Degradable Magnesium Implants with Caerin 1.9-Polycaprolactone Coatings Provide Extended Antibacterial Resistance and Outstanding Biocompatibility

Implant-associated infections and foreign body responses remain major challenges in orthopedic and biomedical implant applications. In this study, we report a novel strategy to enhance the antibacterial and biocompatibility properties of magnesium (Mg) alloy implants by applying a biodegradable polycaprolactone (PCL) coating embedded with the host-defense peptide, caerin 1.9 (F3). Three Mg-based specimens, including pure Mg, cold-extruded AZ31, and fully annealed AZ31 (3A), were evaluated following PCL-F3 surface modification. The PCL-F3 coatings demonstrated sustained antibacterial efficacy both in vitro and in vivo, effectively inhibiting methicillin-resistant Staphylococcus aureus (MRSA) for up to 168 h. Among the groups, the 3A-PCL-F3 condition exhibited the most notable performance, with substantially enhanced corrosion resistance, reduced inflammatory responses, and no detectable toxicity to vital organs. In vivo proteomic and metabolomic analyses further revealed that the 3A-PCL-F3 implants promoted the expression of osteogenic markers and activated pathways related to bone mineralization and hemostasis, while avoiding prolonged inflammatory activation at 3 months post-implantation. Notably, histological and cytokine ELISA data confirmed favorable tissue responses, including suppressed IL-1β and IL-10 levels and signs of early immune activation that subsided over time. These findings indicate that PCL-F3-coated Mg alloys, particularly the 3A variant, represent a promising solution for biodegradable implants with dual antibacterial and regenerative functionality. This work lays the foundation for developing degradable Mg alloy biomaterials with enhanced biocompatibility and multifunction for clinical use.