Stimuli Sensitive Hydrogels in Drug Delivery Systems

Hydrogels are the 3 dimensional cross linked polymeric networks which absorb the water 10-20 times of its molecular weight. Hydrogels are sensitive to different environmental stimuli like pH, temperature, ion, electric signals, light, pressure, antigen specific, enzyme sensitive, and glucose levels. When the environment is get change they get swell, and swelling is the most important characteristics for release of drug through hydrogel devices, and release by either diffusion or swelling or chemically controlled. These stimuli sensitive hydrogel used in delivery of drug through various routs like oral, ophthalmic parenteral drug, nasal TDDS, and also in novel drug delivery like in nanoparticles. Now a day’s stimuli sensitive hydrogels are also used in administration of DNA. Most widely stimuli sensitive hydrogels used are pH and temperature sensitive hydrogels because in body wide pH range available so it is used for targeted drug delivery. Hydrogels that are responsive to specific molecules, such as glucose or antigens, can be used as biosensors as well as drug delivery systems. INTRODUCTION: Hydrogels are a network of hydrophilic polymers that can swell in water and hold a large amount of water while maintaining the structure . Approaches of dosage form designs require a carrier which should be biocompatible and biosensitive like hydrogels . A three-dimensional network was formed by cross linking polymer chains. The crosslinking renders these structures insoluble in water due to anionic interaction and hydrogen–bonding. These structures imbibe water or biological fluids in large amount at least 10-20 times of their molecular weight, thus become swollen . Drug release in response to external stimuli, and are most investigated. Hydrogels having such ‘sensor’ properties can undergo reversible volume phase transitions or sol-gel phase transitions upon changes in the environmental condition such stimuli and response are shown in fig. 1. These properties of polymers play important role in drug delivery . Hydrogel-based drug delivery devices have become a major area of research interest Hydrogels can protect drugs from hostile environments, e.g. the presence of enzymes and low pH in the stomach. Their porosity permits loading of drugs into the gel matrix and subsequent drug release at a predesigned rate . FIG. 1: POTENTIAL STIMULI AND RESPONSES OF POLYMERS 4