A strong and tough gelatin/polyvinyl alcohol double network hydrogel actuator with superior actuation strength and fast actuation speed.

Hydrogels are widely used in actuators that are applied in numerous fields such as multifunctional sensors, soft robots, artificial muscles, manipulators and microfluidic valves, and yet their applications in soft robots and artificial muscles are often limited by low actuation strength and slow actuation speed. Here, we develop a hydrogel actuator with high actuation strength (contraction strength of 850 kPa), fast actuation speed (response time of 90 s) and high energy density (output working density of 72 kJ m -3 ) by introducing a storing-releasing elastic potential energy method into a double network hydrogel. The high actuation strength is owing to the double network hydrogel, which possesses a high elastic modulus of 1.3 MPa, fracture strength of 1.8 MPa, and fracture energy of 16 kJ m -2 . The fast actuation speed is due to the storing-releasing elastic potential energy method, which stretches the hydrogel and locks the hydrogel at deformed shape under external stimuli to store the elastic potential energy and then makes the hydrogel contract rapidly under new stimuli to release the pre-stored energy. A capture actuator and a hand muscle actuator are fabricated to achieve strong and fast actuation. The hydrogel actuator has shown potential applications in soft robots and artificial muscles.