Corrosion of Implant Materials

Biomedical engineering, involving the application of engineering knowledge, expertise, and techniques to medicine and surgery, is a subjcct that tends to attract engineers and physical scientists because of the attitude that here one may apply technology to the improvement of life righ t at its source, within or about the human body. This applies to biomaterials science as much as to any other area of biomedical engineering and initially there can be a significant feeling of achieve­ ment at the sight of a well-designed, well-manufactured implant, made of suitable materials, being inserted into the body, where it offers that human being the enhanced capability to survive or the chance to lead a far more useful and effective life. There are few things more discouraging, however, than to witness the removal of an implant from the patient, which has degraded or even disintegrated within the human body environment, possibly in a relatively short period of time. It is a most instructive experience to see nominally inert materials, which survive or appear to survive a whole range of what are usually considered hostile environments, succumb to the physiological surround ings. The corrosion of implant materials is therefore a topic of major significance in biomaterials science. In discussing this phenomenon in this review, the term corrosion is used in the broadest sense and defined as the process of interaction between a solid material and its chemical environment, which leads to a loss of substance from the material, a change in its structural characteristics, or a loss of structural integrity. This review, therefore, includes all materials, potentially covering metals, plastics, elastomers, ceramics, and glasses, and is not confined to the simple case where obvious corrosion products are formed. In the context of implant materials, it is necessary to take this �ider view of the corrosion process since we are involved with a wide range of materials and since any interfacial reaction might be of clinical significance, however slight that reaction might appear in the context of traditional materials science.