Corrosion, fatigue and corrosion fatigue behaviour of metal implant materials, especially titanium alloys

In recent years, implants have gained growing importance in all areas of medicine. Of these, orthopaedic and dental implants are routinely exposed to high mechanical loads such as friction and wear together with multiaxial, multistep fatigue. Sustaining these loads is one prime challenge of these implants which is complicated by the need to survive in body electrolytes (proteins, enzymes, salts) that are very corrosive. Even though titanium and its alloys form a very stable oxide layer in physiological environments bestowing them exceptional biocompatibility as compared to other metal implant materials, surface reactions do take place. Such reactions, for example ion exchange or adsorption of proteins, determine the quality and stability of the bone-implant-interface, and consequently mechanical activation of the surface plays an important role. The present paper reviews the current knowledge on the corrosion, fatigue, and corrosion fatigue behaviour of titanium and its alloys, with a special emphasis on the influence of simulated in vivo conditions.