Tribological Characterization of Surface Treated Titanium for Orthopaedic Joints

Abstract

Most not cemented total hip replacements combine a titanium alloy stem, a CoCrMo femoral head and an uUltra High Molecular Weight Polyethylene (UHMWPE) acetabular cup. In spite of the suboptimal biocompatibility, the higher cost and some difficulties in machining, CoCrMo alloy is often preferred to titanium alloys thanks to its outstanding tribological properties, higher hardness and elastic modulus. Therefore, nowadays most of the heads of hip prostheses use CoCrMo as bearing material. Biocompatibility problems of CoCrMo are often associated with a nickel content of up to 1% in this alloy. In some clinical situations such a nickel percentage cannot be neglected. The rationale of the present study was to investigate the effect of various surface treatments and combinations of treatments, such as electrochemical oxidation (anodization), laser surface treatments and barrel polishing, on the tribological properties of commercially pure grade 2 titanium. The goal was to find a surface treatment capable to provide a wear resistant titanium surface, with tribological properties as good as those of CoCrMo. Wear tests were performed on a multidirectional pin-on-flat screening wear testing machine, using UHMWPE pins as second bearing material. The experiments showed the possibility to improve wear resistance of titanium to the CoCrMo levels.