Microstructures, mechanical and cytocompatibility of degradable Mg–Zn based orthopedic biomaterials

• Sr is an effective grain refiner to backward extruded Mg–Zn–Sr alloy.
• The improved strength is associated with fine grain and homogenous precipitates.
• The corrosion properties are decreased with increased Sr concentration.
• The stable degradation rate is achieved after backward extrusion.
• High biocompatibility is observed by extract assay method using L929 cell line.

The Mg–1Zn–xSr (x = 0.2, 0.5, 0.8 and 1 wt.%) alloys have been prepared by zone purifying solidification followed by backward extrusion (BE). The grain size was reduced and the hardness was improved with the increased concentration of strontium (Sr) after backward extrusion. The BE–Mg–1Zn–0.8Sr alloy was mostly composed of fine precipitates (MgZn and Mg17Sr2) and Mg matrix. At the same time, the mechanical properties of BE–Mg–Zn–Sr alloys were increased with the increment of strontium, which were strongly associated with fine average grain size and homogeneous secondary precipitates. The degradation rate is significantly increased when Sr content is over 0.8 wt.%. The homogenous degradation rate is achieved. The degradation products show good biocompatibility evaluated by MTT method using L929 cell line. It is demonstrated that the micro-alloying element of Sr is a potential approach to develop novel Mg–Zn based biomaterials.