Electrochemical behavior of metals in the biological milieu

Corrosion in the biological milieu presents the basic science background to understand the nature of corrosion processes associated with medical devices and the metallic biomaterials from which they are made. This chapter introduces the concepts of corrosion, the factors that affect corrosion (oxidation and reduction reactions), and the role of passive oxide films in the behavior of metallic biomaterials. Links between the environmental conditions, including biological molecules and mechanical factors, and interactions between the biological system and the metal-oxide surface are described. Current state-of-the-art corrosion testing methods including polarization testing, scratch testing, and impedance spectroscopy are described and related to currently used materials. The importance of the biological environment is also presented to provide a better understanding of how inflammation, infection, or other local conditions may enhance or alter corrosion behavior. Finally, aspects of corrosion that are not typically considered, including the reduction half-cells, are presented and shown to significantly affect cell behavior. Overall, much is known about corrosion in the biological milieu; however, there is also much that is not yet understood. This chapter lays the foundation upon which additional studies could be designed.