A Fast, Reversible, and Robust Gradient Nanocomposite Hydrogel Actuator with Water-Promoted Thermal Response.

Poly(N-isopropylacrylamide)/Laponite (PNIPAM/Laponite) gradient nanocomposite hydrogel actuators are developed as temperature-controlled actuators with excellent performance using a facile electrophoresis method. The actuators exhibit a rapid (20 s response time) and reversible response, as well as large deformation (bending angle of 231 degrees), which is due to the graded forces generated by the thermo-induced anisotropic shrinkage and extension of the gradient hydrogels. A good linear relationship is observed between the maximum bending angles and the corresponding temperatures for the actuators with fixed sizes. Moreover, the gradient hydrogel with high water content achieved larger actuation angles and shorter response time than the one with low water content, showing an interesting water-promoted effect. Meanwhile, different types of actuators are designed to suit for more specific scenarios, and may be used for various applications, such as biosensing, artificial organization, and transportation of targeted objects.