The influence of protein concentration, temperature and cathodic polarization on the surface status of CoCrMo biomedical grade alloys

CoCrMo alloys have been widely used in hip replacements. On the one hand they have exhibited excellent long-term survival rates, but recently high failure rates have been observed, associated with adverse local tissue reactions. It is still a puzzle why CoCrMo alloys sometimes work very well, while at the other times the failure rate is unacceptably high. The current work aims to investigate the influence of protein adsorption on the oxide layer properties and consequently on corrosion behaviour of CoCrMo biomedical grade alloys in different surface and media conditions. Electrochemical Impedance Spectroscopy (EIS), SEM and AFM were employed to characterise the surfaces. TEM was also used to reveal the subsurface chemical composition. The results showed a significant drop in the resistance of the oxide layer on the surfaces after some cathodic potential polarization. It was also shown that higher protein content and temperature reduced the oxide layer/metal surface interface resistivity. EDX quantitative chemical composition spot analysis of the subsurface after cathodic polarization showed a depletion of chromium in the outermost layer. AFM imaging and peak-force quantitative nanomechanical mapping QNM revealed lower adhesion forces for a relatively thick proteinaceous adsorbed layer on the surface after high cathodic polarization in particular at 50 °C.