pH/temperature-responsive behaviors of semi-IPN and comb-type graft hydrogels composed of alginate and poly(N-isopropylacrylamide)

Thermo- and pH-sensitive comb-type graft and semi-IPN hydrogels were prepared by using alginate and poly(N-isopropylacrylamide) (PNIPAAm). Comb-type graft hydrogels are composed of crosslinked alginate network and grafted with PNIPAAm. They exhibited fast pH and thermal responses due to free and mobile graft chains. Comb-type graft hydrogels reached an equilibrium swelling and deswelling states within about 10 min. By contrast, semi-interpenetrating polymer network (semi-IPN) hydrogels formed polyelectrolyte complex between carboxyl groups in alginate and amino groups in PNIPAAm-NH2, resulting in a relatively compact structure and slow swelling and deswelling compared with comb-type graft hydrogel. All the hydrogels exhibited a reasonable sensitivity to temperature, pH and ionic strength of the swelling medium.