Magnesium-induced strengthening, degradation and osteogenesis for additively manufactured Zn-Mg orthopedic implants

Additively manufactured biodegradable metals demonstrate great potential in orthopedic implants, enabling patient-specific designs and eliminating the need for secondary surgeries through degradation. Zinc (Zn)-magnesium (Mg) alloys reconcile the dilemma between Zn's low biological activity and Mg's rapid degradation, and become promising bone-repair materials. However, Zn-Mg alloys currently fabricated via additive manufacturing exhibit high strength but low ductility, and the effects and mechanisms by which Mg influences their degradation and bone regeneration remain unclear. Here, Zn-xMg alloys (x = 0, 0.1, 0.2, 0.4, 1.0 wt%) are prepared using laser powder bed fusion (L-PBF). Adding Mg refines the microstructure and forms brittle secondary phases, improving strength but reducing ductility. Zn-0.4Mg shows superior balance, with an ultimate tensile strength of 289.40 MPa and elongation of 12.53 %. The addition of Mg slows degradation by forming protective Mg-containing products and accelerating the passivation. Furthermore, Mg alloying significantly enhances bone regeneration, as indicated by both in vitro and in vivo tests. This improvement is driven by the release of less Zn²⁺ and more Mg²⁺, which promotes cytocompatibility and osteogenic differentiation. This study offers critical insights for optimizing Zn-based biodegradable metals and advancing the development of next-generation orthopedic implants. STATEMENT OF SIGNIFICANCE: Laser powder bed fusion (L-PBF) enables the fabrication of customized implants. Zn-Mg alloys are among the most promising materials for bone repair. However, Zn-Mg alloys fabricated by l-PBF exhibit high strength but low ductility, while the effects and mechanisms of Mg alloying on degradation and osteogenesis remain unclear. This study first fabricated Zn-Mg bulk materials (0-1 wt% Mg) via l-PBF, clarifying their microstructure and degradation products. Mg enhanced mechanical strength, with Zn-0.4Mg achieving a balanced combination of strength and ductility. Mg slowed degradation by forming protective Mg-containing products and accelerating passivation, while promoting osteogenesis by releasing more Mg²⁺ and less Zn²⁺. These findings offer valuable insights for optimizing Zn-based metals and developing next-generation biodegradable implants.