Development of functional films for enhanced photodynamic therapy against resistant S. aureus

Abstract

The treatment of wounds infected with multidrug-resistant bacteria, particularly methicillin-resistant Staphylococcus aureus (MRSA), remains a significant therapeutic challenge. In this work, we developed and characterized polymeric films based on type B gelatin crosslinked with 5% w/v polyvinylpyrrolidone (PVP) and 5% w/v cerium nitrate, incorporating zinc(II) phthalocyanine (ZnPc, 20 μM final concentration) as a photosensitizer for antimicrobial photodynamic therapy (aPDT). Glycerol (50% w/w with respect to gelatin) was included as a plasticizer in selected formulations. UV-vis spectroscopy and confocal fluorescence microscopy confirmed the incorporation and homogeneous distribution of ZnPc within the films. The films exhibited suitable mechanical and barrier properties, with modulated swelling, permeability, and bioadhesiveness depending on the composition. In vitro assays demonstrated that ZnPc-loaded films achieved significantly higher photoinactivation of MRSA compared to free ZnPc in solution, reaching up to 2.3 log CFU per mL reduction after 30 minutes of irradiation. These findings support the potential of ZnPc-containing gelatin–PVP films as effective and accessible topical systems for treating antibiotic-resistant skin infections through aPDT.