The purpose of the study was to compare the mechanical properties, oxidation and wear resistance of a vitamin E blended and moderately crosslinked polyethylene for total knee arthroplasty (MXE) in comparison with clinically established polyethylene materials. The following polyethylene materials were tested: CPE (30 kGy e-beam sterilized), XLPE (75 kGy gamma crosslinked @ 100°C), ViXLPE (0.1 % vitamin E blended, 80 kGy e-beam crosslinked @ 100°C), and MXE (0.1 % vitamin E blended polyethylene, 30 kGy gamma sterilized). For the different tests, the polyethylene materials were either unaged or artificially aged for two or six weeks according to ASTM F2003-02. The oxidation index was measured based on ASTM F2102 at a 1 mm depth. Small punch testing was performed based on ASTM F2977. Mechanical properties were measured on unaged materials according to ASTM D638. Wear simulation was performed on a load controlled 3 + 1 station knee wear simulator (EndoLab GmbH, Thansau, Germany) capable of reproducing loads and movement of highly demanding activities (HDA) as well as ISO 14243-1 load profiles. The load profiles were applied for 5 million cycles (mc) or delamination of the polyethylene components. Medium size AS e.motion. ®. PS Pro (Aesculap AG, Tuttlingen, Germany) femoral and tibial components with a ZrN-multilayer surface, as well as Columbus. ®. CR cobalt-chrome alloy femoral and tibial components were tested. Particle analysis was performed on the serum samples of the ISO 14243-1 wear simulations based on ISO 17853:2011 and ASTM F1877. The analysis of the mechanical properties show that moderately crosslinked polyethylene (MXE) might be a superior material for total knee arthroplasty applications [Schwiesau et al. 2021]. The addition of vitamin E in a moderately crosslinked polyethylene prevented its oxidation, kept its mechanical characteristics, and maintained a low wear, even under a HDA knee wear simulation

While high-performance ceramics like alumina and zirconia exhibit excellent wear resistance, they provide poor osseointegration capacity. As osseointegration is crucial for non-cemented joint prostheses, new techniques have been successfully developed for biofunctionalizing high-performance ceramic surfaces. Stable cell adhesion can be achieved by covalently bound specific peptides. In this study we investigate the effect of sterilization processes on organo-chemically functionalized surfaces. To enhance the performance of alumina-toughened zirconia ceramics (ATZ), a 3-aminopropyldiisopropylethoxysilane (APDS) monolayer was applied and coupled with cyclo-RGD peptides (cRGD) by using bifunctional crosslinker bis(sulfosuccinimidyl)suberat (BS³). The samples were sterilized using e-beam or gamma-sterilization at 25 kGy, either before or after biofunctionalization with cRGD. Functionalization stability was investigated by contact angle measurements. The functionality of cRGD after sterilization was demonstrated using proliferation tests and cytotoxicity assays. Immunofluorescence staining (pFAK, Actin, DAPI) was conducted to evaluate the adhesion potential between the samples and human mesenchymal stem cells (hMSCs). Functionalized samples before and after sterilization showed no significant difference regarding their contact angles. A proliferation test demonstrated that the cells on functionalized samples proliferate significantly more than on untreated samples before and after sterilization. hMSCs showed a significant higher proliferation on gamma sterilized samples compared to all other groups after 14 days. It was confirmed that the samples did not exhibit cytotoxic behavior before or after sterilization. Fluorescence microscopy demonstrated that both, cells on sterilized and on non-sterilized samples, expressed high levels of pFAK-Y397. The investigated functionalization enables improved adhesion and proliferation of hMSCs and is stable against the investigated sterilization processes. This is of importance as the option of having a sterile product enables the start of the translation of this biofunctional coating towards preclinical and subsequently first-in-man applications. Acknowledgments: We acknowledge the financial support of the Federal Ministry of Education and Research, BMBF (13GW0452A-C)

Summary. Fifteen irradiated, vitamin E-diffused UHMWPE retrievals with up to three years in vivo service showed no appreciable oxidation, nor change in material properties from a never-implanted liner, and showed a 94% decrease in free radical content. Introduction. Radiation cross-linking, used to improve wear resistance of ultra-high molecular weight polyethylene (UHMWPE) bearings used in total joint arthroplasty, generates residual free radicals which are the precursors to oxidative embrittlement. First generation materials adopted thermal treatments to eliminate or reduce free radical content, but came with compromises in reduced mechanical properties or insufficient stabilization. A second generation alternative method infuses an antioxidant, vitamin E, into irradiated UHMWPE to stabilise free radicals while maintaining fatigue strength. In vitro studies predict excellent oxidation and wear resistance in vitamin E-stabilised bearings, but the long-term in vivo oxidation behavior, influenced by lipid absorption and cyclic loading, remains largely unknown. Our aim was to investigate in vivo changes in UHMWPE surgically-retrieved explants that were radiation cross-linked and stabilised by vitamin E. Patients & Methods. Fifteen surgically-retrieved irradiated, vitamin E-diffused and inert-gamma sterilised bearings (E1™, Biomet, Inc., Warsaw IN) with in vivo durations ranging from 3 days to 36.6 months were analyzed at unloaded rim/eminence and the articular surface along with one never-implanted component. Total lifetime of components was summed as shelf storage prior to implantation, in vivo duration and ex vivo duration in air. Fourier Transform Infrared Spectroscopy (FTIR) was used to measure carbonyl index (CI; per ASTM F2102-01ε1) both before and after 16 hour hexane extraction to. Extracted thin films were also reacted with nitric oxide to quantify hydroperoxides, an intermediate oxidation product associated with oxidation potential. Cross-link density was calculated from gravimetric swelling analysis per ASTM F2214. Crystallinity measurements were performed regionally using differential scanning calorimetry (DSC). Free radical content was measured by electron spin resonance (Memphis, TN). Results. Irradiated and vitamin E-diffused retrievals showed scratching at the articular surface, but retained machining marks up to three years in vivo, indicative of no measurable wear. Retrievals showed no significant oxidation at the time of surgical removal with maximum post-hexane carbonyl indices in the barely detectable range (MCI=0.029–0.154), located at the surface of retrievals. Ex vivo oxidation was not observed after 18 months of aging in air at room temperature. There was no increase in hydroperoxides (never-implanted HI=0.62±0.04; retrieval HI= 0.62±0.04), nor change in cross-link density (never-implanted: 0.275±0.015 mol/dm. 3. ; retrieval: 0.295±0.016 mol/dm. 3. ) or crystallinity (never-implanted: 58.3±1.4%; retrievals: 60.0±3.5%). Lipid penetration increased with time, showing a higher rate of diffusion in loaded regions. Free radical content was observed to decay with increasing in vivo duration (R. 2. =0.44; p<0.05), and by one order of magnitude (94%) by 36.6 months. A stronger negative correlation (R. 2. =0.65) was observed between the total lifetime of the liner and free radical content. Discussion/Conclusion. The free-radical scavenging activity of the vitamin E appears to successfully prevent both in vivo and ex vivo oxidation for short durations. Without an increase in hydroperoxides, the oxidation cascade initiated by radiation-induced and lipid-derived free radicals appears to have been halted. Retrievals also gave no indication of wear in this timeframe, similar to improved wear resistance seen in first generation materials. Continued monitoring will be necessary at longer implant durations

Summary. Low energy irradiation of vitamin E blended UHMWPE is feasible to fabricate total joint implants with high wear resistance and impact strength. Introduction. Irradiated ultra-high molecular weight polyethylene (UHMWPE), used in the fabrication of joint implants, has increased wear resistance. But, increased crosslinking decreases the mechanical strength of the polymer, thus limiting the crosslinking to the surface is desirable. Here, we used electron beam irradiation with low energy electrons to limit the penetration of the radiation exposure and achieve surface cross-linking. Methods. Medical grade 0.1wt% vitamin E blended UHMWPE (GUR1050) was consolidated and irradiated using an electron beam at 0.8 and 3 MeV to 150 kGy. Fourier Transform Infrared Spectroscopy (FTIR) was used from the surface along the depth at an average of 32 scans and a resolution of 4 cm. −1. A transvinylene index (TVI) was calculated by normalizing the absorbance at 965 cm. −1. (950–980cm. −1. ) against 1895 cm. −1. (1850 – 1985 cm. −1. ). TVI in irradiated UHMWPE is linearly correlated with the radiation received [3]. Vitamin E indices were calculated as the ratio of the area under 1265 cm. −1. (1245–1275 cm. −1. ) normalized by the same. Pin-on-disc (POD) wear testing was conducted on cylindrical pins (9 mm dia., 13 mm length, n=3) as previously described at 2 Hz [4] for 1.2 million cycles (MC). Wear rate was measured as the linear regression of gravimetric weight change vs. number of cycles from 0.5 to 1.2 MC. Double notched IZOD impact testing was performed (63.5 × 12.7 × 6.35mm) in accordance with ASTM F648. Cubes (1 cm) from 0.1wt% blended and 150 kGy irradiated pucks (0.8 MeV) were soaked in vitamin E at 110°C for 1 hour followed by homogenization at 130°C for 48 hours. Results. The penetration of the electron beam for cross-linking was limited at low beam energy and cross-linking of the surface 2 mm was achieved. The wear rate of samples irradiated at 0.8 and 3 MeV was 1.12±0.15, and 0.98±0.11, respectively (p»0.5). In addition, the wear rate of the surface (0.8 MeV) irradiated UHMWPE was 0.33±0.02 mg/MC 1 mm below the surface. The impact strength of UHMWPE irradiated at 0.8 MeV was 73 kJ/m. 2. and 54.2 kJ/m. 2. for that irradiated at 3 MeV (p=0.001). Doping with vitamin E and homogenization increased the surface vitamin E concentration from undetectable levels to 0.11±0.01. Discussion. The wear rate of this surface cross-linked UHMWPE was comparable to uniformly cross-linked UHMWPEs irradiated at higher electron beam energies. Even lower wear rate subsurface suggested the feasibility of machining 1 mm from the surface in implant fabrication. Limiting cross-linking to the surface resulted in higher impact strength compared to a uniformly cross-linked UHMWPE. Vitamin E was optionally replenished by additional doping after cross-linking; an advantage of this method may be increased oxidation resistance

In 2011, approximately 1.6 million total hip arthroplasties (THAs) were conducted in 27 of the 34 member countries in the Organization for Economic Cooperation and Development (OECD) However, approximately 10–15% of patients still require revision surgery every year. Therefore, new technologies are required to increase the life-spam of the prosthesis from the current 10–15 years to at least 20–30 years. Our strategy focuses on surface modification of the bearing materials with a hydrophilic coating to improve their wear behaviour. These coatings are biocompatible, with high swelling capacity and antifouling properties, mimicking the properties of natural cartilage, i.e. wear resistance with permanent hydrated layer that prevents prosthesis damage. Clear beneficial advantages of this coating have been demonstrated in different conditions and different materials, such as UHMWPE, PEEK, CrCo, Stainless steel, ZTA and Alumina. Using routine tribological experiments, the wear for UHMWPE substrate was decreased by 75% against alumina, ZTA and stainless steel. For PEEK-CFR substrate coated, the amount of material lost against ZTA and CrCo was at least 40% lower. Further experiments on hip simulator adding abrasive particles (1-micron sized aluminium particles) during 3 million cycles, on a total of 6 million, showed a wear decreased of around 55% compared to uncoated UHMWPE and XLPE. In conclusion, CIDETEC‘s coating technology is versatile and can be adapted to protect and improve the tribological properties of different types of surfaces used for prosthesis, even in abrasive conditions

Knee arthroplasty with a rotating hinge knee (RHK) prosthesis has become an important clinical treatment option for knee revisions and primary patients with severe varus or valgus deformities and instable ligaments. The rotational axle constraints the anterior-posterior shear and varus-valgus moments, but currently used polyethylene bushings may fail in the mid-term due to insufficient creep and wear resistance of the material. Due to that carbon-fibre-reinforced (CFR) PEEK as an alternativ bushing material with enhanced creep, wear and fatigue behaviour has been introduced in a RHK design [Grupp 2011, Giurea 2014]. The objective of our study was to compare results from the pre-clinical biotribological characterisation to ex vivo findings on a series of retrieved implants. In vitro wear simulation according to ISO 14243-1 was performed on rotating hinge knee devices (EnduRo® Aesculap, Germany) made out of cobalt-chromium and of a ZrN multi-layer ceramic coating for 5 million cycles. The mobile gliding surfaces were made out of polyethylene (GUR 1020, β-irradiated 30 ± 2 kGy). For the bushings of the rotational and flexion axles and the flanges a new bearing material based on CFR-PEEK with 30% PAN fiber content was used. Analysis of 12 retrieved EnduRo. ®. RHK systems in cobalt-chromium and ZrN multi-layer in regard to. -. loosening torques in comparison with initial fastening torques. -. Optical, DSLR camera and stereo light microscope analysis. -. distinction between different wear modes and classification with a modified HOOD-score. -. SEM & EDX of representative samples. -. surface roughness and depth profilometry. with a focus on the four CFR-PEEK components integrated in the EnduRo. ®. RHK design. For the rotating hinge knee design with flexion bushing and flanges out of CFR-PEEK the volumetric wear rates were 2.3 ± 0.48 mm. 3. /million cycles (cobalt-chromium) and 0.21 ± 0.02 mm. 3. /million cycles (ZrN multi-layer), a 10.9-fold reduction (p = 0.0016). The UHMWPE and CFR-PEEK particles were comparable in size and morphology and predominantly in submicron size [5]. The biological response to representative sub-micron sized CFR-PEEK particles has been demonstrated in vivo based on the leucoyte-endothelian-cell interactions in the synovia of a murine intra-articular knee model by Utzschneider 2010. Schwiesau 2013 extracted the frequency of daily activities in hip and knee replacement patients from literature and estimated an average of 1.76 million gait cycles per year. Thus, the 5 million cycles of in vitro wear testing reflect a mean in vivo service life of 2.9 years, which fits to the time in vivo of 12–60 months of the retrieved RHK devices. The in vitro surface articulation pattern of the wear simulation tests are comparable to findings on retrieved CFR-PEEK components for both types of articulations – cobalt-chromium and ZrN multi-layer coating. For the rotating hinge knee design the findings on retrieved implants demonstrate the high suitability of CFR-PEEK as a biomaterial for highly loaded bearings, such as RHK bushings and flanges in articulation to cobalt-chromium and to a ZrN multi-layer coating

Medical grade polyurethanes have been widely promoted for biomedical applications. In particular, the use of polycarbonate-urethanes (PCU) has drawn considerable attention in the orthopaedic device industry as a result of their excellent mechanical properties, biostability and biocompatibility. PCUs have been extensively utilized in vascular grafts, stents and artificial heart valves. Specifically, bionate thermoplastic PCU, commercially produced by DSM PTG (Berkeley, California), has been of great interest in the field of orthopaedics because of its outstanding load-bearing properties and excellent wear resistance. Also, it is characterized by its long-term durability and resistance to hydrolytic degradation making it a good candidate for in-vivo orthopaedic applications. PCUs have been considered for meniscal replacement because of its unique weight-bearing capabilities, ability to withstand intense forces within the knee joint and ease of lubrication due to its hydrophilic nature. In addition, the low frictional properties essential for a meniscal replacement is obtainable with PCUs. Materials used for this study were a commercial polycarbonate-urethanes, Bionate PCU 80A (B8) and 90A (B9) pellets, and polyethylene continuous strands fibres (PE) obtained from DSM Polymer Technology Group, USA. Some quantity of the B8 and B9 pellets were dried separately in a vacuum oven at 100°C for 14 hours. A custom mould was designed for the production of the mechanical test samples. The quantity of the constituent materials was determined using composite theory known as the Rule of Mixtures. E. c. =. E. m. V. m. +. E. f. E. f. where V. m. and V. f. are the volume fraction of the matrix and fibre respectively. Three specimens each of the prepared composites were tested for tensile and compression strength and at a crosshead speed of 12 mm/min using a Zwick/Roell 1484 Material Testing Machine. The PCUs were not as stiff as their fibre-reinforced composites, which indicate that the stiffness of the PCU composite materials is a function of both the stiffness of the PCU matrix and the interspersed fibres. The tensile moduli of composites of B8 and B9 increased appreciably with PE. An increase of 227% was obtained for the B8 with the incorporation of PE fibres while percentage increase in stiffness for B9 was 148% for PE reinforcement fibres. The compressive modulus dropped with the inclusion of the PE fibres in the B9, a reduction of 55% was recorded while an increment of 4% was obtained with PE added to the B8. The results from this study demonstrate that the tensile and compressive properties of PCU can be custom-tailored to that of the meniscal tissue by systematically embedding reinforcement fibres into the PCU matrix such that a composite with desirable mechanical properties is obtained. The results of both tensile and compressive results visibly revealed the reinforcing effect of the fibres used in this study. However, additional studies are required to completely describe the PCU composite as a candidate meniscal substitute capable of gaining its full functionality

Summary. Prosthetic UHMWPE added with vitamin E and crosslinked UHMWPE are able to decrease significantly the adhesion of various bacterial and fungal strains limiting biomaterial associated infection and consequent implant failure. Introduction. Polyethylene abrasive and oxidative wear induces overtime in vivo a foreign-body response and consequently osteolysis, pain and need of implant revision. To solve these problems the orthopaedic research has been addressed to develop new biomaterials such as a crosslinked polyethylene with a higher molecular mass than standard Ultra High Molecular Weight Polyethylene (UHMWPE), and consequently a higher abrasive wear resistance and an antioxidant (vitamin E)-added UHMWPE to avoid oxidative wear. Nevertheless a feared complication of implant surgery is bacterial or fungal infection, initiated by microbial adhesion and biofilm formation, and related to the biomaterial surface characteristics. Staphylococci are the most common microorganisms causing biomaterial associated infection (BAI), followed by streptococci, Gram-negative bacilli and yeasts. With the aim to prevent BAI, the purpose of this study was to evaluate the adhesion of various microbial strains on different prosthetic materials with specific surface chemical characteristics, used in orthopaedic surgery. Methods. We compared the effects of vitamin E-added UHMWPE and crosslinked UHMWPE with that of standard GUR 1020 UHMWPE, upon the adhesion of ATCC biofilm-producing strains of Staphylococcus epidermidis, S. aureus, Escherichia coli and Candida albicans. After different incubation times the samples were sonicated to release the attached microorganisms and spread onto agar to quantify colony forming units (UFC)/ml. The biomaterials were physico-chemically characterised by means of scanning electron microscopy (SEM), water contact angle (CA) measurements and attenuated total reflectance (ATR)-fourier transform infrared (FTIR) spectroscopy, before and after adhesion assays. The experiments were assayed in triplicate and repeated a minimum of three times. A statistical analysis on results was conducted. Results. No significant difference of the surface roughness, CA and ATR-FTIR spectroscopy was found among the different biomaterials. After 3 and 7 h of incubation microbial adhesion rates were similar with no statistically relevant differences among the samples assayed. On the contrary, after 24 and 48 h of incubation a significantly (p<0.05 and p<0.01) different adhesion trend was achieved on the three biomaterials, highlighting a microbial adhesion significantly lower on vitamin E-added UHMWPE and crosslinked UHMWPE compared with that on standard UHMWPE. Discussion/Conclusion. Standard UHMWPE, vitamin E-added UHMWPE and crosslinked UHMWPE were chosen because of their diffusion in the clinical use. Previously we showed that vitamin E addition to the UHMWPE reduces the adhesive ability of various staphylococcal strains, compared with standard UHMWPE, and we correlated this results with its antioxidant properties. The results of this study indicate a quite similar significant reduction of bacterial and fungal adhesion on either vitamin E-added UHMWPE and crosslinked UHMWPE, if compared to standard UHMWPE at 48h. Further analysis on the chemical- physical characteristics of the UHMWPE surfaces and on their morphology are needed to explain the different adhesions

Summary. Sequentially irradiated and annealed UHMWPE hip and knee retrievals showed subsurface in vivo oxidation in both the articular surface and unloaded surfaces, while three of four never-implanted shelf stored liners had oxidation in the bulk. Introduction. Highly cross-linked polyethylene was developed to improve the wear resistance of UHMWPE bearing surfaces in total hip arthroplasty. First generation irradiated and annealed polyethylene showed high oxidation in vivo, largely attributed to only the partial-quenching of free radicals, along with additional radicals generated during terminal gamma sterilization. A second generation, three-step sequential irradiation and annealing method was advanced with the promise of better oxidative stability and improved mechanical properties. We hypothesised that without the complete elimination of free radicals combined with gas plasma sterilization requiring oxygen-permeable packaging, that this second generation material would be prone to shelf-oxidation in addition to in vivo oxidation. Patients & Methods. Fifty surgically-retrieved sequentially irradiated and annealed, gas plasma-sterilised UHWMPE acetabular liners and tibial bearings (X3™, Stryker, Mahwah, NJ), with in vivo durations of 0.5–73 months, were analyzed at their articular surface and an unloaded surface, along with four never implanted acetabular liners. Infrared microscopy was used to evaluate lipid absorption, oxidation (per ASTM F2102-01ε1) and hydroperoxide levels after nitric oxide staining. Gravimetric swelling analysis assessed cross-link density (per ASTM F2214), and crystallinity measurements were performed using differential scanning calorimetry. Results. There was detectable oxidation (OI > 0.1) in 37 of the 50 components with as little as 2 weeks of in vivo service. Maximum oxidation values averaged OI = 0.30 ± 0.30 (range = 0.03–1.59). Oxidation profiles were predominantly characterised by subsurface oxidation peaks approximately 1–2 mm below the surface, in both the articular surface and rim, along with a pattern of embrittlement induced white banding in four and six year liners. Three short in vivo duration liners (0.1–15.5 month) showed oxidation and degradation of material properties throughout the bulk. Three of four never-implanted liners, with up to five years shelf storage, also showed bulk oxidation (Max OI ≤ 1.5), loss of cross-link density and increased crystallinity. Discussion/Conclusion. High levels of detectable oxidation, subsurface oxidation peaks, and white banding were all identified in sequentially irradiated and annealed UHMWPE retrievals with short in vivo durations. These results raise concerns about the long-term clinical performance of these materials. Oxidation measured in shelf-stored, never implanted liners also raises concerns that liners may already be oxidatively compromised before being implanted into patients. Due to gas plasma sterilization methods, these free-radical containing liners are packaged and stored in air, likely resulting in a pre-implantation oxidation effect similar to that historically reported in gamma-in-air sterilised UHMWPE. Longer-term retrievals are needed to better understand the progress of these in vivo changes and whether or not it will compromise the longevity of the implants

Summary Statement. A new 28mm-diameter ceramic-on-ceramic (COC) acetabular bearing couple (Biomet Orthopedics) showed extremely low wear, even under adverse microseparation conditions∗. The wear results are similar or more favorable than those reported for clinical retrievals and wear testing of similar ceramic bearings. Introduction. A new acetabular shell and ceramic insert design (Biomet) incorporates features to help prevent malalignment during implantation, while still providing secure fixation within the acetabular shell. The incorporation of Biolox. ®. Delta (zirconia toughened alumina, CeramTec) material should provide improved wear resistance over pure alumina ceramics. The goal of this study is to evaluate the wear durability of this system for standard and microseparation testing. Materials & Methods. The 28 mm diameter ceramic heads and inserts (CeramTec) were seated on taper spigots and within acetabular shells (Biomet), respectively. Six sets of parts were tested for 5M cycles of standard hip wear testing (ISO 14242) and an additional six sets of parts for 2M cycles of microseparation testing. The microseparation testing protocol included a steep cup angle (60° in-vivo), side load, and reduced axial load to induce head-liner separation. The lateral displacement was increased from 0.5mm, to 1mm, and then to 2mm in order to replicate wear features observed in extreme situations of clinical retrievals. [1]. The parts were weighed (gravimetric wear rates) and photographed throughout the test. SEM, transformation, and wear debris analyses were completed. Results. The steady-state wear rate throughout standard testing was 0.0094 +/− 0.0029 mm. 3. /10. 6. cycles (+/-95% CI). The initial 0.5mm microseparation distance (0–1M cycles) showed no signs of wear. Most heads showed wear stripes after increasing to 1.0mm (1–1.5M cycles), and then all test parts showed stripes after increasing to 2mm. The increased visibility in wear stripes correlated with an increased level of measured wear. For the 2mm separation-distance testing interval, the wear rate was 0.178 +/− 0.052mm. 3. /10. 6. cycles. Discussion/Conclusion. The lack of wear stripes during 0.5mm of microseparation is an indication of the strength of the implants. A distance of 1–2mm is an extreme level of microseparation and the 60° in-vivo cup inclination created an even worse-case situation for wear; however, the implants showed excellent mechanical strength and low wear rates. SEM and transformation analyses showed minimal wear and evidence of stress-induced ceramic toughening. Microseparation testing at another lab . [2]. has shown a similarly low wear rate (0.5 mm. 3. /10. 6. cycles) for Biolox. ®. Delta ceramic, with Biolox. ®. Forte (alumina ceramic, without zirconia) showing a considerably higher wear rate (6.3mm. 3. /10. 6. cycles). The standard testing wear rate (0.0094+/-0.0029 mm. 3. /10. 6. cycles) was much lower than the average wear rate (0.69+/-0.63 mm. 3. /10. 6. cycles) of several COC implant retrievals by Walter . [1]. The 28mm steady-state wear rate of this test is better than or equal to the wear rate (0.0101 mm. 3. /10. 6. cycles) observed in other 28mm COC systems.∗∗. ∗Ceramic-on-Ceramic articulation is not cleared for use in the United States. ∗∗Laboratory results are not necessarily indicative of clinical performance

Summary. Understanding of the role of the radical-generating ability of wear particles of the existing and new implant materials as well as application of efficient antioxidants is one of the necessary conditions for improvement of the results of joint replacements. Introduction. Functioning of joint prostheses is accompanied by a continuous formation of wear particles and their accumulation in surrounding tissues. The impact of microroughnesses of joint prosthesis friction units may bring about chemical bond breakage and free-radical generation on a newly-formed wear surface. Wear particles of orthopedic alloys are capable to produce free radicals, and Co-Cr-Mo alloy particles are especially active. Free radicals generated by wear particles can cause oxidation and reduced wear resistance of polyethylene. Oxidised polyethylene particles stimulate the activity and release of bone-resorbing cytokines by human monocytes/macrophages. The ability of free radicals to cause damage to surrounding tissues and implant components makes it necessary to estimate comprehensively the radical-generating activity of wear particles of different orthopedic materials and develop the ways of its inhibition. Methods. Artificial Co-Cr-Mo alloy wear particles were obtained using dry friction of a ball against a disk. The radical-generating ability of orthopedic alloy wear particles was estimated by oxygen consumption using the model reaction of cumene oxidation. The radical-generating ability of wear particles was determined at different moments after their formation and storage at room temperature and humidity. In the experiments, a pro-inflammatory action of wear particles during their continuous formation was also simulated. Fresh cobalt alloy wear particles were used for a consecutive triple oxidation of 2 ml of cumene at a particle concentration of 0.3 mg/ml. After the first 40 min oxidation, a suspension of particles in cumene was centrifuged, and the used particles were removed. Fresh particles were added to oxidised cumene, and the second and third oxidations were carried out in a similar way. The ability of some antioxidants to inhibit the radical-generating ability of cobalt alloy wear particles was also determined. Results. Fresh cobalt alloy wear particles demonstrated an expressed radical-generating ability which remained practically at the initial level after a one-week storage. The ability gradually reduced in the process of storage. After a one-month storage the particles’ radical-generating ability decreased 2.6 times. A six-month storage of cobalt alloy particles resulted in a tenfold reduction of the radical-generating ability as compared to that of fresh particles. The intensification of radical formation was studied during three consecutive oxidations of cumene by wear particles. It was established that each consecutive oxidation of cumene by fresh wear particles occurred with a growing radical-generation ability. That parameter of the newly-formed particles increased more than two- and threefold during a consecutive double and triple cumene oxidation, respectively. Synthetic antioxidant BHT and natural antioxidant alpha-tocopherol were used for inhibition of wear particles-initiated free-radical reactions. Introduction of the antioxidants inhibited cumene oxidation with an antioxidant dose-dependent duration of this effect. In a mixture of alloy and orthopedic polyethylene particles, alpha-tocopherol completely inhibited the radical-generating activity of alloy particles thus preventing the polymer's oxidative destruction. Conclusion. The use of commercially available particles of orthopedic alloys with an uncontrolled duration storage in experiments considerably reduce or do not reveal the negative effects conditioned by their radical-generating ability. A proper study of the effect of the radical- generating ability of wear particles on the properties of implant components and surrounding tissues is possible only with the use of fresh particles. Permanent generation of free radicals in the process of wear of joint prosthesis metal components creates conditions for self-potentiation of negative free radical reactions during joint replacement. This requires the necessity of a preclinical estimation of the radical-generating ability of orthopedic materials and application of efficient antioxidants during the post-implantation period

Hip simulators have been used for ten years to determine the tribological performance of large-head metal-on-metal devices using traditional test conditions. However, the hip simulator protocols were originally developed to test metal-on-polyethylene devices. We have used patient activity data to develop a more physiologically relevant test protocol for metal-on-metal devices. This includes stop/start motion, a more appropriate walking frequency, and alternating kinetic and kinematic profiles.

There has been considerable discussion about the effect of heat treatments on the wear of metal-on-metal cobalt chromium molybdenum (CoCrMo) devices. Clinical studies have shown a higher rate of wear, levels of metal ions and rates of failure for the heat-treated metal compared to the as-cast metal CoCrMo devices. However, hip simulator studies in vitro under traditional testing conditions have thus far not been able to demonstrate a difference between the wear performance of these implants.

Using a physiologically relevant test protocol, we have shown that heat treatment of metal-on-metal CoCrMo devices adversely affects their wear performance and generates significantly higher wear rates and levels of metal ions than in as-cast metal implants.