Corrosion and trib-corrosion behaviour of metallic orthopaedic implant materials

Since the introduction of medical implants into human bodies, corrosion and wear have been regarded as key issues for their long-term durability. There has been a recent renewed interest in the use of large diameter metal-on-metal (MoM) hips, primarily because of the reduced volumetric wear compared with the wellestablished polyethylene-on-metal joints. Long term durability of MoM joints relies on control of both their corrosion resistance (relating to ion release) and wear behaviour (relating to creation of nanometre-scale wear debris). Concerns about the potential risk of released metal ions to the biological environment (patient) are of great importance. In this respect tribocorrosion is a serious consideration in joint performance. An integrated electrochemical cell on a reciprocating tribo-meter was employed to evaluate the corrosion and tribocorrosion behaviour in a protein rich solution (Bovine Serum), a cell culture solution (DMEM) and a saline solution (NaCI) with the attempt to isolate the organic species effects. Three commonly used orthopaedic materials were involved in this study. A High Carbon Cobalt-Chromium-Molybdenum alloy, a Low Carbon Cobalt-Chromium-Molybdenum and UNS S31603 Stainless Steel (316L). A range of electrochemical methods were used in the assessment of materials under biotribocorrosion systems and results were supported by surface analysis and bulk solution analysis techniques. The material degradation rate is strongly dependent upon the charge transfer (corrosion), the mechanical damage (tribology) and also their interactions (tribocorrosion) in these simulated biological environments.