In vitro and in vivo studies on ultrafine-grained biodegradable pure Mg, Mg–Ca alloy and Mg–Sr alloy processed by high-pressure torsion

High-pressure torsion (HPT) can refine the microstructure and consequently modify the properties, such as mechanical and corrosion properties, of Mg and its alloys. Biodegradable magnesium materials alloyed with the essential elements of life, such as Ca and Sr, are a current research frontier. In this study, biodegradable ultrafine-grained pure Mg, Mg-Ca alloy, and Mg-Sr alloy were prepared using HPT processing. The microstructure, mechanical properties, biodegradable behaviors, and biocompatibility in vitro and in vivo of these materials were systematically investigated. Our results revealed that HPT pure Mg with a bimodal and ultrafine-grained microstructure showed higher mechanical strength, ductility, and degradation rate compared with the as-received materials. The good biocompatibility of HPT pure Mg was confirmed both in vitro and in vivo. The HPT Mg-Ca alloy and Mg-Sr alloy with homogeneous ultrafine-grained microstructures showed higher mechanical strength and lower degradation rate than their as-cast counterparts. The good biocompatibility of the HPT Mg-Ca alloy and Mg-Sr alloy was also revealed. All these findings indicate that HPT is an alternative avenue to fabricate biodegradable Mg-based materials.