Macroscopic environmental heterogeneity and corrosion behavior derived from in vitro degradation of pure magnesium and their in vivo investigation

Magnesium (Mg) alloys have attracted considerable attention as promising implant materials for biodegradable medical devices. In this study, we focused on investigating the effect of macroscopic environmental heterogeneity due to the degradation of Mg on its corrosion behavior. The immersion experiments using pure Mg plates, which were placed vertically in a culture medium (Dulbecco's Modified Eagle's Medium (DEME) + 10% fetal bovine serum (FBS)) for 1, 5, and 10 days, were conducted. Surface analyses for the corrosion product layers and the measurements of the pH values and concentrations of eluted ions in the immersion medium around the upper and lower areas of the Mg plate were performed. The significant effect of the macroscopic environmental heterogeneity derived from Mg degradation on the corrosion behavior was demonstrated by in vitro tests. Additionally, the in vivo tests were carried out by implanting the pure Mg plates in the femur of rabbits. The in vivo results exhibited macroscopically heterogeneous Mg degradation, with areas of more severe corrosion compared to the in vitro test; it is especially noticeable during the early stage of degradation, even though the average corrosion rate was lower.