Molecular design of graft-type poly (N-isopropylacrylamide) gels containing rapid thermo-response

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Conventional drug release regulation using hydrogels was depended on drug diffusive transport in the gels. In contrast, we investigated a novel thermo-responsive drug release regulation synchronized with convectional water outflow induced by aggregation of network containing comb-type graft chains. Deswelling kinetics of conventional gel without graft chains becomes slow : size-depended kinetics is obtained. This is because swelling to deswelling changes of the conventional gel is governed by collective diffusion of network. In contract, poly(N-isopropylacrylamide) (PIPAAm) network containing comb-type PIPAAm grafts with freely mobile ends shows rapid deswelling changes in response to stepwise temperature changes above 32ﾟC.The graft chains undergo rapid dehydration with temperature changes, accelerating the deswelling changes of the graft-type gel due to strong hydrophobic interaction between dehydrated graft chains. Difference is apparent in drug release pattern from the conventional gel and the graft-type gel. Upon increasing temperature, the conventional gel stops the drug diffusion due to formation of skin layers at the gel surface. In contract, pulsed drug release is achieved synchronized with the convectional water release during the rapid deswelling of the graft-type gel. Details are studies for a new function of thermo-responsive graft-type gel as a micro-pumping matrix.