to sluggish actuation speed (response time typically on the order of minutes). Conventional one-way SMPs do not remember the temporary shapes and the recovery speed is relatively slow (response time from tens of seconds to minutes) since it is heat-activated. LCEs, in contrast, owning to their inherent anisotropy, offer promises for fast (e.g., 10 ms [11]) and reversible actuation, large actuation strain, and high energy conversion efficiency. [12] LCEs are lightly crosslinked polymer networks containing main-chain or sidechain mesogenic units. [13] The deformation

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.

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).

Plasmonic resonance from 2D anisotropic metallic nanoparticles for surface-enhanced Raman scattering (SERS) has attracted substantial attention for applications in chemical and environmental monitoring because of its intrinsic electromagnetic “hotspot” and orientation-dependent optical properties. Nevertheless, their sensing applications have been limited by their poor stability toward oxidation and moisture and complicated fabrication processes for large-scale assembly, especially on flexible substrates. In this work, we demonstrate water-stable nanofibers as active SERS substrates electrospun from anisotropic gold nanoprisms (AuNPs) mixed with poly­(vinyl alcohol) (PVA) at a concentration of 2.5–20 nM, followed by cross-linking by glutaraldehyde (GA) vapor at room temperature. Using 4-mercaptobenzoic acid (4-MBA) as the target molecule, we show that the nanofiber mat with 20 nM AuNPs exhibits high sensitivity at a concentration as low as 10–10 M 4-MBA with an enhancement factor of 107 and good uniformity over a very large area (20 cm2) with an average relative standard deviation of <0.074. The cross-linked PVA/AuNP nanofibers are stable against water without an obvious decrease in the SERS signal. In the detection of Rhodamine 6G (R6G) molecules in the water solution, the Raman intensity of R6G shows almost no decay over 3 months compared to that of the as-prepared mat. Further, we show the detection of trace pesticide (10–6 M) on the orange exocarp, suggesting that our fiber mat could be applied for potential applications including food safety, biomedicine, and environmental monitoring.

Fibrous soft actuators with high molecular anisotropy are of interest for shape morphing from 1D to 2D and 3D in response to external stimuli with high actuation efficiency. Nevertheless, few have fabricated fibrous actuators with controlled molecular orientations and stiffness. Here, we fabricate filaments from liquid crystal networks (LCNs) with segmental crosslinking density and gradient porosity from a mixture of di-acrylate mesogenic monomers and small-molecule nematic or smectic liquid crystals (LCs) filled in a capillary. During photopolymerization, phase separation between the small-molecule LCs and LCN occurs, making one side of the filament considerably denser than the other side. To direct its folding mode (bending or twisting), we control the alignment of LC molecules within the capillary, either along or perpendicular to the filament long axis. We show that the direction of UV exposure can determine the direction of phase separation, which in turn direct the deformation of the filament after removal of the small-molecule LCs. We find that the vertical alignment of LCs within the filament is essential to efficiently direct bending deformation. By photopatterning the filament with segmental crosslinking density, we can induce a reversible folding/unfolding into 2D and 3D geometries triggered by deswelling/swelling in an organic solvent. Moreover, by taking advantage of the large elastic modulus of LCNs and large contrast of the modulus before and after swelling, we show that the self-folded LCP filament could act as a strong gripper.