Morphology of in vitro generated ultrahigh molecular weight polyethylene wear particles as a function of contact conditions and material parameters.

Osteolysis in total joint replacements has been linked to ultrahigh molecular weight polyethylene (UHMWPE) wear particles. Although the biological response to these UHMWPE particles is poorly understood at present, it has been demonstrated that particle size and morphology are important factors in such a response. The goal of the present study was twofold: to develop a comprehensive set of particle size and shape descriptors, and to use these descriptors to analyze the effects of different contact conditions and material parameters during the wear process on the size and morphology of UHMWPE wear debris. The three parameters studied were average contact stress (6.9 and 13.8 MPa), macromolecular orientation of the UHMWPE with respect to the wear direction (0 degrees , 45 degrees , and 90 degrees ), and UHMWPE initial surface roughness (Ra = 1 and 3 microm). Tests were performed using pin on disk or cylinder on plate systems for 3 million cycles each. The results indicated that the initial surface roughness of the UHMWPE test samples had no effect on the morphology of UHMWPE wear particles. However, particle size and morphology were a function of the average contact stress and molecular orientation of the UHMWPE.