Complex formation between PDMAAm as a hydrogen-bonding acceptor and PAAc as a hydrogenbonding donor, the temperature dependence of the equilibrium swelling for interpenetrating polymer network (IPN) hydrogels composed of PDMAAm and PAAc, and changes in ketoprofen release of these IPN hydrogels were investigated. Interpolymer complexes between PDMAAm and PAAc were very stable at 70 °C in aqueous solution. Dissociation temperatures of the complex between poly(DMAAm-co-AAm) and PAAc shifted to higher values with increasing DMAAm content. These IPNs composed of poly(DMAAm-co-AAm) and PAAc showed limited swelling ratios between their swelling transition temperatures and lower swelling ratios above these transition temperatures. Transition temperatures shift to higher values with increasing DMAAm content. Reversible and pulsatile solute release, reflecting the "on" state at higher temperatures and the "off" state at lower temperatures, was achieved by fabricating these IPN hydrogels.

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ABSTRACT:Interpenetrating polymer networks (IPNs) composed ofpoly(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.KEY WORDS

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Downloaded from 107 water structure in water swollen PEUU films. These results reveal that the ternary microdomain structures are composed of PBD, PEO, and hard segments.The drug release profiles of these PEUU devices are strongly affected by the physicochemical nature of soft segment matrices in PEUUs. The PEUUs with high PEO content exhibited slow and steady (zero-ordered) release of drug in contrast with those with low PEO content from which drug release was entirely restricted. This result indicates the importance of a matrix to perform the function not only as a drug reservoir but also a transport channel. The solubility parameters of both constituent segments and the drug must be realized for regulated drug release from microdomain-structured polymeric devices.