ABSTRACT
The widespread application of hydrogels is linked to their unique property of exhibi ting an intermediate behavior between solid and liquid materials. The physicochemical, mechanical, and biological properties, as well as new functional properties, can be easily modulated. For example, hydrogels can be made to respond to environmental stimuli, such as temperature, pH, light, and specific molecules. Hydrogels can be prepared from both natural and synthetic materials. Natural polymers, such as proteins, polysaccharides and deoxyribonucleic acids, can be cross-linked to form hydrogels. Hydrogels with interconnected pores provide unique properties of fast-swelling kinetics and high swelling ratios. Porous hydrogels can be prepared by a variety of methods, such as the porosigen technique, phase separation technique, cross-linking of individual hydrogel particles and gas-blowing technique. Chemical hydrogels can also be prepared by cross-linking water-soluble polymers using chemical reactions that involve functional groups of the polymers. Functional groups for cross-linking reactions include vinyl, hydroxyl, amine, and carboxyl groups.
