[unreadable] The longevity of total hip and knee arthroplasty has been compromised primarily by wear and fatigue failure (delamination) of the polyethylene load-bearing components. In clinical use in total hip arthroplasty since 1998, crosslinking and melting markedly reduces polyethylene wear, but it also reduces its fatigue strength, potentially limiting its use in high stress applications, such as total knee replacements and certain total hip replacements. [unreadable] [unreadable] We hypothesize that the fatigue-strength loss that occurs with crosslinking and melting is due to reduced plasticity of polyethylene through reduced chain mobility and reduced crystallinity. Crosslinking also lowers the efficiency of energy absorbing mechanisms in the process zone that precedes fatigue cracks. We further hypothesize that the fatigue strength of highly crosslinked polyethylene can be increased by incorporating a plasticizing agent, such as a-tocopherol or very low molecular weight polyethylene, and/ or using methods (other than melting) that do not affect the crystallinity of polyethylene to improve postirradiation oxidative stability. [unreadable] [unreadable] Our general aim is to improve the fatigue strength of highly crosslinked polyethylene. Our specific aims are to: 1) Identification of mechanisms that resist fatigue crack propagation and how such mechanisms change with crosslinking and melting; 2) Increasing the fatigue strength of highly crosslinked polyethylene; and 3) Simulated gait and adverse testing of the optimum low-wear, high-fatigue polyethylene formulation. [unreadable] [unreadable]