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The performance of titanium and its alloys in surgical implant applications is examined with respect to the materials' biocompatibility and ability to withstand the corrosive fluids of the human body. Both in-vitro and in-vivo experimentation is reviewed, as well as the reported clinical results. For comparative purposes, other commonly used implant alloys are discussed. Since the corrosion resistance of titanium and its alloys is due to a passive film which covers the metal, a portion of the paper is devoted to the nature of the passive film. Studies dealing with formation, compositions, and structures of titanium passive films, as well as environmental effects on these films are examined. In-vitro studies have been carried out in numerous physiological solutions using various electrochemical techniques. Among the parameters studied were pH, pO2, surface finish, surface treatments, crevice corrosion, galvanic coupling, stress, fatigue, and fretting corrosion. In every study titanium and its alloys compared favorably with the other materials tested. In-vivo studies as early as 1940 showed that titanium is as well tolerated biologically as is stainless steel and Vitallium. More recent animal studies confirmed the early conclusions, and, in fact, it appears that titanium and some of its alloys may be actually better tolerated than stainless steel and the cobalt-chromium alloys. Clinical findings have been consistent with the results of in-vitro and in-vivo studies; not a single corrosion-related failure of a titanium or titanium-alloy implant could be found in the clinical literature. In summary, the available information indicates that titanium and some of its alloys may be the most biocompatible and corrosion-resistant metallic implant materials in present use.
titanium, implant materials, alloys, implant, corrosion resistance, passivity, biocompatibility, in vivo, in vitro, clinical
Supervisor, Edwards Pacemaker Systems, Division of American Hospital Supply Corp., Irvine, Calif