A high-performance, biodegradable Zn-3Cu-0.8Sr alloy with superior strength, biotribology, osteogenesis, and antibacterial activity for orthopedic fixation through deep-cryogenic rolling.

Abstract

Biodegradable Zn alloys have attracted considerable attention as candidates for load-bearing bone-fixation implants, yet simultaneously optimizing mechanical strength, corrosion-wear resistance, and multifunctional biofunctionalities remains challenging. Herein, a Zn-3Cu-0.8Sr (ZCS) alloy was successfully fabricated by a synergistic processing route that integrated hot rolling (HR) with deep-cryogenic rolling (DCR). The HR+DCR processing effectively refined coarse and brittle SrZn₁₃ and primary ε-CuZn₅ phases into uniformly dispersed, well-bonded fine reinforcements, while simultaneously promoting grain coarsening and precipitate growth by suppressing dynamic recovery and restricting atomic diffusion at cryogenic temperatures. This microstructural engineering strategy produced an optimal combination of mechanical properties, including an ultimate tensile strength (σ_uts) of ∼301.7 MPa, a yield strength of ∼245.0 MPa, an elongation at break (ε) of ∼33.5%, the lowest σ_uts loss of 12.5% and ε loss of 6.6% after 30 d of immersion in Hanks' Balanced Salt Solution, and the highest biotribological resistance among all thermomechanically processed specimens. The HR+DCR processed specimen exhibited the lowest electrochemical corrosion rate of ∼162 µm/y and degradation rate of ∼20.1 µm/y in Dulbecco's Modified Eagle Medium with fetal bovine serum among all thermomechanically processed specimens. Notably, the alloy displayed enhanced osteoblast viability, osteogenic differentiation and mineralization, and near-complete antibacterial activity against Staphylococcus aureus in both in vitro and in vivo settings. Moreover, the alloy effectively modulated the immune response, driving macrophage polarization toward a pro-healing M2 phenotype. Overall, the alloy combines high mechanical, biotribological, degradation, osteogenic, antibacterial, and immunomodulatory biofunctions, underscoring its potential for next-generation biodegradable orthopedic-fixation devices. STATEMENT OF SIGNIFICANCE: This work reports a multifunctional Zn-3Cu-0.8Sr alloy fabricated using a synergistic hot rolling and deep-cryogenic rolling process for next-generation orthopedic applications. The alloy exhibits exceptional mechanical properties: σ_UTS of ∼301.7 MPa, σ_YS of ∼245.0 MPa, and ε of ∼33.5%, with minimal strength/ductility loss after 30-day immersion in Hanks' Balanced Salt Solution (HBSS). It demonstrates a favorable electrochemical corrosion rate (∼162 µm/y), degradation rate (∼20.1 µm/y), and superior biotribological resistance in Dulbecco's Modified Eagle Medium supplemented with fetal bovine serum (DMEM+FBS). Biologically, it enhances osteoblast viability and mineralization while providing near-complete S. aureus antibacterial efficacy in vitro and in vivo. This synergistic combination of strength, corrosion-wear resistance, and bioactivity highlights the alloy's significant potential for advanced biodegradable orthopedic applications.