Multi-directional pin-on-plate apparatus was developed to evaluate wear of ultra-high molecular weight polyethylene (UHMWPE) in joint prosthesis. UHMWPE molecule is an orientative polymer and its orientation influences its mechanical properties. Therefore, mechanical properties of UHMWPE can change easily by uni-directional rubbing process. It is important for appropriate evaluation to duplicate the motion in joint prosthesis. We indicate that availability of multi-directional motion becomes useful for experimental evaluation of UHMWPE wear that corresponds to clinical wear. Generally hip joint prosthesis consists of UHMWPE-ceramic or UHMWPE-metal. Consequently, we adopted high purely alumina, zirconia and Co-Cr alloy against UHMWPE. The trends of wear rates of UHMWPE against several materials for joint prosthesis were similar to the clinical results. It follows that our multi-directional pin-on-plate apparatus stands up for evaluating wear rate of UHMWPE for joint prosthesis. Furthermore we adopted nitride Co-Cr alloy. In the uni-directional apparatus, there was little difference between Co-Cr alloy and nitride Co-Cr alloy. On the contrary, in the multi-directional apparatus, we could catch the difference clearly. Gamma irradiation is used as a sterilization method for joint prosthesis. For this procedure, gamma irradiation causes crosslinking of UHMWPE. Crosslinked UHMWPE molecules connect each other strongly. However gamma irradiation causes the reduction in mechanical properties such as tensile strength and elongation because primary chain scission occurrs. Therefore, excessive irradiation would cause some problems. We suggest the existence of the optimum dose for minimum wear and moderate reduction in tensile strength and elongation. Furthermore we indicate mechanism of wear resistance of gamma irradiated UHMWPE.
|ジャーナル||Tribology and Interface Engineering Series|
|出版ステータス||出版済み - 1 1 2005|
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