Surface & Coatings Technology 200 (2005) 2518 2524

www.elsevier.com/locate/surfcoat

Biomedical applications of diamond-like carbon (DLC) coatings:

A review
Geoffrey Dearnaley *, James H. Arps
Southwest Research Institute\, 6220 Culebra Road, San Antonio, TX 78238-5166, United States

Received 8 June 2004; accepted in revised form 4 July 2005

Available online 13 September 2005

Abstract

To resist wear, biomedical components require coatings that are exceptionally hard, have low friction, and are bioinert. Diamond-like
carbon has been shown to provide this capability and to prevent leaching of metallic ions into the body. There are many ways to deposit such
coatings from carbonaceous precursors, and some offer the means to incorporate other elements such as nitrogen, titanium, or silver. All
reported tests of the biocompatibility of DLC coatings have been successful. This review will summarize work done on orthopedic and
cardiovascular components together with other medical applications. For optimum tribological performance, the DLC must be deposited onto
highly polished surfaces. The stage has been set for more simulation tests, leading to clinical trials, but the prospects appear to be very good.
D 2005 Published by Elsevier B.V.

Keywords: Diamond-like carbon; Biocompatibility; Leaching; Orthopedic components; Cardiovascular components; Importance of smoothness

1. Introduction DLC coatings. Other additives often introduced include

nitrogen, silicon, sulfur, tungsten, titanium, or silver.
Coatings that are very hard, have low friction and are As is well known, carbon carbon interatomic bonds can
fully biocompatible have obvious applications in orthope- be of two types: the near-planar trigonal or sp2 form found in
dics, cardiovascular components, guidewires, etc. Diamond- graphite, or the tetragonal sp3 variety that occurs in diamond.
like carbon (DLC) coatings provide these properties and It is the three-dimensional character of sp3 bonding, together
have been the subject of much recent research which has with the strength of the short C C covalent bond that give
revealed that care must be taken in order to achieve the best diamond its great strength. DLC is intermediate in that it
performance. contains both types of bonding and clearly it is harder and
Though it is called diamond-like, DLC is in fact not more brittle if the sp3 : sp2 ratio is high.
like crystalline diamond for it is black, not as hard, and is Fig. 1 shows a cross-sectional TEM photograph of a
virtually amorphous. Its microstructure allows the incorpo- typical DLC containing about 14% residual hydrogen, and it
ration of other species, and DLC comprises a family of such can be seen that there is no extended microstructure; the
materials, the properties of which can be tailored far more substance is nanocrystalline and this makes it relatively
readily than those of diamond. Hydrogen is frequently tough. It can also provide coating surfaces that are smooth
present in amounts up to 40 at.%, occupying regions of low on a nanometric scale.
electron density in the matrix. Its presence strongly There have been several attempts to produce useful
influences the mechanical and tribological behavior of biomedical coatings of crystalline diamond, but the dis-
advantage has been that these are rough and faceted due to
the polycrystalline growth morphology. As a consequence,
* Corresponding author. such surfaces produce excessive wear in the counterface
E-mail address: cambritec@yahoo.com (G. Dearnaley). material, and methods that might serve to polish them could
0257-8972/$ - see front matter D 2005 Published by Elsevier B.V.
doi:10.1016/j.surfcoat.2005.07.077
 G. Dearnaley, J.H. Arps / Surface & Coatings Technology 200 (2005) 2518 2524 2519

2.2. Pulsed laser ablation

Voevodin et al. describe a process for the deposition of

DLC coatings using KrF excimer laser to vaporize material,
in vacuum, from either a graphite target or one consisting of
polycarbonate [2]. The latter results in hydrogenated DLC
films sometimes designated as a-C:H. Steel substrates were
either negatively biased as unbiased with regard to the
target. Those coatings deposited under bias, from 100 to
800 V, have somewhat lower friction coefficients. The
wear rates of the carbon films against sapphire pins were
remarkably low at about 10 9 mm3/N m while for the softer
a-C:H films the wear rate was around 10 6 mm3/N m at a
contact pressure of 0.8 GPa.
A potential drawback to pulsed laser ablation (PLD) is
that occasionally droplets or chunks of the target material
are ablated and cause a surface roughness that is not easily
Fig. 1. TEM micrograph of DLC coating showing graphitic nanostructure. removed. The internal stress can also be very high, but Wei
et al. [3] have described a functionally graded DLC coating
not easily be applied in a production situation, e.g., to with reduced compressive stress and improved adhesion.
femoral components.
2.3. Ion beam conversion coatings

2. Deposition of DLC coatings One of the more versatile methods for depositing DLCs
is by the simultaneous ion bombardment and condensation
Many methods have been developed for the deposition of of a low vapor pressure compound. The rupture of C H
DLC coatings, from a variety of carbonaceous precursor bonds releases hydrogen into the vacuum leaving a largely
materials. They include: carbonaceous coating. Deposition rates are high, up to 10
Am/h, and the compressive stress in such coatings is low (1
& Direct ion beam deposition, GPa or less), perhaps due to the progressive removal of
& Pulsed laser ablation, hydrogen from within. The precursor materials may either
& Filtered cathodic arc deposition, be diffusion pump fluids or solids such as adamantane or
& Ion beam conversion of condensed precursor, coronene. Previous internal work at SwRI has shown that if
& Magnetron sputtering, ferrocene is used, the coating may contain up to 24 wt.% of
& RF plasma-activated chemical vapor deposition, iron. Siloxane precursors such as pentaphenyl trimethyl
& Plasma source ion implantation and deposition. siloxane produce films with a few percent of silicon and
oxygen, with advantageous properties, such as reduced
dependence of friction coefficient or relative humidity. The
2.1. Direct ion beam deposition ion energies used may range from 100 eV to 100 keV.
Accounts of the process have been published by Fountzou-
The principle of this method is to bombard a surface, in las et al. [4].
vacuum, with energetic ions usually of methane so that, upon It is also possible to incorporate elements such as sulfur,
impact, the molecule dissociates and most of the hydrogen is fluorine, or nitrogen by choice of the precursor, and some of
liberated. Ion energies of 100 to 750 eV have been used, e.g., these assist in providing a low friction coefficient. The
by Liu et al. [1] and the current density of about 2.5 A/cm2 coatings produced by these methods are smooth, but due to
corresponds to an arrival rate of approximately 1.5  1016 the residual hydrogen content, typically 15 at.%, they are
carbon atoms/cm2/s, most of which are retained. This is not as hard as amorphous carbon coatings, though they can
approximately a growth rate of 1 Am/h. still be comparable with hard tool coatings such as titanium
With a uniform atom-by-atom arrival, the coatings are nitride or alumina.
very smooth and have Knoop microhardness of 6000 kg/
mm2 according to Liu et al. [1]. Though the residual 2.4. Filtered cathodic arc deposition
hydrogen content is not stated, this hardness value suggests
that it is relatively low. Against a zirconia pin the wear rates This is a method for producing very hard, virtually
were below 10 7 mm3/N m with friction coefficients for dry hydrogen-free DLC coatings. An arc is drawn in vacuum
sliding of 0.02 to 0.10 increasing with relative humidity for between a graphite cathode and an anode, typically at 50
reasons to be discussed below. 60 A [5]. A radial magnetic field steers and filters carbon
2520 G. Dearnaley, J.H. Arps / Surface & Coatings Technology 200 (2005) 2518 2524

ions and rejects macroparticles. A bias voltage of 100 to 300 comparisons between DLC and carbon nitride coatings in
V is applied to the substrate. terms of their orthopedic hemocompatibilities.
That the filtering is effective is shown by the high degree The technique of unbalanced magnetron sputtering for
of smoothness of the films. Xu et al. [5] report an R a value the deposition of amorphous carbon films has been
of about 0.4 nm. Stresses in the coatings are high at 7 to described recently by Ahmad et al. [10].
10 GPa and this contributes to coating hardness, that may
reach superhard values of 40 to 50 GPa. 2.7. RF plasma-activated chemical vapor deposition
Such hardness is advantageous in resisting abrasive wear,
but the high compressive stress means that there will be a Chemical vapor deposition, involving the thermal
tendency to decohesion unless adhesion is strong. Most of dissociation of a selected precursor is extensively used
the reports refer to substrates of silicon or quartz, to which for coating tools and semiconductor devices. The addition
carbon adheres strongly. of an electrical plasma lowers process temperatures. It is
easy to apply the method for DLC, and Erdemir et al. [11]
2.5. Plasma source ion implantation and deposition describe a careful study of the results of using four
different source gases; namely, methane, ethane, acetylene
In this method, described by Anders et al. [6] a plasma is and ethylene, at pressures of 1.3 to 1.7 Pa. The substrate
created in the work chamber and the workpieces are bias was 1600 V, and the substrates were of steel. The
immersed in it. Periodic pulsing to around 2 kV accelerates lowest friction and wear, against steel balls, were obtained
carbon ions from the expanding plasma sheath during the for methane, and the highest for acetylene. The authors
pulse, of duration 1 ms. The carbon plasma may be formed attribute the difference to the hydrogen : carbon ratio, the
by a pulsed cathodic arc, with a magnetic filter (as described role of hydrogen being possibly to promote a higher sp3
above) to remove macroparticulates. The films are virtually content, or else to decorate the coating surface and reduce
free of hydrogen and are hard. Cui et al. report values up to friction. Methane/hydrogen mixtures in the plasma (1 : 1)
45 GPa, with low friction coefficients [9]. gave even lower friction, the coefficient against steel
The compressive stress in such coatings is high, but falling to 0.01. It is a pity that these results were not
Anders et al. describe a method for varying the substrate correlated with determinations of the residual hydrogen
bias during deposition to produce alternating hard and softer present in the coatings which can be done by elastic-recoil
layers with a net reduction in stress. Some of these coatings ion beam technique.
have been the subject of orthopedic testing (see below), with The wear resistance corresponded to the friction behavior
outstanding results. being about 9  10 9 mm3/N m for methane-grown films
and two orders of magnitude greater for the acetylene-grown
2.6. Magnetron sputter coating film. In conclusion, methane/hydrogen mixtures are shown
to be best for tribological applications of DLC, and this
Magnetron sputtering is a widely used process for work shows clearly that the method of preparation of the
physical vapor deposition and it can be employed for coating is very important.
carbon, though deposition rates are relatively low due to
the low sputtering coefficient. Peng et al. [7] used DC
magnetron sputtering as one of the four methods of 3. The tribological properties of DLC
deposition in the study of the smoothness of DLC coatings.
Non-hydrogenated films up to 1 Am thick were prepared In many biomedical applications the wear rate and
by sputtering from a pure graphite target in an argon friction must be very low and the hardness of the coating
plasma. A bias voltage was applied to the substrate and must not induce excessive wear of the counterface material.
could be varied from 200 to 300 V. The argon pressure It has been shown both experimentally and in computer
was around 1 Pa. Magnetron sputtering of carbon or forms (molecular dynamics) modeling that during sliding wear the
of carbon nitride (CNx ) is used extensively to provide thin outer layers of DLC are transformed to graphite oriented
(3 nm) protective coatings on magnetic storage media, the with its basal plane parallel to the surface. Subsequently,
nitrogen being introduced by reactive sputtering in an N2/ easy shear can occur at load-bearing asperities and as Liu
Ar plasma. Broitman et al. [8] described the application of and Meletis have reported [12] both friction and wear rates
such coatings to certain orthopedic substrates such as are very low.
zirconia in order to reduce the friction coefficient against The surface of carbon, whether bonded as diamond or
UHMWPE. graphite, is generally decorated by a monomolecular layer
Because of the low sputtering coefficient of carbon this is of hydrogen. For contact pressures up to about 1 GPa this
not an efficient means for depositing thick (2 3 Am) film remains in place and greatly reduces the tendency for
coatings and possibly this is why it has not been adhesion to the counterface, especially if it consists of a
investigated more widely in the biomedical field. An up- polymer such as polyethylene, the surface of which is also
to-date review by Cui et al. [9] is shortly to appear with terminated by hydrogen atoms.
 G. Dearnaley, J.H. Arps / Surface & Coatings Technology 200 (2005) 2518 2524 2521

High humidity causes an increase in friction for reasons the findings, though all good, have been variable and it is
not well understood. Water molecules may bond to the interesting to arrive at an explanation for this in terms of
hydrogen and simply provide a more reactive surface. coating roughness and test procedure.
Additions of a few percent of silicon to DLC substantially Saikko et al. [13] compared femoral heads of CoCr,
reduce this effect. alumina, and CoCr coated with DLC prepared by an RP
The surface roughness of hard coatings has a strong plasma discharge in acetylene. Tests were done in bovine
influence on the wear of the counterface, especially when serum, with no additives, in an anatomical hip wear
this is a soft material such as UHMWPE. A careful study simulator operating at 1 Hz. The wear of UHMWPE over
has been made by Peng et al. [7] of the roughness of DLC 3 million cycles was similar for each type of head.
coatings prepared by three different techniques, and the Sheeja et al. [14] tested Co Cr alloy disks coated with
effects of post-deposition treatments. DLC by the filtered cathodic arc method and compared
The methods chosen were RF plasma-activated CVD in them with uncoated Co Cr against UHMWPE pins in a
methane, DC magnetron sputtering in argon, and a carbon simulated body fluid. The wear rates were similar, but it was
ion beam extracted from a cathodic arc discharge. In each found that the corrosion rate for the coated alloy was
case the bias voltage applied to the substrate could be varied reduced by a factor of about 10,000. In subsequent work
up to about 350 V. After deposition, some specimens were Sheeja et al. [15] explored the benefits of treating both the
subjected to argon plasma sputtering, or to hydrogen etching Co Cr alloy and the UHMWPE with DLC and found a
in a plasma, or heat treatment at 500 -C in vacuum. The significant reduction in the wear rates of both sliding
substrates were of silicon, argon sputter cleaned and had a surfaces. If the polymer alone is coated, its wear rate is
roughness of only 0.046 nm. reduced but there was found to be severe wear of the Co
The coating roughness was similar for all three deposi- Cr. Prior implantation of these materials with C+ ions before
tion methods, but depended markedly on the bias voltage, as coating did not provide any superior behavior.
ion impingement energy, with the lowest values of about In an NSF-funded study, Xu and Pruitt [16] examined
0.04 nm being obtained at a bias of 250 300 V. Heating at DLC coatings on Ti 6Al 4V alloy against UHMWPE in
500 -C increased roughness, as did argon sputtering and pin-on-disk tests in water. The DLC was prepared by the
hydrogen etching, which perhaps removes graphitic clusters plasma source method described above. The rate of PE wear
from certain regions of the surface. was reduced by a factor of 3 4, compared with uncoated
Thus, under preferred conditions DLC coatings up to 700 alloy.
nm in thickness could be as smooth as a carefully prepared Onate et al. [17] used a knee wear simulation machine to
silicon crystal substrate, and we shall see below that in compare Co Cr, alumina, and Co Cr coated with DLC
orthopedic applications this is highly beneficial. from acetylene. In this case there was a substantial
improvement over the uncoated alloy, by a factor of 4,
and 40% less wear than against alumina.
4. Orthopedic applications of DLC A hip joint simulator was used by Lappalainen et al. [18]
to compare DLC coatings on stainless steel, Ti 6Al 4V
The load-bearing surfaces of total hip and knee arthro- and CoCrMo alloy, by the filtered cathodic arc method, with
plasties are subject to wear and it is well recognized that the a chromium bond coat. With ultra-smooth coatings with a
most serious consequences are those due to the formation of roughness of 7 nm the wear rate of UHMWPE was reduced
polyethylene debris at a rate of perhaps 1010 particulates per by factors of 30 to 600 times compared with the uncoated
year. These particulates are phagocytosed resulting in metal. Corrosion rates in 10% HCl were decreased by over
granulomatosis lesions, osteolysis and bone resorption, 10,000 times. In a very recent invited review Lappalainen
causing pain and aseptic loosening of the prosthesis. [19] mentions that amorphous diamond coating can
DLC coatings have been explored over the past ten years improve corrosion and wear resistance even by a factor of
as a means for eliminating this problem, with some highly million compared to conventional materials and he
encouraging results. The goal is to demonstrate lower PE discussed special procedures to achieve these goals.
wear than what occurs against metals and ceramics such as Affatato et al. [20] made use of a hip joint simulator to
alumina or zirconia. Fractures have occurred in ceramic compare DLC coated titanium alloy with CoCr and alumina
femoral heads, and so a hard, low friction coating on metal over 5 million cycles in bovine serum with addition of
would potentially be the best solution. EDTA (ethylene diamine tetra acetic acid) to minimize
Some early investigations of DLC, by Davidson and precipitation of calcium phosphate, which they state can
Mishra, were beset by problems of high compressive stress strongly affect friction and wear properties. The DLC, made
and decohesion, but work referred to above has done much by PACVD from methane, was comparable to alumina in
to reduce the likelihood of coating delamination, either by terms of PE wear.
bond coats or control of coating stress. A comparison of these results shows that care must be
Results over the past five years have indicated the taken with regard to the source of DLC, methane being
excellent potential for DLC in total joint replacements, but superior to acetylene, and above all to the smoothness of the
2522 G. Dearnaley, J.H. Arps / Surface & Coatings Technology 200 (2005) 2518 2524

substrate. In hip joint simulator tests it is advisable to coated CoCr cylinders into intramuscular locations in rats
provide an additive to serum to inhibit calcification. and transcortical sites in sheep. After 3 months, histologic
When conditions are favorable, the tests indicate that analysis showed that the specimens were well tolerated.
DLC coatings have the potential to provide the lowest wear Based on this excellent biocompatibility the authors have
rates of UHMWPE, perhaps half that against alumina, initiated a long-term animal study of a DLC-coated knee
without the risks associated with fracture of ceramic arthroplasty.
components. Corrosion and leaching of metal into body The most recent published work on biocompatibility has
fluids has been shown to be very markedly reduced by DLC been that of Singh et al. [26] who evaluated DLC coatings
coatings. for improved biocompatibility in chronic neurasthenic
implants. They assessed the cytotoxicity and cell adhesion
of DLC exposed to glial and fibroblast cell lines in vitro.
5. Biocompatibility of DLC coatings DLC coatings did not adversely affect 3T3 fibroblast and
T98-G glial cell function in vitro. There was also success in
It would hardly be possible to use DLC as a coating for rendering DLC coatings non-adhesive by the application, by
items in vivo unless it has been shown to be biocompatible, conventional means, of surface immobilized dextran.
and all studies to date agree this is the case. Finally, for some applications, it can be reported from our
In an early study, Thomson et al. [21] used mouse own research that DLC adheres very strongly to silicone
peritoneal macrophages and mouse fibroblasts on DLC elastomers, probably due to the formation of strong Si C
prepared by the dual beam ion method, monitoring levels of bonds at the interface.
lactate dehydrogenase (LDH) as a measure of cell viability.
There was no indication of cytotoxicity. Similar results were
obtained by Allen et al. [22] using the murine macrophage 6. Cardiovascular applications of DLC
cell line, IC-21, in a growth medium supplemented with calf
serum, or DLC made by plasma-activated CVD. Cell Heart valves are conventionally made from LTI carbon
growth studies were made using human synovial fibroblasts and, despite great care in manufacture, there remains a very
and a human osteoblast-like cell line, SaOS-2. Cell small but finite risk of failure due to fracture initiated at an
growth kinetics were determined by counting after each undetected surface or subsurface flaw. Therefore, there has
24 h incubation period, following disaggregation and been interest in replacing this brittle material with a metal
staining. Cells grew well on DLC-coated glass and coated with hard carbon that is non-thrombogenic.
polystyrene with no evidence of abnormal morphology. Butter and Lettington [23] suggest the use of NiCr18
Cells generally grew faster on DLC, adhered well, and stainless steel coated by a non-line-of-sight method with
produced extensive filopodia. carbon. The plasma conversion method would be a suitable
Butter and Lettington [23] report preliminary in vivo choice. It has been reported that a silicon-containing DLC
studies involving the implantation of DLC-coated pins into may be a better coating for cardiovascular purposes, but
soft tissue and femurs of sheep. Much better bonding was Butter and Lettington comment that in tests it showed no
observed at DLC rather than metal tissue interfaces difference from the controls. The published studies all show
indicating a lower risk of infection. They also describe DLC to be a promising biomaterial for heart valve
work done by Mitura on the coating of orthopedic screws applications and it is known that proprietary work is in
with DLC by the RF plasma method. Over 52 weeks progress on this topic.
implantation of DLC-coated metal showed no evidence of Arterial stents can induce platelet activation and may
corrosion products or chronic inflammatory reaction. initiate thrombosis by shear forces on the flow and by
Ex vivo experiments with whole blood have shown that platelet adhesion to the metal. Gutensohn et al. [27]
DLC-coated stainless steel and titanium compare well with evaluated in vitro the performance of stents coated with
LTI carbon and are superior to glass. There is a need, DLC. Growth arrays using smooth muscle cells and
however, for in vivo trials, justified by the fact that all endothelial cells showed that DLC did not affect prolifer-
biocompatibility tests of DLC-coated surfaces have been ation rates and no cytotoxic effects were observed. Flow
successful, with no contrary indications. cytometric analyses showed no significant changes in mean
In an extension of the biocompatibility of DLC, Steffen channel fluorescence intensity for the structural antigens
et al. [24] used it as a substrate for heparin following CD41a and CD42b, while by contrast expression of the
treatment in an ammonia plasma to form reaction amino activation-dependent antigens CD62p and CD63 increased
sites for attachment. The optimum plasma exposure time at significantly in uncoated compared with DLC-coated stents.
a pressure of 0.3 Pa was around 45 s. This treatment with Release of metal ions into the bloodstream is a matter of
heparin increased blood coagulation times from 25 to over concern, and Gutensohn et al. [27] used atomic adsorption
250 s. spectrometry to detect a significant release of nickel and
Successful in vivo tests of the biocompatibility of DLC chromium ions into human plasma over a 96-h period, from
have been reported by Allen et al. [25] who implanted DLC- non-coated stents. However, only minimal concentrations of
 G. Dearnaley, J.H. Arps / Surface & Coatings Technology 200 (2005) 2518 2524 2523

released ions could be detected in the case of DLC-coated against polished alumina or zirconia and without risks
stents. Similar results were obtained by inductively coupled associated with fracture of a brittle ceramic.
plasma mass spectrometry analysis, and in this case the All studies of the biocompatibility of DLC are in
release of metal ions from DLC-coated stents was virtually agreement that there is no cytotoxicity and cell growth is
undetectable. The authors conclude that the coating of normal on a DLC-coated surface. Its blood compatibility is
intracoronary stents with DLC may contribute to a reduction as good as that of the well-established LTI carbon used in
in thrombogeneticity and consecutively in the incidence of heart valves. DLC coatings on stainless steel have performed
acute occlusion and restenosis in vivo. very well in in vitro studies of haemocompatibility.
Catheters have been coated at Southwest Research Undoubtedly there is more work in progress than has
Institute with a mixture of silver and DLC. In vitro tests been reported in the open literature, and the stage has been
confirmed the efficacy of this coating for local freedom reached at which in vivo testing of DLC is warranted. With
from bacterial infection. Diamond-like carbon coatings on cautious optimism, we look forward to the application of
segmented polyurethane were tested for blood compatibility well-bonded DLC coatings in a variety of orthopedic and
by Alanazi et al. [28] and it was shown that they could be cardiovascular applications. All of these procedures, of total
superior to an excellent non-thrombogenic polymer, 2- joint replacements, heart valves and stenting, for which
hydroxyethyl methacrylate (HEMA), in tests carried out in DLC may provide greater efficacy and an extended service
an parallel flow chamber. The authors conclude that greater life, are ones which give patients a much greater quality of
attention should be paid to DLC for use in the medical field. life.

7. Other biomedical applications of DLC

References
Elinson et al. [29] applied thin coatings of DLC (20 200
[1] Y. Liu, A. Erdemir, E.I. Meletis, Surf. Coat. Technol. 82 (1996) 48.
nm) to soft contact lenses and contact lens cases to reduce [2] A.A. Voevodin, M.S. Donley, J.S. Zabinski, Surf. Coat. Technol. 92
the problems of biofilm formation. The authors regard (1997) 42.
microbial contamination of contact lenses to be as major a [3] Q. Wei, J. Sankos, J. Narayan, Surf. Coat. Technol. 146 147 (2001)
problem as that of the lenses themselves, and showed that 250.
lenses stored in DLC-coated cases were free from any [4] C.G. Fountzoulas, T.Z. Kattanis, J.D. Demaree, J.K. Hirvonen, in: A.
Feldman, Y. Tzeng, W.A. Yarbrough, M. Yoshikawa, M. Murakawa
contaminations. (Eds.), Applications of Diamond Films and Related Materials,
McLaughlin et al. [30] investigated RF plasma deposited National Institute of Standards and Technology, Washington, DC,
DLC on stainless steel medical guidewires and found good 1995, p. 907.
adherence with a coefficient of friction superior to that of [5] S. Xu, B.K. Tay, H.S. Tan, L. Zhong, S.R.F. Silva, W.I. Milne, J. Appl.
PTFE. Furthermore, the thin DLC coating did not alter the Phys. 79 (1996) 7234.
[6] S. Anders, A. Anders, I.E. Brown, B. Wei, J.W. Ager, K.M. Yu, Surf.
overall stiffness of the guidewires, in contrast to PTFE or Coat. Technol. 68 69 (1994) 388.
silicon coatings that may be up to 300 Am thick. [7] X.L. Peng, Z.H. Barber, T.W. Clyne, Surf. Coat. Technol. 138 (2001)
In ophthalmic surgery, the surgeon may need to suture 23.
the corneal region while causing the least distortion of the [8] E. Broitman, W. Macdonald, N. Hellgren, G. Radnoczi, Z. Czigany, A.
eyeball. Butter and Lettington [23] refer to experiments that Wennerberg, M. Jacobsson, L. Hultman, Diamond Relat. Mater. 9
(2000) 1984.
have shown that a DLC coating on the needle reduces the [9] F.Z. Cui, X.L. Qing, D.J. Li, J. Zhao, Surf. & Coatings Technol.
force required to penetrate the cornea of pigs eyes by about (in press).
30%. There may be more such applications in microsurgery, [10] I. Ahmad, S.S. Roy, P.D. Maguire, P. Papakonstantinou, J.A. Mc
and the authors point out that the dark color of DLC would Laughlin, Thin Solid Films 482 (2005) 45.
have the further benefit of reducing reflections from the [11] A. Erdemir, J.B. Nilufer, O.C. Eryilmaz, G.R. Fenske, Surf. Coat.
Technol. 120 121 (1999) 589.
lights of operation microscopes. [12] Y. Liu, E.I. Meletis, J. Mater. Sci. 32 (1997) 3491.
[13] V. Saikko, T. Altroos, O. Calonius, J. Keranen, Biomaterials 22 (2001)
1507.
8. Conclusion [14] D. Sheeja, B.K. Tay, S.P. Lau, L.N. Nung, Surf. Coat. Technol.
146 147 (2001) 410.
[15] D. Sheeja, B.K. Tay, L.N. Nung, Surf. Coat. Technol. 190 (2005) 231.
While diamond coatings may have some applications in [16] T. Xu, L. Pruitt, J. Mater. Sci., Mater. Med. 10 (1999) 83.
biomedicine, it is diamond-like carbon (DLC) that has [17] J.I. Onate, M. Comin, I. Braceras, A. Garcia, J.I. Alava, Suf. Coat.
emerged over the past decade as a most versatile and useful Technol. 142 144 (2001) 1056.
biomaterial. Harder than most ceramics, bioinert, and with a [18] R. Lappalainen, A. Anttila, H. Heinonen, Clin. Orthop. Relat. Res.
low friction coefficient, DLC is one of the best materials for 352 (1998) 118.
[19] R. Lappalainen, Intl. Conf. on Metallurgical Coatings and Thin Films,
orthopedic applications. If deposited with the preferred San Diego, CA (in press), May.
composition on a very smooth substrate, it offers the lowest [20] S. Affatato, M. Frigo, A. Toni, J. Biomech. Mater. Res. (Appl.
wear rate of a UHMWPE counterface, below that observed Biomater.) 41 (2000) 221.
2524 G. Dearnaley, J.H. Arps / Surface & Coatings Technology 200 (2005) 2518 2524

[21] L.A. Thompson, F.C. Law, N. Rushton, J. Franks, Biomaterials 12 [27] K. Gutensohn, C. Beyrhien, M. Brockmann, J. Bau, P. Keuhnl, 10th
(1991) 37. Congress on Thrombosis, Porto, May, 2000, Abstract No. 24.
[22] M. Allen, F. Law, N. Rushton, Clin. Mater. 17 (1994) 1. [28] A. Alanazi, C. Nojiri, T. Noguchi, T. Kido, Y. Komatsu, K. Hirakuri,
[23] R.S. Butter, A.H. Lettington, J. Chem. Vapor Depos. 3 (1995) 182. A. Funakubo, K. Sakai, ASAIO J. (2000) 440.
[24] H.J. Steffen, J. Schmidt, A. Gonzalez-Elipe, Surf. Interface Anal. 29 [29] V. Elinson, V.V. Sleptsov, A.N. Laymin, A.D. Moussina, Diamond
(2000) 386. Relat. Mater. 8 (1999) 2103.
[25] M. Allen, B. Myer, N. Rushton, J. Biomed. Mater. Res. 58 (2001) 319. [30] J. McLaughlin, B. Meenan, P. Maguire, J. Jamieson, Diamond Relat.
[26] A. Singh, G. Ehteshami, S. Massia, J. He, R.G. Storer, G. Raupp, Mater. 5 (1996) 486.
Biomaterials 24 (2003) 5083.