Antimicrobial efficiency of pH-responsive PAA/PAH-coated and flucloxacillin loaded titanium implants in the Galleria mellonella model.

Implant-associated infections are a leading cause of implant failure in orthopedics and dentistry, often necessitating revision surgery. These infections arise primarily from biofilm formation on implant surfaces, which shields pathogenic microorganisms from host immunity and systemic antibiotics. To address this issue, we used a pH-responsive poly(acrylic acid)/poly(allylamine hydrochloride) (PAA/PAH) coating applied to nanostructured titanium rods with controlled nanotube pore sizes and loaded with flucloxacillin (FCX) to address Staphylococcus aureus infections. The release behavior of FCX from the PAA/PAH coating was first evaluated in vitro under different pH conditions. Drug release and antibacterial efficacy were assessed using UV-Vis spectroscopy to detect released FCX, optical density measurements at 600 nm for bacterial growth inhibition monitoring, as well as bacterial viability assays. In vitro experiments revealed that FCX release increased markedly under acidic conditions, whereas minimal release was observed at neutral pH. The antibacterial efficacy of the FCX-loaded coating was subsequently evaluated in vivo using the Galleria mellonella implantation model as a biologically relevant and ethically acceptable platform. Treatment efficacy was quantified by a five-day survival analysis. Controlled nano-structuring of the titanium surface alone did not affect larval survival. In addition, the tolerability of FCX and the dose-dependent antimicrobial activity of FCX against S. aureus were assessed under planktonic conditions, followed by implantation of FCX-loaded, S. aureus colonized titanium rods. Overall, the FCX-loaded PAA/PAH coating was associated with improved larval survival under both experimental conditions, highlighting its potential as a localized antimicrobial strategy for implantable medical devices.