Phytic acid coating on Mg-based materials for biodegradable temporary endoprosthetic applications

Mg-based materials are especially attractive as biodegradable implants, but they degrade so fast in physiological media that some corrosion protection is needed. This paper evaluates the long-term biodegradation kinetics of powder metallurgy Mg and AZ31 alloy coated with a phytic acid chemical conversion layer and tested in a saline phosphate buffer solution (PBS) at 37 °C. The morphology and chemical nature of the conversion coating and the corrosion products were analysed by SEM/EDX, XRD and FTIR. Corrosion resistance of the as-received and coated specimens was determined by hydrogen release, mass loss and potentiodynamic polarisation curves. The results indicate that the inherent heterogeneity and porosity of the powder metallurgy magnesium specimens, both as-received and coated with phytic acid, promoted rapid hydrogen release and led to their premature fragmentation and complete dissolution before 250 h of immersion. In contrast, the phytic acid coating on AZ31 improves corrosion resistance in long-term tests up to 336 h without affecting biocompatibility, biodegradability and resorbability for use as a temporary endoprosthetic implant.