Corrosion and other electrochemical aspects of biomaterials

Metallic materials are used extensively as orthopedic implants, dental materials, sensing elements of bioelectrodes, and other applications. The electrochemical behavior of these biomaterials is of interest for a variety of reasons. The corrosion resistance of an implant material influences its functional performance and durability and is a primary factor governing biocompatibility. Among the aspects affecting biocompatibility are the amounts and forms of released corrosion products and their disposition in the body after release. Electrochemical principles are very useful for understanding the factors affecting corrosion resistance and also form the foundation for many biosensors that measure the concentration of various chemical entities (including released corrosion products and naturally occurring substances). Many electrochemical measurement techniques have been used to study biomaterials for years (e.g., polarization curve measurement), while others (such as polarography and AC impedance methods) have been applied more recently. This work focuses on four main topics. The first is the nature of the body's environment as it affects in vivo electrochemical phenomena, that is, the chemical, mechanical, biological, and bioelectrical phenomena that affect the behavior and performance of biomaterials. The second deals with methodology--the techniques used for corrosion measurement and concentration determination, the appropriate environment (laboratory, cell culture, in vivo, etc.), and experimental problems encountered. The third topic treated is the knowledge accumulated regarding the performance of implant alloys in various applications, for example, the forms of corrosion to which they are susceptible, etc. Finally, improvements that may come about in the future regarding both materials and testing methodology are considered.