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Review Ultra High Molecular Weight Polyethylene UHMWPE

Literature Review Ultra high molecular weight polyethylene UHMWPE due to its various properties such as biocompatibility high wear resistance low friction coefficient suitable stiffness and fatigue resistance has been emerged as a proven bearing material for implants in various arthroplasties such as acetabular cups and tibial inserts 13 18 20 Beside the extensive use of UHMWPE in total joint replacements for many years the primary problem is the constant generation of wear debris resulting from articulation against the metallic parts These wear particles induced osteolysis and aseptic loosening and has been considered as critical failure which limits the service life of prosthesis 21 In order to consider the former concern i e wear resistance the process of crosslinking or irradiation of UHMWPE are used and highly cross linked PE 22 However main interest continues to refer the long term oxidation of highly cross linked UHMWPE following the formation of free radicals during the process of irradiation These free radicals may responsible for continuing long term reactions hence leading to oxidative degradation in the presence of molecular oxygen 23 24 and transforming UHMWPE into brittle polymer with disappointing performance 25 Many orthopedics manufacturers have utilized the process of high energy radiation accompanied by the thermal stabilization processes to stabilize the cross linked polyethylene against oxidation Both of these processes appear to optimize the wear resistance of highly cross linked UHMWPES which usually take place below annealing or above re melting the melting transition temperature of 1 2 UHMWPE Anyhow the actual crystallinity of the polymer is decreased by re melting consequently influencing the polymer s mechanical properties such as yield and ultimate stress but annealing maintains these properties 26 Moreover as during annealing process crystals do not melt hence complete oxidative stability is not guaranteed by annealing methods because of the fact that fewer mobile free radicals entrapped within the crystalline phase of polymer do not have the ability of recombination Additionally the manipulation of α tocopherol vitamin E has been considered as the substitute of the thermal stabilization process 27

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