Hydrogels are one of the upcoming classes of polymer-based controlled-release drug
delivery systems. Besides exhibiting swelling-controlled drug release, hydrogels also
show stimuli-responsive changes in their structural network and hence, the drug release.
Because of large variations in physiological pH at various body sites in normal as
well as pathological conditions, pH-responsive polymeric networks have been extensively
studied. This review highlights the use of hydrogels (a class of polymeric systems)
in controlled drug delivery, and their application in stimuli-responsive, especially
pH-responsive, drug release.