Wear 301 (2013) 234–242

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Biotribological study of multilayer coated metal-on-metal hipprostheses in a hip joint simulator

J.A. Ortega-Saenz, M. Alvarez-Vera, M.A.L. Hernandez-Rodriguez n

Universidad Autonoma de Nuevo Leon, FIME, Mexico

a r t i c l e i n f o

Article history:

Received 3 September 2012

Received in revised form

9 January 2013

Accepted 10 January 2013Available online 23 January 2013

Keywords:

Biotribology

Co-Cr alloy

Metal-on-Metal

PVD coatings

Multilayer coatings

Hip joint simulator

48/$ - see front matter & 2013 Elsevier B.V. A

x.doi.org/10.1016/j.wear.2013.01.024

esponding author. Tel.: þ52 8114920375x57

ail address: malhdz@gmail.com (M.A.L. Herna

a b s t r a c t

Metal-on-metal (MOM) hip joint bearings have demonstrated low wear rates and nowadays this

contact pair has being considered as an alternative to metal-on-polymer (MOP) joint replacements.

However, wear of MOM joints is a concern due to the toxicity and biological reaction of wear debris and

metallic corrosion. This has motivated to investigate the possibility to apply thin hard coatings on

metallic heads to reduce the wear and metallic ion release. The aim of the present study was to

investigate the wear properties of metal-on-metal hip prostheses with surface engineered femoral

heads using a multilayer coating (TiN/CrN)�3, in comparison with metal-on-metal pairs in a hip joint

simulator. Different surface PVD coatings were applied on surgical grade wrought cobalt–chromium

alloy femoral heads: multilayer (TiN/CrN)�3, CrN single layer and diamond-like carbon (DLC). These

femoral heads were tested against high carbon content cast cobalt–chromium alloy acetabular cups

using a three-axial multi-station hip joint simulator (FIME II). During the wear tests three directions

of motion were applied with the following amplitudes: flexion–extension (FE) 7231, abduction–

adduction (AA) 7231 and internal–external (IER) 781. All components were tested at 1.2 Hz under a

Paul-type loading curve and bovine calf serum solution as lubricant. Results showed that both; the PVD

coatings protects the femoral heads reducing wear up to 5 times in the case of the DLC coating and 28

and 55 times in the case of (TiN/CrN)�3 and CrN respectively compared with the MOM femoral heads.

& 2013 Elsevier B.V. All rights reserved.

1. Introduction

The total hip arthroplastic surgery was a major medical advance ofthe 20th century. The materials used in this medical application mustpossess satisfactory mechanical properties such as stiffness andfatigue strength, wear and corrosion resistance, and biocompatibility.The first metal-on-metal (MOM) total hip prostheses implantedduring the 1960s decade presented unsatisfactory short-term perfor-mance due to geometrical inaccuracies which led to high frictionalforces and increased wear [1–5]. However, in some cases the implantslasted at least for two decades without osteolysis [2,5–7] andnegligible wear [2,8–11]. In recent years, the use of second generationCo–Cr alloy metal-on-metal bearing joints in total hip arthroplastysurgery represents an attractive alternative to the traditional metal-on-polyethylene pairs [12].

Despite the triblological pair metal-on-metal has proven to bemore wear resistant than metal-on-polyethylene couple, thetoxicity of metallic ions of cobalt and chromium released fromwear particles from metal-on-metal hip prostheses into the

ll rights reserved.

70; Fax: þ52 8110523321.

ndez-Rodriguez).

human body [13–16] is a concern which has motivated to lookfor alternatives to solve or diminish this problem.

PVD coatings are well known for providing surfaces withimproved tribological properties in terms of low coefficient offriction and high wear resistance. This technology has beenbrought to the field of surgical implants with promising results[17–19]. Nowadays, there has been great scientific and commer-cial interest in nanostructured coatings, like multilayer or nano-layered films [20]. The main idea is that the coating needs to behard to avoid abrasive wear, but it also needs to be strain tolerantand tough, in order to prevent crack propagation, thereforeavoiding fracture or delamination of the coating [21]. In conse-quence, multilayer films can be designed to show an improvedwear resistance [22]. In a previous study, the authors havereported the improved wear resistance of a multilayer TiN/CrNcoating deposited by plasma assisted phisycal vapor depositionon wrought Co–Cr substrates [23]. These films also exhibitimproved corrosion resistance [23,24], making them good candi-dates for orthopedic applications.

The main aim of the present study was to assess the tribolo-gical behavior of femoral heads surface modified with a multi-layer TiN/CrN coating articulating against uncoated metallicacetabular cups in an anatomical hip joint simulator. Femoralheads coated with two of the most successful coatings in the

J.A. Ortega-Saenz et al. / Wear 301 (2013) 234–242 235

recent years: CrN and DLC, were also included in the study andcompared with metal-on-metal Co–Cr alloy bearing couple.

2. Material and methods

2.1. Samples preparation

For the present study, a total of eight prototype cups and headsimplants with 31.5 mm diameter were manufactured. Femoralheads were manufactured from wrought Co–Cr alloy ASTMF1537-08 (BioDur CCM Plus) supplied by Carpenter Technology,whereas the acetabular cups were manufactured by the invest-ment casting method complying with the chemical compositionof the ASTM F75/98 [25]. The chemical composition of the alloysused in this investigation is shown in Table 1.

Femoral heads were modified using three different coatings:a multilayer coating (TiN/CrN)�3, monolayer CrN and, DLC. Thefirst two coatings were created by the plasma assisted physicaldeposition (PAPVD) method, whereas the DLC coating (a-C: H)was supplied by Balzers (BALINITs DLC). The thicknesses of thecoatings were 3.25 mm, 3.75 mm and, 2 mm respectively.

Multilayer (TiN/CrN)�3 and monolayer CrN coatings were depos-ited by means of an industrial multi-source vacuum device equippedwith five sources. A double rotation planetarium fixture was used.The substrates were precleaned in an ultrasonic cleaning line withtrichloroethylene, alkaline detergent and demineralized water. Thefinal drying was performed in hot trichloroethylene vapor. Prior todeposition, the vacuum chamber was pumped down to 2�10�3 Pato initiate the etching/heating stage. A current of 80 A, for each of thefive cathodes in operation, and a negative substrate bias voltage of950 V was used. No nitrogen was introduced into the chamber duringthis stage. The etching/heating stage was interrupted when a tem-perature of 400 1C, as measured with a pyrometer, was reached;whereupon the deposition stage was initiated. Coating depositionwas performed with five sources in operation. Parameters usedduring the PAPVD process such as: nitrogen gas pressure, substratebias voltage (UBias), cathode source current (ICathode), and depositiontime are presented in Table 2. The total thickness of the coating wascontrolled by the deposition time. The samples were cooled down toless than 100 1C in an N2 atmosphere before venting the chamber.

The components were machined and finished following con-trolled standard implant specifications. For this purpose a coor-dinate measurement machine (Mitutoyo QM-Measure 353) andsurface profilometer (with 0.8 mm cut-off) were used to measurethe diametral clearance (Cd), sphericity and roughness (Ra). Theseparameters for the eight bearings are given in Table 3.

Table 1Chemical composition (wt%) of the pair specimens used in this investigation.

Cr Mo Si Ni Fe Ni Mn C Co

Femoral heads 27.13 5.53 0.63 0.13 0.21 0.13 0.79 0.05 65.40

Acetabular cups 27.9 6.51 0.7 0.24 0.7 0.24 0.39 0.31 63.01

Table 2Parameters used in PAPVD coating process.

Coating Particular

layer

Atmosphere Pressure

(Pa)

UBias

(V)

ICathode

(A)

Time

(min)

Multilayer (TiN/

CrN)�3

TiN N2 1.2 �200 80 30

CrN N2 3.5 �200 80 30

Monolayer CrN CrN N2 3.5 �200 70 120

2.2. Surface characterization

Scanning Electron Microscopy observations of the cross-sectionsof the samples were carried out in a JEOL JSM-6510LV apparatusoperated in backscattering mode and the thickness of the coatingswas determined. Morphology of the treated surfaces was analyzedusing the secondary electron mode. Surface roughness was deter-mined by measuring the Ra value by means of AFM using a QuesantInstruments Corporation Q-Scope 250. The measurements wereperformed applying a square area of 50 mm using contact mode.The hardness and Young’s modulus of the samples were measured bymeans of the indentation method. To achieve this aim, the nano-hardness tester (NHT) made by the CSEM was used. Measurementswere carried out with the Berkovich indentor in a single cycle withoutstopping under the following conditions: max depth¼250 nm, load-ing rate¼60 mN/min and unloading rate¼60 mN/min. To eliminatethe influence of the substrate material on the result of the measure-ment of Young’s modulus, the range of the indentor’s penetrationdepth (g) was limited to the value of gr0.1d (d-layer thickness). Thehardness and Young’s modulus were determined by the Oliver andPharr method [26].

2.3. Scratch test

The measurements of coating adhesion were carried out usingthe scratch-test method by means of a Revetest (CSEM) scratch-tester. The scratch indenter was a diamond stylus with a sphericaltip having a radius of 200 mm. For the 10 mm scratch length, theapplied load was progressively increased from 0 to 100 N at a rate of10 N/mm. Three scratch tests were performed for each sample andan average value of the critical loads was obtained. After the test, acritical load, where failure occurred, was determined by observationof the scratch track using an optical microscope Nikon MM40.Thefriction force and acoustic emission signals were recorded duringthe scratch tests and later compared with the results of microscopeobservations of the scratches. The scratch resistant properties of thenitride layer and the coatings were then quantified in terms of thecritical loads corresponding to the failure modes as defined asfollows: first crack (LC0), beginning of the material removal (LC1),first breakthrough or lose of adhesion (LC2) and total materialremoval or worn out (LC3) [27].

2.4. Hip joint simulator test

Wear testing was performed using the four-station FIME II hipwear simulation rig [28]. During tests, the implants specimens weremounted in the normal orientation with the acetabular cups abovethe femoral heads. Femoral heads were mounted in a base devicewith rotational movement at an angle of 231 to the horizontal planeand rotated about a vertical axis at a frequency of 1.2 Hz achieving7231 for flexion–extension, 7231 for abduction–adduction and77.51 for internal–external rotation. A single axis Paul-type loadingpattern [29] with a maximum load peak of 2 kN was appliedthrough the vertical axis of the simulator.

Table 3The average values of surface roughness (Ra) of the heads and diametral clearance

of head and cup components.

Sample Mean Diametral

Clearance cd (mm)

Average surface

roughness Ra (nm)

MOM (n¼2) 50–89 10.072.52

CrN–Metal (n¼2) 65–49 51.072.14

(TiN/CrN)�3–Metal (n¼2) 33–39 47.0713.68

DLC–Metal (n¼2) 96–64 20.576.18

J.A. Ortega-Saenz et al. / Wear 301 (2013) 234–242236

Fetal bovine serum solution (25%72%) diluted with deionizedwater was used as a lubricant, according to ISO 14242-1 standard[30]. The resulting protein content of the bovine serum was15.2 g/l. No additives like antibacterial or antifungal agents wereused in the solution. The volume of lubricant, in which each jointwas immersed during the test, was 150 ml. An automatic deio-nized water replenishment system compensated for the evapora-tion, preventing volume and concentration changes of thelubricant during the tests. The tests were conducted at controlledroom temperature in a range of 2571 1C.

The specimens were tested up to 2�106 cycles. Gravimetricmeasurement of wear and lubricant change was undertakenevery 333,000 cycles during the first million cycles, and thenevery 500 000. Prior to gravimetric measurement of wear, speci-mens were brushed with a soft nylon and washed with detergent,then the specimens were ultrasonically cleaned [31]. Wear wasdetermined gravimetrically using an analytical balance (accuracyof 0.1 mg). Weight loss was converted into volume loss usingspecific densities 8.33 g/cm3 for Co–Cr, 6.0 g/cm3 for CrN, 5.4 g/cm3

for multilayer coating (TiN/CrN)�3 and, 2.5 g/cm3 for DLC tocompare the wear between different materials.

The surface condition of the specimens was examined at1�106 cycles by SEM in the secondary electron mode as wellas qualitative elemental analysis using an energy dispersivespectrometer (EDS).

Three-dimentional surface topography analysis of the eightMOM components were carried out at the end of test using aconfocal microscopy 3D Axio CSM 700.

Table 4Parameters and properties of the different conditions of CoCrMo alloy samples.

Sample Thickness (mm) Hardness (GPa) Young’s modulus (GPa)

Co–Cr untreated — 8.3170.21 267711.80

CrN 3.25 19.4071.62 283728.32

(TiN/CrN)�3 3.75 26.6271.69 384736.42

DLC 2.00 14.1070.94 14277.35

3. Experimental results

3.1. Configuration and coating parameters

Cross-sectional SEM images from all the surface conditions areshown on Fig. 1. Multilayer (TiN/CrN)�3 coating micrograph

Fig. 1. Cross-sectional SEM micrograph of: (a) multilayer coa

is shown in Fig. 1a. The configuration of this coating consisted ofthree TiN layers intercalated with three CrN layers with athickness of 1 and 0.25 mm respectively, resulting in a 3.75 mmthickness coating. Fig. 1b shows the cross-sectional image of theCrN coating with a thickness of 3.25 mm deposited on Co–Cr alloy.Fig. 1c shows the cross-sectional image of the DLC coating with athickness of 2 mm.

The basic parameter and mechanical properties of the condi-tions mentioned above are summarized on in Table 4 andcompared with the sample Co–Cr untreated.

3.2. Morphology analysis of the coated femoral heads

The morphology of the coatings was analyzed by scanningelectron microscopy. SEM micrographs of the surface modifiedfemoral heads with CrN and (TiN/CrN)�3 are shown in Fig. 2aand b, respectively. Small rounded pits and droplets were foundon these surfaces. Surface of the DLC coating (Fig. 2c) showed asmooth finish and just a few number of localized defectswere found.

3.3. AFM analysis

Topography of the coatings was analyzed by AFM. Fig. 3 showsthe three-dimensional AFM images of the coated femoral heads.

ting (TiN/CrN)�3, (b) CrN coating, and (c) DLC coating.

Fig. 2. SEM micrographs of femoral heads coated with: (a) CrN, (b) multilayer (TiN/CrN)�3 and (c) DLC.

J.A. Ortega-Saenz et al. / Wear 301 (2013) 234–242 237

For comparison, a three-dimensional AFM image of an untreatedCo–Cr head was included (Fig. 3a). The roughness values pre-sented in Table 3 are supported by the AFM images in Fig. 3,where the uncoated femoral head (Fig. 3a) showed the smoothersurface. Femoral head DLC-coated (Fig. 3d) presents a homoge-nous surface where some grooves can be detected. These groovesprobably remain from the polishing process. Femoral headscoated with multilayer (TiN/CrN)�3 and CrN (Fig. 3b and c)present rough surfaces. Pits observed on the surface of the(TiN/CrN)�3 coating in Fig. 2a are also detected on the three-dimensional AFM image (Fig. 3b).

3.4. Scratch test

The scratch resistant properties of samples were quantified interms of the critical loads corresponding to the failure modesmentioned before. The mean values of critical loads correspond-ing to the different failure modes are summarized in Table 5.

According to the results, multilayer (TiN/CrN)�3 and CrN andcoatings showed similar values for the critical loads during thescratch test. Worn out of the coating for CrN and multilayer (TiN/CrN)�3 occurred at 60 and 58.50 N respectively. On the otherhand, DLC coating showed very low adhesion to the Co–Crsubstrate, where the first breakthrough occurred at 4.8 N andworn out of the coating at 18.79 N.

3.5. Tribological results

The mean wear results for the half coated prosthesis togetherwith the MOM reference prostheses were recorded as a functionof the number of loading cycles. According to the results from thewear tests, wear results of the femoral heads and cups arepresented separately in Figs. 4 and 5. Mean volumetric wear ofthe coated femoral heads are shown in Fig. 4. Femoral headscoated with the PVD multilayer system (TiN/CrN)�3 and CrN

single layer showed a very low wear rate, transition from runningin to steady state was not identified. Femoral heads DLC-coatedshowed a running in wear rate very similar to the multilayersystem (TiN/CrN)�3 and CrN-coated and heads. However,a transition on wear behavior was identified near to 0.6�106

cycles. In the case of the uncoated heads it was observed thetypical trend of wear for metal-on-metal hip joint implant witha high running-in wear rate followed by a low steady statewear rate.

Mean volumetric wear of the cups is shown in Fig. 5. Cupstested against heads coated with multilayer system (TiN/CrN)�3and CrN single layer showed the highest wear rates. These cupspresented a running in wear rate 85 times higher than the cupstested against heads coated with DLC and uncoated MOM heads.Cups tested against femoral heads coated with DLC and untreatedshowed the lowest wear rate.

3.6. Wear surfaces

Scanning electron micrographs depicting the changes in sur-face condition of the femoral heads and acetabular cups speci-mens during the simulation tests are presented in Figs. 6 and 7.For the MOM prostheses (Figs. 6 and 7a) micropittings wereobserved in the surface of both components. In addition, evidenceof carbide detachments was found in the femoral heads (Fig. 6a).Fig. 6b and c show SEM micrographs of the femoral heads surfacemodified with multilayer (TiN/CrN)�3 and CrN coatings, remain-ing undamaged after the wear tests supporting the low wear rate,almost negligible, presented on Fig. 3. On the other hand, the cupstested against these two conditions (Fig. 7b and c) presentedsevere damage showing evidence of carbide detachments andabrasion grooves. Damage of femoral head DLC-coated is pre-sented on Fig. 6d showing mild abrasion grooves. On the otherhand, slight adhesion in the cups (Fig. 7d). Adhesion of organicprotein films was observed for all conditions, (Fig. 8).

Table 5Critical loads of the different Co–Cr surface conditions corresponding to the failure

modes occurring during the scratch test.

Sample Critical loads

LC0 (N) LC1 (N) LC2 (N) LC3 (N)

First crack Beginning of

material

removal

First

breakthrough

Worn out

CrN 5.5070.57 22.4870.61 57.4071.11 60.0071.25

(TiN/CrN)�3 7.9670.68 12.9071.25 55.0071.06 58.5071.20

DLC 3.3070.39 4.8070.41 4.8071.04 18.7971.17

Fig. 4. Mean volumetric wear of the coated femoral heads.

Fig. 5. Mean volumetric wear of the Co–Cr acetabular cups.

Fig. 3. Three-dimensional AFM images of prototype femoral heads: (a) untreated; surface modified with, (b) multilayer (TiN/CrN)�3, (c) CrN and (d) DLC coating.

J.A. Ortega-Saenz et al. / Wear 301 (2013) 234–242238

3.7. Surface topography analysis

Surface topography of the samples after wear test is shown inFig. 9. Damage on the uncoated femoral head from the tribologicalpair MOM is shown in Fig. 9a. Deep scratches and part of a proteinlayer attached to the surface can be observed. The topographyof the femoral heads coated with the multilayer system (TiN/CrN)�3 and CrN single layer are shown in Fig. 9b and c. Fromthese figures it can be seen that after 2�106 cycles of weartesting, the coatings remained undamaged. Surface topography ofthe DLC-coated femoral head is shown in Fig. 9d. From this figuresome light scratches can be observed, some of them probablyremaining from the polishing process before wear test.

Fig. 6. SEM micrographs of femoral heads worn surfaces: (a) uncoated, �800; (b) multilayer (TiN/CrN) �3 coated, �500; (c) CrN-coated and (d) DLC-coated.

J.A. Ortega-Saenz et al. / Wear 301 (2013) 234–242 239

4. Discussion

In the present study, the tribological behavior of femoral headssurface modified with a multilayer coating system (TiN/CrN)�3coating was investigated articulating against uncoated metallicacetabular cups using a hip joint simulator. For comparison,femoral heads coated with two of the most successful coatingsin the recent years: CrN and DLC, were also included in the studyand compared with a metal-on-metal bearing couple.

In order to obtain similar diametral clearances in the allconditions, the MOM samples were manufactured followingthe same manufacture procedures and specifications; howeverchanges in roughness were identified due to inherent propertiesof coating process, as can be seen on Table 3. In spite of theseobservations; this work is in accordance with the publishedsignificance of diametral clearance on the wear behavior ofMOM hip bearings [32–34].

Femoral heads coated with the multilayer system (TiN/CrN)�3 presented similar volumetric wear values than femoralheads CrN-coated (Fig. 4). In these two conditions it was notpossible to identify the transition from the running in to thesteady sate. For the CrN condition the results are in accordancewith other authors [17,18].

In the case of the multilayer coating system (TiN/CrN)�3,surface damage was not identified; just slight scratches andprotein films attached to the surface (Figs. 6 and 9b). Fisheret al. reported localized cohesive failures in femoral heads coatedwith TiN single layer [17–18]. However, in the present studycohesive failures were not detected on the multilayer system(TiN/CrN)�3. This could be due to the effect of the multilayers.According to the literature, some authors ascribe the enhance-ment of the tribological properties of the multilayer coatings to a

modification of their mechanical properties such as hardness orthe H/E ratio [35,36]. To verify this statement, in the present studyboth hardness and elastic modulus were measured by nanoin-dentation. The investigated range of plastic depth was limited to10% of the thickness of the coatings to reduce the influence of thesubstrate. Multilayer coating hardness was 26 GPa while formonolayer CrN coating was 19 GPa (Table 4). The hardeningeffect of the multilayer coatings can be attributed to the Hall–Petch effect, to the variations of shear modulus or on internalstresses [37–39]. From Table 4, it can be seen that the H/E ratio isalmost the same and thus mechanical properties do not representthe key parameter to explain the enhanced tribological behavior.For other authors [40], the explanation lies in the cracks propaga-tion. Mendebide et al. [35,36] found that monolayer coatings aresubjected to decohesion at the grain boundaries, while multilayerstructure induce a deviation of the cracks at the multiple inter-faces, associated with a slight degradation.

However, when the counter faces (cups) of the two conditionsmentioned above were examined, it was observed severe abrasionand fatigue with presence of carbide detachments. This can beattributed to the high roughness (Ra value) presented by the PVDcoatings, as shown in Table 3. These cups presented a running inwear rate 85 times higher than the cups tested against headscoated with DLC and uncoated heads with MOM contact. Thissuggests that these coatings can work better self mated. Furtherworks will be necessary to study it.

Femoral heads DLC-coated showed a running in wear rate verysimilar to the CrN and multilayer system (TiN/CrN)�3 coatedheads. However near to 0.6�106 cycles, the wear rate increasedconsiderably compared to the other two coatings. This behaviorcan be explained by de-adhesion coating which can be attributedto the poor coating adherence resistance showed in the scratch

Fig. 7. SEM micrographs of acetabular cups worn surfaces tested against femoral heads: (a) uncoated, �1000; (b) multilayer (TiN/CrN)�3 coated, �200; (c) CrN-coated,

�200 and (d) DLC-coated.

Fig. 8. SEM micrographs of femoral heads worn surfaces showing organic layers due to protein precipitation: (a) multilayer system (TiN/CrN)�3 coating and (b) CrN

coating.

J.A. Ortega-Saenz et al. / Wear 301 (2013) 234–242240

test, Table 5. In spite of this phenomenon, in this condition theCo–Cr cups exhibited a low rate in contrast with the Co–Cr cupstested against CrN and multilayer system (TiN/CrN)�3.

For the case of the uncoated heads it was observed the typicaltrend of wear for metal-on-metal hip joint implant with a highrunning-in wear rate followed by a low steady state wear rate[17]. From SEM analyses shown in Figs. 6 and 7a it can beobserved abrasion, pullout of carbides and micropitting producedby fatigue wear. The deepness of the abrasion grooves can beobserved on the surface topography analysis (Fig. 9a). For allconditions, adhesion of organic protein films was observed(Fig. 8); however the roll of this phenomenon in the wearbehavior was not elucidated in this work.

5. Conclusions

Based on the experimental results of this work where differentcoated femoral conditions were tested against high carbon Co–Crcups in a hip simulator; the following main conclusions canbe drawn:

(a)

Femoral heads:

� The multilayer system (TiN/CrN)�3 showed similar volu-metric mass loss than CrN coatings. In addition, both coat-ings presented similar critical loads during the scratch test.

Fig. 9. Surface topography for the femoral heads: (a) uncoated, (b) multilayer (TiN/CrN)�3 coated, (c) CrN-coated and (d) DLC-coated.

J.A. Ortega-Saenz et al. / Wear 301 (2013) 234–242 241

� For the MOM condition, the femoral head showed a highrunning-in wear rate with a transition to steady state. Thewear mechanisms in this condition were abrasion and

fatigue wear with presence of micropitting.

(b)

Cups:

� The high carbon cups exhibited a severe damage byabrasion and fatigue wear when tested against multilayersystem (TiN/CrN)�3 and CrN coatings. These cups pre-sented a running in wear rate 85 times higher than thecups tested against heads coated with DLC and uncoatedMOM heads.

Multilayer (TiN/CrN)�3 coatings are a promising solution toimprove the wear resistance of hip prostheses. These coatings arehard enough to avoid abrasive wear and strain tolerant, in orderto prevent crack propagation, therefore avoiding fracture ordelamination of the coating. Considering the total volumetricmass loss of the cup and head; the femoral head DLC-coatedevaluated against high carbon cups showed the lowestvolumetric wear.

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