Publications & Reports

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3rd UHMWPE International Meeting Presentation: Monotonic and Cyclic Fatigue Behaviors of Conventional and Sequentially Annealed Highly Crosslinked UHMWPE

This study examined the effect of notch-induced triaxial stress state on the monotonic and cyclic tensile true stress-strain behavior of conventional and second generation, sequentially annealed UHMWPE. Two geometries of cylindrical dog-bone tensile specimens, smooth and notched, were tested to failure. The materials showed stress hardening and strain hardening in the smooth and notched conditions. Fractographic analysis showed a difference in the fracture micromechanism between the two materials.

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3rd UHMWPE International Meeting Presentation: Analyses of Oxygen-Induced Radicals in UHMWPE

Researchers from the University of Memphis have compiled a review of free radical measurements on UHMWPE following sterilization with gamma rays (Co-60) at room temperature in open air, vacuum, nitrogen, or argon and subsequently aged at room temperature, 37°C or 75°C for approximately 10 years. Measurements made on vitamin E-mixed UHMWPE powder as well as compression-molded bulk materials are also presented. Additionally, this report includes data obtained from measurements on retrieved acetabular cups and tibial inserts. All free radical measurements were conducted using X-band (~9 GHz) electron spin resonance (ESR) technique.

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3rd UHMWPE International Meeting Presentation: Influence of Centrifugation on Morphology of UHMWPE Wear Particles

It has been proposed that centrifugation of UHMWPE wear debris at high speeds might influence the shape of the particles. In this study, UHMWPE wear particles were isolated and separated by flotation or centrifugation at (i) 2 min at 500g, (ii) 5 min at 16000g or (iii) 30 min at 105000g. The highest centrifugation speed and time did not influence particle shapes.

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3rd UHMWPE International Meeting Presentation: Aging of Gamma-Sterilized UHMWPE- Influence of Oxygen Concentration in Barrier Packaging

The goal of this study was to evaluate the effect of different barrier packaging combinations on the oxidation and oxidation potential of contemporary gamma sterilized UHMWPE. Accelerated aging was performed on the UHMWPE stored in its packaging at 55°C, corresponding to a ten-fold thermal acceleration for the packaging (ASTM F1980). In contrast with oxidation, which appeared to be insensitive to packaging conditions, the oxidative potential of the material strongly varied with the amount of oxygen present. Small differences in the oxygen concentration within the packaging resulted in large differences in the oxidative potential of gamma inert-sterilized UHMWPE.

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3rd UHMWPE International Meeting Presentation: Nanoscale Modification of UHMWPE using MPC

Investigators from Japan have used photo-induced radical polymerization to graft 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer onto the surface of cross-linked polyethylene (CLPE-g-MPC) in order to reduce friction and wear at the orthopaedic bearing surface. Various grafted poly(MPC) layers 10 to 200 nm thick were clearly observed on the surface of the CLPE substrate. Even after 5.0 x 106 cycles in the hip joint simulator test, no wear of MPC-g-CLPE cups with a poly(MPC) layer 10 nm thick was observed.

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3rd UHMWPE International Meeting Presentation: Review of Highly Crosslinked UHMWPE Clinical Literature

The introduction of highly cross-linked polyethylene has attempted to solve the problem of increased wear. A detailed review of short-term clinical studies indicates that the volumetric wear of highly cross-linked polyethylene is significantly less than conventional polyethylene. Long-term clinical follow-up is needed to establish the durability of highly cross-linked polyethylene, especially in conjunction with larger diameter femoral heads so as to guide use.

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3rd UHMWPE International Meeting Presentations: Advances in Wear and Oxidation Resistance of 2nd Generation UHMWPE

An alternative second-generation highly crosslinked polyethylene that is irradiated and stabilized by Vitamin-E (alpha-tocopherol) doping has been proposed. Because Vitamin-E stabilization replaces melting, the crystallinity of the irradiated polyethylene is not decreased and hence mechanical properties and fatigue strength are preserved. We investigated the effect of vitamin E presence on the wear and oxidation resistance of acetabular liners.

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3rd UHMWPE International Meeting Presentation: UHMWPE Stabilization with Vitamin E during E-Beam Irradiation

In the present work researchers from Torino have studied both the stability of macroradicals produced during irradiation under inert atmosphere and the thermal stability of hydroperoxides (ROOH) produced during irradiation in air. The oxidation process induced by e-beam of UHMWPE stabilized with Vitamin E has also been studied. The stabilization effect is a function of the concentration of Vitamin E. These results will be considered in the stabilization process of oxidation of UHMWPE in presence of vitamin E.

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3rd UHMWPE International Meeting Presentation: Practical Considerations in the Scale Up and Manufacture of Vitamin E-Blended UHMWPE for Orthopedics

This study focuses on the results of blending Vitamin E with UHMWPE on a commercial scale. Although blending UHMWPE resins is nothing new in the industrial landscape, it is certainly a challenge when considering the requirements that have become commonplace in producing Medical Grade materials over the last decade. There is the affect on color, the increased complexity of the process and hence the opportunity to increase inclusions, and finally the new testing and inspection challenges that arise from all of this.

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3rd UHMWPE International Meeting Presentation: Spectroscopic and Nanoindentation Study of In Vivo Degradation in Total Knee Replacements

In the present study, FTIR and Raman spectroscopies, as well as nanoindentation were chosen to characterize oxidative, microstructure, and mechanical changes in gamma sterilized UHMWPE for total knee replacement. Raman spectra performed on surface, subsurface and bulk regions were used to calculate the crystalline content according to Strobl and Hagedorn. This study corroborates in vivo oxidation as the underlying phenomenon responsible for the chemical and microstructure changes, as well as mechanical degradation, in tibial components for total knee replacement.

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