Thermoresponsive Actuation Enabled by Permittivity Switching in an Electrostatically Anisotropic Hydrogel.

Younsoo Kim, Mingjie Liu, Yasuhiro Ishida, Yasuo Ebina, Minoru Osada, Takayoshi Sasaki, Takaaki Hikima, Masaaki Takata, and Takuzo Aida

Nature Mat. 2015, 14, 1002–1007.

[DOI: 10.1038/nmat4363]

  Owing to their large potential applicability to biomedical fields, hydrogel actuators have been extensively studied so far.  However, reported actuators have a number of limitations in terms of their speed, efficacy, programmability, and operating conditions.  We herein developed a hydrogel actuator that addresses all these issues, based on an unprecedented operation mechanism.

  Our hydrogel actuator contains ionic nanosheets anisotropically aligned within it.  Its actuation is driven by the modulation of electrostatic repulsion between the nanosheets, which is triggered by the changes of electrostatic permittivity associated to the thermoresponsive phase transition of the gel network.  In the absence of water uptake and release, the distance between the nanosheets rapidly expands and contracts on heating and cooling, respectively, so that the hydrogel lengthens and shortens significantly, even in air.