Nanogel-crosslinked thermo-rasponsive hydrogels: Synthesis and function

Cholesteryl-group bearing pullulans (CHP)s form stable monodispersive nanogels (20-30 nm) by inter-macromolecular self-association in water. We reported that CHP nanogels were useful for drug carrier and artificial molecular chaperon. In this study, we prepared thermo-responsive hydrogel composed of methacrylate-bearing CHP nanogels as a crosslinker and N-isopropylacrylamide (NIPA) as a thermo-responsive unit in semi-dilute aqueous solution. Thermo-responsibility of the hydrogel was evaluated by the weight reduction while the temperature changes from 40°C to 20°C. The CHP-NIPA hydrogel showed remarkable rapid deswelling behavior. The deswelling of the hydrogel was derived from the volume phase transition at a lower critical solution temperature (LCST) of PNIPA. The half-deswelling time of the CHP-NIPA hydrogels was only 1 min, though that of PNIPA hydrogels, which crosslinked by N,N′-methylenebisacrylamide, was over 30 h. The multi-crosslinking by nanogels significantly affected the deswelling kinetics of PNIPA gels.