Long-term in vivo Response to Biodegradable Anodized Magnesium AZ91 Alloy for Bone Repair

Biodegradable metals, such as magnesium-based alloys, are of great interest for use as intracorporeal implants that disappear once the tissue or function is restored. These materials are even suitable for load-bearing applications, but their degradation rate still needs to be reduced and controlled to avoid hydrogen gas liberation. A surface treatment of anodization has already been described for the magnesium AZ91 alloy, which acts as a barrier to prevent degradation and reduce hydrogen release, showing good in vivo results after 30 days of implantation in a murine model. In this study, the performance of anodized AZ91 alloy was evaluated over a long-term period of 6 months in the same animal model. The new bone in contact with the implants exhibited a continuous interface, without gas pockets or fibrous tissue. Bone-to-implant contact was better than that of a polymeric implant (control), and the new bone showed favorable results in terms of volume, trabecular thickness, mineral apposition rate, maturity, and crystallinity. All this evidence supports the potential of anodized AZ91 as a candidate for biodegradable bone fixation devices.