The physical and chemical properties of hydrogels based on natural polymers

Hydrogels are three-dimensional networks which are highly swellable. Natural polymers are interesting compounds due to their excellent biocompatibility, biodegradability, and nontoxicity. Biopolymers can be extracted from different natural sources, where the isolation method and procedure influence their properties. Hydrogels can be obtained from natural polymers by chemical reactions and physical interactions. Proteins and polysaccharides have been proposed for hydrogel preparation, however, the material properties depend on the polymer type and its characteristics. It is important to detect the hydrogel properties, such as mechanical parameters, swelling behavior, thermal stability, and degradation rate. Also, the biological response on materials has to be studied for biomedical purposes. In this review hydrogel properties based on polysaccharides including chitosan, alginate, carrageenan, hyaluronic acid, starch, and cellulose are discussed, and proteins including silk, keratin, and collagen, are discussed.