Thermoresponsive hydrogel with rapid response dynamics

Intelligent hydrogels, particularly poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogels, have attracted extensive interest because the soft wet hydrogels can change their shapes in response to the small changes of environmental factors like temperature. In order to fully make use of this unique property of PNIPAAm-based hydrogels, the response rates of the PNIPAAm hydrogels have to be improved since the dynamics property is critical to certain applications of this material. In this paper, the thermo-sensitive PNIPAAm hydrogels were successfully synthesized by carrying out the polymerization of N-isopropylacrylamide monomer in vacuum (−100 kPa) at room temperature (22 °C). The resultant hydrogel has tremendously improved shrinking rate as well as the large volume changes upon temperature stimulation when comparing with the normal PNIPAAm hydrogel. The SEM micrographs revealed that the improved properties were attributed to the macroporous network structure generated during the synthesis under vacuum.