Biodegradable ternary Zn–3Ge–0.5X (X=Cu, Mg, and Fe) alloys for orthopedic applications

Biodegradable zinc (Zn) and its alloys have great potential to be used for orthopedic applications due to their suitable degradation rate and good biocompatibility. However, pure Zn has insufficient mechanical properties, such as low strength and hardness, and poor plasticity, which limits its clinical applications. Here, we report on a new series of ternary Zn–3Ge–0.5X (X=Cu, Mg, and Fe) alloys aiming to achieve good corrosion resistance and biocompatibility, and enhanced mechanical properties via micro-alloying with copper (Cu), magnesium (Mg), and iron (Fe). Hot-rolling has also been applied to the new ternary alloys to further enhance their mechanical properties. Mechanical testing results indicate that both the strength and hardness of hot-rolled Zn–3Ge are significantly improved with micro-alloying of Cu, Mg, and Fe; of which the hot-rolled Zn–3Ge–0.5Mg exhibits the highest ultimate tensile strength of 253.4 MPa and yield strength of 208.5 MPa among all the alloys, 25.9% and 44.7% higher than those of the hot-rolled Zn–3Ge. The degradation rate of the as-cast alloys is lower than that of the hot-rolled alloys in Hanks’ solution for 1 month and the hot-rolled Zn–3Ge–0.5Mg alloy exhibits the highest degradation rate of 0.075 mm/y. CCK-8 assay using MG-63 cells indicates that the diluted extracts of Zn–3Ge–0.5X (X=Cu, Mg, and Fe) alloys with concentrations of 12.5% and 25% exhibit no or slight cytotoxicity, and the diluted extracts of Zn–3Ge–0.5Cu alloys show high cell viability of over 100%, showing the best cytocompatibility

Development of biodegradable Zn–1Mg–0.1RE (RE = Er, Dy, and Ho) alloys for biomedical applications

Zinc (Zn) and its alloys are receiving great attention as promising biodegradable materials due to their suitable corrosion resistance, good biocompatibility, and highly desirable biofunctionality. Nevertheless, the low mechanical strength of pure Zn impedes its practical clinical application and there have been calls for further research into the Zn alloys and thermomechanical processes to enhance their mechanical properties and biocompatibility. Here, we report on the alloying efficacy of rare earth elements (REEs) including erbium (Er), dysprosium (Dy), and holmium (Ho) on the microstructure, mechanical properties, corrosion and wear behavior, and in vitro biological properties of Zn-1Mg-0.1RE alloys. Microstructural characterization revealed that the addition of 0.1\ua0wt.% REEs had a significant refining effect on the grain size of the α-Zn matrix and the second phases of the alloys. Alloying of the REEs and hot-rolling effectively improved the mechanical properties due to both precipitation strengthening of the second phases of ErZn, DyZn, and HoZn and grain-refinement strengthening. The highest ultimate tensile strength of 259.4\ua0MPa and yield strength of 234.8\ua0MPa with elongation of 16.8% were achieved in the hot-rolled Zn-1Mg-0.1Ho. Alloying of REEs also improved the wear and corrosion resistance, and slowed down the degradation rate in Hanks' solution. Zn-1Mg-0.1Er showed the highest cytocompatibility of MC3T3-E1 cells cultured directly on the alloy surface and of MG-63 cells cultured in the alloy extract. Zn-1Mg-0.1Dy showed the best anticoagulant property among all the alloys. Overall, these Zn-1Mg-0.1RE (Er, Dy, and Ho) alloys can be considered promising biodegradable metallic materials for orthopedic applications