Thermoresponsive hydrogel artificial muscles

Thermoresponsive hydrogels (TRHs) are intelligent materials that, when wet, show volumetric shape deformation in response to temperature change. In contrast to other stimuli-responsive hydrogels with slow deformation behavior, TRHs provide rapid displacement or movement when a hydrothermal stimulus is applied, thus enabling their effective usage as soft polymeric actuators or artificial muscles. The capability of dynamic macrostructural shape changes in axial, radial, and angular directions allows TRH artificial muscles to be advantageous for various state-of-the-art applications, including soft robotics, medical devices, sensors, and smart textiles. Herein, we discuss early-stage innovations and further advances of TRH artificial muscles from both fundamental materials science and engineering perspectives. We highlight the end-to-end fabrication methods, relevant actuating mechanisms, and performances, with an emphasis on their design flexibility to meet current bioengineered actuator needs. Finally, we investigate the enduring challenges and anticipate future research strategies that will provide a practically feasible soft actuator solution.