For example, when an LCE fiber is lifting a heavy load, a high contraction ratio produces a larger displacement and thus a higher external work output. A fast contraction rate, on the other hand, shortens the time required to lift the load and increases the work efficiency of the LCE fiber. In nature, human skeletal muscle can produce larger than 40% contraction at a contraction rate of higher than 50% s −1 , [1,18] allowing it to perform intense movements. For example, when humans are doing sports, e.g., basketball shooting, their muscles can contract both substantially and rapidly. However, none of the LCE fibers reported so far can simultaneously deform with a large contraction ratio and fast contraction rate comparable to human muscles, restricting its applications to conduct intense movements. To date, thermal-responsive LCE fibers are capable of generating large deformation. [19][20][21][22] But the heating rate is limited by the low thermal conductivity of air, leading to a slow contraction of LCE. Second, although light is a precise and fast stimulus, it can only propagate along a straight line. Thus, photo-responsive LCE fibers are usually exposed to light only on one side and typically demonstrate bending deformation, bringing about difficulties to achieve substantial contractile deformation. [23][24][25][26] Overall, with the development of LCE fibers, the gap that LCE fibers can output large contraction at an ultrafast rate needs to be filled.Herein, we report electrothermal-responsive liquid metal (LM) containing LCE (LM-LCE) fibers that can export large contraction with an ultrafast speed. Comparing to rigid conductive fillers, the fluidic property of LM alleviates the restriction to the deformation of LCE, [27,28] ensuring a large contraction generated by LCE. As a high temporal resolution stimulus, the electrical trigger (e.g., voltage value and pulse time) can be adjusted to achieve high instantaneous input of electrical energy and rapidly heat the entire LM-LCE fibers, resulting in a high contraction rate. The electrothermal-responsive LM-LCE fibers can be used as artificial muscles to drive soft robots to perform various functions with intense actuation. Result and DiscussionLM-LCE fibers were fabricated as shown in Figure 1a. First, LCE fibers oriented along the long axis were prepared according to Liquid crystal elastomer (LCE) fibers are capable of large and reversible deformations, making them an ideal artificial muscle. However, limited to stimulating source and structural design, current LCE fibers have not yet achieved both large contraction ratio and fast contraction rate to perform the intense motion. In this work, electrothermal-responsive liquid metal (LM) containing LCE (LM-LCE) fibers is reported. By introducing flexible liquid metal, LM-LCE fibers retain deformability with a large contraction ratio similar to that of pure LCE fibers and are endowed with electrical responsiveness. Applying precisely controlled electrical stimulation, the contraction ratio and rate of LM-LCE fibers ...

too small, the fibers will untwist before use; an excessive anchoring force will, on the other hand, prevent the fibers from moving and responding to external stimuli. [5][6][7][8] Therefore, the development of twist fibers in an untethered form will avoid the need for anchoring, simplify experimental design, and make various operations feasible. In practical applications, reversible rotational actuation is also important for twist fibers because it allows the fibers to respond to external stimuli repeatedly without the need to insert twists into the fibers each time before use. [9][10][11] In addition, high torque and rotational deformation are key factors in the operation of rotating microengines. The torque produced by the twist fibers must be sufficiently large to rotate objects. A large rotational deformation of the twist fibers is desirable for moving objects over a large distance in a wide range of applications. [12,13] So far, various materials have been utilized for untethered twist fibers that exhibit reversible rotational deformation upon stimuli. The actuation performance of these materials varies with the material. For example, twist fibers made from carbon materials or polymers can generate large rotational deformation of 588° mm −1 , but the generated specific torque reaches only 0.63 N m kg −1 . [9,10] To date, the construction of untethered twist fibers with reversible responsiveness, high torque, and large rotational deformation remains a challenge. A possible solution is the development of a material with high intrinsic deformation ratio and reversible responsiveness for fabricating twist fibers. [14] Among the various stimuli-responsive materials, liquid crystal elastomers (LCEs) have attracted increasing attention because of their dramatic and reversible stimuli-responsive deformation. [15][16][17][18][19][20][21][22][23] LCEs exhibit the two properties of high intrinsic deformation ratio and reliable reversibility which originate from the change in mesogenic alignment upon external stimuli. [24] These properties are important for improving the rotational performance of twist fibers. Here, we develop a template method based on a two-step cross-linking strategy to fabricate liquid crystal elastomer twist fibers (LCETFs). These untethered LCETFs can reversibly generate high torque and large rotational deformation. Fibers made from LCE have been widely exploited as actuators, [25][26][27][28] artificial muscles, [29][30][31][32] and soft robots. [33,34] In this work, we insert twists into LCE fibers Untethered twist fibers do not require end-anchoring structures to hold their twist orientation and offer simple designs and convenient operation. The reversible responsiveness of these fibers allows them to generate torque and rotational deformation continuously upon the application of external stimuli. The fibers therefore have potential in rotating microengines. In practical applications, high torque and rotational deformation are desirable to meet work capacity requirements. However, the simultan...

Human muscles, including skeletal, smooth, and cardiac muscles, are able to perform diverse deformations and execute complex biofunctions stimulated by nerve signals. Similarly, liquid crystal elastomer (LCE), which can respond to external stimuli with large and reversible deformations, demonstrates superior advantages to mimic nature muscles to fabricate artificial muscles. Till now, LCE has been utilized to simulate deformations and related functions of skeletal and smooth muscles. However, limited by the existing fabrication strategy, employing LCE to mimic the motion of cardiac muscles and further realizing the structure‐determined pumping functions, is still an open challenge. Learning from the specific spatial arrangements and synergistic actuation of cardiac muscle fibers within human heart, a simple and general strategy to construct artificial cardiac muscles with LCE fibers is proposed. In this work, LCE fibers with similar modulus and actuation behavior to muscle fibers are fabricated and spatially arranged in biological architectures as cardiac muscle fibers. As a result, artificial cardiac muscles are constructed and are able to perform simultaneous contraction and torsion motions, realizing heart‐pumping functions. This general strategy should be also applicable for other smart materials to conduct challenging tasks.

Photoresponsive materials offer local, temporal, and remote control over their chemical or physical properties under external stimuli, giving new tools for interfacial regulation. Among all, photodeformable azobenzene-containing liquid crystal polymers (azo-LCPs) have received increasing attention because they can be processed into various micro/nanostructures and have the potential to reversibly tune the interfacial properties through chemical and/or morphological variation by light, providing effective dynamic interface regulation. In this feature article, we highlight the milestones in the dynamic regulation of different interfacial properties through micro/nanostructures made of photodeformable azobenzene-containing liquid crystal polymers (azo-LCPs). We describe the preparation of different azo-LCP micro/nanostructures from the aspects of materials and processing techniques and reveal the importance of mesogen orientation toward dynamic interfacial regulation. By introducing our recently developed linear azo-LCP (azo-LLCP) with good mechanical and photoresponsive performances, we discuss the challenge and opportunity with respect to the dynamic light regulation of two- and three-dimensional (2D/3D) micro/nanostructures to tune their related interfacial properties. We have also given our expectation toward exploring photodeformable micro/nanostructures for advanced applications such as in microfluidics, biosensors, and nanotherapeutics.

365 nm UV light at desired position for 300 s. The recovery of POTSMP from TS2 to PS was under the irradiation of 150 mW cm −2 , 365 nm UV light. The sample after each shape recovery could be irradiated by 80 mW cm −2 , 530 nm visible light for 3 min to recover POTSMP from cis-form to trans-form.

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Liquid crystal elastomer (LCE) exhibits large and reversible deformability originating from the alignment of liquid crystal mesogens. Additive manufacturing provides high controllability in the alignment and shaping process of LCE actuators. However, it still remains a challenge to customize LCE actuators with both diverse 3D deformability and recyclability. In this study, a new strategy is developed to exploit knitting technique to additively manufacture LCE actuators. The obtained LCE actuators are fabric‐structured with designed geometry and deformability. By accurately adjusting the parameters of the knitting patterns as modules, diverse geometry is pixel‐wise designed, and complex 3D deformations including bending, twisting, and folding are quantitatively controlled. In addition, the fabric‐structured LCE actuators can be threaded, stitched, and reknitted to achieve advanced geometry, integrated multi‐functions and efficient recyclability. This approach allows the fabrication of versatile LCE actuators with potential applications in smart textiles and soft robots.