Surface State of Metals in Biological Environment and its Control

Abstract

Metals are widely used for medical devices such as implants and about 80％ of implants consist of metals, due to their excellent fracture toughness and durability. Metals are used for treatments in orthopedics and dentistry as well as cardiovascular treatments. Crevice and pitting corrosion is sometimes observed on stainless steel in the human body, while there are little examples of macroscopic corrosion in Ti and Co-Cr alloys. On the other hand, Ti element is detected from surrounding tissues and the mechanism of dissolution of Ti is discussed. Corrosion resistance of a metal is an essential property to acquire the biocompatibility and biofunction of the metal. Surface oxide film and surface hydroxyl groups on the film play an important role to determine the biological property. In addition, calcium phosphate formation on Ti is a key phenomenon to appear its good tissue compatibility. Surface treatment techniques to add biocompatibility and biofunction to metals, especially electrochemical treatments such as cathodic polarization, micro-arc oxidation, and electrodeposition of biofinctional molecule, are reviewed. Finally, importance of evaluation of corrosion resistance are demonstrated.