Salt-mediated modulation of the mechanical properties and photothermal response of a chitosan/hyaluronic acid hydrogel.

A noncovalent chitosan (CS)/hyaluronic acid (HA) hydrogel characterized by favorable cytocompatibility, biodegradability and non-toxicity is reported. It bears a close resemblance to human skin and holds promising potential for application in medical engineering. Nevertheless, CS/HA hydrogels have not yet achieved widespread application due to their relatively weak mechanical properties. In this study, salts were utilized to regulate the mechanical properties of a CS/HA hydrogel. The results indicated that copper nitrate was the most effective regulator, as it transformed intramolecular hydrogen bonds into intermolecular hydrogen bonds and electrostatic interactions into cation chelations, respectively. The regular domains in the hydrogel were reduced, while the crosslinking was strengthened. Consequently, the toughness of the hydrogel was increased to 7.8 MJ m^-3, 1253-fold that of the covalent CS/HA hydrogel. The salt effect was replicated in another two hydrogels, attesting to its generality. Hence, salt regulation proves to be an effective way to enhance the mechanical properties of hydrogels. In addition, the copper nitrate-regulated hydrogel exhibited favorable drug delivery behavior and photothermal response. Under near-infrared light exposure, the release rate and release amount of the loaded drug from the hydrogel increased by 40% and 39%, respectively, within 20 minutes, demonstrating its significant potential as a drug carrier.