Robust Fabrication of Anisotropic Bilayer Hydrogel Embedded With a Gradient Structure in One Layer: Enhanced Temperature‐Responsive Bending, Shape Programmability, and Actuator and Sensor Applications

ABSTRACT Anisotropic hydrogel actuators with gradient structures offer tunable mechanical properties, like directional stiffness or bending. However, creating these gradient‐structured bilayer hydrogels is challenging, as current methods rely on complex, single‐force programming. Developing a double‐actuating bilayer hydrogel with temperature‐responsive and auxiliary layers could address these limitations and enhance their applicability. In this study, an anisotropic hydrogel actuator was developed using a simple, cost‐effective method to create a unique multi‐asymmetric structure with an embedded gradient in one layer. The resulting hydrogels exhibited excellent temperature‐responsive bending (360° within 9 s) and adaptive, complex shape‐programmable deformation (2D letters, flowers, butterflies, leaves). In addition, the hydrogels demonstrated good shape memory, mechanical strength, and conductivity. Prototypes of a hydrogel gripper and humidity alarm were successfully fabricated, showcasing the potential of this strategy for designing smart hydrogels for applications in sensors, smart humidity alarms, grippers, and actuators.