ABSTRACT
Hydrogels are water-swollen networks of hydrophilic homopolymers or copolymers. They are three-dimensional and the cross-links can be formed by covalent or ionic bonds. Often, weaker forces such as van der Waals forces and hydrogen bonds can serve as cross-links, thus forming swollen networks which behave as hydrogels. Hydrogels may be classified in various ways depending on their chemical or physical structure. Typical hydrophilic monomers used in the preparation of biocompatible hydrogels. A. S. Hoffman and Y. Ikada et al. discuss various radiative methods of preparation of hydrogels and point out the advantages of the techniques, which include lack of impurities such as unreacted monomers, cross-linking agents, and emulsifiers. Polymers either cross-link or degrade according to their chemical structure. A number of theories have been advanced in order to account for the fact that some polymers cross-link, while others degrade. It seems that large side groups in a long linear chain lead to degradation.
