Fast-reversible light-driven hydrogels consisting of spirobenzopyran-functionalized poly(N-isopropylacrylamide)

We introduced different spirobenzopyran derivatives into poly(N-isopropylacrylamide) gels and evaluated the effects of spontaneous ring-opening rates of the spirobenzopyrans on light-responsive volume change behaviors of the gels. Rates of reswelling from the light-induced shrunken state of the spirobenzopyran-functionalized poly(N-isopropylacrylamide) (p(Sp-NIPAAm)) gels increased with increasing ring-opening rates of spirobenzopyrans in the gels. Bending motion of a rod-like p(Sp-NIPAAm) gel was invoked by local light-irradiation because of asymmetric shrinkage of the gel. Two types of bending motions were observed depending on the reswelling rates of the gels; a gel with a fast reswelling rate was steadily bent only during light-irradiation, whereas another gel with a slow reswelling rate showed a continuous bending motion even after the irradiation. In addition, a sheet-like gel with a fast reswelling rate was operated as a micro-conveyor whose conveying direction was arbitrarily controlled with a light-irradiation.