C. elegans-inspired undulatory motion in a light-driven liquid crystal elastomer fiber.

Integration of multiple functions into a simple unit can simplify the device design and facilitate the miniaturization and portability of soft robots. Actuating and sensing functions are the basis of soft robots to interact with the environment. In this work, a modified melt‐spinning method is used to produce liquid crystal elastomer (LCE) fibers with a hollow structure and fill the core with liquid metal (LM) to construct LCE–LM coaxial fibers with integrated sensing and actuation functions. The inner LM generates Joule heat upon an electrical trigger to actuate the outer LCE shell. When LCE–LM coaxial fibers are actuated or loaded with objects, the deformation of LCE shell forces the inner LM to reform, allowing to sense the motion of the fibers or the mass of objects, by measuring the feedback voltage or resistance change of the inner LM. Benefitting from the material selection and structural design, the LCE–LM coaxial fibers with integrated actuating and sensing capability exhibit large reversible contraction (40%) and reliable durability (5000 cycles for actuation and motion sensing). Finally, a soft three‐arm Delta robot is fabricated to complete object identification, sorting tasks, and in situ monitoring the motion process.

A method for fabricating long, soft, and reversibly actuatable liquid crystal elastomer (LCE) fibers by using direct ink write (DIW) printing was developed. Here, the LCE was produced based on a two-stage thermal-photo curingreaction between a difunctional acrylate monomer and thiol. The LCE ink, mixed with nanoclay to increase the viscosity, was extruded through a nozzle onto a rotating mandrel to obtain a long fiber. After printing, the fiber was first thermally cured on the mandrel, then mechanically stretched, and photocured to achieve liquid crystal chain alignment for stress-free reversible activation. Upon optimizing the ink viscosity and DIW printing parameters, long fibers (up to 1.5 m long from the laboratory) were obtained. The resulting fiber had a modulus of 2 MPa, 51% actuation strain, and a failure strain of well over 100%. The potential of these fibers for applications was demonstrated. The LCE fibers were knit, sewn, and woven to form a variety of smart textiles. The fiber was also used to mimic bicep muscles with both large activation force and activation strain. By incorporating further intelligent characteristics, such as conductivity and biosensing into a single fiber, the LCE fibers could be potentially used for smart clothing, soft robotics, and biomedical devices.

Synthesis-Processing-Property Relationships in Thermomechanics of Liquid Crystal Elastomers

A light-powered liquid crystal elastomer semi-rotary motor

Liquid crystal elastomers (LCEs) are shape-morphing materials whose large and reversible shape transformations are caused by the coupling between the mobile anisotropic properties of liquid crystal (LC) units and the rubber elastic of polymer networks. Their shape-changing behaviors under certain stimuli are largely directed by the LC orientation; therefore, various strategies have been developed to spatially modulate the LC alignments. However, most of these methods are limited as they require complex fabrication technologies or have intrinsic limitations in applicability. To address this issue, programmable complex shape changes in some LCE types, such as polysiloxane side-chain LCEs, thiol-acrylate main-chain LCEs, etc., were achieved by using a mechanical alignment programming process coupled with two-step crosslinking. Here, we report a polysiloxane main-chain LCE with programmable 2- and 3D shape-changing abilities that were created by mechanically programming the polydomain LCE with two crosslinking steps. The resulting LCEs exhibited a reversible thermal-induced shape transformation between the initial and programmed shapes due to the two-way memory between the first and second network structures. Our findings expand on the applications of LCE materials in actuators, soft robotics, and smart structures where arbitrary and easily programmed shape morphing is needed.

Asymmetric bending enables rapid and efficient crawling motions in a soft robotic system. However, achieving asymmetric motion in soft robots with temperature‐responsive liquid crystal elastomers (LCEs) necessitates complex Joule heating configurations or precise temperature regulation. Herein, a simple electroless plating method is presented for patterning asymmetric temperature gradients on paper substrates, thereby facilitating the development of Joule heating, caterpillar‐inspired soft robots. Cellulose‐based paper substrates provide distinct advantages due to their porous structure, which enables facile electrode deposition via solution‐based processes and offers high mechanical deformability. Leveraging these material properties, Cu electrodes are asymmetrically deposited onto paper substrates by varying electrode widths. This variation induces differences in electrical resistance, generating significant temperature gradients across the substrate. Furthermore, it is demonstrated that temperature gradients could be modulated by adjusting the extent of Cu enhancement in the electrode patterns. it is fabricated energy‐efficient soft robots capable of directional crawling at a low actuation voltage of 0.5 V by integrating the paper substrate with LCEs in a bilayer architecture. The simplicity of the electrode patterning process, combined with the eco‐friendly nature of paper‐based actuators, presents a promising approach for the scalable and sustainable fabrication of soft robots with complex locomotion capabilities.

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.

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials that transduce an input energy into a mechanical response. LCE composites prepared with photothermal agents, such as nanoinclusions, are a means to realize wireless, remote, and local control of deformation with light. Amongst photothermal agents, gold nanorods (AuNRs) are highly efficient converters when the irradiation wavelength matches the longitudinal surface plasmon resonance (LSPR) of the AuNRs. However, AuNR aggregation broadens the LSPR which also reduces photothermal efficiency. Here, the surface chemistry of AuNRs is engineered via a well-controlled two-step ligand exchange with a monofunctional poly(ethylene glycol) (PEG) thiol that greatly improves the dispersion of AuNRs in LCEs. Accordingly, LCE-AuNR nanocomposites with very low PEG-AuNR content (0.01wt%) prepared by 3D printing are shown to be highly efficient photothermal actuators with rapid response (>60%strains-1) upon irradiation with near-infrared (NIR; 808nm) light. Because of the excellent dispersion of PEG-AuNR within the LCE, unabsorbed NIR light transmits through the nanocomposites and can actuate a series of samples. Further, the dispersion also allows for the optical deformation of millimeter-thick 3D printed structures without sacrificing actuation speed. The realization of well-dispersed nanoinclusions to maximize the stimulus-response of LCEs can benefit functional implementation in soft robotics or medical devices.

Light-powered self-oscillation of a liquid crystal elastomer bow

Direct ink writing of liquid crystal elastomers (LCEs) offers a new opportunity to program geometries for a wide variety of shape transformation modes toward applications such as soft robotics. So far, most 3D‐printed LCEs are thermally actuated. Herein, a 3D‐printable photoresponsive gold nanorod (AuNR)/LCE composite ink is developed, allowing for photothermal actuation of the 3D‐printed structures with AuNR as low as 0.1 wt.%. It is shown that the printed filament has a superior photothermal response with 27% actuation strain upon irradiation to near‐infrared (NIR) light (808 nm) at 1.4 W cm−2 (corresponding to 160 °C) under optimal printing conditions. The 3D‐printed composite structures can be globally or locally actuated into different shapes by controlling the area exposed to the NIR laser. Taking advantage of the customized structures enabled by 3D printing and the ability to control locally exposed light, a light‐responsive soft robot is demonstrated that can climb on a ratchet surface with a maximum speed of 0.284 mm s−1 (on a flat surface) and 0.216 mm s−1 (on a 30° titled surface), respectively, corresponding to 0.428 and 0.324 body length per min, respectively, with a large body mass (0.23 g) and thickness (1 mm).

Morphing of stiffness-heterogeneous liquid crystal elastomers via mechanical training and locally controlled photopolymerization

The development of smart actuators that integrate robust mechanical properties with rapid responsiveness remains a critical challenge for advancing artificial muscles. To address this, this study incorporates lignin—a renewable resource—into liquid crystalline elastomer (LCE) to fabricate a high‐performance photothermal‐responsive artificial muscle material. By leveraging the inherent aromatic conjugated structure of lignin as an efficient photothermal unit, we successfully integrated it with mesogens to construct a liquid crystalline network featuring a nanoscale microphase‐separated architecture. This network incorporates lignin‐based phenolic carbamate bonds and disulfide bonds concurrently, forming a dual dynamic crosslinking architecture that significantly enhances the mechanical properties of LCE, achieving a tensile strength of 21.5 MPa and an elongation at break exceeding 754%, thereby substantially surpassing conventional single‐network LCEs. It also confers outstanding photothermal response, enabling rapid, self‐actuated reversible deformation (33% strain). As a light‐driven artificial muscle, it achieves 40% reversible strain and 30.0 kJ/m 3 output power density. This work presents a novel strategy for developing high‐performance light‐driven LCEs through the integration of biomass lignin as both a reinforcing phase and an intrinsic photothermal converter. This approach not only enhances the material's performance but also offers promising pathways for the design and fabrication of next‐generation soft robots and artificial muscles.

Liquid crystal elastomers (LCEs), owing to their intrinsic anisotropic property and capability of generating programmable complex morphologies under heat, have been widely used for applications ranging from soft robotics, photonic devices, cell culture, to tissue engineering. To fulfill the applications under various circumstances, high actuation efficiency, high mechanical strength, large heat and electrical conductivity, or responses to multiple stimuli are required. Therefore, design and fabrication of LCE composites are a promising strategy to enhanced physical properties and offer additional stimuli responses to the LCEs such as light, electric, and magnetic fields. In this review, we focus on recent advances in LCE composites, where LCEs are defined as anisotropic elastomeric materials in a broader context. Classic LCE composites with metallic nanoparticles, magnetic particles, liquid metal, carbon nanotubes, graphene and its derivative, and carbon black, and LCE composites from cellulose nanocrystals within the polymer network where cellulose can provide the unique liquid crystal anisotropy will be discussed. We conclude with the challenges and future research opportunities.

Herein, we report a remotely controlled soft robot employing a photoresponsive nanocomposite synthesized from liquid crystal elastomers (LCEs), high elastic form-stable phase change polymer (HEPCP), and multiwalled carbon nanotubes (MWCNTs). Possessing a two-stage deformation upon exposure to near-infrared (NIR) light, the LCE/HEPCP/MWCNT (LHM) nanocomposite allows the soft robot to exhibit an obvious, fast, and reversible shape change with low detection limitations. In addition to the deformation and bending of the LCE molecular chains itself, the HEPCP in the composite material can also be triggered by a reversible solid-liquid transition due to the temperature rise caused by MWCNTs, which further promotes the change of the LCE. In particular, the proposed photodriven LHM soft robot can bend up to 180° in 2 s upon NIR stimulation (320 mW, distance of 5 cm) and generate recoverable, dramatic, and sensitive deformation to execute various tasks including walking, twisting, and bending. With the capacity of imitating biological behaviors through remote control, the disruptive innovation developed here offers a promising path toward miniaturized untethered robotic systems.

Stimuli-responsive liquid crystal elastomers with molecular orientation coupled to rubber-like elasticity show a great potential as elements in soft robotics, sensing, and transport systems. The orientational order defines their mechanical response to external stimuli, such as thermally activated muscle-like contraction. Here we demonstrate a dynamic thermal control of the surface topography of an elastomer prepared as a coating with a pattern of in-plane molecular orientation. The inscribed pattern determines whether the coating develops elevations, depressions, or in-plane deformations when the temperature changes. The deterministic dependence of the out-of-plane dynamic profile on the in-plane orientation is explained by activation forces. These forces are caused by stretching-contraction of the polymer networks and by spatially varying molecular orientation. The activation force concept brings the responsive liquid crystal elastomers into the domain of active matter. The demonstrated relationship can be used to design coatings with functionalities that mimic biological tissues such as skin.