Effects of Cross-Linked Structure on Temperature-Responsive Hydrophobic Interaction of Poly(N-isopropylacrylamide) Hydrogel-Modified Surfaces with Steroids

Abstract

Cross-linked poly(N-isopropylacrylamide) (PIPAAm) hydrogel-modified surfaces were prepared to investigate the effects of a three-dimensionally cross-linked structure of PIPAAm layers on both wettability changes and hydrophobic interactions with hydrophobic solutes in response to temperature changes. The temperature-responsive surface was prepared by polymerization of IPAAm in the presence of cross-linker on the substrates on which an azo polymerization initiator was covalently bonded. The PIPAAm hydrogel-modified surface showed temperature-responsive hydrophilic/hydrophobic surface property alterations as demonstrated by a large and discontinuous wettability changes in a range of 27−32 °C, a slightly lower temperature range than the phase transition temperature for soluble PIPAAm in aqueous media. This implies that the dynamic motion in response to temperature for PIPAAm segments in the modified hydrogel is restricted due to the cross-linked structure. The effect of the three-dimensional PIPAAm structure ...