Double layered asymmetrical hydrogels enhanced by thermosensitive microgels for high-performance mechanosensors and actuators

Thermosensitive hydrogels have found extensive applications in soft devices, but they often suffer from limited functionalities, low response rate and small response amplitude. In this work, double layered asymmetrical hydrogels composed of a thermosensitive layer and a non-thermosensitive layer are developed to simultaneously achieve high-performance mechanosensing and actuating properties in a single hydrogel. In thermosensitive layer, thermosensitive microgels are introduced to construct hierarchical structure, which accounts for the enhanced thermosensitive behaviors by cooperative responsiveness. In non-thermosensitive layer, poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) hydrogel is constructed. KCl is introduced as conductive component. Mechanosensors for monitoring various mechanical stimuli in daily life have been fabricated utilizing such hydrogels and high gauge factors (GF) have been achieved, 0.38 for resistive strain sensors, 9.40 kPa(-1) for piezoresistive pressure sensors and 3.92 kPa(-1) for capacitive pressure sensors. Because of the asymmetrical structure, such hydrogels also exhibit outstanding actuating properties with a fast response rate of 863 degrees/min and a bending amplitude about 360 degrees. Interestingly, grasping -releasing of target objects utilizing an octopus -shaped hydrogel actuator and temperature alerting based on hydrogel actuator are also demonstrated. Overall, the double layered asymmetrical ionic hydrogels have provided a new clue to construct hydrogel devices with multiple functionalities and enhanced response properties.