ABSTRACT
Hydrogels are polymer networks that contain a substantial amount of water. Dry polymer networks can absorb tens, hundreds, or even thousands of times their weight in water without dissolving, as illustrated in Figure 14.1. As a result, hydrogels have properties that are very similar to those of soft biological tissues such as cornea, cartilage, and intercellular matrix, and because of these characteristics, they are of great utility in pharmacy and in other biomedical elds. First, they are soft and slippery and have a very low interfacial tension when they are in contact with tissues. As a result, they often cause little irritation. Second, hydrogels can behave both like solids and like liquids. Like solids, they are elastic and return to their original shape after they are momentarily deformed. Like liquids, they permit diffusion of small molecules such as salts, metabolites, and drugs. Under proper circumstances, they also allow larger molecules such as proteins and nucleic acids to diffuse.
