title: Surface-modulated skin layers of thermal responsive hydrogels as on-off switches: I. Drug release.
abstract: Thermosensitive co-polymers of isopropyl acrylamide (IPAAm) with butyl methacrylate (BMA) are capable of 'on-off' regulation of drug release in response to external temperature changes due to skin formation with increasing temperature. To clarify the role of the surface-modulated skin and controlled pulsatile drug release patterns, the surface shrinking process was regulated by changing the length of the methacrylate alkyl side-chain. Release of indomethacin in response to stepwise temperature changes between 20 and 30 degrees C from co-polymers of IPAAm with BMA, hexyl methacrylate (HMA), and lauryl methacrylate (LMA) was studied. The drug release rate during the 'on' state (20 degrees C) remained constant before and after the 'off' state (30 degrees C) when the period of the 'off' state was increased. These results suggest that the drug in the polymeric matrices diffused from the inside to the surface during the 'off' state even when no drug release was seen. The length of alkyl side-chain was found to be an important parameter in controlling the thickness and density of the surface skin layer.
authors.affiliation: Department of Chemical Engineering, Waseda University, Tokyo, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Yoshida
authors.forename: K
authors.initials: K
authors.lastname: Sakai
authors.forename: T
authors.initials: T
authors.lastname: Ukano
authors.forename: Y
authors.initials: Y
authors.lastname: Sakurai
authors.forename: Y H
authors.initials: YH
authors.lastname: Bae
authors.forename: S W
authors.initials: SW
authors.lastname: Kim
mesh_terms: D003432:Cross-Linking Reagents; D016503:Drug Delivery Systems; D006358:Hot Temperature; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D007213:Indomethacin / Q000494:pharmacology; D008567:Membranes, Artificial; D008689:Methacrylates; D011092:Polyethylene Glycols; D011108:Polymers; D013499:Surface Properties / Q000187:drug effects
chemical_list: D003432:Cross-Linking Reagents; D008567:Membranes, Artificial; D008689:Methacrylates; D011108:Polymers; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D011092:Polyethylene Glycols; C016285:butyl methacrylate monomer; D007213:Indomethacin