Tribofilm formation in biotribocorrosion - does it regulate ion release in metal-on-metal artificial hip joints?

Metal-on-metal prostheses have been considered as alternatives to the well-established metal-on-polyethylene implants due to polyethylene wear debris-induced osteolysis. The release of metal ions from metallic components of metal-on-metal joint implants is of great concern to patients and surgeons. Clinical studies have shown that the level of ions in blood and urine samples of patients does not increase linearly with time. Understanding the processes of metallic ion release from the bearing surfaces of metal-on-metal implants is urgent, as more and more younger and active patients demand longer-lasting joint prostheses. In this study, a hip joint simulator with a novel integrated corrosion cell was used. The diameter of the hip joint head was 36 mm. In situ electrochemical measurements were carried out to investigate the interactions between the tribological contacts and corrosion (ion release) processes in simulated biological environments. The role of the tribofilm on the bearing surfaces is discussed. As a conclusion, the complex organometallic tribofilm once formed can protect the bearing surface from further ion release and act to control the level of overall damage from the implant.