Giant Stroke, Thermally Powered Twisted LCE Yarn Actuators Driven by Reversible Twist–Coil Transition

ABSTRACT

Actuation performance in fiber‐based artificial muscles is commonly improved by introducing sufficient twist to produce fully coiled structures. Here, we present a new strategy to achieve large‐stroke actuation in twisted‐only liquid crystal elastomer (TLCE) yarn muscles through a thermally triggered, reversible twist‐to‐coil transition. Continuous, high‐strength, and scalable LCE fibers were fabricated using direct ink printing. These fibers were then integrated with carbon nanotube yarns to fabricate electrothermal hybrid TLCE muscles. Above a critical twist density, the hybrid muscles electrothermally transform into coiled or plectoneme configurations, delivering a maximum quasi‐static contractile stroke of up to 86%, a fast response time of 1.8 s, and stable cyclic operation over 10 000 cycles. The stroke enhancement originates from the reversible twist‐to‐coil transition, which is driven by a pronounced thermal reduction in both fiber length and Young's modulus, thereby lowering the critical torque needed for coiling. This mechanism introduces a new actuation mode for fiber‐based artificial muscles and shows promising potential for confined‐space manipulation, robotic grippers, and adaptive smart structures.