“…While retaining the properties, such as nontoxicity, pH-responsive, hydrophilicity, and biodegradability, of the individual original polymers, e.g., chitosan and hyaluronic acid, the chemical, physical, and other functional properties of the hydrogel are different [ 70 , 71 ]. Moreover, polyelectrolyte complexes, such as chondroitin sulfate [ 72 ], carrageenan [ 73 , 74 , 75 ], and carboxymethyl cellulose [ 76 , 77 ], or other water-soluble nonionic polymers, such as polyvinyl alcohol (PVA) [ 78 , 79 , 80 ], can also form polymeric bonds with chitosan, resulting in the hydrogel. By amide bond crosslinking between the carboxylated PVA and chitosan, as well as coordination crosslinking between chitosan and Fe 3+ , mechanical, adhesive, and self-healing properties of the hydrogel can be enhanced [ 81 ].…”