Microstructure, mechanical properties, biocompatibility, and in vitro corrosion and degradation behavior of a new Zn-5Ge alloy for biodegradable implant materials.

Zinc (Zn)-based alloys are considered a new class of biodegradable implant materials due to their superior chemical stability and processability compared to biodegradable magnesium (Mg) alloys. In this study, we report a new biodegradable Zn-5Ge alloy with highly desirable mechanical, corrosion, and biological properties. Microstructural characterization revealed the effective grain-refining effect of germanium (Ge) on the Zn alloy. Tensile test results indicated that the hot-rolled Zn-5Ge alloy showed an ultimate tensile strength of 237.0 MPa, a yield strength of 175.1 MPa, and an elongation of 21.6%; while as-cast pure Zn showed an ultimate tensile strength of 33.6 MPa, a yield strength of 29.3 MPa, and an elongation of 1.2%. The corrosion rates measured by potentiodynamic polarization tests in Hank's solution in ascending order are: as-cast Zn-5Ge (0.1272 mm/y) < as-cast pure Zn (0.1567 mm/y) < hot-rolled Zn-5Ge (0.2255 mm/y) < hot-rolled pure Zn (0.3057 mm/y). Immersion tests revealed that the degradation rate of as-cast Zn-5Ge is 0.042 mm/y, less than half of that of hot-rolled pure Zn and ∼62% of that of as-cast pure Zn. Moreover, the Zn-5Ge alloy showed excellent in vitro hemocompatibility and the addition of 5% Ge effectively enhanced the hemocompatibility of pure Zn. CCK-8 assay using murine preosteoblast MC3T3-E1 cells indicated that the diluted extracts at a concentration <12.5% of both the as-cast Zn-5Ge alloy and pure Zn showed grade 0 cytotoxicity; the diluted extracts at the concentrations of 50% and 25% of Zn-5Ge alloy showed a significantly higher cell viability than those of pure Zn. STATEMENT OF SIGNIFICANCE: Zinc (Zn)-based alloys are currently considered a new class of biodegradable implant materials due to their excellent processability. Here, we report a novel Zn-5Ge alloy with highly desirable mechanical, corrosion and biological properties. The tensile test results indicated that the hot-rolled Zn-5Ge alloy showed an ultimate tensile strength of 237.0 MPa, a yield strength of 175.1 MPa and an elongation of 21.6%; while as-cast pure Zn showed an ultimate tensile strength of 33.6 MPa, a yield strength of 29.3 MPa and an elongation of 1.2%. The corrosion rate measured by potentiodynamic polarization tests in Hank's solution in the ascending order is: as-cast Zn-5Ge (0.1272 mm/y) < as-cast pure Zn (0.1567 mm/y) < hot-rolled Zn-5Ge (0.2255 mm/y) < hot-rolled pure Zn (0.3057 mm/y). Immersion tests revealed that the degradation rate of the as-cast Zn-5Ge is 0.042 mm/y, less than half of that of the hot-rolled pure Zn, ∼62% of that of as-cast pure Zn. Moreover, the Zn-5Ge alloy showed excellent in vitro biocompatibility.