Novel Zn-2Cu-0.2Mn-xLi (x = 0, 0.1 and 0.38) alloys developed for potential biodegradable implant applications

Abstract

Due to the moderate degradation rates and acceptable biocompatibility, Zn-based alloys have attracted more and more attention as biodegradable materials. However, the inferior strength and ductility significantly limit their further applications. In this work, biodegradable Zn-2Cu-0.2Mn- x Li ( x = 0, 0.1 and 0.38) alloys were developed with enhanced comprehensive mechanical properties. Also, these novel alloys were found to possess extraordinary antibacterial activity and good biocompatibility. Annealing and hot extrusion were performed on the as-cast alloys. The microstructures, mechanical properties, corrosion behavior, antibacterial ability, hemocompatibility and cytocompatibility of the alloys were systematically studied. Microstructure analysis indicates that primary ɛ-CuZn 4 particles are distributed in the Zn grains in all as-cast alloys. Addition of Li leads to formation of β-LiZn 4 phase in eutectics and β-LiZn 4 precipitates within the Zn grains. In the as-annealed alloy, secondary ε-CuZn 4 precipitates and fine β-LiZn 4 precipitates appear in the Zn matrix of the Li-containing alloys. All the as-extruded alloys reveal fibrous morphology and develop (0001) basal texture. Mechanical property test shows that all as-extruded alloys exhibit excellent strength and ductility which can fully meet the benchmark requirement for biodegradable materials. It is worth to notice that, Zn-2Cu-0.2Mn-0.38Li alloy has a tensile yield strength, ultimate tensile strength and elongation as high as 424 ± 28.3 MPa, 445 ± 11.1 MPa and 76 ± 3.35%, respectively. The 24-day in vitro immersion test in the SBF solution shows that the corrosion rates were 0.212 ± 0.007 mm/year for Zn-2Cu-0.2Mn, 0.197 ± 0.005 mm/year for Zn-2Cu-0.2Mn-0.1Li and 0.184 ± 0.008 mm/year for Zn-2Cu-0.2Mn-0.38Li, respectively. It indicates that addition of Li improves the corrosion resistance of the alloys. All as-extruded alloys have antibacterial rates of ≥ 99% and hemolysis rates of< 5%, exhibiting strong antibacterial activity and good hemocompatibility. The MC3T3-E1 cells show more than 95% viability in 25% extracts of all as-extruded alloys in all culturing days. In addition, in this low concentration of extracts, the cells in the alloy groups exhibit good spreading morphology and high ALP expression, suggesting good cytocompatibility. • Alloy with 0.38%Li has tensile strength of 445 ± 11.1 MPa & elongation of 76 ± 3.35%. • All alloys exhibit antibacterial rates of ≥ 99% & hemolysis rates of< 5%. • Cell show over 95% viability & good spreading morphology in 25% extract. • Cell show high ALP expression in 25% extract & Li boost osteoblast differentiation.