ABSTRACT
Hydrogels are classified in several ways (Table 1). The most simple classification is hydrogels obtained from natural products and hydrogels made of synthetic materials. Peppas classified hydrogels in three ways: method of preparation, ionic charge, and physical structure features (5). Based on the method of preparation, hydrogels are classified further into four groups: homopolymer hydrogels, copolymer hydrogels, multipolymer hydrogels, and interpenetrating polymeric hydrogels. Based on ionic charges, hydrogels are classified as neutral, cationic, anionic, or ampholytic hydrogels. Based on physical structural features, they are classified as amorphous hydrogels, semicrystalline hydrogels, or hydrogen-bonded structures.
