Microstructure, anticorrosion, biocompatibility and antibacterial activities of extruded Mg-Zn-Mn strengthened with Ca

To find suitable biodegradable materials for implant applications, Mg-6Zn-0.3Mn-xCa (x=0, 0.2 and 0.5, wt.%) alloys were prepared by semi-continuous casting followed by hot-extrusion technique. The microstructure and mechanical properties of Mg-6Zn-0.3Mn-xCa alloys were investigated using the optical microscope, scanning electron microscope and tensile testing. Results indicated that minor Ca addition can slightly refine grains of the extruded Mg-6Zn-0.3Mn alloy and improve its strength. When 0.2 wt.% and 0.5 wt.% Ca were added, the grain sizes of the as-extruded alloys were refined from 4.8 to 4.6 and 4.2 mu m, respectively. Of the three alloys studied, the alloy with 0.5 wt.% Ca exhibits better combined mechanical properties with the ultimate tensile strength and elongation of 334 MPa and 20.3%. The corrosion behaviour, cell viability and antibacterial activities of alloys studied were also evaluated. Increasing Ca content deteriorates the corrosion resistance of alloys due to the increase of amount of effective cathodic sites caused by the formation of more Ca2Mg6Zn3 phases. Cytotoxicity evaluation with L929 cells shows higher cell viability of the Mg-6Zn-0.3Mn-0.5Ca alloy compared to Mg-6Zn-0.3Mn and Mg-6Zn-0.3Mn-0.2Ca alloys. The antibacterial activity against Staphylococcus aureus is enhanced with increasing the Ca content due to its physicochemical and biological performance in bone repairing process.

Automated summary

The addition of minor amounts of Ca in Mg-6Zn-0.3Mn alloy can refine the grains slightly and improve strength, with the alloy containing 0.5 wt.% Ca showing the best mechanical properties. However, increasing Ca content deteriorates the corrosion resistance of the alloys, while positively impacting cell viability and antibacterial activity.