Effect of Molding Conditions and Irradiation on Polymeric Wear

1. 2 Effect of Molding Conditions and Irradiation on Polymeric Wear:
Wear of polymeric materials used in implants is perhaps the most difficult to understand .As a result, numerous reports on polymeric wear have emerged over the years . In biomedical applications such as occluders in mechanical heart valves and joint prostheses, fatigue fracture and wear of the polymers have been considered to be an important factor in determining the durability of the prostheses. In the case of UHMWPE, many factors influence its wear properties. For example, when UHMWPE was molded between 190 and 200°C and some antioxidants were added during processing, its wear resistance appeared to improve. Molding at higher pressures and increasing the molecular weight, on the other hand, were reported to be detrimental. Nonetheless, there is a possibility that there could be an optimum processing condition and molecular weight distribution that could give the best wear characteristics. More recent work has shown that processing conditions play a vital role on the cyclic fatigue of UHMWPE. In particular, ?-radiation and oxidative aging are very detrimental to the fatigue threshold and crack propagation resistance (Table 2). Moreover, compression molding appears to render a better fatigue resistance when compared to extrusion.