Biological activity evaluation of magnesium fluoride coated Mg-Zn-Zr alloy in vivo

Aim: To explore the biodegradable characteristics and biological properties, which could promote new bone formation, of MgF2 coated magnesium alloy (Mg-3wt%Zn-0.5wt%Zr) in rabbits. Methods: Magnesium alloy with MgF2 coating was made and the MgF2/Mg-Zn-Zr was implanted in the femoral condyle of rabbits. Twelve healthy adult Japanese white rabbits in weight of 2.8-3.2 kg were averagely divided into A(Mg-Zn-Zr) group and B(MgF2/MgZn-Zr) group. Indexes such as microstructural evolution, SEM scan, X-ray, Micro-Cr and mechanical properties were observed and detected at 1th day, 2th, 4th, 8th, 12th, 24th week after implantation. Results: Low-density regions occurred around the cancellous bone, and the regions gradually expanded during the 12 weeks after implantation. The implant was gradually absorbed from 12 to 24 weeks. The density of surrounding cancellous bone increased compared with the 12th week data. The degradation rate of B group was lower than that of A group (P < 0.01), while the density of the surrounding cancellous bone increased more evenly. In B group, SEM images after 12 weeks showed the rich bone tissues on the alloy surface that were attached by active fibers. Micro-Cr also presented alloy residue potholes on the surfaces of alloy combinated with bone tissues. Additionally, the trabecular bone had relatively integrated structures with surrounding cavities. Conclusions: MgF2 can effectively decrease the degradation rate of Mg-Zn-Zr in vivo. Mg-Zn-Zr coated with MgF2 can effectively inhibit the corrosion, and delay the release of magnesium ions. The biological properties of the coating itself presented good biocompatibility and bioactivity. (C) 2017 Elsevier B.V. All rights reserved.