Polyethylene wear-debris induced inflammatory osteolysis is known as the main cause of aseptic loosening and long term revision total hip arthroplasty. Although recent reports suggest that antioxidant impregnated ultra-high molecular weight polyethylene (UHMWPE) wear-debris have reduce the osteolytic potential in vivo when compared to virgin UHMWPE, little is known about if and/or how PE rate of oxidation affects osteolysis in vivo. We hypothesized that oxidized UHMWPE particles would cause more inflammatory osteolysis in a murine calvarial bone model when compared to virgin UHMWPE. Male C57BL/6 eight weeks old received equal amount of particulate debris overlaying the calvarium of (n=12/group): sham treatment (no particles), 2mg (6,75×107 particles/mg) of endotoxin-free UHMWPE particles (PE) or of endotoxin-free highly oxidized-UHMWPE (OX) particles. In vivo osteolysis was assessed using high resolution micro-CT and inflammation with L-012 probe dependent luminescence. At day 10, calvarial bone was examined using high resolution micro-CT, histomorphometric, immunohistochemistry analyses and qRT-PCR to assess OPG, RANK, RANK-L, IL-10, IL-4, IL-1b and TRAP genes expression using the protocol defined by individual TaqManTM Gene Expression Assays Protocol (Applied Biosystems). In vivo inflammation was significantly higher in the OX (1.60E+06 ± 8.28E+05 photons/s/cm2) versus PE (8.48E+05 ± 3.67E+05) group (p=0.01). Although there was a statistically significant difference between sham (−0.27% ± 2.55%) and implanted (PE: −9.7% ± 1.97%, and OX: − 8.38% ± 1.98%) groups with regards to bone resorption (p=0.02), this difference was not significant between OX and PE (p = 0.14). There was no significant difference between groups regarding PCR analyses for OPG, RANK, RANK-L, IL-10, IL-4, IL-1b and TRAP (p = 0.6, 0.7, 0.1, 0.6, 0.3, 0.4, 0.7 respectively). Bone volume density was significantly decreased in PE (13.3%±1.2%) and OX (12.2%±1.2%) groups when compared to sham (15%±0.9%) (p < 0 .05). Histomorphometric analyses showed a significantly decreased Bone Thickness/Tissue Thickness ratio in the implanted group (0.41±0.01 mm and 0.43±0.01 mm) compared to sham group (0.69± 0.01) (p < 0 .001). However, there were no significant difference between OX and PE (p = 0.2). Our findings suggest that oxidized UHMWPE particles display increased inflammatory potential. Results were not significant regarding in vivo or ex vivo osteolysis. As antioxidant-diffused UHMWPE induce less inflammation activity in vivo, the mechanism by which they cause reduced osteolysis requires further investigation

Introduction. Ultra high molecular weight polyethylene (UHMWPE) has been used successfully as a bearing material in hip, knee, and shoulder joint replacements. However, there are problems to cause a failure in UHMWPE component, which are wear behavior and creep deformation. Continuous bearing motion and dynamic load have occurred to UHMWPE wear debris caused osteolysis in periprosthetic tissue and to plastic deformation of joint component, and subsequent aseptic loosening of components. Therefore, many studies have being carried out in order to reduce wear debris and to improve mechanical strength from UHMWPE, and there is tremendous improvement of mechanical property in UHMWPE from gamma irradiated conventional UHMWPE (GIPE), highly crosslinked PE (XLPE), and XLPE with vitamin E1, 2. Friction has a significant one of the factors effect on the wear and creep deformation. In this study, the short-term frictional behaviors of three typical types of GIPE, remelted XLPE (R-XLPE), and s annealed XLPE (A-XLPE), and XLPE with Vitamin E against Co-Cr alloy were compared under three levels of contact pressures which occured in hip, knee, and shoulder joints. Methods. Friction tests were conducted with UHMWPE against Co-Cr alloy by using pin-on-disk type triboteter. For test, tribotester performed in a repeat pass rotational slidintg motion with a velocity of 60rpm. Applied contact pressure selected three kinds of levels, 5, 10, and 20MPa which were within the range of maximum contact pressures for total hip, knee, and shoulder joint replacements. To analyze the frictional effect of UHMWPE type, it conducted t-test and p-values less than 0.05 were used to determine the statistically significant difference. Results. In this study, it was observed that coefficients of friction (COF) were affected by various conditions, kinds of materials and applied load. We can reveal the frictional behavior of UHMWPE in various contact pressures. The average of the COF measured that GIPE was 0.029∼0.0423, R-XLPE was 0.018∼0.031, A-XLPE was 0.023∼0.038, and XLPE with Vitamin E was 0.013∼0.027 under 5, 10, and 20MPa. Discussion. COF of R-XLPE, A-XLPE, and XPLE with Vitamin E were lower than GIPE for all levels of contact pressures. This study showed the trend that COF decreased as contact pressure increased. Also, XPLE with Vitamin E has lowest frictional values among UHMWPEs. In the viewpoint of applied load, it was decreased as a contact pressure increased for COF of GIPE, RXLPE, and AXLPE against Co-Cr alloy. COF of GIPE, XLPEs, and XLPE with Vitamin E against Co-Cr alloy were as low as using bio materials compared with the COF of cartilage to cartilage, which was about 0.024. Conclusions. In conclusion, average COF of XLPE with Vitamin E was significantly lower than those of R-XLPE and A-XLPE. XLPEs showed much lower COF than GIPE

Introduction. UHMWPE particle-induced osteolysis is one of the major causes of arthroplasty revisions. Recent in vitro findings have suggested that UHMWPE wear particles containing vitamin-E (VE) may have reduced functional biologic activity and decreased potential to cause osteolysis (Bladed C. L. et al, JBMR B 2012 and 2013). This is of significant importance since VE-stabilized cross-linked UHMWPEs were recently introduced for clinical use, and there is no in vivo data determining the effects of wear debris. In this study we hypothesized that particles from VE-stabilized, radiation cross-linked UHMWPE (VE-UHMWPE) would cause reduced levels of osteolysis in a murine calvarial bone model when compared to virgin gamma irradiated cross-linked UHMWPE. Methodology. Study groups were the following: 1). Radiation cross-linked VE-UHMWPE (0.8% by weight) diffused after 100 kGy; 2). Radiation cross-linked virgin UHMWPE (virgin UHMWPE); 3). Sham controls. Particle generation and implantation: UHMWPE was sent to Bioengineering Solutions (Oak Park, IL) for particle generation. After IACUC approval, C57BL/6 mice (n=12 for each group) received equal amount of particulate debris (3mg) overlying the calvarium and were euthanized after 10 days. Micro-CT scans: High resolution micro-CT scans were performed using a set voltage of 70 kV and current of 70 µA. Topographical Grading Scale: Each calvarial bone was blindly scored using the following scale: 0=No osteolysis, defined as intact bone; 1=Minimal osteolysis, affecting 1/3 or less of the bone area; 2=Moderate osteolysis, affecting at least 2/3 of the bone area; 3=Severe osteolysis, defined as completely osteolytic bone. Histology: H&E and TRAP staining was done on tissue to confirm micro-CT findings and quantify osteoclasts. Statistical Analysis: Inter-rater analysis was done using Cohen's kappa analysis. An inter-rater coefficient >0.65 was considered as high inter-rater agreement. Comparison between groups was made using one-way ANOVA with post hoc Bonferroni correction for multiple comparisons. Correlations are reported as Spearman's rho. P-value<0.05 was considered statistically significant. Results. More than 83% of the VE-UHMWPE and more than 85% of the virgin UHMWPE particles measured less than 1 µm in mean particle size. There was a statistically significant greater level of osteolysis visualized on the topographical grading scale in calvaria implanted with virgin UHMWPE wear particles. Micro-CT findings were confirmed histologically (Fig. 1). A greater amount of inflammatory tissue overlaying the calvaria was observed in the virgin UHMWPE group when compared to both shams and VE-UHMWPE groups. Post hoc analysis revealed significant difference between VE-UHMWPE and virgin UHMWPE for the topographical osteolysis grading score (p=0.002) but no difference in osteoclast counts (p=0.293). Discussion and Conclusion. This is the first in vivo study reporting the effects of clinically-relevant UHMWPE particles generated from a VE-UHMWPE implant that is in current clinical use. These results suggest that VE-UHMWPE particles have reduced osteolysis potential in vivo when compared to virgin, highly cross-linked UHMWPE in a murine calvarial bone model. Arthroplasty procedures using VE-UHMWPE might be less susceptible to peri-prosthetic loosening caused by wear debris

Introduction. In vitro findings (Bladed CL et al. ORS 2011 and J Biomed Mater Res B Appl Biomater, 2012) have suggested that UHMWPE wear particles containing vitamin-E (VE) may have reduced functional biologic activity and decreased osteolytic potential. Currently, there is no in vivo data determining the effects of wear debris from this new generation of implants. In this study we hypothesized that particles from VE-stabilized, radiation cross-linked UHMWPE (VE-UHMWPE) would cause reduced levels of osteolysis in a murine calvarial bone model when compared to virgin gamma irradiated cross-linked UHMWPE. Methods. Study groups: 1). Radiation cross-linked VE-UHMWPE, 0.8% by weight, diffused after 100 kGy; 2). Radiation cross-linked virgin UHMWPE (virgin UHMWPE); 3). Shams. Particle generation and implantation: UHMWPE was sent to Bioengineering Solutions for particle generation. After IACUC approval, C57BL/6 mice (n = 12 for each group) received 3 mg of particulate debris overlying the calvarium and euthanized after 10 days. Micro-CT scans: Performed using an X-Tek-HMX-ST-225 with 70 kV voltage and 70 μA current. Topographical Grading Scale: Each calvarial bone was blindly scored with the following scale: 0 = No osteolysis, defined as intact bone; 1 = Minimal osteolysis, affecting 1/3 or less of the bone area; 2 = Moderate osteolysis, affecting at least 2/3 of the bone area; 3 = Severe osteolysis, defined as completely osteolytic bone. Histology H&E and TRAP staining was performed. Statistical Analysis: Inter-rater analysis was performed using Cohen's kappa analysis. Inter-rater coefficient >0.65 was considered as high inter-rater agreement. Comparison between groups was made using one-way ANOVA with post hoc Bonferroni correction for multiple comparisons. Correlations are reported as Spearman's rho. A p-value<0.05 was considered statistically significant. Results. More than 83% of the VE-UHMWPE and more than 85% of the virgin UHMWPE particles measured less than 1 μm in mean particle size. There was a statistically significant greater level of osteolysis visualized on the topographical grading scale in calvaria implanted with virgin UHMWPE wear particles. The micro-CT findings were confirmed histologically (Fig. 1). A greater amount of inflammatory tissue overlaying the calvaria was observed in the virgin UHMWPE group when compared to both shams and VE-UHMWPE groups. Post hoc analysis revealed significant difference between VE-UHMWPE and virgin UHMWPE for the topographical osteolysis grading score (p = 0.002) but no difference in osteoclast count (p = 0.293). Discussion/Conclusion. This is the first in vivo study reporting the effects of clinically-relevant UHMWPE particles generated from a VE-UHMWPE implant that is in current clinical use. These results suggest that VE-UHMWPE particles have reduced osteolysis potential in vivo when compared to virgin, highly cross-linked UHMWPE in a murine calvarial bone model

Introduction. Periprosthetic joint infection (PJI) and particle-induced osteolysis are closely related to peri-implant local immunity and macrophage function. We previously demonstrated that titanium particles attenuate the immune response of macrophages caused by chronic inflammation [1]. In a separate study, we have determined that UHMWPE wear particles containing vitamin E (VE) induce less osteolysis compared to HXL UHMWPE wear particles in a murine calvarium model [2]. For this study we hypothesized that macrophages exposed to HXL UHMWPE particles containing VE would better maintain their ability to respond to S. aureus compared to HXL UHMWPE without VE. Methods. A gamma-sterilized, HXL UHMWPE tibial bearing containing VE (E1, Biomet, “VE-PE”) and 100kGy irradiated and melted UHMWPE (“CISM 100”) were cryomilled to particles by Bioengineering Solutions (Oak Park, IL). In the first in vitro study, RAW 264.7 mouse macrophages were exposed (inverted co-culture) to either VE-PE particles or CISM100 particles and lipopolysaccharide (LPS) for 1–7 days. Macrophage viability was measured using a cell counting kit (CCK-8). Control group with no particles and a LPS group were also included. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed to determine macrophage apoptosis rate in response to particle exposure over time. In the second study, macrophages were exposed to VE-PE or CISM100 particles for 48h, then exposed to LPS for 30 min. Subsequently, reactive oxygen species (ROS) generation and extracellular regulated protein kinase (ERK) phosphorylation were measured. In a third study, after exposure to particles for 48h, fatigued macrophages were co-cultured with bioluminescent S. aureus strain Xen29 for 3h and 6h. Bioluminescence signal was determined to measure the total amount of bacteria. Bacterial live/dead staining and optical density at 600 nm (OD 600) were also performed to determine S. aureus viability. Statistical analysis was performed using one-way or two-way ANOVA with a post hoc examination. *indicates p<0.05. Results. CISM100 particles significantly decreased macrophage viability at day 5 and day 7 (p<0.05, Fig. 1A), while the viability of macrophages exposed to VE-PE particles was similar to controls (macrophages not exposed to particles). After 48h, macrophages exposed to VE-PE particles showed a lower TUNEL-positive rate (less apoptosis) compared to CISM100 particles (Fig. 1B, C). 48h-exposure to VE-PE particles increased ROS generation and ERK phosphorylation in 30 min-LPS-activated macrophages when compared to CISM100 particles (Fig. 2). This immune response caused by VE-PE particles resembles that of macrophages without particles. Furthermore, 48h exposure to E1 particles showed less S. aureus at 6h (Fig. 3). Conclusions. These results suggest that VE-PE particles cause reduced macrophage apoptosis and protect the macrophages' immune response. VE-PE particles also preserved the innate immunity of macrophages, unlike CISM100, as evidenced by the S. aureus co-culture study. Thus, patients with vitamin-E containing implants may be less likely to develop PJI

Introduction. According to American Joint Replacement Registry, particle mediated osteolysis represents 13 % of the knee revision surgeries performed in the United States. The comprehension of mechanical and wear properties of materials envisioned for TJR is a key step in product development. Furthermore, the maintenance of UHMWPE mechanical properties after material modification is an important aspect of material success. Initial studies conducted by our research group demonstrated that the incorporation of ibuprofen in UHMWPE had a minor impact on UHMWPE physicochemical and mechanical properties. Drug release was also evaluated and resulted in an interesting profile as a material to be used as an anti-inflammatory system. Therefore, the present study investigated the effect of drug release on the mechanical and biological properties of ibuprofen-loaded UHMWPE. Experimental. UHMWPE resin GUR 1020 from Ticona was for sample preparation. Samples with drug concentrations of 3% and 5% wt were consolidated as well as samples without anti-inflammatory addition through compression molding at 150 °C and 5 MPa for 15 minutes. Mechanical properties were evaluated via the tensile strength experiment (ASTM D638) and dynamic mechanic tests. Wear resistance was measured using the pin on disc (POD) apparatus. Finally, cytotoxicity analysis was conducted based on ISO 10993–5. Results. Dynamic-mechanic analysis demonstrated no difference in flexion modulus and stress for all materials (Table 1). No difference was also verified during cyclical loading experiments (Table 1), which indicates that the drug concentration added to material composition did not affect these properties. POD experiments were proposed to evaluate wear resistance of ibuprofen-loaded UHMWPE samples considering the combination of materials similar to those employed in TJR. Results from POD tests are presented in Table 1. Volumetric wear was close to zero for all samples after 200 thousand cycles. Comprehension of the effect of drug release on mechanical properties is essential to estimate how the material will behave after implantation. Therefore, mechanical properties were assessed after 30 days of ibuprofen release and the results were compared with those obtained in samples as prepared (Table 2). Initial results demonstrated a decrease in elastic modulus in samples prepared with ibuprofen. However, no difference was verified between UHMWPE, UHMWPE 3% IBU and UHMWPE 5% IBU after ibuprofen release. Finally, cell viability of UHMWPE 3% IBU and UHMWPE 5% was found to be superior to 100% (Figure 1). Therefore, both materials can be considered nontoxic. Conclusions. Ibuprofen-loaded UHMWPE did not demonstrate a significant influence on the mechanical and biological behavior of UHMWPE. Dynamic-mechanical tests demonstrated constancy for all samples under analysis. Wear testing resulted in gravimetric wear close to zero, for all tested materials. Mechanical properties conducted after 30 days of ibuprofen release also had a positive outcome. Although presenting a difference in modulus prior and after release tests, modulus and tensile yield stress remained inside acceptable range indicated to UHMWPE used in orthopedic implants. Furthermore, after drug elution UHMWPE 3% IBU and UHMWPE 5% IBU recovered original UHMWPE properties. Cytotoxicity assessment was performed and both ibuprofen-based formulations were considered nontoxic according to ISO 10993–5. For any figures or tables, please contact the authors directly

Introduction. Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is the most common bearing surface used in total joint arthroplasty due to its excellent wear resistance. While radiation cross-linking is currently used, cross-linking using a cross-linking agent such as a peroxide can also be effective with improved oxidative stability, which can be achived by an antioxidant such as vitamin E. The peroxide cross-linking behavior of UHMWPE in the presence of vitamin E was unknown. We investigated the cross-linking behavior and the clinically relevant mechanical and wear properties of peroxide cross-linked, vitamin E-blended UHMWPE. Materials and Methods. Medical grade UHMWPE (GUR1050) was blended with vitamin E and the peroxide (2,5-Dimethyl-2,5-di(t-butylperoxy)hexyne-3 or P130) before compression molding. Various vitamin E (0.1, 0.2, 0.3, 0.5, 0.6, 0.8 and 1.0 wt%) and peroxide concentrations (0.5, 1 and 1.5 wt%) were studied. The cross-link density was calculated as previously described (Oral 2010). The wear rate was determined using a custom-designed pin-on-disc wear tester against CoCr polished discs at 2 Hz and a rectangular path of 5 × 10 mm in undiluted bovine serum (Bragdon 2001). Tensile mechanical properties were determined using Type V dogbones according to ASTM D638. Oxidative stability was determined using oxidation induction testing (Braithwaite 2010). Double-notching and IZOD impact testing was performed according to ASTM D256. Samples prepared with vitamin E concentrations of 0.3 wt% and above and P130 concentrations of 0.5 and 1 wt% were also terminally gamma sterilized. Controls were 150-kGy irradiated vitamin E blends of UHMWPE. Results and Discussion. The cross-link density of peroxide cross-linked UHMWPEs were higher than the irradiated controls at a given vitamin E concentration (For example 250, 301 and 355 mol/dm3 for 0.5, 1 and 1.5 wt% peroxide cross-linked UHMWPE compared to 217 mol/dm3 for 150 kGy irradiated UHMWPE; Figure 1). The cross-link density dependence of wear was similar to radiation cross-linked UHMWPE, resulting in clinically relevant wear rates of 0.5 to 1.5 mg/MC. While the cross-link density of radiation cross-linked UHMWPE became saturated at vitamin E concentrations above 0.3 wt% (Oral 2008), this was not observed in peroxide cross-linked UHMWPE (Figure 2), suggesting more efficient cross-linking in the presence of the antioxidant. The impact strength was 30% higher for the peroxide cross-linked UHMWPEs at the comparable wear rate compared to irradiated controls (72 vs. 56 kJ/m2). The oxidation induction time of all peroxide cross-linked UHMWPEs (up to 57 min) was higher than that of the 0.1 wt% vitamin E-blended, 150-kGy irradiated UHMWPE (6 min). Gamma sterilization of peroxide cross-linked vitamin E blends decreased wear (0.5 wt% peroxide in Figure 3). Thus, peroxide concentration for cross-linking can be reduced if terminal sterilization is used. The mechanical properties and the oxidative stability of the material were not significantly affected by gamma sterilization. Significance. Peroxide cross-linking enabled good wear resistance for high vitamin E concentration blends of UHMWPE (>0.3 wt%), previously not possible by irradiation. Peroxide cross-linking of vitamin E-blended UHMWPE can provide a one-step, cost-effective method to manufacture wear resistant total joint implants with improved oxidative stability

Introduction. Orthopedic implants are subject to wear and release ultra-high molecular weight polyethylene (UHMWPE) debris. Analysis of UHMWPE wear particles is critical in determining the safety and effectiveness of novel orthopedic implants. Complete digestion of periprosthetic tissue and wear fluid is necessary to ensure accurate morphological and quantitative particle analysis. Acid digestion methods are more effective than enzymatic and base digestion approaches [Baxter+ 2009]. However, optimal digestion times, quantity, and type of acid are unclear for particle isolation. In addition, imaging and analysis techniques are critical to ensure accurate reporting of particle characteristics. Here, we 1) compared the efficacy of three acid-based digestion methods in isolating particles from a) bovine serum and b) animal/human tissue, and 2) analyzed the effects of imaging location on particle quantity/morphology results. Methods. 1a) UHMWPE (GUR 150) particles were generated by Mode I knee wear testing for 1 million cycles in bovine serum. Serum was digested in one of four solutions: 12.2M HCl, 15.8M HNO. 3. , a 1:1 volume ratio of HNO. 3. :HCl (aqua regia), or filtered H. 2. O (control). The serum:solution volume ratio was 1:5 [Niedzwiecki+ 2001, ISO 17853:2011]. Digestion occurred for 60min on a stir plate at 60°C. Each digest was combined with MeOH at a 1:5 digest:MeOH volume ratio and filtered using a 100 nm polycarbonate membrane. The particle-containing membranes were imaged (12 images/membrane) using scanning electron microscopy (SEM) to determine particle characteristics, including quantity, equivalent circular diameter (ECD) and aspect ratio (AR). 1b) Based on 1a, HNO. 3. was used to digest porcine and human tissue at concentrations of 1:40, 1:60, or 1:80 tissue:HNO. 3. volume ratios for either 1, 12, or 24 hours, followed by SEM analysis. 2) Particle characteristics were compared at nine locations (20 images/location) across a particle-containing membrane to determine the effects of imaging location. Results. 1a) HNO. 3. and aqua regia methods successfully digested the bovine serum, whereas the HCl and H. 2. O methods were unsuccessful (Fig.1A). Comparing HNO. 3. and aqua regia groups, particle characteristics and ECD frequency distribution were nearly identical (Fig.1B). 1b) Nitric acid did not fully digest porcine or human tissues. 2) Similar particle characteristics were observed in all nine locations analyzed across the polycarbonate membrane. The particle quantity, ECD, and AR for a representative center vs. intermediate location were 808 vs. 780 particles, 0.33±0.28 vs. 0.35±0.29 µm, and 1.57±0.56 vs. 1.51±0.4, respectively (Fig.2). Conclusions. Nitric acid and aqua regia are capable of digesting bovine serum using low quantities of acid for short duration, allowing precise analysis of UHMWPE particle debris from orthopedic implants. However, further optimization of digestion techniques for animal/human tissue is warranted. In addition, an accurate representation of particle distribution can be achieved without analyzing hundreds of images, because membrane location does not strongly influence particle results. Finally, ASTM F1877-16 – Standard Practice for Characterization of Particles – could benefit from adding software-based automated particle characterization as an optional method. An automated approach that uses k-means clustering image segmentation to identify particles and computer vision tools to extract relevant morphological features is under development and validation

Introduction. Radiation cross-linking of ultrahigh molecular weight polyethylene (UHMWPE) has reduced the in vivo wear and osteolysis associated with bearing surface wear (1), significantly reducing revisions associated with this complication (2). Currently, one of the major and most morbid complications of joint arthroplasty is peri-prosthetic infection (3). In this presentation, we will present the guiding principles in using the UHMWPE bearing surface as a delivery device for therapeutic agents and specifically antibiotics. We will also demonstrate efficacy in a clinically relevant intra-articular model. Materials and Methods. Medical grade UHMWPE was molded together with vancomycin at 2, 4, 6, 8, 10 and 14 wt%. Tensile mechanical testing and impact testing were performed to determine the effect of drug content on mechanical properties. Elution of the drug was performed in phosphate buffered saline (PBS) for up to 8 weeks and the detection of the drug in PBS was done by UV-Vis spectroscopy. A combination of vancomycin and rifampin in UHMWPE was developed to address chronic infection and layered construct containing 1 mm-thick drug-containing UHMWPE in the non-load bearing regions was developed for delivery. In a lapine (rabbit) intra-articular model (n=6 each), two plug of the layered UHMWPE construct were placed in the trochlear grove of the rabbit femoral surface and a porous titanium rod with a pre-grown biofilm of bioluminescent S. Aureus was implanted in the tibia. Bioluminescent imaging was employed to visualize and quantify the presence of the bacteria up to 3 weeks. Results and Discussion. Increasing drug content decreased both the ultimate tensile strength (UTS) and the impact toughness of vancomycin-containing UHMWPE (Figure 1). Elution data and structural analysis suggested that a percolation threshold was reached at above 6 wt% drug in UHMWPE, which resulted in sustained drug delivery above the minimum inhibitory concentration (MIC; 1 mg/ml) for up to 8 weeks (Figure 2). The layered constructs implanted in rabbits were able to eradicate all detectable bacteria from the biofilm on the titanium surfaces implanted on the counterface (Figure 3), suggesting clinically relevant efficacy. Significance. To our knowledge, this is the first study showing the design and efficacy of an antibiotic-eluting UHMWPE bearing surface. Such a device has the potential of reducing all two-stage revisions to single-stage treatment with load-bearing components, enhancing the mobility and quality of life for the patients and reducing the cost of infection treatment in arthroplasty. For figures/tables, please contact authors directly.

Introduction. Radiation cross-linked UHMWPE is preferred in total hip replacements due to its wear resistance [1]. In total knees, where stresses are higher, there is concern of fatigue damage [2]. Antioxidant stabilization of radiation cross-linked UHMWPE by blending vitamin E into the polymer powder was recently introduced [3]. Vitamin E greatly hinders radiation cross-linking in UHMWPE [4]. In contrast peroxide cross-linking of UHMWPE is less sensitive to vitamin E concentration [5]. In addition, exposing UHMWPE to around 300°C, increases its toughness by inducing controlled chain scission and enhanced intergranular diffusion of chains, simultaneously [6]. We present a chemically cross-linked UHMWPE with high vitamin E content and improved toughness by high temperature melting. Methods and Materials. Medical grade GUR1050 UHMWPE was blended with vitamin E and with 2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne or P130 (0.5% Vitamin-E and 0.9% P130). The mixed powder was consolidated into pucks. The pucks were melted for 5 hours in nitrogen at 300, 310 and 320°C. One set of pucks melted at 310°C was accelerated aged at 70°C at 5 atm. oxygen for 2 weeks. Tensile mechanical properties were determined using ASTM D638. Izod impact toughness was determined using ASTM D256 and F648. Wear rate was determined using a bidirectional pin-on-disc (POD) tester with cylindrical pins of UHMWPE against polished CoCr discs in undiluted, preserved bovine serum. Results. The vinyl index increased as a function of temperature (Fig 1a). Cross-link density steadily decreased and impact strength increased with increasing vinyl index (Fig 1b). The ultimate tensile strength (UTS) was not affected by HTM (Table 2). Impact strength was significantly improved for all treatment temperatures (P<0.05) and wear was significantly increased only for the sample melted at 320°C (Table 2). Discussion. High temperature melting (HTM) was shown to increase toughness of UHMWPEs presumably due to controlled chain scissioning and increased intergranular diffusion of chains [6]. For radiation cross-linked UHMWPE, it was shown that an increase in elongation-at-break and impact strength could be obtained without sacrificing wear resistance up to an elongation of about 500% [7]. This vitamin E-blended, peroxide cross-linked, high temperature melted UHMWPE has very high oxidation resistance due to its high antioxidant content, high wear resistance due to cross-linking and much improved toughness, representing an optimum joint replacement surface. For figures/tables, please contact authors directly.

Introduction. Dl-α-Tocopherol (VE)-blended non-crosslinked UHMWPE has been developed as a bearing surface material for knee prostheses due to the radical scavenging capabilities of vitamin E and has demonstrated a low wear rate in knee simulator testing [1,2]. In previous our study, VE-blended, crosslinked UHMWPE has demonstrated a low wear rate in hip simulator testing [3, 4]. As the radical scavenging capabilities also reduce the crosslinking degree of the material, multiple dose crosslinking has been investigated. However, these crosslinked UHMWPE materials may have different mechanical properties, as each crosslinking process, especially the annealing condition, is different. Additionally, there is little information about VE-blended, crosslinked UHMWPE with different annealing conditions. In this study, the effect of annealing temperature was investigated with regard to tensile strength, crosslink density, and crystallinity of VE blended, crosslinked UHMWPE. Method. VE blended samples were manufactured via direct compression molding following the blending of UHMWPE resin powder (GUR1050, Ticona Inc.) with VE (dl-α-tocopherol, Eisai Co. Ltd.) at 0.3wt%. The virgin samples were derived similarly, but without the addition of VE. Both materials underwent crosslinking by irradiation via a 10MeV electron beam at 300kGy and were then heat treated at several temperatures (25, 80, 110, 130 and 150 °C) for 24 hours. Gel content, which can be interpreted as cross-link density, was determined by measuring the weight of the samples before and after soaking in decahydronaphthalene at 150 °C for twelve days. Tensile tests were carried out following JIS K 7113, with the cross head speed set at 50 mm/min. Crystallinity was determined by using DSC and integrating over the enthalpy curve from 80 to 150 °C and normalizing with the enthalpy of melting for 100% crystalline polyethylene. Result. Fig. 1 shows the gel content of UHMWPE samples after crosslinking. Raising the annealing temperature caused an increase in the gel content regardless the VE content. Additionally, among samples with the same annealing temperature, VE samples had the lower gel content. Fig. 2 shows the yield strength of UHMWPE samples. Higher annealing temperature decreased the yield strength, and increased elongation. Fig. 3 shows the crystallinity of each UHMWPE sample. Higher annealing temperature decreased the crystallinity of UHMWPE. Discussion. In this study, the effect of annealing temperature on the mechanical properties of crosslinked UHMWPE was investigated. The results indicated that a greater volume of crystalline UHMWPE melted and reformed at the higher annealing temperatures. This was thought to occur due to the fact that UHMWPE consists of a range of different molecular weight chains, allowing for melting below 135°C. Therefore, the crystallinity and crosslink density changed for each annealing temperature. The annealing is a simple but effective method for designing the crystallinity and crosslinking of UHMWPE

Introduction. UHMWPE articulating against PEEK-OPTIMA® has the potential for use as a novel bearing couple in joint arthroplasty due to its potentially low wear rates and the bioinertness of its wear debris. The aim of this study was to investigate the role of protein in the lubricant on the wear of UHMWPE articulating against PEEK at both room and physiological temperature. Methods. The wear of GUR1020 UHMWPE pins articulating against PEEK plates (R. a. ∼0.06µm) was compared to highly polished cobalt chrome plates (R. a. <0.01µm) in a 6-station multi-axial pin-on-plate rig using kinematics to replicate those in total knee arthroplasty. Tests were carried out at either ∼20°C or ∼36°C and wear was investigated under varying concentrations of bovine serum (0, 25 or 90%). Studies were carried out for 1 Million cycles with wear of the UHMWPE pins assessed gravimetrically using unloaded soak controls to compensate for moisture uptake. Statistical analysis was carried out using ANOVA with significance taken at p<0.05. Results. Figure 1 shows wear factors for the UHMWPE pins. In 0% serum, the wear of UHMWPE against both PEEK and cobalt chrome tested at room and physiological temperatures was very low. When lubricated with 25% serum and tested at room temperature as per standard practice at Leeds, the wear of UHMWPE against cobalt chrome was comparable to previously published data (2.13×10. −7. mm. 3. /Nm) and the wear of UHMWPE articulating against PEEK was 3.53×10. −7. mm. 3. /Nm. At physiological temperatures, the wear of UHMWPE against cobalt chrome was similar to tests at room temperature but against PEEK, there was a significant (p=0.017) decrease in wear factor [1]. The wear of UHMWPE against cobalt chrome was significantly (p=0.003) higher when tested in 90% serum compared to 25% serum at room temperature but this effect was not seen in UHMWPE articulating against PEEK (p=0.38). Testing at elevated temperature in 90% serum significantly (p=0.007) decreased the wear of UHMWPE against cobalt chrome and a deposition, likely to be protein, was evident on the surface of the plates. However, against PEEK, there was no significant difference in wear under the different temperature conditions. Discussion. In pin-on-plate tests of UHMWPE against smooth metal counterfaces, the low wear rate and polymer deposition in tests lubricated with water has previously been observed. A similarly low wear rate has now been observed for UHMWPE against PEEK. Water does not produce adequate boundary lubrication. At 25% and 90% serum and varying temperatures the wear behaviour of UHMWPE against PEEK is not the same as UHMWPE against cobalt chrome. There may be a number of factors contributing to these differences, including surface topography, protein precipitation, protein deposition, differing wear mechanisms and lubrication regimes. For example, UHMWPE-PEEK is a higher friction bearing couple than UHMWPE-CoCr and when tested at elevated temperatures, frictional heating at the bearing surfaces may accelerate protein precipitation and adsorption of protein onto the articulating surfaces which may affect wear. This study shows that testing under different lubricant and environmental conditions can have a significant effect on wear

Introduction. Increased oxidative stability of orthopedic implants can be achieved by adding an antioxidant, such as Vitamin E (VE) to UHMWPE[1]. The effect of shelf live and accelaterated aging in combination with shelf live on antioxidative effectiveness of VE needs to be investigated to better understand the long-time behavior of VE-blended UHMWPE in an oxidative environment. Currently, IR techniques provide detection limits as low as 0.05 %w/w[2], also it is known that thermo analytical techniques can push the limit of detection down to 10 ppm[3]. The goal of this study was to quantify VE in UHMWPE powder and compression molded UHMWPE with 11 different VE concentrations using FTIR and DSC techniques and to establish respective regression curves. Methods & Materials. GUR 1050 UHMWPE resin (Ticona, Germany) was blended with VE (DSM, Netherlands) to the following target concentrations (%w/w): 0.01, 0.02, 0.05, 0.1, 0.25, 0.35. Concentrations of 0.001, 0.002, 0.003, 0.004, 0.005 were obtained by mixing of the 0.1 powder with virgin GUR 1050 powder. VE-free GUR 1050 was used as reference. Samples of blended resin were compression molded in a low oxygen environment atmosphere at Zimmer Inc. (Warsaw, IN). Subsequently the blocks were microtomed, creating films with a thickness of 200µm for each concentration. The VE concentration was measured using infrared (IR) spectroscopy (BioRad FT6000). The ratios were calculated by normalizing the integrated ether C-O(R) signal (1232cm. −1. to 1275cm. −1. ) and the integrated hydroxyl C-O(H) signal (1190cm. −1. to 1228cm. −1. ) using the twisting CH bond (1980cm. ∗∗∗∗∗. to 2100cm. −1. ) as reference peak area. Oxidative induction time (OIT) at 200°C was measured according to ASTM D 3895–98 using blended and mixed powder samples. Results. Infrared spectroscopy. A strong positive linear correlation between the normalized peak areas and the effectively blended VE content was detected for both ether (Figure 1) and hydroxyl ratios. Figure 1: Normalized ether signal plotted over blended VE sample (928 IR spectra / 7 VE concentrations). Samples below 0.01 %w/w were not FTIR tested as they fell below the detection limits of 0.0074 and 0.0092 %w/w[4] based on ether and hydroxyl ratios. Oxidative-induction time. A logarithmic correlation between oxidation time and the effectively blended VE content was detected (Figure 2). Figure 2: OIT over effectively blended VE concentration (36 data points / 12 VE concentrations). Using OIT, VE concentrations down to 0.001 and 0.002 %w/w VE were quantified with D. absolute. of below 0.0002 %w/w and D. relative. of below 20% to the regression (Figure 3). Figure 3: Relative differences of quantification of VE over blended VE to regression via OIT and IR. Discussion. This study proves detectability of VE concentrations of 0.01 %w/w via calibrated IR absorbance and 0.001 %w/w using a calibrated OIT method at 200°C. Thus, mapping of VE chemical moities within UHMWPE samples below 0.05 %w/w VE by IR and detection of antioxidative stabilization in UHMWPE samples containing less than 0.002 %w/w VE can be achieved. Based on these findings, highly accurate VE measurements for aged, unaged, retrieved and differently processed materials shall be enabled

First, we need to define “contemporary UHMWPE”. Then we can discuss whether or not this is “the ultimate bearing partner”. The essential criterion for contemporary UHMWPE is intentional crosslinking. There are a number of such acetabular bearing products in the worldwide marketplace. They can differ in several ways including the base resin, the method of consolidation, the method of crosslinking, remelting v. annealing, the packaging and method of sterilisation, and the incorporation of any antioxidant. Thus “contemporary UHMWPE” is not one material, but a family of materials that may have some practical (clinical) differences. There is one essential similarity: substantially reduced wear and osteolysis compared to UHMWPE that is not intentionally crosslinked. In one literature review, Kurtz et al. reported a weighted-average femoral head penetration rate (wear) for crosslinked acetabular bearings of 0.042 mm/year based on 28 studies (n = 1,503 hips) and 0.137 mm/year for non-crosslinked bearing based on 18 studies (n = 695 hips). The pooled odds ratio for the risk of osteolysis in crosslinked versus conventional liners was 0.13 (95% CI, 0.06–0.27) among studies with minimum 5-year follow-up. Reduction in femoral head penetration or osteolysis risk was not established for large-diameter (>32 mm) femoral heads. In another minimum 5 year follow-up study, Lachiewicz et al. reported that there was no hip with pelvic or femoral osteolysis. They found no association between femoral head size and the linear wear rate, but observed an association between larger (36- and 40-mm) head size with higher volumetric wear rate and higher total volumetric wear. Leung et al. compared wear, osteolysis incidence, location, and volume on CT scans between 40 hips with non-crosslinked UHMWPE and 36 hips with crosslinked UHMWPE, at a minimum of 5 years. The incidence of osteolysis was statistically greater for patients with non-crosslinked UHMWPE (11/40, 28%) compared to patients with crosslinked UHMWPE (3/36, 8%; P = 0.04). The average lesion volume for hips with non-crosslinked liners (7.5 ± 6.7 cm. 3. ) was significantly greater than the average lesion volume for hips implanted with crosslinked liners (1.2 ± 0.1 cm. 3. , P = 0.01). Bragdon et al. combined a single-centre and two multicentre studies to include 768 primary patients (head size 26–36 mm) with a minimum of 7 years follow-up. Serial plain radiographs showed no osteolysis. The average femoral head penetration rates did not correlate with time in vivo for patients with standard femoral head sizes. There was an indication of higher wear in patients with 36-mm diameter bearings; it was below the threshold for producing osteolysis. Battenberg et al. quantified the activity of 14 healthy patients with a well-functioning THA at two time periods: early (within 3.5 years of implantation) and late (10–13 postoperative years). Wear was measured on serial radiographs using edge detection-based software. Mean activity decreased by 16% from the early to the late period. Mean gait speed decreased by 9%. Gait speed was 26% slower for patients ≥65 years than for patients <65 years. The mean linear penetration rate decreased by 42% from the first 5 years (early wear rate) to the next 8 years (late wear rate, 5–13 years): 0.043 mm/year to 0.025 mm/year. The greatest patient activity and wear occur during the first 5 years. Walking speed and gait cycles both decreased with aging, resulting in deceasing wear and risk of osteolysis over time. Crosslinked UHMWPE has consistently demonstrated decreased wear and osteolysis with up to 13 years follow-up. Volumetric wear is increased with larger diameter bearings but appears to be below the osteolysis threshold for most hips, especially considering that patient activity decreases with their aging

Introduction. The input mechanical properties of knee replacement bearing materials, such as elastic modulus and Poisson's ratio, significantly contribute to the accuracy of computational models. They should therefore be determined from independent experimental studies, under similar test conditions to the clinical and experimental conditions, to provide reliability to the models. In most cases, the reported values in the literature for the elastic modulus and Poisson's ratio of the bearing materials have been measured under tensile test conditions, in contrast to the compressive operating conditions of the total knee replacements (TKR). This study experimentally determined the elastic modulus and Poisson's ratio of conventional and moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE) under compressive test conditions. These material parameters will be inputs to future computational models of TKR. Materials/Methods. To determine the Poisson's ratio of the conventional and moderately cross-linked UHMWPE, contact areas of 12mm diameter cylindrical specimens of 10.2mm length were measured experimentally under a compressive displacement of 1mm, at a strain rate of 12mm/min that was held for 10minutes. A computational model was developed in Abaqus, 6.14–1, to simulate this experimental test assuming different values for the Poisson's ratio of the UHMWPE cylindrical specimens. The curve fitted relationship between the computationally predicted contact area and Poisson's ratio was used to calculate the Poisson's ratio of the UHMWPE specimens, using the experimentally measured contact areas. Using a similar approach, the equivalent elastic modulus of the UHMWPE was calculated using the computationally calculated curve fitted contact area-elastic modulus relationship, from the computational simulation of a ball-on-flat compression test, and the experimentally measured contact area from a ball-on-flat dynamic compression test. This experiment used 10mm thick UHMWPE flat specimens against a 63.5mm rigid ball, under a compressive dynamic sinusoidal loading of 250N average load, and 6000 cycles. The applied test conditions maintained the stress level within the reported range for the TKR. Results. The predicted maximum contact stress was 26 and 35 [MPa] for the conventional and moderately cross-linked UHMWPE respectively. The measured Poisson's ratio was 0.33±0.04 (mean ± 95% confidence interval (CI), n=5) and 0.32±0.08 (mean ± 95% CI, n=3) for conventional and moderately cross-linked UHMWPE respectively. The corresponding values for the equivalent elastic modulus were 365±31 and 553±51 [MPa] (mean ± 95% CI, n=3) respectively (Fig.1). Discussion. The Poisson's ratios and elastic moduli for the conventional and moderately cross-linked UHMWPE materials were more than 20% lower than values reported in literature that have been measured under tensile test conditions [1–3]. Computational wear models adopting mechanical properties of the bearing materials delivered under more realistic compressive loading conditions are more appropriate. Conclusion. The current study presented a reverse engineering approach to characterise the mechanical properties of conventional and moderately cross-linked UHMWPE for TKR bearing materials, under realistic compressive test conditions. The measured mechanical properties, were lower than that reported in literature under tensile loading conditions, and should be adopted in future computational models of TKR for a more realistic and robust virtual modelling platform

Introduction. Corrosion of the femoral head-trunnion junction in modular hip components has become a concern as the corrosion products may lead to adverse local tissue reactions. A simple way to avoid trunnion corrosion is to manufacture the femoral head with a non-metallic material, such as ceramics that are widely. An alternative solution may lie in advanced polymers like polyaryletherketones (PAEKs). These thermoplastics have high mechanical strength necessary for use as femoral heads in hip arthroplasty, but they must be tested to ensure that they do not adversely affect the wear of the ultrahigh molecular weight polyethylene (UHMWPE) liner counterface. Pin-on-disc (POD) wear testing has been extensively used to evaluate the wear properties of UHMWPE prior to more extensive and costly analysis with joint simulators. We hypothesized that the wear of crosslinked UHMWPE would not be adversely affected in POD tests when articulated against an advanced thermoplastic counterface. Methods. 0.1 wt.% VitE blended UHMWPE stock was e-beam irradiated to 100, 125, 140, 160, and 175 kGy and machined into cylindrical pins for testing. An additional group of 100 kGy e-beam irradiated and melted UHMWPE (with no vitamin E) was also machined and tested. Three different counterface materials were tested: (1) Cobalt-chrome (CoCr) with a surface roughness (R. a. ) of <0.5 μm, (2) Biolox™ ceramic (CeramTec), and (3) Polyetheretherketone (PEEK), a member of the PAEK family (Fig 1). A bidirectional POD wear tester [1] was used to measure the wear rate of UHMWPE specimens, where the specimens moved in a 10 mm × 5 mm rectangular pattern under a Paul-type load curve [2] synchronized with the motion. The peak load of the loading curve corresponded to a peak contact pressure of 5.1 MPa between each UHMWPE pin specimen and the counterface disc. Each test was conducted at 2 Hz in undiluted bovine serum stabilized with ethylenediamine tetraacetate (EDTA) and penicillin. The pins were cleaned and weighed daily, and a wear rate was calculated at the end of each test by linear regression. Results. As expected, higher radiation doses led to lower wear rates against all counterface materials (Fig 2). The PEEK discs produced the lowest UHMWPE wear in each group and the CoCr discs produced the highest UHMWPE wear; however, the two UHMWPE groups with the lowest wear rates showed no difference between the three counterface materials. Conclusions. Even though the PEEK discs had visible machining marks – that is they were not polished to an implant surface finish – they still yielded the lowest wear rates for UHMWPE articulating against them when compared to the highly polished and smooth CoCr and ceramic materials. Implementing further steps to better the surface roughness of the PEEK counterface may yield even better wear rates. Using PEEK in femoral heads may alleviate issues with trunnion corrosion without increasing the incidence of osteolysis or other wear related issues. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Vitamin-E (VE)-blended UHMWPE has been developed as a bearing-surface material due to the antioxidant ability of VE and has demonstrated a low wear rate in knee simulator [1]. Additionally, in vitro biological response testing has revealed that wear particles from VE blended UHMWPE induce the secretion of inflammatory cytokines at significantly lower levels compared to conventional UHMWPE [2]. However, as the joint kinematics are different between the knee and the hip, it is not guaranteed that these improvements will be repeated in the hip. In this study, the wear resistance of VE-blended UHMWPE was evaluated in knee and hip simulator tests and the effects of VE concentration and electron-beam irradiation were investigated. Materials and Methods. VE blended samples (GUR_VE xx%) were manufactured via direct compression molding following the blending of UHMWPE resin powder with VE at several concentrations (0, 0.1, 0.3, 1.0%). Cross-linking for the VE samples was achieved by 10 MeV electron beam at several irradiance doses (30, 90, 300 kGy) and annealed below the melting point of UHMWPE. Knee and hip simulator testing were carried out according to ISO 14243 and ISO 14242, respectively, and the volumetric wear was calculated. The gel fraction was determined by measuring the weight of the samples before and after soaking in decahydronaphthalene at 150°C. The oxidative resistance of the material was determined by measuring the Oxidation Index (OI) following ASTM F2102 before and after compulsory aging (ASTM2003). Radical measurements were made using high-sensitivity X-band ESR. Results & Discussion. In knee simulator testing, the volumetric wear for GUR_VE was lower than that for non-blended UHMWPE (GUR), with this difference amplified by aging. Conversely, in hip simulator testing, the wear rates were the same for the GUR and GUR_VE samples, while the GUR_XL samples showed almost no wear both before and after aging. Additionally, the wear for the non-XL samples (GUR and GUR_VE) actually decreased after aging. Treatment utilizing electron-beam irradiation and annealing below the melting point achieved a high degree of cross-linking in VE-blended UHMWPE, while also preserving the antioxidant ability of VE. These results suggest that electron-beam irradiated VE blended UHMWPE can be used as a bearing surface material for hip prostheses. However, the longevity of prosthesis is determined not only by its wear performance, but also by its biocompatibility. ESR measurements have revealed that VE radicals are formed during radiation crosslinking of VE blended UHMWPE, and it is thought that the VE radicals may reduce the anti-inflammatory effects of UHMWPE particles containing VE. We are now developing a multidirectional lift-off type aseptic wear simulation device and procedures to measure the biological response to wear particles produced therein [3]. Acknowledgement. A part of this study was supported by the “Super special consortia” for supporting the development of cutting edge medical care (Cabinet office, Government of Japan) and Innovation promotion program (NEDO)

Ultra-high molecular weight polyethylene (UHMWPE) has been the gold standard material of choice for the load-bearing articulating surface in knee joint prostheses. However, the application of joint replacements to younger (aged < 64 years) and more active people plus the general increase in life expectancy results in an urgent need for a longer lasting material with better in-use performance. There are three major material related causes that can lead to joint failure in UHMWPE knee joint replacements: free radical induced chemical degradation; mechanical degradation through wear and delamination; and UHMWPE micron and submicron wear debris induced osteolysis. As a potential solution to these problems, highly crosslinked UHMWPE stabilised with infused antioxidant vitamin E (α-Tocopherol), which is abbreviated as E-Poly, has been of great interest. In the current work, the wear performance and mechanical properties of Vanguard cruciate retaining (CR) E-Poly tibial inserts were assessed and compared with Vanguard CR Arcom tibial inserts. Also E-Poly plates were compared with direct compression moulded UHMWPE wear plates. Both a multi-directional pin-on-plate tester and a six-station Prosim (Manchester, UK) knee wear simulator were used to assess wear properties of E-Poly plates and E-Poly tibial inserts respectively. All E-Poly plates and tibial inserts were sterilised and vacuum packed in the same way as Vanguard implants before wear testing. The wear knee simulator test was conducted in accordance with ISO 14243-3:2004 with the exception that a more aggressive Tibial Rotation and Anterior/Posterior displacement profiles, based on the kinematics of the natural knee were incorporated. Under the same aggressive pre-clinical wear testing condition, compared with Vanguard Arcom CR tibial inserts, Vanguard E-Poly CR tibial inserts experienced an 85% reduction in the mean wear rate. The former had a mean wear rate of 6.51±1.75 mm. 3. per million cycles (MC) and the latter had a mean wear rate of 0.96±0.11 mm. 3. /MC over the 7 million cycle testing period. A similar reduction (80%±8.5) in the mean wear factor was also observed on E-Poly plates compared with a series of direct compression moulded GUR1050 UHMWPE plates processed under a range of manufacturing processing conditions. Wear testing was conducted with a configuration of flat-ended stainless steel indenters multi-directionally sliding against the UHMWPE plates. Mechanical properties on Vanguard Arcom UHMWPE and E-Polys were evaluated using the small punch test. All tests were carried out using an Instron 5565 Universal Testing System at a constant crosshead speed of 0.5mm/min. With regard to work-to-failure, no statistical difference was observed, with the former being 254.2±4.1 mJ and the latter 255.6±28.2 mJ. However, all E-Polys exhibited strain stiffening due to the stretch of crosslinks. This resulted in a ca 12% reduction in elongation to break observed for E-Polys compared with that of Arcom UHMWPE. The former had an elongation to break of 4.1±0.2 mm and the latter of 4.7±0.3 mm. In conclusion, we have found that Vitamin E Stabilised UHMWPE tibial inserts are promising for knee joint prostheses. However, further investigations are needed to address potential issues such as the particle size and size distribution of E-Poly wear debris and the associated reactivity

INTRODUCTION. Multiple sources have consistently reported oxidation indices less than 0.1 with Marathon® inserts implanted up to 10 years. Understanding effects of oxidation level on UHMWPE wear in vivo is of great value. The objective of this study is to characterize the wear performance of Marathon® acetabular inserts at various levels of artificially induced oxidation, quantified using Bulk Oxidation Index (BOI) as determined per ASTM F2102, and to ascertain if wear rate is affected by progressive polyethylene oxidation. METHODS. GUR 1050 UHMWPE acetabular inserts, re-melted and cross-linked at 5.0Mrad (Marathon®, DePuy Synthes Joint Reconstruction, Warsaw, IN), were artificially aged per ASTM F-2003 in a stainless steel chamber at 5 atm. oxygen pressure and 70°C. Samples were maintained at temperature for 9, 10.4 and 11 weeks. After aging was completed, Fourier Transform Infra-Red (FTIR) spectroscopy was employed on one insert from each time point to evaluate the induced oxidation as a result of artificial aging. Resulting induced BOI values measured by FTIR were 0.195, 0.528 and 1.184. UHMWPE inserts had an inner diameter of 28mm and an outer diameter of 48mm and were articulated against 28mm diameter M-Spec® metal femoral heads (DePuy Synthes Joint Reconstruction, Warsaw, IN). Testing was conducted on a 12-station AMTI ADL hip simulator (AMTI, Watertown, MA) with load soak controls per ISO 14242-1:2014(E) in bovine serum (18mg/mL total protein concentration) supplemented with 0.056% sodium azide (preservative) and 5.56mM EDTA (calcium stabilizer). The UHMWPE inserts were removed from the machine, cleaned, and gravimetric wear determined per ISO 14242-2:2000(E) every 0.5 million cycles (MCyc) for 4.0 MCyc total. A two-tailed student's t-test was used (variance determined by F-test results) to analyze differences in wear rates between the three test groups. RESULTS. After 4.0 MCyc of wear testing, the average wear rate of the Marathon® UHMWPE acetabular inserts with OI levels of 0.195, 0.528 and 1.184 articulated against the CoCrMo femoral heads were 6.0 ± 4.2 mg/MCyc (±95% confidence interval), 8.7 ± 0.4 mg/MCyc and 15.3 ± 2.2 mg/MCyc, respectively (Figure 1). As BOI level increased, the wear rate also increased. Wear rates of inserts with BOI of 0.195 compared to 0.528 were not significantly different (p=0.11). Wear rates of inserts with BOI of 0.195 were significantly lower (p=0.00) compared to 1.184. Wear rates of inserts with BOI levels of 0.528 were significantly lower (p=0.00) compared to 1.184. DISCUSSION. This study aimed to characterize the wear performance of Marathon® acetabular inserts at three levels of oxidation created by accelerated aging. Artificially aged inserts with a BOI level similar to those reported from clinically retrieved Marathon® inserts (0.195) had a wear rate equivalent to non-aged inserts previously tested (data not shown), indicating the in vivo oxidation of this highly cross-linked UHMWPE has no effect on wear rate. Although not measured clinically, higher levels of oxidation may result in significantly higher wear rates in vivo

Introduction. Oxidation of ultrahigh molecular weight polyethylene (UHMWPE) can lead to failure of implants used in total joints. Cyclic loading is postulated to be one mechanism of in vivo oxidation in UHMWPE components as one previous study has shown [1]. We developed an accelerated aging test that incorporated compressive cyclic loading that the UHMWPE components would be exposed to in vivo. Surgeons are moving towards larger femoral heads in hip arthroplasty and removing less bone in knee arthroplasty necessitating thinner UHMWPE components. We hypothesized that, in this accelerated aging test, thinner UHMWPE components would be more susceptible to oxidation caused by the cyclic loading due to higher stresses in the material. Materials and Methods. All samples tested in this study were Conventional PE: GUR1050 was machined into test specimens, vacuum packaged and gamma sterilized. Test samples were blocks 100 mm × 89 mm in cross-section with 3 different thicknesses: 1 mm, 3 mm, and 10 mm (n=3 each). Three cylinders were cored out of each test sample to serve as controls (Fig 1a) that were physically separated and thereby isolating the oxidation attributable to an applied compressive cyclic load. The controls were placed back into the holes from where they were cored during testing. Compressive loading was administered by a 12.5 mm diameter applicator affixed to a hydraulic test frame (Fig 1b), and all testing was done at 80°C in air. A sinusoidal compressive cyclic stress between 1 and 10 MPa was applied at 5 Hz for 7 days. Microtomed thin films from all samples were analyzed via Fourier Transform Infrared Spectroscopy (FTIR) to quantify oxidation [2] after testing. Oxidation was measured through the thickness of the sample at targeted points along the length from directly underneath the center of the load applicator to 10mm away (Fig 1a). Oxidation was also measured through the thickness of the cylindrical controls. Results. The oxidation profiles of each sample at 0.0mm (Fig 2a) and 3.0mm (Fig 2b) from the center point of load application showed that as one decreases the thickness of the test sample the oxidation levels of the sample increase. Both locations showed increased oxidation over the control samples. Discussion. Cyclic loading increased the rate of oxidation of gamma sterilized UHMWPE. The oxidation also increased with decreasing thickness of the UHMWPE samples. This oxidation could potentially accelerate the long term oxidative instability and could contribute to the delamination failure of tibial inserts. For figures/tables, please contact authors directly.