The evaluation of a gelatin-based soft pad for photodynamic therapy application with controlled release of methylene blue

Hydrogels with antimicrobial photodynamic therapy properties show considerable promise for applications such as skin infection management and chronic wound healing. To ensure biocompatibility and functionality, hydrogels must be derived from natural materials that mimic the properties of skin. In this study, a gelatin-based hydrogel was synthesized using a one-pot method, incorporating glutaraldehyde as a crosslinking agent and methylene blue as a photosensitizer. The influence of glutaraldehyde and methylene blue on the hydrogel's physicochemical properties, mechanical behaviour, swelling capacity, and enzymatic activity was systematically evaluated. The mechanical properties, including elongation at yield, ultimate tensile strength, and Young’s modulus, were measured, revealing a strong dependence on the synthesis parameters. The swelling ratio of the hydrogels demonstrated significant variation; the gelatin hydrogel exhibited a decrease from 361.8% to 298.1%, while the addition of methylene blue increased swelling from 436.8% to 325.3%. To assess enzymatic degradation, trypsin was selected as the proteolytic enzyme. Results indicated that methylene blue-modified hydrogels underwent enzymatic hydrolysis at twice the rate of unmodified hydrogels. Furthermore, the controlled release of methylene blue was analyzed, showing a decrease in concentration from 0.51 mg/g to 0.32 mg/g over time.