Progress in Wear Resistant Materials for Total Hip Arthroplasty

Current trends in total hip arthroplasty (THA) are to develop novel artificial hip joints with high wear resistance and mechanical reliability with a potential to last for at least 25-30 years for both young and old active patients. Currently used artificial hip joints are mainly composed of femoral head of monolithic alumina or alumina-zirconia composites articulating against cross-linked polyethylene liner of acetabular cup or Co-Cr alloy in a self-mated configuration. However, the possibility of fracture of ceramics or its composites, PE wear debris-induced osteolysis, and hypersensitivity issue due to metal ion release cannot be eliminated. In some cases, thin ultra-hard diamond-based, TiN coatings on Ti-6A-4V or thin zirconia layer on the Zr-Nb alloy have been fabricated to develop high wear resistant bearing surfaces. However, these coatings showed poor adhesion in tribological testing. To provide high wear resistance and mechanical reliability to femoral head, a new kind of ceramic/metal artificial hip joint hybrid was recently proposed in which 10-15 mu m thick dense layer of pure alpha-alumina was formed onto Ti-6Al-4V alloy by deposition of Al metal layer by cold spraying or cold metal transfer methods with 1-2 mu m thick Al3Ti reaction layer formed at their interface to improve adhesion. An optimal micro-arc oxidation treatment transformed Al to dense alpha-alumina layer, which showed high Vickers hardness 1900 HV and good adhesion to the substrate. Further tribological and cytotoxicity analyses of these hybrids will determine their efficacy for potential use in THA.