The effects of cathodic polarization and simulated infection on the electrochemical properties of CoCrMo and coupled Ti6Al4V+CoCrMo alloy
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Metallic biomaterials are the most commonly used materials for medical devices because of their unique combination of; strength, wear resistance, and corrosion resistance. However, they also pose some concern due to how they interact electrochemically with the body and the risk of metallic ion release due to corrosion. Therefore, it is important to fully understand the interactions present with the human body during the corrosion of metallic implant materials. This study evaluated the effects of simulated infection and cathodic polarization on the electrochemical properties of cobalt-chromium-molybdenum (CoCrMo), as well as, titanium-6%aluminum-4%vanadium (Ti6Al4V) coupled with cobalt-chromium-molybdenum. A coupled coupon of Ti6Al4V+CoCrMo was made by using an EPOXY resin to hold the two metals onto the same sample. Normal conditions consisted of each sample being submerged in phosphate buffer saline (PBS) at a pH 7.4 at Open Circuit Potential (OCP). To simulate an environment with an infection, PBS was titrated to a pH of 5 with hydrochloric acid (HCl). Cathodic stimulation conditions for each couple was determined by a polarization scan. Both samples were stimulated at -1.0V at both pH5 and pH7.4. The purpose of this study was to evaluate the voltage and pH dependent electrochemical properties of common orthopedic implant materials CoCrMo and Ti64+CoCrMo. Following the 24-hour immersion in PBS, electrochemical impedance spectroscopy (EIS) was performed to assess the faradaic and non-faradaic electrochemical properties of the interface. The OCP and current densities of each sample was analyzed. In addition, inductively coupled plasma mass spectroscopy (ICP-MS) was used to quantify the concentration of metal ion released into the test electrolyte. Initial and final pH after immersion and/or stimulation was also recorded. Finally, the surfaces of the samples were also viewed utilizing scanning electron microscopy (SEM) and analyzed using energy dispersive spectroscopy (EDS).