Investigation on the microstructure, mechanical performances, in vitro degradation behavior and biocompatibility of biodegradable Zn-0.5Sr alloy by Li alloying and extruded deformation

Abstract

Zn-based alloys are becoming an interesting material in the medical field because of their good biocompatibility and suitable degradation rate. However, the lower strength and poor plasticity severely limit their future applicability. To enhance the mechanical performance and meet the requirement of degradation rate after implantation, the alloying, extrusion, and rolling of Zn alloys have been widely applied. In this work, the effects on the microstructure, mechanical performances, and corrosive behavior of biomedical degradable Zn-0.5Sr alloy with 0.6 wt% Li addition and extrusion deformation were systematically investigated. The microstructure evolution revealed that the α-Zn grains size was significantly reduced from 8.7 μm to 4.8 μm when 0.6 wt% Li was added to Zn-0.5Sr alloy. Furthermore, Zn-0.5Sr-0.6Li alloy had a more obvious texture structure along the extrusion direction after extrusion than that of Zn-0.5Sr alloy. Compared to the mechanical properties of extruded Zn-0.5Sr-0.6Li alloy and Zn-0.5Sr alloy, the yield strength (YS) was enhanced from 125 MPa to 378 MPa, and the ultimate tensile strength (UTS) was improved from 173 MPa to 541 MPa. However, the plasticity occurred to deterioration, and the elongation (El) decreased from 10.85 % to 7.69 %. In addition, the electrochemical testing results showed that the degradation rate of extruded Zn-0.5Sr alloy was 4.098 mm/year, while the degradation rate of Zn-0.5Sr-0.6Li alloy was dramatically reduced to 2.146 mm/year. Meanwhile, following 30 days of in vitro immersion corrosion, the degradation rate of the extruded Zn-0.5Sr alloy was 1.987 ± 0.007 mm/year, while the rate of corrosion of Zn-0.5Sr-0.6Li alloy was 1.216 ± 0.015 mm/year. The result indicated that the addition of Li to Zn-0.5Sr alloy resulted in a decrease in the corrosion rate. Furthermore, it was demonstrated that adding Li to Zn-0.5Sr alloy can improve biocompatibility through in-vitro cell experiments. This work indicated that the Zn-0.5Sr alloy treated by Li element addition and extruded deformation has great potential for application in the field of bone repair.