Polymeric gel‐based artificial muscles exhibiting tissue‐matched Young's modulus (10 Pa–1 MPa) promise to be core components in future soft machines with inherently safe human–machine interactions. However, the ability to simultaneously generate fast, large, high‐power, and long‐lasting actuation in the open‐air environment, has yet been demonstrated in this class of ultra‐soft materials. Herein, to overcome this hurdle, the design and synthesis of a twisted and coiled liquid crystalline glycerol‐organogel (TCLCG) is reported. Such material with a low Young's modulus of 133 kPa can surpass the actuation performance of skeletal muscles in a variety of aspects, including actuation strain (66%), actuation rate (275% s−1), power density (438 kW m−3), and work capacity (105 kJ m−3). Notably, its power density is 14 times higher than the record of state‐of‐the‐art polymeric gels. No actuation performance degradation is detected in the TCLCG even after air exposure for 7 days, owing to the excellent water retention ability enabled by glycerol as co‐solvent with water. Using TCLCG, mobile soft robots with extraordinary maneuverability in unstructured environments are successfully demonstrated, including a crawler showing fast bidirectional locomotion (0.50 mm s−1) in a small‐confined space, and a roller that can escape after deep burying in sand.

The first solid‐state engine that converted heat into continuous mechanical motion using a thermally responsive actuating material was introduced almost a century ago. These engines used vulcanized rubber where the cyclically heating and cooling of the rubber generate continuous mechanical power in pendulum or wheel type engines. The development of solid‐state heat engines has seen several waves of activity with interest stimulated by the introduction of new actuating materials capable of responding to different environmental stimuli. Opportunities for improved engine outputs are afforded by recently developed artificial muscle materials. A theoretical connection between engine output and the characteristics of the actuator material is developed to compare the performances of vulcanized rubber, shape memory alloys (SMAs), and twisted and coiled polymer (TCP) fiber artificial muscles. It is shown that with an engine designed to suit the actuation performance of TCPs engines powered by the tensile actuation of such materials would exceed the output of SMA heat engines. The properties needed in actuator materials to further enhance engine output are identified and polymer structures that may produce such properties are described.

Coiled Artificial Muscles In article number 2210419, Zhen Jiang, Geoffrey M. Spinks, and co‐workers introduce a liquid crystalline organogel combined into a twisted and coiled fiber geometry to generate a powerful soft artificial muscle with fast response to small temperature changes.

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