Chapter 4 - Preparation of hydrogels based on natural polymers via chemical reaction and cross-Linking

Abstract

Hydrogels are cross-linked networks of water-soluble polymers which have a tendency to swell under physiological conditions. Their rubbery consistency and high water content make them an ideal material for biomedical and pharmaceutical applications. Hydrogels made from natural polymers such as cellulose, sodium alginate, chitosan, dextran, gelatin, hyaluronic acid, and albumin possess inherent biocompatibility, biodegradability, and support cellular activities. Natural polymer-based hydrogels can be prepared using physical, chemical, or radiation cross-linking. The physically cross-linked hydrogels exhibit poor gel strength. Chemical cross-links can help to improve the stability of the network structure of the hydrogels. Chemical cross-linking amongst the natural polymers can be achieved by targeting the complementary groups present on two adjacent polymer chains. The most common reactions involved in the cross-linking of natural polymers include Schiff base reaction, epoxide coupling, addition reaction, click reaction, condensation reaction, and free radical polymerization. In this chapter, all the conventional and novel chemical cross-linking methods used for the preparation of natural polymer-based hydrogels are discussed.