Ultrafast thermo-responsive bilayer hydrogel actuator assisted by hydrogel microspheres

Extensive attention is focused on layered hydrogel actuators, but realizing the fast bending in short time is still a challenge. In this work, thermo-responsive bilayer hydrogel actuator composing of one layer of microspheres incorporated poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel and another layer of PNIPAM hydrogel was fabricated by using the layer-by-layer method. Thanks to the anisotropic swelling of two layers, the bilayer hydrogel exhibited rapid, reversible, and repeatable bending motions under different temperatures. The huge difference in the deswelling rates of the two layers accorded the bilayer hydrogel pretty fast bending speed as high as 103 degrees /s at 50 degrees C. The bilayer hydrogel applied as a four-armed gripper to clamp toy, a hydrogel flower to imitate the blooming and closing of petals, and a reliable fluid valve was successfully realized, enabling its potential applications in a load of fields, including environmental sensors, soft robotics and biomedical engineering.