Electrochemically induced tribolayer with molybdenum for hip implants: Tribocorrosion and biocompatibility study

As the number of annual Total Hip Replacement (THR) surgeries continues to increase, the longevity of metal based hip implants is a major concern. Tribochemical reactions cause the Cobalt-Chromium-Molybdenum (CoCrMo) hip implant to release wear debris that interacts with decomposed proteins to form a tribolayer. We conducted an electrochemical investigation in order to understand the role of molybdenum in the stability of the tribolayer under mechanical wear and electrochemical corrosion. Tribolayers made of a bovine calf serum (BCS) and bovine calf serum with sodium molybdates (BCS-Mo) were electrochemically deposited on high carbon CoCrMo discs and subjected to corrosion and tribocorrosion experiments under potentiodynamic conditions in a hip-simulator. Potentiodynamic-polarization curve, Electrochemical Impedance Spectroscopy (EIS) tests and surface characterization techniques were carried out. The results indicate an increased resistance to corrosion under mechanical wear by BCS-Mo coated surface which is more distinct when Mo is added into the electrolyte. In addition, biocompatibility evaluation using MG63 osteosarcoma cells on BCS and BCS-Mo coated samples did not show any statistically significant difference in cell growth compared to uncoated CoCrMo discs. These findings suggest a pre-formed electrochemical tribolayer with sodium molybdates may be a promising pre-implantation treatment of THRs to extend the longevity of implants in vivo.