Biological Compatibility– Nontoxic, Noncarcinogenic, Noninflammatory

• Chemical Compatibility– Corrosion Resistance

• Mechanical Compatibility– Surface Hardness, Wear Resistance

Diamond-like Carbon :Diamond-like Carbon :as a Strong Candidate Coating as a Strong Candidate Coating

Contents

1. Introduction to DLC

2. Blood Contacting Applications Stents, Heart valves, Flow Accelerators

3. Load Bearing Applications Hip Joints, Knee Joints, Artificial Disk

4. Summary and Technical Issues

Diamond-like Carbon : DLC• Amorphous Solid Carbon Film• Mixture of sp1, sp2 and sp3 Hybridized Bonds• High Content of Hydrogen (20-60%)

t-aC

sp2 H

sp3

DLC

No film

diamond

graphite

Polymer-like

Graphitic

t-aC:H

DLC: A Group of Carbon Mat’l

Properties of Solid Carbon

Property Diamond DLC Graphite

Density (g/cm3) 3.51 1.8 – 3.6 2.26

Atomic Number Density (Mole/cm3)

0.3 0.2 – 0.3 0.2

Hardness (Kgf/mm2) 10000 2000 - 8000 500

Friction Coeff. 0.05 0.03 – 0.2 0.1

Refractive Index 2.42 1.8 – 2.6 2.15 – 1.8

Transparency UV-VIS-IR VIS-IR Opaque

Resistivity (cm) >1016 1010 - 1013 0.2 – 0.4

Applications of DLC

VCR Head Drum

Wrist Pin

Hard Disk & Slider

CD/DVD Mold

Spacer Tool

Form Die

Digital VCR Tape

Razor Blade

Blood Contacting Applications• Heart valves, Stents, Blood pumps etc.

- Surface has to prevent thrombus formation and restenosis

Adsorption of proteins

Increased platelet adhesion

Platelet activation and aggregation

Formation of a thrombusThrombus on a mechanical heart valve

(courtesy of RWTH-Aachen)

albumin/fibrinogen ratio

Steps for Thrombus formation

Protein Adsorption on DLC

a high ratio of albumin/fibrinogen

low number of adhering platelets

low tendency of

thrombus formation 0

0.2

0.4

0.6

0.8

1

1.2

1.4

Ti TiN TiC DLC silicone elastomer

PMMA CN

Alb

um

in /

Fib

rinog

en R

atio

Jones et al.Dion et al.Cui et al.

Albumin/fibrinogen ratio for different surfaces.

Excellent Hemocompatibility

Clotting Time Measurement

On glass

On DLC

Excellent Hemocompatibility

Blood platelets deposited on different surfaces as a function of exposure time.

DLC coated accelerator

PC coated accelerator

DIAMOND AS® Stent

- Reduce thrombus formation

- Prevent Cr, Ni release from 316 L steel

DLC Coated Stents

Potentiodynamic Polarization

10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

P

oten

tial (

mV

vs

SC

E)

Current Density (A/cm2)

Substrate Si-C:H, Bias voltage = -400V a-C:H, Bias voltage = -800V a-C:H, Bias voltage = -400V

DLC Coated Stents

Evolution of Coating Failure

0.00 0.02 0.04 0.06 0.08 0.10 0.120

100

200

300

400

500

Fo

rce

(N)

L/L

(a) (b) (c) (d)

(a)

(b)(c) (d)

CARBOFILM™ made by PVD using a pyrolytic turbostratic carbon target. Probably it is a-C.

Chrome-cobalt alloy cage, coated with CARBOFILM™

Problems: Wear in hinges, Hemocompatibility

DLC Coated Heart Valves etc.

Titanium alloy coated with DLC Products under development by Cardio Carbon Company Ltd.

CarbofilmTM by Sorin Biomedica, Inc.

Polyethylene wear debris is the main factor limiting the lifetime of the implants Aseptic loosening, wear debris initiates inflammatory response, leading to osteoclast cells activation resulting in bone resorption

DLC shows in atmosphere a low wear and also low friction coefficients against most materials

DLC coated femoral heads for low wear ?

DLC slides against its own transfer layer and only DLC is worn at a very low wear rate, whereas the softer partner surface will not be worn

Load Bearing Implants

V. Saikko et al., Biomaterials 22 (2001) 1507

Polyethylene wear debris

DLC Coating on Femoral Ball

RF Power

Cathode

In vitro Wear Test

Pin on Disk

DLC/UHMWPE (literature overview)Hip joint simulator (Lappalainen, Finnland)

Pin on Disk

Lubrication: - air- dest. water - 1wt% NaCl in water

reduction of UHMWPE wear

Hip joint simulator

Lubrication: - diluted calf serum- synovial fluid

no change in UHMWPE wear

To be clinically relevant, tribological investigations on DLC/UHMWPE require:- Adequate tribological setup- Adequate lubricant

In vitro Test

Hip joint simulator

Lubrication: - diluted calf serum- synovial fluid Characterize surface

Texture

single scratches increase the wear rate of UHMWPE by a factor of 30-70

Tribological setup Lubrication Surface quality

phospholipids, adsorbed on the surfaces, strongly influences the tribological behavior and may take part in tribochemical reactions

J. Fisher et al., J. of Engineering in Medicine 209 (1995) 263

S.C. Scholes et al., Phys. Med. Biol. 45 (2000) 372V. Saikko, T. Ahlroos, Wear 207 (1997) 86

Pin-on-Disk setup leads to clinically non relevant results

In vitro Test (only a few papers found)

Lappalainen: Shi: Tiainen:

2003 2003 2001

ta-C/ta-C DLC/stainless steel ta-C/ta-C

hip simulator PoD PoD / hip simulator

bovine serum bovine blood serum NaCl-water

<10-4 mm3/year 50x less than st./st. 100x less than Al2O3/Al2O3

promising result questionable setup questionable lubricantpromising result promising result

Ref: steel/UHMWPE: 20-60 mm3/year (wear particles) steel/steel: 1-5 mm3/year (future allergies)

ceramic/ceramic: 10-2 mm3/year (can only be replaced by ceramic)

R. Lappalainen et al., J. Biomed. Mater. Res. 66B (2003) 410-413 B. Shi et al., Wear 255 (2003) 1015-1021V.-M. Tiainen, Diamond Relat. Mater. 10 (2001) 153-160

DLC/DLC or DLC/metal

Hip Joints: in vivo Test

G. Taeger et al., Mat.-wiss. u. Werkstofftech. 34 (2003) 1094

101 patients DLC/PE101 patients Al2O3/PE

8.5 year’s follow-up50% of DLC/PE failed

DLC/PE

Al2O3/PE

Retrieved DLC-head: Numerous pits revealing the metallic substrate, severe PE wear

Adhesive Wear in Body Fluid

200㎛200㎛

Shoulder-joint, the Ti-alloy ball coated with DLC (carbioceram™)

ankle-joint, AISI Z5 CNMD 21 steelcoated with DLC (carbioceram™)

knee-joints coated with DLC (carbioceram™)

No medical follow-up on these products found

DLC Coated Artificial Joints

Failure Case (Knee Joint)

”Diamond Rota Gliding” DLN/UHMWPE knee-joints have been sold (without the necessary tests and permission) by Implant Design AG in 2001. Dylyn®, DLN (Diamond-like Nanocomposite) produced by Beckaert.

The implanted joints showed increased wear and partial coating delamination and had to be replaced. Additionally, residual coating on the upper side of the implant was held responsible for the inadequate bone ingrowth.

In July 2001 the implantation of this knee joint was forbidden by the Swiss Federal Office of Public Health (SFOPH). www.swissmedic.ch

Summary

• DLC film is not a specific materials but a group of amorhpous carbon materials

• Blood Contacting Applications– Good hemocompatibility– DLC Coated stents, heart valves, blood pumps are

now available in the market.

• Artificial Joints Application– Needs an improved test method to obtain clinically

relevant results. – DLC/DLC or DLC/metal combinations show more

promising results than other combinations.

Technical Issues

• Careful consideration on the DLC film itself is required, because the DLC film is not a specific material.

• Stability of DLC coating in body fluid condition is one of the most critical issues for the biomedical applications.

• Stents– Stability of the coating with respect to the plastic deformation– Interface design would be helpful to increase the reliability.

• Artificial Joints– Characterization of the coating under an adequate test condition

• Does it really reduce the PE debris?• Is it possible to have new design such as DLC/DLC or DLC/metal?

– Stability of the coating during sliding in body fluid condition– Need tight control of the substrate surface

Diamond-like Carbon Coating for Diamond-like Carbon Coating for Bio-medical Implant MaterialsBio-medical Implant Materials

Kwang-Ryeol Lee

Future Technology Research DivisionKorea Institute of Science and Technology

krlee@kist.re.krhttp://diamond.kist.re.kr/DLC

Cells in contact with DLC

Many in vitro experiments with

different cell types (macrophages,

fibroblasts, human embryo kidney 293

cells, ML-1 cells, osteoblasts etc. )

- good growth rate

- good viability

- no morphological changes

- no cellular damage

- no inflammatory reactions

- no cytotoxicity

DLC may be expected to be

biocompatible in vivo.Cell viability on control and DLC-coated plastic

dished for ML-1 cells [L. Lu, M.W. Jones, R.L.C. Wu, Bio-Med. Mater. Eng. 3 (1993) 223].

Cell Growth Behavior

Thermanox DLC si-DLC0

20000

40000

60000

80000

100000

Cel

l N

um

ber

[/c

m2 ]

Thermanox DLC si-DLC0.00

0.05

0.10

0.15

0.20

AL

P A

ctiv

ity

Proliferation Differentiation

3 days 10 days

(HOS: Human Osteo-sarcoma)

Protein adsorption on Ti-DLC

Adsorption of human plasma proteins on a-C:H/Ti Chromatographic analysis of the proteins. Molecular weight marker is indicated on the left side.

184 kD

115 kD

86.3 kD61.5 kD

50.8 kD

37.6 kD

25.4 kD

Plasma Glas Ti 23 13 7 0

a-C:H, at% Ti

Molecular weight

Tunable protein adsorption between Ti and DLC by the Ti concentration in Ti-DLC.

a-C:Ha-C:Ha-C:H/3% Va-C:H/3% V

a-C:H/7.4% a-C:H/7.4% VV

a-C:H/15% Va-C:H/15% V

after 10 days in vitroafter 10 days in vitro

BMC on V-DLC

Tunable poisoning:

Poisoning of the BMC cells due to vanadium dissolution out of the V-DLC film

300 µm