Development of a multifunctional and fully biobased hydrogel loaded with tannins for wound healing

Wound healing is a complex process critical for maintaining skin barrier function. Chronic and non-healing wounds subject the patient to significant discomfort and distress while burdening the healthcare system. Hydrogels are among the most promising materials as wound dressing systems capable of offering physical protection to the wound, maintaining the moist environment, and absorbing the wound exudate. However, beyond these properties, interest has grown in enriching hydrogels with multifunctional substances, with the aim of promoting skin regeneration through a wide range of properties, including antioxidant, UV-blocking, and antimicrobial effects. The present study aimed to develop a fully bio-based multifunctional hydrogel based on chitosan and containing tannins derived from the bark of chestnut trees. The first part of the study was dedicated to the identification of the conditions for obtaining a stable hydrogel. After a preliminary investigation on different solvents and crosslinking mechanisms, the solvent casting method at the optimized conditions was employed to prepare chitosan films at increasing amounts of tannins (0, 1, 5, and 10 wt%). The films were obtained in the form of rigid and dry systems that, once subjected to swelling in water (swelling degree up to 7000%), become soft and malleable materials with an elongation at break up to 80%, suitable for envisioning their easy application on the skin. Then, thanks to their well-known properties, the effect of the increasing amounts of tannins on the antioxidant and UV protection properties of the material was evaluated. All tannin-containing films showed 100% Radical Scavenging Activity within a few hours and effective absorption in the UV-A and UV-B wavelengths, without significantly compromising the material’s transparency. These outcomes suggest that tannins can add multifunctional properties to chitosan-based films, offering a new strategy for developing advanced wound healing hydrogels.