Optimizing strength-ductility, biotribological, angiogenic, and antibacterial properties of hot-rolled and hot-extruded Zn-4Ag-0.4Sr alloys for biodegradable orthopedic fixation.

Abstract

Biodegradable zinc (Zn) alloys are promising candidates for bone implants due to their suitable degradation rate and inherent bioactivity. However, current Zn alloys require enhancement of their mechanical properties and biological functions through alloying and thermomechanical processing. Herein, we report the outstanding mechanical properties, corrosion, biocompatibility, and biofunctionalities of hot-rolled (HR) and hot-extruded (HE) Zn-4Ag-0.4Sr (ZAS) alloy in comparison with those of Zn-4Ag (ZA) for biodegradable orthopedic fixation. The HE ZAS sample exhibited the optimal balance of mechanical properties, including ultimate tensile strength of 318.0 MPa, tensile and compressive yield strengths of 257.3 MPa and 343.3 MPa, respectively, elongation at break of 22.3%, and Vickers and Brinell hardness values of 116.7 HV and 105.7 HB, respectively, satisfying the mechanical requirements for bone-implant applications. Nanoindentation identified the SrZn₁₃ phase as a key reinforcement. The HE ZAS alloy exhibited the highest electrochemical corrosion rate of 614 μm/y and the highest degradation rate of 39.7 μm/y after 30 days of immersion, as well as the best biotribological performance in Hanks' solution, among all ZA and ZAS samples. Biologically, extracts of the HE ZAS alloy enhanced osteoblast viability, promoted angiogenesis in HUVECs, and stimulated osteogenic differentiation and mineralization in hBMSCs. Furthermore, the HE ZAS alloy displayed higher antibacterial efficacy against S. aureus in both in vitro and in vivo models while maintaining high biosafety. These results collectively indicate that the HE ZAS alloy is a promising candidate for next-generation biodegradable orthopedic-fixation devices, offering a notable balance of mechanical integrity, controllable degradation, and multifunctional bioactivity. STATEMENT OF SIGNIFICANCE: This work reports the notable mechanical performance, controlled corrosion, enhanced biotribological behavior, and multifunctional bioactivity of the hot-extruded Zn-4Ag-0.4Sr (HE ZAS) alloy for biodegradable orthopedic fixation devices. The HE ZAS alloy exhibits an optimal strength-ductility balance, with an ultimate tensile strength of 318.0 MPa, tensile yield strength of 257.3 MPa, and 22.3% elongation, satisfying the mechanical requirements for bone implants. The alloy also demonstrates the highest electrochemical corrosion rate (614 μm/y), degradation rate (39.7 μm/y), and biotribological performance among the tested alloys. Biologically, the alloy enhances osteoblast viability, stimulates angiogenesis and osteogenic differentiation, and exhibits effective antibacterial activity against Staphylococcus aureus both in vitro and in vivo, while maintaining complete biosafety.