3. Biodegradable Mg Alloys: Corrosion, Surface Modification, and Biocompatibility

Metallic materials used in biomedical applications traditionally are highly corrosion resistant, in order to prevent degradation of permanent implants and to diminish possibly harmful metal ion release. Therefore, metallic materials used for instance in orthopaedic applications include Ti base alloys, stainless steels, or Co–Cr–Mo alloys. As these materials are passive in the human body, only a quite small amount of metal ions is released into the surroundings by electrochemical corrosion. A very different approach is the use of low-corrosion-resistant metals for biodegradable, temporary implants. Biodegradable (or bioabsorbable) implants are of interest for applications, in which from medical point of view the implant is not required to stay in the body permanently. An example of such an application is stenting, where remodeling of the arterial wall is expected to take place and a continuous presence of the stent becomes unnecessary. For biodegradable metals, once implanted, the device would stay in human body only for the time it takes to heal, and then it will spontaneously dissolve away. Permanent metallic implants can lead to certain biocompatibility problems related to continuous physical/mechanical irritation and long-term release of metallic ions and/or particles through corrosion or wear processes. Moreover, implantation in children would require an additional surgery in order to remove the permanent implant which cannot adapt to growth of the human body. Such problems could be avoided using a bioabsorbable implant.