Thermally Responsive Multi-Spiral-Shaped Liquid Crystal Elastic Artificial Muscle

Inspired by the stimuli-responsive deformation mechanism in nature, this study proposes a biomimetic actuation strategy based on liquid crystal elastomers (LCE) and silicone. Three types of shape-programmable actuating fibers, namely straight fibers (LCEP-1), slightly coiled fibers (LCEP-2), and highly coiled fibers (LCEP-3), were successfully fabricated by constructing a skin–core heterostructure fiber (LCEP) and combining prestretching regulation with a two-step cross-linking process of photo and thermal stimulation. Under thermal stimulation, the LCE core layer produced axial contraction strain due to the sudden drop in the order degree of mesogenic units. Therefore, the contraction behavior occurs, mainly based on the entropy-elastic recovery of the core and the resulting strain mismatch between the core and elastic outer matrix. Furthermore, the substantial difference in modulus between the skin and core layers constitutes a key factor contributing to the fabrication of the three types of LCEP fibers and the eventual spiral contraction of the fibers. Among them, LCEP-1 (prestretched 1.5 times) has a contraction ratio of 88.79% at 80 °C and LCEP-2/LCEP-3 (prestretched 1.8/2.2 times) have contraction ratios of 86.65% at 52 °C and 68.78% at 48 °C, respectively. The response times for LCEP-2 and LCEP-3 to reach their maximum bending deformation have been further reduced to 5.8 and 4.7 s, respectively, at 140 °C. Application verification shows that LCEP-3 fibers can actuate bionic butterfly wings to achieve 36° bending and simulate the biceps of an artificial arm to lift a load (2.11 g) to 68°, demonstrating their potential in the fields of soft robotics and artificial muscles.