Covalent grafting of gelatin/ZnO onto an alkali-activated polymer scaffold via EDC/NHS chemistry: a dual-functional interface for anti-infective bone regeneration.

Infected bone defects demand biomaterials that reconcile potent antibacterial activity with osteogenic capacity-a challenge that originates from the inert surface chemistry of polyester scaffolds. Here, we present a covalent interface engineering strategy to transform a 3D-printed nano-hydroxyapatite/polylactic acid/polycaprolactone (n-HA/PLA/PCL) scaffold into a dual-functional platform. Building on our previously reported osteogenic scaffold, we introduce antibacterial functionality via EDC/NHS-mediated grafting of a gelatin/nano-zinc oxide (Gel/n-ZnO) composite onto an alkali-activated scaffold surface. This covalent approach creates robust amide bonds that ensure stable, long-term immobilization of the antibacterial component, addressing the instability issues inherent to physical adsorption or blending, while the alkali activation and grafting steps preserve scaffold porosity and mechanical integrity, with the resulting scaffold (ZP-S) exhibiting controlled degradation behavior. ZP-S achieves 89.7% inhibition against methicillin-resistant Staphylococcus aureus through a dual mechanism of sustained Zn2+ release and direct contact-mediated membrane damage. Zn2+ release is pH-responsive, accelerating in acidic infectious microenvironments. Notably, no reactive oxygen species generation is detected under physiologically relevant dark conditions, confirming a light-independent antibacterial mechanism suitable for in vivo implantation. ZP-S exhibits excellent cytocompatibility, promoting MC3T3 cell adhesion, proliferation, alkaline phosphatase activity, and matrix mineralization in vitro. In a rat MRSA-infected tibial defect model, ZP-S reduces bacterial load by 87.1%, mitigates inflammation, and achieves functional cortical bone reconstruction with medullary cavity recanalization. This work demonstrates that EDC/NHS-mediated covalent grafting offers a viable chemical route to convert an osteogenic scaffold into an integrated antibacterial-osteogenic platform, providing a single-stage strategy for infected bone defect repair.