Photosensitive PLA-cationic porphyrin films: robust antibacterial materials for fighting multidrug-resistant bacteria

The global rise of multidrug-resistant (MDR) bacteria highlights the urgent need for alternative strategies to prevent their spread, particularly in healthcare environments. Here, we report the synthesis and evaluation of a novel mono-cationic <i>meso</i>-imidazolyl porphyrin (3) and its integration into biodegradable poly(lactic acid) (PLA) films, resulting in potentially effective, reusable, and broad-spectrum photodynamic antibacterial surfaces. The porphyrin was prepared using a mixed aldehyde condensation followed by microwave-assisted methylation, reducing reaction time to just 1 minute with near-quantitative yield. PLA films containing porphyrin 3 (+PLA-3) were successfully prepared and fully characterized, showing exceptional photostability and minimal leaching in aqueous environments, even under prolonged light exposure. Notably, cationic +PLA-3 exhibited superior material stability compared to analogous PLA films incorporating tetra-cationic porphyrins, attributed to the improved amphiphilic balance of the mono-cationic photosensitizer. Antibacterial studies confirmed that cationic +PLA-3 films achieved complete photodynamic inactivation (7 log CFU reduction) of both Gram-positive (<i>Staphylococcus aureus</i>) and Gram-negative (<i>Escherichia coli</i>) bacteria under blue LED irradiation. They also demonstrated great effectiveness against clinical multidrug-resistant strains, including MRSA, <i>E. coli</i>, <i>Acinetobacter baumannii</i>, <i>Pseudomonas aeruginosa</i>, and <i>Klebsiella pneumoniae</i>, reaching total inactivation under light doses up to 23.5 J cm^-2. Reusability tests confirmed full retention of antibacterial efficacy after up to 11 irradiation cycles, totalling 258.5 J cm^-2. These results position cationic +PLA-3 as a promising candidate for use in self-disinfecting surfaces with potential to reduce nosocomial infection risks and environmental impact in healthcare settings.