A metal-semimetal Zn–Ge alloy with modified biodegradation behavior and enhanced osteogenic activity mediated by eutectic Ge phases-induced microgalvanic cells

Implants with strong osteogenic properties are crucial for effective bone repair in clinical settings. Recently, biodegradable zinc (Zn)-based metals have shown significant potential as orthopedic implants. However, pure Zn is prone to pitting corrosion and exhibits insufficient osteogenic activity in vivo. To enhance the degradation behavior and osteogenic potential of Zn-based implants, this study developed metal-semimetal Zn–Ge alloys with varying Ge content. The addition of Ge significantly promotes the formation of eutectic Ge phases, refines the microstructure, and improves the mechanical properties of the implants. Incorporating ∼3 wt% Ge into the matrix also facilitates enhanced Zn²⁺ release and ensures uniform biodegradation. Besides, the formation of uniformly distributed heteroid Zn–Ge microgalvanic cells provides a balance between osteogenic and bacteriostatic effects. In vivo tests using a femoral condyle defect model demonstrate that Zn–3Ge implants have favorable osteogenic property and excellent biosafety; the enhanced osteogenic activity of the alloy is attributed to intracellular Zn²⁺ activation of the Wnt signaling pathway, which promotes osteoblast differentiation, cell proliferation, survival, as well as extracellular matrix mineralization and osteogenesis. The incorporation of eutectic Ge phases and effective creation of microgalvanic cells offer a promising strategy for optimizing the biological function of Zn-based implants.