Abstract
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 and in isolated cases when abnormally high levels have caused adverse local tissue reactions. An understanding of the origin of metal ions is really important in order to design alloys for reduced ion release. The welfare of patients and concerns of hypersensitity and other potential side effects have been recognised by both patients and surgeons. Both simple reciprocating pin-on-plate wear tests and hip simulator tests have been carried out to characterize the relationship and interactions between electrochemical reactions (corrosion), mechanical damage (wear) and biological environments. It was found that metal ions originated from two sources: (a) depassivation/repassivation of the contacting surfaces due to the interaction with tribology and corrosion processes under simulated motion and load and, (b) corrosion of nano-sized wear particles generated from the contacting surfaces.
