In vitro degradation and biocompatibility of Mg-Li-Ca alloys—the influence of Li content

Mg-Li based alloys hold much attention as potential biomedical materials due to their excellent ductility. A reduced mechanical strength and concern for biocompatibility are exhibited for Mg-Li binary alloys due to the presence of Li element. Addition of the Ca element into Mg-Li alloys leads to an improvement in mechanical strength and biocompatibility. In the present work, the microstructure, mechanical property and corrosion behaviors of three kinds (α, α+β, β) of as-extruded Mg-Li (1, 9 and 15 wt.%)-1Ca alloys were investigated using optical microscope, X-ray diffraction (XRD), tensile, immersion and electrochemical polarization measurements. In vitro biocompatibility was evaluated by cytotoxicity assays, hemolysis and four coagluation tests. The results indicated that the Mg-1Li-1Ca and Mg-15Li-1Ca alloys were characterized by α-Mg and β-Li phases besides Mg2Ca particles, respectively; while the Mg-9Li-1Ca by dual (α-Mg+β-Li) phase together with Mg2Ca phase. The Mg-1Li-1Ca alloy had the highest ultimate tensile strength (UTS) and yield strength (YS) and the lowest elongation (EL) to failure (10.1±1.24%) as well. The EL for the Mg-9Li-1Ca alloy was the highest (52.2±0.01%). The long-term immersion tests revealed a decrease in corrosion resistance with increasing Li content. The results of cytotoxicity assays clearly showed that the Mg-Li-Ca alloys demonstrated no toxicity to L-929 cells in 10% concentration of extracts. The Mg-1Li-1Ca alloy also exhibited an acceptable hemolysis ratio. The results of four coagulation tests designated no sign of thrombogenicity for the Mg-Li-Ca alloys except for the Mg-15Li-1Ca alloy.