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Abstract Materials that exhibit varied optical responses to different modes of mechanical stimuli are attractive for complex sensing and adaptive functionalities. However, most mechanochromic materials are fabricated from films or fibers with limited actuation modes. Here, hollow tubes of a symmetric sheath are created using cholesteric liquid crystal elastomers (CLCEs) at the sub‐millimeter scale. The oligomeric precursor is sheared in an elastomeric microchannel to form uniform thickness, overcoming gravity effect and Plateau‐Rayleigh instability. In addition, the coloration is achieved to be faster and have higher reflectivity compared to that of solid fibers. The tube can undergo axial, circumferential, and radial strains upon extension and inflation. The combination of molecular anisotropy and geometry of the tube enables highly sensitive mechanochromic responses in both azimuthal and axial directions: inflation causes red‐to‐violet shift (≈220 nm) at a circumferential strain of 0.57. The inflation of a bent tube generates another mechanochromic mode with a higher sensitivity to strain. Finally, display of 26 alphabets is achieved using 5 tubes, of which the positions can be reconfigured, and curvature‐dependent 3D photonic skins are demonstrated from tubes wrapped around 3D objects. The multi‐mode mechanochromic tubes will find applications for soft robotics, adaptive displays, wearable sensors, and spectrometers. 

Abstract Cellular solids composed of a network of interconnected pores offer low‐density and high strength‐to‐weight ratio as exemplified by wood, bones, corks, and shells. However, the slender edges and low connectivity of the structs in cellular lattices make them vulnerable to buckle, fracture, or collapse. Here, by taking advantage of the continuity of a thin film that can follow curvatures and dissipate energy, shellular materials are created by dip coating a wireframe of the primitive triply periodic minimal surface (TPMS) with an aqueous solution of lyotropic liquid crystalline graphene oxide (GO)/polymer composites. Regulated by surface tension, GO nanosheets align on the polymer soap film as the stress builds up during drying. When the wireframe mesh density is low, the shellular material is film‐dominated, demonstrating superior mechanical strength (384.30 Nm kg⁻¹) and high specific energy absorption (1.59 kJ kg⁻¹) yet lightweight (equivalent density, 0.063 g cm⁻³), with an energy absorption rate comparable to that of carbon nanotube‐based lattices but a lower equivalent density. The study offers insights into designing lightweight yet high‐strength structural materials that also function as impact energy absorbers. 

Abstract Liquid crystalline elastomers (LCEs) are promising candidates for the development of soft, environmentally‐responsive actuators and have recently been explored for application in smart textiles and soft robotics. To realize the potential of LCEs within these systems, the fast, scalable, and continuous production of LCE filaments at controlled diameters is critical. Here, a wet‐spinning method is presented for the scalable manufacturing of graphene/LCE composite filaments. Through a double diffusion mechanism, the graphene/LCE precursors rapidly crosslink into tangible filaments without the use of UV light, instead taking advantage of solvent exchange and high catalyst influx. The continuous production of polydomain graphene/LCE filaments can achieve speeds up to 4500 m h⁻¹. Through π−π interactions between graphene and the LCE matrix, the composite graphene/LCE filaments across a broad range of diameters (137 to 1128 µm) can be obtained with high integrity, achieving actuation stresses and strains up to 3.66 MPa and 44%, respectively, in 3 s. The filaments are showcased as artificial muscles, where both thin and thick filament sizes are of interest. The presented scalable wet‐spinning method will open new opportunities to design smart textiles and soft robotics from fibers of controlled sizes. 

Abstract Direct ink writing (DIW) of core‐shell structures allows for patterning hollow or composite structures for shape morphing and color displays. Cholesteric liquid crystal elastomers (CLCEs) with liquid crystal mesogens assembled in a helix superstructure are attractive for generating tunable iridescent structural colors. Here, by fine‐tuning the rheology of the core and shell materials, respectively, this study creates droplets or a continuous filament in the core from the precursors of polydimethylsiloxane (PDMS) or poly(vinyl alcohol), whereas CLCE forms the outer shell. By introducing a dye in the droplets, the skin structures of cephalopods, consisting of chromatophores and iridocytes, are mimicked for enhanced color saturation, lightness, and camouflage. After removal of the core material, a CLCE hollow fiber is obtained, which can switch colors upon mechanical stretching and pneumatic actuation, much like papilla along with iridocytes. Further, liquid crystal mesogens assembled in the bulk of the fiber are in polydomain. Thus, the skin appears opalescent at room temperature, much like how leucophores enhance reflectins. Upon heating above the nematic to isotropic transition temperature, the skin becomes transparent. Lastly, a cephalopod model is constructed, where different parts of the model can change colors independently based on different mechanisms. 

Abstract A liquid crystalline elastomer (LCE) network consisting of dynamic covalent bonds (DCBs) is referred as a LCE vitrimer. The mesogen alignment and the network topology can be reprogrammed locally in the LCE vitrimer by activating the bond exchange reactions using an external stimulus. After removal of the external stress, a new network is formed and the reprogrammed shape can be fixed, leading to a different set of the physical properties of the LCE vitrimers. Herein, this type of emerging materials is reviewed by a brief introduction of the fundamentals of LCEs, followed by discussions of various DCBs and the design principles for LCE vitrimers. After a presentation of different strategies to improve the stability and reprogrammability of the registered mesogen alignment, approaches to prepare LCE vitrimers with complex shapes and their actuations are discussed. Potential applications such as self‐healing and recycling, mechanochromic effects, and post‐functionalization of nanopores are also reviewed, followed by the conclusion of the remaining challenges and opportunities. 

Abstract Repairing fractured metals to extend their useful lifetimes advances sustainability and mitigates carbon emissions from metal mining and processing. While high‐temperature techniques are being used to repair metals, the increasing ubiquity of digital manufacturing and “unweldable” alloys, as well as the integration of metals with polymers and electronics, call for radically different repair approaches. Herein, a framework for effective room‐temperature repair of fractured metals using an area‐selective nickel electrodeposition process refered to as electrochemical healing is presented. Based on a model that links geometric, mechanical, and electrochemical parameters to the recovery of tensile strength, this framework enables 100% recovery of tensile strength in nickel, low‐carbon steel, two “unweldable” aluminum alloys, and a 3D‐printed difficult‐to‐weld shellular structure using a single common electrolyte. Through a distinct energy‐dissipation mechanism, this framework also enables up to 136% recovery of toughness in an aluminum alloy. To facilitate practical adoption, this work reveals scaling laws for the energetic, financial, and time costs of healing, and demonstrates the restoration of a functional level of strength in a fractured standard steel wrench. Empowered with this framework, room‐temperature electrochemical healing can open exciting possibilities for the effective, scalable repair of metals in diverse applications. 

Abstract 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). 

Abstract Natural materials are highly organized, frequently possessing intricate and sophisticated hierarchical structures from which superior properties emerge. In the wake of biomimicry, there is a growing interest in designing architected materials in the laboratory as such structures could enable myriad functionalities in engineering. Yet, their fabrication remains challenging despite recent progress in additive manufacturing. In particular, soft materials are typically poorly suited to form the requisite structures consisting of regular geometries. Here, a new frugal methodology is reported to fabricate pixelated soft materials. This approach is conceptually analogous to the watershed transform used in image analysis and allows the passive assembly of complex geometries through the capillary‐mediated flow of curable elastomers in confined geometries. Emerging from sources distributed across a Hele–Shaw cell consisting of two parallel flat plates separated by an infinitesimally small gap, these flows eventually meet at the “dividing lines” thereby forming Voronoi tesselations. After curing is complete, these structures turn into composite elastic sheets. Rationalizing the fluid mechanics at play allows the structural geometry of the newly formed sheets to be tailored and thereby their local material properties to be tuned. 

Abstract Owing to the fact that effective properties of low‐density cellular solids heavily rely on their underlying architecture, a variety of explicit and implicit techniques exists for designing cellular geometries. However, most of these techniques fail to present a correlation among architecture, internal forces, and effective properties. This paper introduces an alternative design strategy based on the static equilibrium of forces, equilibrium of polyhedral frames, and reciprocity of form and force. This novel approach reveals a geometric relationship among the truss system architecture, topological dual, and equilibrium of forces on the basis of 3D graphic statics. This technique is adapted to devise periodic strut‐based cellular architectures under certain boundary conditions and they are manipulated to construct shell‐based (shellular) cells with a variety of mechanical properties. By treating the materialized unit cells as representative volume elements (RVE), multiscale homogenization is used to investigate their effective linear elastic properties. Validated by experimental tests on 3D printed funicular materials, it is shown that by manipulating the RVE topology using the proposed methodology, alternative strut materialization schemes, and rational addition of bracing struts, cellular mechanical metamaterials can be systematically architected to demonstrate properties ranging from bending‐ to stretching‐dominated, realize metafluidic behavior, or create novel hybrid shellulars. 

Atmospheric water vapor is an abundant and renewable resource that can alleviate growing water scarcity. Hybrid hydrogel desiccants composed of hygroscopic salts hold significant promise for atmospheric water harvesting (AWH) due to their increased capacity for water uptake. Thus far, many efforts in fabricating these desiccants require multistep processes, where the salt impregnation is achieved post-hydrogel fabrication. Here, we develop a scalable wet spinning methodology using aramid nanofibers (ANFs) to template and coagulate hydroxypropyl cellulose (HPC) into filaments in a coagulation bath consisting of water and lithium chloride (LiCl). HPC serves as the matrix to retain the captured water vapor, and later releases it upon heating. ANFs serve as the physical cross-linker between HPC, allowing for wet spinning at a speed up to 61 m h–1. The composite filaments achieve up to 0.55 g g–1 water uptake at 30% relative humidity (RH) and 21 °C, reaching 80% saturation in 40 min. With a lower critical solution temperature of 39 °C, the desiccant filaments can release up to 72% of the captured water at 60 °C after 30 min. In an AWH chamber, the filaments can achieve daily water production of 5.21 L kg–1 day–1 at 30% RH and 21 °C.