The influence of lipid and proteins on the wear behaviour of ultra-high molecular weight polyethylene (UHMWPE) used in joint prostheses was examined by using multidirectional sliding pin-on-plate wear testers. In vivo wear behaviour of polyethylene components should be controlled to maintain the joint performance throughout the entire life cycle of artificial joints. However, there are many uncertainties about the wear mechanism of UHMWPE, especially about the effect of physiological environment. The physiological environment contains various kinds of biological molecules, such as proteins and lipids etc. These molecules can be entrained into a contact zone and possibly affect the friction and wear process of artificial joints. The aim of the current study is to examine the effects of proteins and lipids on the UHMWPE wear behaviour for better understanding of in vivo polyethylene wear process. The wear behaviour of UHMWPE on a stainless steel sliding pair for joint prostheses was evaluated by using our multidirectional sliding pin-on-plate wear testers, which can make a multidirectional sliding pathway similar to that of hip joint prostheses. Several phosphate buffered saline (PBS) solutions containing a synthetic lipid, dipalmitoyl phosphatidylcholine (L-α-DPPC), and two kinds of serum proteins, albumin and γ-globulin, were prepared. These solutions were used as lubricants in the wear test and the effect of the lipid and protein concentration on the UHMWPE wear was evaluated. Results of this study indicated that the wear behaviour of a UHMWPE-on-metal sliding pair was clearly affected by the lipid and protein concentration. Especially, the wear amount of UHMWPE increased significantly by increasing the γ-globulin concentration. Lipid could play a role of boundary lubricant and reduced wear of UHMWPE, if the protein content was significantly low. On the other hand, the polyethylene wear amount was increased with increasing lipid concentration in the case of relatively high protein concentration.
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