光で内部の静電反発力をオンオフする、高速・異方性ヒドロゲルアクチュエータの創成

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In my research, I successfully developed a photoresponsive hydrogel actuator which can deform quickly (0.5 s) and largely (80 %) in an open air. The hydrogel, composed of thermoresponsive PNIPA, is embedded with magnetically aligned titanate nanosheets (TiNSs) for generating internal electrostatics, together with gold nanoparticles for photothermal conversion. We at first confirmed that AuNPs realize efficient photothermal conversion when irradiated at their conduction band (<450 nm), where the temperature becomes higher than the LCST of PNIPA. The phase transition of PNIPA should cause the enhancement of the electrostatic repulsion between the TiNSs, thereby leading to the deformation of the hydrogel. Indeed, this cascade mechanism worked in the PNIPA hydrogel embedded with TiNSs and AuNPs. When irradiated with a 445-nm laser beam, the hydrogel expanded very quickly and largely in the direction perpendicular to the TiNS plane. The response time was less than 1 second, while the deformation ratio was more than 80 %. These deformation profiles are at the highest level of reported hydrogel actuators. The deformation was totally reversible and repeatable without any notable deterioration. These excellent behaviors of our hydrogel actuator inspired us to use it as artificial muscle to mimic the motion of the earthworm. Owing to the large, quick, reversible, and spatiotemporally controlled deformation, our hydrogel actuator encapsulated in a capillary can perfectly mimic this movement.