The effects of simulated inflammatory conditions on the corrosion and fretting corrosion of CoCrMo alloy

In vivo corrosion of CoCrMo alloy and its potential adverse effects on the body have been recognized as major concerns in recent years. While the underlying concepts of general and mechanically-assisted corrosion have been well documented, recent report of inflammatory cell-induced corrosion (ICIC) of CoCrMo alloy challenged traditional understanding of the relationship between biology and corrosion of hip implants. To better understand the role biology may play in the corrosion of CoCrMo-based implants, this study explored the mechanism of ICIC on CoCrMo alloy and investigated how simulated inflammatory (SI) conditions affected the electrochemistry, oxide film and fretting corrosion behavior of CoCrMo alloy. A range of SI solutions, based on phosphate buffered saline with H2O2, HCl, HClO and Fe3+ additions, were investigated. Results of electrochemistry tests (open circuit potential, polarization and electrochemistry impedance spectroscopy) indicated the corrosion susceptibility of CoCrMo alloy can be significantly increased by SI solutions, increasing the oxidizing power and decreasing the passivity of the oxide film. Physiologically possible potential of CoCrMo alloy has been found to be as positive as 0.9 V, a much higher level than previously thought. Inflammatory cell-based chemicals such as H2O2, HClO, acid and Fenton reaction (H2O2 and Fe3+) were able to facilitate the corrosion of CoCrMo alloy and demonstrated part of the mechanism of inflammatory cell induced corrosion. The effect of inflammatory species hydrogen peroxide and voltage on the passive oxide film of CoCrMo alloy was studied by Electrochemical Atomic Force Microscopy (ECAFM). The results showed that simulated inflammatory condition (H2O2) and potential significantly altered oxide film behavior (surface roughness, topography, corrosion resistance). Variation of surface roughness, corrosion resistance were related with potential and time-dependent oxide film topography. Fretting corrosion behavior of CoCrMo/CoCrMo alloy combinations was significantly affected by SI conditions and potential. Presence of Fenton reaction resulted in less stable oxide film and increased oxidizing ability of solution, altering the fretting corrosion behavior of CoCrMo alloy. Additionally, a fundamental study was conducted to investigate the effect of electrode area on the cathodic voltage excursion of metallic biomaterials due to fretting corrosion. This work linked the area-dependent impedance characteristics to the time dependent voltage changes observed during fretting corrosion. Results showed that voltage shifts decreased as the exposed area increased and that this behavior was described well using the impedance-based theory model