Control of degradation rate of bioabsorbable magnesium by anodization and steam treatment

The control of degradation rate of bioabsorbable magnesium devices is crucial for their biomedical applications. In this study, the influence of anodizing voltages and autoclaving on the degradation behavior of anodized pure magnesium was examined by immersion tests in a culture medium for 14 d. The anodization and autoclaving varied the morphology of surface film. Porous films were formed at 7 V and 100 V, and non-porous films were formed at 2 V and 20 V. The microscopic appearance of the anodized films did not change by autoclaving. The degradation rate on Day 1 was the highest and subsequently decreased to a quasi-steady state within the initial 3-5 d. The 7 V- and 100 V-anodized specimens showed the highest and the lowest quasi-steady degradation rate, respectively. The autoclaving significantly retarded the degradation of the anodized specimens. These facts revealed that anodization and autoclaving are useful for the control of the degradation rate of magnesium and its alloys. The porous anodized films showed local corrosion, whereas the non-porous anodized film formed at 20 V did not show apparent local corrosion. The local corrosion was prevented by autoclaving. These results suggest that the occurrence of local corrosion depends on the porous morphology of surface film.