Photoactive Hydrogels as Materials for Biological Applications Such as Antimicrobial Patches: Preparation of Thermally Stable Photoactive Films

Hydrogel materials have emerged as an efficient, bioactive, and multifunctional alternative with significant potential for biomedical applications. This work aims to provide a valuable contribution to the design and implementation of stimulus-response films for optical processing and subsequently evaluate the usefulness of the photoactivity of the hydrogel films in photodynamic therapy (PDT) as antimicrobial patches. The design of stimulus-response polymeric hydrogel films is based on a hydrophilic polymer using vinyl monomers, 2-hydroxyethyl methacrylate (HEMA) and acrylamide (AAm) in molar ratios of 1:1 and the photochromic agent 3,3-dimethylindolin-6’-nitrobenzoespiropirano (BSP) for biological applications. The hydrogel films were prepared using the photoinitiator 2-hydroxy-4’-(2-hydroxyethoxy)-2-methylpropiophenone in the presence of a crosslinking agent, N, N’-methylene bisacryl amide (MBA) and BSP as a photoactive agent at different concentrations (0.1, 0.3, and 0.5 mol.%) to generate photoactive hydrogel films, which were subsequently used in biological photodynamic therapy (PDT). The PDT for Staphylococcus aureus using Ru(bpy) requires concentrations between 4 and 8 µg/mL to fully eliminate methicillin-sensitive strains (MSSA), while only partial inactivation is achieved for methicillin-resistant strains (MRSA). However, the incorporation of Ru(bpy) into a photoactive polymeric film containing the BSP significantly enhances its antimicrobial efficacy, reducing the minimum inhibitory concentration (MIC) to just 2 µg/mL for the complete inactivation of both strains. The new synergistic effect of BSP and Ru(bpy) confirm that these materials hold promise as next-generation antimicrobial coatings and innovative, light-sensitive materials.