Injectable photosensitizing supramolecular hydrogels: A robust physically cross-linked system based on polyvinyl alcohol/chitosan/tannic acid with self-healing and antioxidant properties

The development of injectable and photosensitizing supramolecular hydrogels has proved to be a challenging and interesting task. In this study, N, N′-di-(L-alanine)-3,4,9,10-perylene tetracarboxylic diimide (PDI-Ala), as a photosensitizing agent, was incorporated into single (PVA-CS-PDI/TA) and double cross-linked (PVA-CS-PDI/TA/Fe (III)) hydrogels formed by poly (vinyl alcohol) (PVA), chitosan (CS), and tannic acid (TA) through a freeze-thawing method based on non-covalent interaction (hydrogen bonding and metal coordination). TA molecules act as cross-linkers to connect polymer chains through multiple hydrogen bonds and cross-link them using coordinate bonds in the presence of Fe (III) ions. The double cross-linked hydrogels had a higher singlet oxygen quantum yield than single cross-linked hydrogels under 660 nm laser irradiation, indicating those that could be more efficient in photodynamic therapy (PDT). Supramolecular hydrogels with interconnected porous morphologies exhibited mechanical strength, injectability, self-healing and shear-thinning capabilities, antioxidant and antibacterial properties. Additionally, the supramolecular photosensitizing hydrogels showed excellent biocompatibility without showing evident cytotoxicity and hemolysis in vitro. This study presents a straightforward and cost-effective approach to prepare multifunctional physical cross-linking supramolecular hydrogels, appropriate for large-scale preparation, which shows great potential in biomedical applications such as PDT and wound dressings.