Improving in vitro and in vivo corrosion resistance and biocompatibility of Mg-1Zn-1Sn alloys by microalloying with Sr

Magnesium (Mg) and its alloys have attracted attention as potential biodegradable materials in orthopedics due to their mechanical and physical properties, which are compatible with those of human bone. However, the effect of the mismatch between the rapid material degradation and fracture healing caused by the adverse effect of hydrogen (H-2), which is generated during degradation, on surrounding bone tissue has severely restricted the application of Mg and its alloys. Thus, the development of new Mg alloys to achieve ideal degradation rates, H-2 evolution and mechanical properties is necessary. Herein, a novel Mg-1Zn-1Sn-xSr (x = 0, 0.2, 0.4, and 0.6 wt%) quaternary alloy was developed, and the microstructure, mechanical properties, corrosion behavior and biocompatibility in vitro/vivo were investigated. The results demonstrated that a minor amount of strontium (Sr) (0.2 wt %) enhanced the corrosion resistance and mechanical properties of Mg-1Zn-1Sn alloy through grain refinement and second phase strengthening. Simultaneously, due to the high hydrogen overpotential of tin (Sn), the H-2 release of the alloys was significantly reduced. Furthermore, Sr-containing Mg-1Zn-1Sn-based alloys significantly enhanced the viability, adhesion and spreading of MC3T3-E1 cells in vitro due to their unique biological activity and the ability to spontaneously form a network structure layer with micro/nanotopography. A low corrosion rate and improved biocompatibility were also maintained in a rat subcutaneous implantation model. However, excessive Sr (>0.2 wt %) led to a microgalvanic reaction and accelerated corrosion and H-2 evolution. Considering the corrosion resistance, H-2 evolution, mechanical properties and biocompatibility in vitro and in vivo, Mg-1Zn-1Sn-0.2Sr alloy has tremendous potential for clinical applications.