| Summary: | Hydrogels are cross-linked polymers with hydrophilic groups which enable them to absorb large amounts of water. Hydrogel based delivery systems have been used for delivery of different types of active pharmaceuticals. Although hydrogels have numerous capability and advantages in drug delivery including biocompatibility, low toxicity and good swelling behavior but depending on chemical moieties of the gel forming polymers and route of administration some limitations would appear in delivery of active pharmaceutical using hydrogel as delivery vehicle. Development of successful hydrogel based delivery system is possible upon knowledge about the hydrogels forming polymers physiochemical properties and understanding the influencing factors which control the swelling behaviors, hydrophilicity, biodegradability, biocompatibility and targetability of the selected polymer. In this review at first classification of the hydrogel with different approaches including chemical moieties, crosslinking agent behaviors and release controller mechanism was performed and limitations arise from each category was described and finally different approaches to overcome each of this limitation was proposed.
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