Medical implant corrosion: Electrochemistry at metallic biomaterial surfaces

Metallic biomaterials represent the class of materials with the largest use in medical devices in humans today. This fact will likely continue for decades to come because of the unique combination of strength, wear resistance, and corrosion resistance. However, metallic biomaterials also pose unique and specific concerns related to electrochemical behavior in the body. This chapter will focus on the elements of most importance in understanding the complex interactions present in the human body during corrosion of metallic implants. The concepts associated with oxide films and their interaction with the biological, mechanical, and electrochemical environments are discussed to provide insight into why corrosion is a critically important factor in the long-term performance of devices. Mechanically assisted corrosion in the biological system is discussed in terms of the structural, electrochemical, and biological interactions, and the idea of electrochemical history is presented to explain why such severe evidence of corrosion is observed in vivo. Finally, specific examples of mechanically assisted corrosion in vivo (or biotribocorrosion) are presented, and recent observations concerning the important role the reduction half-cell plays in the biological response to corrosion are discussed.