ABSTRACT
Gels are cross-linked networks of polymers or the networks swollen with liquids. They are insoluble in any solvents.1 Gels are classified as hydrogels swollen in aqueous solvents, organogels swollen in organic solvents, and xerogels without solvents. Gels swollen in solvents have unique properties in that they show both liquid-like and solid-like behavior. Such swollen gels are interesting from the viewpoint of fundamental science and because they have various applications due to their unique properties. The term “gel” often means a gel swollen in solvents and does not include xerogels. Most gels used for biological applications are hydrogels swollen in water or physiological solutions, so this chapter focuses on hydrogels.
