The history, challenges and the future of biodegradable metal implants

New interest in magnesium alloys as temporary biomaterials was reborn in the recent years. Especially metals based on physiological trace elements seem to be promising as an alternative to current biodegradable implant materials in cardiovascular and musculoskeletal applications. First clinical reports can be dated back before 1900. Magnesium alloys were used by surgeons of different clinical background in cardiovascular, neural, skin, general and musculoskeletal surgery. All patients have benefited from the treatment with magnesium alloys, although rapid corrosion caused sometimes painless subcutaneous gas cavities. These reports encouraged researchers to study and invent new magnesium alloys which aim to provide more uniform and slow corrosion rates. The most challenging part was to analyze the corrosion of implanted magnesium alloys in-vivo, since the magnesium alloys interlock with the surrounding tissue during corrosion. Therefore, the implanted samples could not be retrieved without damaging the fragile implant-tissue interface. Synchrotron-radiation based microtomography (SRμCT) was introduced as a solution to this challenge. SRμ CT enables to measure non-destructively the in-vivo corrosion rates of magnesium alloys as well as their corrosion morphology. Based on these data, it was concluded that suitable magnesium implants should provide small grains, which are distributed very homogenously and should be produced with highest purity. The future of biodegradable magnesium alloys might be directed towards implant areas where high ductility, maximal tensile strength as well as high compression strength is needed and the properties of current biodegradable implant-materials are exceeded by the properties of magnesium alloys.