Hasan BASAN*, Dilek IMREN**, Menemse GÜMÜŞDERELİOĞLU**°

*Gazi University, Faculty of Pharmacy, Department of Analitical Chemistry, 06330, Ankara, TURKEY.**Hacettepe Üniversitesi, Kimya Mühendisligi Bölümü, Beytepe, Ankara, TÜRKIYE. Pages, 81-92
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° Correspondence

Summary:
Hypogels are defined as three-dimensional polymeric networks containing a considerable amount of water, e.g., more than 20%. Enviromentally-sensitive hydrogels exhibit dramatic changes in their swelling behavior, network structure, permeability or mechanical strength in response to changes in the pH or ionic strength of the surrounding fluid, or temperature. Hydrogelsexhibiting pH-dependent swelling behavior can be swollen from ionic networks. These ionic networks contain either acidic or basic pendant groups. pH-sensitive swelling can be exploited in the development of drug delivery systems, which would release the drug in response to the pH of the surrounding solution. pH-sensitive hydrogels have a potential use in the site-specific delivery of drugs to spesific regions of the gastrointestinal (GI) tract due to pH variations througout the GI tract, and for more complex systems where a physiological stimuli results in a change in pH and release of drug.

Key words:
pH-sensitive hydrogels, drug delivery, site-spesific drug delivery, GI tract