Pretension-Free and Self-Recoverable Coiled Artificial Muscle Fibers with Powerful Cyclic Work Capability

Similar to natural muscle fibers, coiled artificial musclefibersprovide a straightforward contraction. However, unlike natural musclefibers, their recovery from the contracted state to the initial staterequires high stress, resulting in almost zero work during a fullactuation cycle. Herein, a self-recoverable coiled artificial musclefiber was prepared by conformally coating an elastic carbon nanotube(CNT) fiber with a very thin liquid crystal elastomer (LCE) sheath.The as-obtained muscle fiber demonstrated excellent actuation propertiescomprising 56.9% contractile stroke, 1522%/s contraction rate, 7.03kW kg(-1) power density, and 32,000 stable cycles.The LCE chains were helically aligned in a nematic phase, and thephase change of the LCE caused by Joule heating drove the actuationprocess. Moreover, the LCE/CNT fiber had a well-separated, torsionallystable, and elastic coiled structure, which permitted large contractilestrokes and acted as an elastic template for external-stress-freerecovery. Thus, the use of self-recoverable muscle fibers to mimicthe natural muscles for object dragging, multidirectional bending,and quick striking was demonstrated.