In-situ Electrochemical Study of the Interaction of Tribology and Corrosion in Artificial Hip Prosthesis Simulators

The second generation Metal-on-Metal (MoM) hip replacements have been considered as an alternative to commonly used Polyethylene-on-Metal (PoM) joint prostheses due to polyethylene wear debris induced osteolysis. However, the role of corrosion and the biofilm formed under tribological contact are still not fully understood. Enhanced metal ion concentrations have been reported widely from hair, blood and urine samples of patients who received metal hip replacements. Due to the high corrosion resistance of the alloys used in such devices, to understand the origins of metal ions is really important to design alloys for reduced ion release.  The welfare of patients and concerns of hypersensitity and other potential side effects have been realized by both patients and surgeons. Hip simulator tests  have been carried out to characterize the relationship and interactions between electrochemical reactions (corrosion), mechanical damage (wear) and biological environments. All heads of tested hip implants were 36 mm in diameter and made from CoCrMo alloys. It was found that metal ions were majorly from two sources: (a) depassivation/repassivation of the contacted surfaces due to the interaction with tribology and corrosion processes under simulated motion and load. (b) corrosion of nano-sized wear particles from tribo-corrosion systems.