DLP-printable GelMA-PVI-Zn hydrogels with high strength and osteoinductivity for critical-sized bone defect repair

Gelatin-based hydrogels are promising for bone tissue engineering due to their inherent biocompatibility and bioactivity, yet developing scaffolds that simultaneously achieve mechanical robustness, osteoinductivity, and structural precision remains a major challenge. Here, we report a high-strength GelMA-PVI-Zn hydrogel constructed through a double-crosslinked (DC) network of gelatin methacryloyl (GelMA), poly(1-vinylimidazole) (PVI), and Zinc ions. Dynamic PVI-Zn coordination bonds act as sacrificial interactions to dissipate energy, endowing the hydrogel with exceptional mechanical performance, including a tensile modulus of 11.72 ± 0.33 MPa (81.8-fold higher than single-network controls) and a fracture strength of 2.50 ± 0.12 MPa (44.0-fold increase). Importantly, the coordination network preserves the rapid photocrosslinking kinetics of GelMA, ensuring compatibility with digital light processing (DLP) 3D printing for the fabrication of complex, high-fidelity scaffolds. Moreover, sustained Zn²⁺ release from the network promoted stem cell osteogenic differentiation in vitro and markedly enhanced bone regeneration in vivo. This work presents a robust and versatile hydrogel platform that integrates high mechanical strength, osteoinductivity, and printability, offering strong translational potential for the treatment of critical-sized bone defects.