DRUG RELEASE OFF BEHAVIOR AND DESWELLING KINETICS OF THERMORESPONSIVE IPNS COMPOSED OF POLY(ACRYLAMIDE-CO-BUTYL METHACRYLATE) AND POLY(ACRYLIC ACID)

Interpenetrating polymer networks (IPNs) composed of poly(acrylamide(AAm)-co-butyl methacrylate (BMA)) and poly(acrylic acid)(PAAc) demonstrate positive swelling changes with an abrupt transition as temperature increases. Temperature-modulated controlled drug release using swelling-shrinking responses of the hydrogels as on-off switches for drug release is reported. The IPNs demonstrate "on" release at higher temperatures. When changing from higher to lower temperatures, an immediate pulsatile drug release is observed followed by a nearly complete "off" state of drug release. The drastic increase of drug release rate is due to mechanical squeezing by a shrinking gel surface layer of the IPNs in response to decreasing temperature. The following decrease of drug release is due to a subsequent formation of a dense layer of polymer at the IPN surface.