Photoactive Polyurethane Nanocomposites with Phloxine B‑Functionalized Poly(diallyldimethylammonium)-Saponite for Staphylococcus aureus Biofilm Inactivation.

Surface modification is an effective strategy to combat microbial colonization by inhibiting growth or directly inactivating bacteria. In this study, polyurethane (PU)-based nanocomposites (NCs) incorporating saponite nanoparticles modified with poly-(diallyldimethylammonium chloride) (PDDA) and functionalized with the photosensitizer phloxine B (PhB) were developed. NCs were developed as thin films fused onto the bulk PU. They were characterized for their physicochemical properties and anti-biofilm activity against Staphylococcus aureus. PDDA modification enabled efficient binding of anionic PhB, resulting in high loading capacity while preserving photoactivity. The NC exhibited diffusion-controlled release of PhB, with rapid release in the first few h, and approximately 18% of the total PhB was released from the NC. Biological assays showed that NCs with PhB loading higher than 0.2 mmol g-1 achieved more than a 2 log10 reduction of S. aureus biofilm cells after irradiation with a green laser, including methicillin-resistant strains. Formation of reactive oxygen species was identified as the anti-biofilm mechanism, with significant increases (more than 10-fold) observed only after laser irradiation. Gene expression analysis showed minimal activation of oxidative stress response genes (sodA, sodM, katA, and ahpC), with no significant differences between irradiated and non-irradiated samples, except for slight sodA activity in the standard strain and one MRSA strain. This suggests that the treatment effect was strong enough to impair bacterial adaptive responses. Overall, the results indicate that photoactive PU-based NCs functionalized with PhB represent a promising platform for effective photodynamic inactivation of bacterial biofilms.