Characterization and biocompatibility of a calcium-containing AZ31B alloy as a biodegradable material

Magnesium has attracted notability as a biodegradable material. Several studies have reported that magnesium containing calcium (Ca) had biosafety with higher mechanical properties. However, Mg–1Ca alloy showed non-uniform corrosion properties with bone. In this study, various Ca amounts were added to commercial magnesium alloy AZ31B to improve the corrosion resistance and microstructure. AZ31B billet was prepared by casting without Ca. The AZ31B alloy ingots were melted and recasted with Ca quantities at 1.5 and 2.5 wt%. Extrusion ingots were pressed out to a plate with thickness of 5 mm and width of 80 mm at 1650 °C. The microstructure of the alloy was observed by optical microscopy and SEM. The composition of the alloy was analyzed by EDX. To examine the corrosion properties, potentiodynamic polarization was used to measure the corrosion potential and current density. Osteoblast cells MC3T3-E1 were incubated with the samples to allow cell attachment and MTT assay. The microstructure of alloys was homogeneously distributed over the surface and observed phase boundary. Preliminary elemental analysis suggested that the second phases were Al₂Ca and Mg₂Ca. Grain refinement by extrude casting was obtained for AZ31B–xCa. The corrosion resistant of AZ31B–xCa by current density was greater than the AZ31B because the standard electrode potential of Mg phase was lower than Mg₂Ca. In vitro studies showed that the reduction of corrosion resistance and mechanical ability of the magnesium alloy after addition of Ca were not correlated with bioactivity. In particular, AZ31B–1.5Ca had higher formation of biomimetic substances and lower cytotoxicity, even though it had more vulnerable mechanical properties than AZ31B. Based on this result, the effect of Ca ion on commercial alloy AZ31B, mechanical properties, and bioactivity as biodegradable implant were discussed.