Improved degradation resistance of biomedical grade polyethylene (UHMWPE)

Ultra High Molecular Weight Polyethylene (UHMWPE) has been used as bearing material for total joint replacement. Wear debris (generated by dynamic loads and chemical degradation in biological fluid) induce osteolysis and aseptic loosening causing the joint failure. Actually, replaced joints in vivo are working under an environment rich of Synovial Fluid (SF). Even if, SF extracting this biological medium from the human body is not allowed by law in many countries. Bovine calf serum could be a good alternative and it contains mainly both Hyaluronic Acid (HA) and proteins [1]. There is not full agreement concerning this last choice because proteins concentration changes in a wide range with dramatic effects on friction and wear. So, degradation effects in UHMWPE can be studied in simulated biological fluids [2]. Generally, UHMWPE degradation results from the interaction of bio-oxidative and hydrolysis reactions and tribofatigue [3,4]. In order to improve the mechanical resistance of UHMWPE and the service life of the joint, we have prepared a new formulation of nanocomposite material based on biomedical UHMWPE GUR 1020 and studied its degradation resistance in Simulated Synovial Fluid (SSF) composed by phosphate buffered saline solution and HA, without proteins. By this way we can distinguish the effect of HA on mechanical and physical features of UHMWPE by that of the proteins that will be investigated in a further study.