Thermoresponsive hydrogel artificial muscles

Thermoresponsive hydrogels (TRHs) are intelligent materials that, when wet, show volumetric shape deformation in response to tem-perature 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 artifi-cial 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 applica-tions, including soft robotics, medical devices, sensors, and smart textiles. Herein, we discuss early-stage innovations and further ad-vances of TRH artificial muscles from both fundamental materials sci-ence and engineering perspectives. We highlight the end-to-end fabrication methods, relevant actuating mechanisms, and perfor-mances, 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 pro-vide a practically feasible soft actuator solution.