ABSTRACT
A hydrophilic three-dimensional cross-linked network swollen with water is referred to as a hydrogel. Hydrogels can also be classified on the basis of the physical structure and the chemical nature. Hydrogels can also be classified based on the presence or absence of the electrical charge localized on the cross-linked chains. Depending upon the polymerization technique involved, hydrogels can be categorized as matrix, microsphere, or films. Hydrogels are of two types based on their origins in natural or synthetic polymer. Synthetic hydrogels have a long life, high gel strength, and, of course, the capacity for a large amount of water absorption as compared to natural hydrogels. Synthetic hydrogels can be integrated with biological entities to create bioresponsive hydrogels. For many applications, the molecular recognition properties of hydrogels can be controlled via various biological analytes and physiological processes. The applicability of hydrogels as biomedical materials and their performances in the biomedical field rely to a large extent on their bulk structure.
