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A new delivery device based on a novel, squeezing hydrogel concept, utilizing specific swelling-deswelling characteristics of temperature-, temperature/pH- and pH-sensitive hydrogels is described. These hydrogels have been designed to exhibit controlled swelling-deswelling kinetics, hence, a variety of release profiles may be generated including: delayed, zero-order or on-off release profiles. A temperature sensitive NiPAAm/AAc hydrogel demonstrated a squeezing controlled `on-off' release profile in response to a temperature change between 35° and 40°C with the `on' phase at higher temperature. Drug release profiles from a pH/T sensitive NiPAAm/BMA/DEAEMA hydrogel were strongly affected by a pH change at 37°C. The gel demonstrated a minimal delayed release at pH 2.0 and a zero-order release at pH 7.4 controlled by mechanical squeezing mechanism that was determined by the gel deswelling kinetics. A delayed and a zero-order release profiles were also obtained for a pH sensitive cationic hydrogel in response to a pH change from pH 2.0 to 7.4. For all studied systems, it was concluded that a gel composition and an applied stimuli (T, pH, pH/T), determined the gel swelling/deswelling kinetics and the release profiles. |
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