Substrate-Independent Antibacterial Coatings with Optimal Concentration of Covalently Immobilised Silver Nanoparticles That Support Osteogenesis

Medical device-associated infections remain a major clinical challenge, frequently leading to implant failure, patient morbidity and mortality, and high healthcare costs. Equally critical is effective device osteointegration, which is often compromised in environments prone to infection. Here, we present a multifunctional, substrate-independent surface coating that simultaneously imparts robust antibacterial activity and promotes osteogenesis through modulation of inflammation. A thin plasma polymer layer derived from 2-methyl-2-oxazoline was deposited on material substrates to facilitate covalent binding of controlled concentrations of silver nanoparticles (AgNPs), functionalized with 2-mercaptosuccinic acid using oxazoline ring-opening chemistry. The coatings exhibited potent antibacterial effects against both Gram-positive and Gram-negative pathogens, including Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa, while maintaining cytocompatibility with human cells. Mechanistic studies revealed that the AgNPs functionalized surfaces exhibited a concentration-dependent modulation of inflammatory cytokine and osteoclastogenic markers expression in macrophages, while promoting osteogenic signalling in co-cultured human bone marrow stromal cells. Coatings having immobilized AgNP at a concentration of 9 At% achieved an optimal balance between antibacterial efficacy and osteoimmunomodulation. This study demonstrates that finely tuning the AgNPs surface concentration can deliver a bioactive coating platform with dual antibacterial and osteogenic functionality, offering promising translational potential for a wide range of medical implants where osteointegration is vital, such as in orthopaedics and dentistry.