The effect of the inflammatory species hypochlorous acid on the corrosion and surface damage of Ti-6Al-4V and CoCrMo alloys.

Performance of metallic orthopedic alloys is dependent on the local biological conditions within the joint. Inflammation within a joint can lead to severe conditions at the surface of the implant and may represent a driving force of corrosion which is not well understood. In this study, the corrosion response of CoCrMo and Ti-6Al-4V alloys was studied in hypochlorous acid (HOCl) saline solutions, which served as a simulated inflammatory environment. Anodic polarization and electrochemical impedance spectroscopy were used to evaluate the electrochemical behavior of these alloys in a range of hypochlorous acid solutions. The open circuit potential of CoCrMo rose to over 600 mV (vs. Ag/AgCl) in 30 mM HOCl solutions while the corresponding corrosion current increased three orders of magnitude over controls. Visual analysis of CoCrMo disks after immersion in 50 mM HOCl for 5 days revealed extensive surface damage. This study shows that HOCl can polarize CoCrMo surfaces above the transpassive potential without an external power source. Ultimately, long-term exposure to HOCl within an inflamed joint may significantly affect patient outcomes through accelerated generation of corrosion products.