A Biodegradable Hydrogel based on Captisol®/Porphyrin Nanoassemblies for Antimicrobial Photodynamic Therapy

Current research focuses on developing advanced strategies for microbial control in wound treatment, aiming to effectively neutralize pathogens and overcome multidrug resistance (MDR). In the context of our investigation on phototherapy and photodiagnostics, we have designed "smart" nanoassemblies that encapsulate photosensitizers[1,2] (PS) for antimicrobial photodynamic therapy (aPDT). Here, we present the development of rapidly resorbable hydrogels based on DAC® (a copolymer of hyaluronic acid grafted with polylactic acid, HA-PLA) that incorporate a nanophotosensitizer (nanoPS) composed of a cyclodextrin/photosensitizer complex for controlling wound infections. Specifically, the nanocarrier Captisol® (sulfobutyl ether-beta-cyclodextrin) encapsulates the porphyrin 5,10,15,20-Tetrakis-(N-methyl-4-pyridyl)-porphine-Zn(II) tetratosylate (ZnTMPyP), rotecting it from photodegradation and enhancing the efficacy of antimicrobial photodynamic therapy. The CAPTISOL®/ ZnTMPyP complex was prepared by mixing the two precursors in ultrapure water with a molar ratio of CD/PS of 5:1, lyophilized, resuspended in water, and mixed with DAC® powder to obtain DAC® loaded with CAPTISOL®/ ZnTMPyP. To evaluate the efficacy of the hydrogel in local wound infection applications, DAC® loaded with CAPTISOL®/ ZnTMPyP was diluted to 0.3% w/v in DAC®, resulting in a nano-hydrogel characterized as an erosion product at the infection site. The interaction of pure ZnTMPyP and in the presence of cyclodextrin within the hydrogel was investigated using spectroscopic techniques such as UV/Vis absorption, steady-state and time-resolved fluorescence, and Dynamic Light Scattering (DLS). Additionally, the kinetic erosion profiles of DAC®/CAPTISOL®/porphyrin hydrogels were studied in biological media. The nanohydrogels exhibited significant photobactericidal activity against both Gram-positive and Gram-negative bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, vancomycin-resistant Enterococcus faecium (VREfm) DSM 17050, and VIM-2 producing Pseudomonas aeruginosa DSM102273. In vitro photoantimicrobial studies confirmed the aPDT efficacy of our photosensitizing hydrogels incorporating cyclodextrin/porphyrin complexes. These results highlight the potential of DAC® nano-hydrogels loaded with CAPTISOL®/ ZnTMPyP as effective delivery systems for treating wound infections, significantly contributing to the fight against drug-resistant infections.