Degradation-tunable coating with sustained silver release for spinal implants to prevent postoperative infections

Irreducible atlantoaxial dislocation is a challenging condition for spine surgeons and carries a particularly high risk of postoperative infection due to its trans-oral approach for peri-odontoid soft tissue release. Conventional antibacterial implant coatings are limited by rapid burst release, leading to short-term efficacy and potential cytotoxicity. To address this, we developed a composite coating of silver nanoparticle-decorated ZIF-8 (AgZ) within a tunable methacrylate gelatin (GelMA) and silk fibroin (SF) matrix (AgZ/GelSF) for 3D-printed Ti-6Al-4V fusion cages. The AgZ nanocomposite enhanced silver dispersibility and potency, reducing the minimum bactericidal concentration against MRSA and E. coli by over 4-fold and 13-fold, respectively. By adjusting the GelMA-to-SF mass ratio, we finely tuned the degradation rate and silver release profile, ensuring a sustained release over 28 days, which aligns with the typical wound healing timeline. RNA sequencing indicated the coating's mechanism involves bacterial membrane disruption and metabolic interference, preventing biofilm formation. Optimization of the coating components demonstrated excellent biocompatibility and osteogenic performance both in vitro and in a rabbit femoral defect model. In a bacteria-contaminated porcine model for atlantoaxial fixation and intra-articular fusion, the AgZ/GelSF-coated implant effectively eliminated bacterial infection and supported successful bone fusion, all while showing no systemic toxicity. Compared with previous studies, this work demonstrates significant advantages in antibacterial efficiency, drug release duration and evaluation models. These findings suggest that the AgZ/GelSF composite coating is a promising strategy for preventing implant-associated infections through a degradation-controlled drug release platform.