ABSTRACT
Hydrogels are physically or chemically cross-linked polymer networks swollen with large amounts of water. Due to their crosslinked nature, these gels do not dissolve in aqueous media but contain an enormous amount of solvated water molecules within the entangled polymer chain matrix. Hydrogel properties are reviewed elsewhere in this book. This chapter is dedicated to a unique hydrogel family that responds to
externally applied stimuli that, in turn, alter these hydrogels’ swelling properties. During the past two decades, much work has been dedicated to the development of stimuli-responsive hydrogel materials. These ‘‘intelligent materials’’ sense external stimuli, alter (depending on the degree or strength of stimulation) their physicochemical network properties, and release drug molecules or absorb water or both to reach an equilibrated state. Such auto-feedback systems are commonly observed in metabolic processes in the human body. Therefore, these intelligent materials are appropriately applied to the development of new drug delivery matrices responding to several physiological stimuli arising from disease states or metabolic events in the human body. One key strategy for drug delivery systems is the spatio-temporal control of drug release responding to any changes in body physiology at specific sites (1,2).
