In vitro and in vivo corrosion, mechanical properties and biocompatibility evaluation of MgF₂-coated Mg-Zn-Zr alloy as cancellous screws

Magnesium (Mg) and its alloys as biodegradable materials have received much attention in the orthopedics applications; however, the corrosion behavior of these metals in vivo remains challenging. In this work, a dense and nanoscale magnesium fluoride (MgF₂) coating was deposited on the surface of Mg-Zn-Zr (MZZ) alloy cancellous screw. The MZZ cancellous screw with MgF₂ coating maintained an integrated shape and high yield tensile stress after 30 days immersion in SBF, comparing with the bare screw. Hydrogen releasing rate of the MZZ samples was suppressed at a lower level at the initial stage, which is in favour of the adhesion of the cells. And in vivo experiments indicated that MgF₂-coated MZZ screws presented advantages in cytocompatibility, osteoconductivity and osteogenesis of cancellous bone in rabbits. Corrosion rate in vivo perfusion environment increased very slowly with time in long-term study, which was an opposite trend in vitro static immersion test. Moreover, maximum corrosion rate (CR_max), a critical calculation method of corrosion rate was introduced to predict fracture regions of the sample. The MZZ alloy with MgF₂ coating possesses a great potential for clinical applications for internal fracture fixation repair.