To solve the materials selection and tribological problems of compatibility, tissue damage, and wear resulting from sports injuries in younger and active populations where total joint replacement is highly undesirable, alternate biomaterials are being developed to repair or replace focal defects in articular cartilage so that the natural life of an articulating joint can be extended. The tribological concerns are most pressing. Articulating joints are not continuously separated by a fluid film. During motionless periods and impact loading conditions, and even in select individuals during the normal gait cycle, the contacting surfaces are not separated by a fluid film and are in the boundary lubrication (BL) regime. Research has shown that BL must occur at some point in time, if not during the majority of the motion cycle [1]. In this regime, the load is supported mainly by a molecular-scale boundary film and the surface asperities. Thus, failure of a synthetic replacement, or the cartilage itself on which it potentially articulates, would occur under BL conditions.

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