Corrosion behavior of metallic bio-implant alloys

The most common metallic biomaterials are 316L, Co-28Cr-6Mo, and Ti-6Al-4V alloys used as prostheses and fixation devices. These materials are biocompatible and have high corrosion resistance. However, metallic biomaterials are not completely inert in the body. The presence of dissolved oxygen, chloride, phosphate, and organic molecules in the body fluids could influence their corrosion behavior. Protein is one of the components of the human body fluids. Body fluids contain different concentrations of protein and even the protein concentration varies at the implant/tissue interface during the healing period. Some proteins are negatively-charged at a neutral body pH and they react with the positively-charged ions released from metallic samples. The reactions either form an absorbed film on the surface of the samples or produce metal/protein/hydroxylated compounds. The primary objective of my project is to investigate influences of protein on corrosion behavior of three commonly used biomaterials. The hypothesis is that the variation of protein concentration can alter corrosion resistance and ion release of biomaterials. This Study could help to develop implants with a better corrosion performance and minimal ion release. This development could promote the physical and mental health of patients and reduce cost and time of revision surgeries. To pursue this study, bovine serum albumin (BSA) and human serum albumin (HSA) were added to phosphate-buffered saline (PBS) solutions. A combination of electrochemical and non-electrochemical corrosion methods was used to understand the kinetics of electrochemical reactions, identify the oxide layer growth mechanism and protein adsorption, and detect ion release and surface morphology with and without input of external energy. The dissolution rates of iron from 316L and cobalt from Co-28Cr-6Mo alloys in the BSA solution were lower than that in the HSA solutions. The surface chemistry of the specimens showed that the adsorption of Na into the Ti-6Al-4V oxide layer depends on the type of protein. In the presence of HSA, sodium (2-methyl-propenoate) was detected whereas Na bound to the sulfhydryl group of bovine serum albumin (BSA) and formed sodium mercaptoacetate. Finally, BSA was a stronger cathodic inhibitor than HSA for 316L and Co-28Cr-6Mo alloys.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat