Stimuli sensitive polymers for drug delivery systems

Temperature sensitive and electric field sensitive hydrogels were prepared for use in modulated drug release systems. Crosslinked poly(N‐isopropyl‐acrylamide) and its networks, modified with hydrophobic components by copolymerization or by interpenetrating polymer networks (IPNs) formation, were utilized as temperature sensitive hydrogels. Indomethacin (a model solute)‐release from polymer matrix and permeation through polymer membrane demonstrated “on‐off” regulation with temperature fluctuation. This was the result of polymer surface properties rather than bulk swelling, as temperature was changed past the swelling transition temperature range of the polymer. The on‐off regulation in an electric field was also obtained with a positively charged solute (Edrophonium chloride) release in distilled‐deionized water from a matrix of crosslinked poly(2‐acrylamido‐2‐methylpropanesulfonic acid‐co‐butyl methacrylate). This was attributed to the ion exchange between Edrophonium ion and protons produced at the anode. The swelling changes produced by local pH or ionic strength changes affected non‐charged solute release.