Aromatic Thermosetting Copolyester (ATSP) / UHMWPE Blends with Improved Wear Properties and Biocompatibility
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1063-OO09-09
Aromatic Thermosetting Copolyester (ATSP) / UHMWPE Blends with Improved Wear Properties and Biocompatibility Yongqing Huang1, and James Economy2 1 MS&E, University of Illinois at Urbana-Champaign, 1304 West Green Street, Urbana, IL, 16801 2 MS&E, University of Illinois at Urbana-Champaign, Urbana, IL, 16801 ABSTRACT Despite the recognized success and worldwide acceptance of ultrahigh molecular weight polyethylene (UHMWPE) for total joint arthroplasty, the generation of UHMWPE wear debris from the articulating surface is of major concern and limits the longevity of the artificial joint device. Blends of UHMWPE with an aromatic thermosetting copolyester (ATSP) at 50:50 volume ratio using poly(ethylene-co-acrylic acid) (PEA) as a compatibilizer were developed to address this problem. The amount of PEA was 0, 5, 10, 15 and 20 weight percent of the weight of ATSP, respectively. The wear properties of these blends were evaluated by a pin-on-disk wear test in which an ASTM F-75 cobalt-chromium alloy disk was chosen as a counterface and sterile filtered bovine serum diluted in deionized water to 75% (volume) was used as a lubricant. The wear tests from 0.2 to 3 million cycles showed that UHMWPE/ATSP blend with 10 wt% PEA had average weight loss smaller than UHMWPE and comparable to crosslinked UHMWPE. The wear debris study indicated that UHMWPE/ATSP blend with 10 wt% PEA created a smaller size percentage of the wear debris particles in the biologically active range than UHMWPE and crosslinked UHMWPE. The direct-contact cytotoxicity tests showed that ATSP and UHMWPE/ATSP blend with 10 wt% PEA were not toxic. INTRODUCTION Ultrahigh molecular weight polyethylene (UHMWPE) has been widely used as a total joint replacement material. However, the formation of wear debris after 8 -10 years of use has been a major concern and sharply limits the longevity of the device. It is believed that the volume of debris, particle size and the proportion of the particles which are within the most biologically active size range, are critical factors in determining the reactivity of particles [1-2]. The study by Matthews et al [3] indicated that particles in the 0.1 – 1.0 μm size range are the most stimulatory for primary human mononuclear phagocytes. Recently, crosslinked UHMWPE (X-UHMWPE) with greatly reduced wear compared to UHMWPE has been developed and commercialized. However, some key mechanical properties, such as fatigue resistance and fracture toughness, tend to decrease [3-5]. To improve the wear resistance of UHMWPE, new blends of UHMWPE and an aromatic thermosetting copolyester (ATSP) were developed. ATSP has been recently developed in our research group and used in relatively diverse areas, such as blending with polytetrafluoroethylene (PTFE) to reduce wear, as a high temperature composite matrix, and as a high temperature adhesive [6-8]. Poly(ethylene-co-acrylic acid) with 10 wt% of acrylic acid (PEA), as a compatibilizer, was used to improve the interaction between UHMWPE and ATSP. In an earlier study, dynamometer wea
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