Biodegradable Metals as Biomaterials for Clinical Practice: Iron-Based Materials

This review presents the state-of-the-art in the development of iron-based degradable medical implants. Basic properties demanded by the new concept of degradable implants are elaborated, along with the work devoted to understand the underlying mechanism and to improve the properties towards best fitted to the natural tissue. Three application areas are considered: vascular stents, orthopedic implants and tissue engineering scaffolds. Each of these has its own specific demands imposed upon the artificial substitution materials. Biocompatibility is an essential feature that each medical implant must have, but different aspects can be considered depending on the end application. Furthermore, adequate mechanical properties and various characteristics related to the fabrication and in vitro and in vivo testing are presented for pure iron, alloys and composites, as well as joint structures. Corrosion control is a foundation in the development of these materials development and different aspects are also given. Iron-based materials need increased degradation rate because they are still more similar to the permanent implants, due to the slow corrosion process and various methods to overcome this issue have been tried. Porosity and its relation to material structures, mechanical properties, degradation behaviour, magnetic properties, and fabrication technologies, as well as methods of numerical simulations as a supporting tool have been elaborated. Porous structures represent one way to enhance corrosion, while maintaining intact other necessary properties of the biomaterial. Economic impact of the biomaterials sector in general is significant and justifies large investments in research. Iron-based materials for degradable implants are not in clinical practice yet, but the research results achieved so far promise the future applications.