Rapid temperature/pH response of porous alginate-g-poly(N-isopropylacrylamide) hydrogels

To improve the swelling and deswelling rate, comb-type macroporous hydrogels were prepared. The temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) was grafted on the surface or bulk of the pH-responsive alginate. The larger surface area in pores and free chain mobility by comb-type graft copolymer reached its equilibrium swollen state within a minute. The swelling ratio of porous hydrogel in equilibrium state was over fifteen times greater than that of nonporous hydrogels. The increase of surface area by pores caused water molecules to transfer easily in and out of the matrix, resulting in a rapid deswelling. The degree of change in swelling ratio during deswelling might be affected by the phase transition behavior of PNIPAAm attached on only the surface of the pore rather than PNIPAAm grafted into mainchain of alginate. Surface-grafted alginate/PNIPAAm gels had a suitable mechanical strength without collapsing during the repeatable shrinkage and expansion due to swelling and deswelling, whereas bulk-grafted gels easily collapsed.