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

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.