Bioactive Multilayer Poly(ε-caprolactone)–Chitosan Coatings for Spinal Screws

Spinal surgery involves highly complex procedures where the risk of severe complications, including postoperative infections, may compromise both surgical success and patient survival. In this study, functional coatings for spinal screws were developed to promote bone integration and simultaneously prevent infection. The coating design employed a multilayer architecture based on poly(ε-caprolactone) (PCL) as the main structural layer, covered with chitosan (CS), a biocompatible polymer that enhances surface interaction with both the metallic substrate and the active agents. To stimulate bone regeneration, calcium β-hydroxy-β-methylbutyrate (HMB) was incorporated, while antimicrobial efficacy was achieved by embedding PLGA-based polymeric microspheres encapsulating gentamicin sulfate, a broad-spectrum antibiotic. The obtained results confirmed the successful integration of all components, as evidenced by FTIR and Raman spectroscopy, along with homogeneous surface morphologies observed via SEM analysis. Biological assays demonstrated significant antimicrobial activity against Staphylococcus aureus and Escherichia coli. The developed coatings therefore exhibit strong potential as bioactive, dual-functional protective layers for spinal screws, providing both osteoconductive and antimicrobial properties.