Light-driven continuous rotating Möbius strip actuators

Hydrogels with Differentiated Hydrogen-Bonding Networks for Bioinspired Stress Response

Stress response, an intricate and autonomously coordinated reaction in living organisms, holds a reversible, multi-path, and multi-state nature. However, existing stimuli-responsive materials often exhibit single-step and monotonous reactions due to the limited integration of structural components. Inspired by the cooperative interplay of extensor and flexor cells within Mimosa's pulvini, we present a hydrogel with differentiated hydrogen-bonding (H-bonding) networks designed to enable the biological stress response. Weak H-bonding domains resemble flexor cells, confined within a hydrophobic network stabilized by strong H-bonding clusters (acting like extensor cells). Under external force, strong H-bonding clusters are disrupted, facilitating water diffusion from the bottom layer and enabling transient expansion pressure gradient along the thickness direction. Subsequently, water diffuses upward, gradually equalizing the pressure, while weak H-bonding domains undergo cooperative elastic deformation. Consequently, the hydrogel autonomously undergoes a sequence of reversible and pluralistic motion responses, similar to Mimosa's touch-triggered stress response. Intriguingly, it exhibits stress-dependent color shifts under polarized light, highlighting its potential for applications in time-sensitive "double-lock" information encryption systems. This work achieves the coordinated stress response inspired by natural tissues using a simple hydrogel, paving the way for substantial advancements in the development of intelligent soft robots.

Closed Twisted Hydrogel Ribbons with Self-Sustained Motions under Static Light Irradiation

Self-sustained motions are widespread in biological systems by harvesting energy from surrounding environments, which inspire scientists to develop autonomous soft robots. However, most-existing soft robots require dynamic heterogeneous stimuli or complex fabrication with different components. Recently, control of topological geometry has been promising to afford soft robots with physical intelligence and thus life-like motions. Reported here are a series of closed twisted ribbon robots, which exhibit self-sustained flipping and rotation under constant light irradiation. Both Möbius strip and Seifert ribbon robots are devised for the first time by using an identical hydrogel, which responds to light irradiation on either side. Experiment and simulation results indicate that the self-regulated motions of the hydrogel robots are related to fast and reversible response of muscle-like gel, self-shadowing effect, and topology-facilitated refresh of light-exposed regions. The motion speeds and directions of the hydrogel robots can be tuned over a wide range. These closed twisted ribbon hydrogels are further applied to execute specific tasks in aqueous environments, such as collecting plastic balls, climbing a vertical rod, and transporting objects. This work presents new design principle for autonomous hydrogel robots by benefiting from material response and topology geometry, which may be inspirative for the robotics community.

Electronic and structural properties of Möbius boron-nitride and carbon nanobelts

For the development of nanofilters and nanosensors, we wish to know the impact of size on their geometric, electronic, and thermal stabilities. Using the semiempirical tight binding method as implemented in the xTB program, we characterized Möbius boron-nitride and carbon-based nanobelts with different sizes and compared them to each other and to normal nanobelts. The calculated properties include the infrared spectra, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), the energy gap, the chemical potential, and the molecular hardness. The agreement between the peak positions from theoretical infrared spectra compared with experimental ones for all systems validates the methodology that we used. Our findings show that for the boron-nitride-based nanobelts, the calculated properties have an opposite monotonic relationship with the size of the systems, whereas for the carbon-based nanobelts, the properties show the same monotonic relationship for both types of nanobelts. Also, the torsion presented on the Möbius nanobelts, in the case of boron-nitride, induced an inhomogeneous surface distribution for the HOMO orbitals. High-temperature molecular dynamics also allowed us to contrast carbon-based systems with boron-nitride systems at various temperatures. In all cases, the properties vary with the increase in size of the nanobelts, indicating that it is possible to choose the desired values by changing the size and type of the systems. This work has many implications for future studies, for example our results show that carbon-based nanobelts did not break as we increased the temperature, whereas boron-nitride nanobelts had a rupture temperature that varied with their size; this is a meaningful result that can be tested when the use of more accurate simulation methods become practical for such systems in the future.

Multimodal Autonomous Locomotion of Liquid Crystal Elastomer Soft Robot

Self-oscillation phenomena observed in nature serve as extraordinary inspiration for designing synthetic autonomous moving systems. Converting self-oscillation into designable self-sustained locomotion can lead to a new generation of soft robots that require minimal/no external control. However, such locomotion is typically constrained to a single mode dictated by the constant surrounding environment. In this study, a liquid crystal elastomer (LCE) robot capable of achieving self-sustained multimodal locomotion, with the specific motion mode being controlled via substrate adhesion or remote light stimulation is presented. Specifically, the LCE is mechanically trained to undergo repeated snapping actions to ensure its self-sustained rolling motion in a constant gradient thermal field atop a hotplate. By further fine-tuning the substrate adhesion, the LCE robot exhibits reversible transitions between rolling and jumping modes. In addition, the rolling motion can be manipulated in real time through light stimulation to perform other diverse motions including turning, decelerating, stopping, backing up, and steering around complex obstacles. The principle of introducing an on-demand gate control offers a new venue for designing future autonomous soft robots.

Spin-controlled topological phase transition in non-Euclidean space

Modulation of topological phase transition has been pursued by researchers in both condensed matter and optics research fields, and has been realized in Euclidean systems, such as topological photonic crystals, topological metamaterials, and coupled resonator arrays. However, the spin-controlled topological phase transition in non-Euclidean space has not yet been explored. Here, we propose a non-Euclidean configuration based on Möbius rings, and we demonstrate the spin-controlled transition between the topological edge state and the bulk state. The Möbius ring, which is designed to have an 8π period, has a square cross section at the twist beginning and the length/width evolves adiabatically along the loop, accompanied by conversion from transverse electric to transverse magnetic modes resulting from the spin-locked effect. The 8π period Möbius rings are used to construct Su-Schrieffer-Heeger configuration, and the configuration can support the topological edge states excited by circularly polarized light, and meanwhile a transition from the topological edge state to the bulk state can be realized by controlling circular polarization. In addition, the spin-controlled topological phase transition in non-Euclidean space is feasible for both Hermitian and non-Hermitian cases in 2D systems. This work provides a new degree of polarization to control topological photonic states based on the spin of Möbius rings and opens a way to tune the topological phase in non-Euclidean space.

Self-sustainable autonomous soft actuators

Self-sustainable autonomous locomotion is a non-equilibrium phenomenon and an advanced intelligence of soft-bodied organisms that exhibit the abilities of perception, feedback, decision-making, and self-sustainment. However, artificial self-sustaining architectures are often derived from algorithms and onboard modules of soft robots, resulting in complex fabrication, limited mobility, and low sensitivity. Self-sustainable autonomous soft actuators have emerged as naturally evolving systems that do not require human intervention. With shape-morphing materials integrating in their structural design, soft actuators can direct autonomous responses to complex environmental changes and achieve robust self-sustaining motions under sustained stimulation. This perspective article discusses the recent advances in self-sustainable autonomous soft actuators. Specifically, shape-morphing materials, motion characteristics, built-in negative feedback loops, and constant stimulus response patterns used in autonomous systems are summarized. Artificial self-sustaining autonomous concepts, modes, and deformation-induced functional applications of soft actuators are described. The current challenges and future opportunities for self-sustainable actuation systems are also discussed.

Miniaturized and untethered McKibben muscles based on photothermal-induced gas-liquid transformation

Pneumatic artificial muscles can move continuously under the power support of air pumps, and their flexibility also provides the possibility for applications in complex environments. However, in order to achieve operation in confined spaces, the miniaturization of artificial muscles becomes crucial. Since external attachment devices greatly hinder the miniaturization and use of artificial muscles, we propose a light-driven approach to get rid of these limitations. In this study, we report a miniaturized fiber-reinforced artificial muscle based on mold editing, capable of bending and axial elongation using gas-liquid conversion in visible light. The minimum volume of the artificial muscle prepared using this method was 15.7 mm3 (d = 2 mm, l = 5 mm), which was smaller than those of other fiber-reinforced pneumatic actuators. This research can promote the development of non-tethered pneumatic actuators for rescue and exploration, and create the possibility of miniaturization of actuators.

Liquid Crystal Elastomer Artificial Tendrils with Asymmetric Core-Sheath Structure Showing Evolutionary Biomimetic Locomotion

The sophisticated and complex haptonastic movements in response to environmental-stimuli of living organisms have always fascinated scientists. However, how to fundamentally mimic the sophisticated hierarchical architectures of living organisms to provide the artificial counterparts with similar or even beyond-natural functions based on the underlying mechanism remains a major scientific challenge. Here,  liquid crystal elastomer (LCE) artificial tendrils showing evolutionary biomimetic locomotion are developed following the structure-function principle that is used in nature to grow climbing plants. These elaborately designed tendril-like LCE actuators possess an asymmetric core-sheath architecture which shows a higher-to-lower transition in the degree of LC orientation from the sheath-to-core layer across the semi-ellipse cross-section. Upon heating and cooling, the LCE artificial tendril can undergo reversible tendril-like shape-morphing behaviors, such as helical coiling/winding, and perversion. The fundamental mechanism of the helical shape-morphing of the artificial tendril is revealed by using theoretical models and finite element simulations. Besides, the incorporation of metal-ligand coordination into the LCE network provides the artificial tendril with reconfigurable shape-morphing performances such as helical transitions and rotational deformations. Finally, the abilities of helical and rotational deformations are integrated into a new reprogrammed flagellum-like architecture to perform evolutionary locomotion mimicking the haptonastic movements of the natural flagellum.

Defected twisted ring topology for autonomous periodic flip-spin-orbit soft robot

Periodic spin-orbit motion is ubiquitous in nature, observed from electrons orbiting nuclei to spinning planets orbiting the Sun. Achieving autonomous periodic orbiting motions, along circular and noncircular paths, in soft mobile robotics is crucial for adaptive and intelligent exploration of unknown environments-a grand challenge yet to be accomplished. Here, we report leveraging a closed-loop twisted ring topology with a defect for an autonomous soft robot capable of achieving periodic spin-orbiting motions with programmed circular and re-programmed irregular-shaped trajectories. Constructed by bonding a twisted liquid crystal elastomer ribbon into a closed-loop ring topology, the robot exhibits three coupled periodic self-motions in response to constant temperature or constant light sources: inside-out flipping, self-spinning around the ring center, and self-orbiting around a point outside the ring. The coupled spinning and orbiting motions share the same direction and period. The spinning or orbiting direction depends on the twisting chirality, while the orbital radius and period are determined by the twisted ring geometry and thermal actuation. The flip-spin and orbiting motions arise from the twisted ring topology and a bonding site defect that breaks the force symmetry, respectively. By utilizing the twisting-encoded autonomous flip-spin-orbit motions, we showcase the robot's potential for intelligently mapping the geometric boundaries of unknown confined spaces, including convex shapes like circles, squares, triangles, and pentagons and concaves shapes with multi-robots, as well as health monitoring of unknown confined spaces with boundary damages.

Mechanochromic and ionic conductive cholesteric liquid crystal elastomers for biomechanical monitoring and human-machine interaction

Cholesteric liquid crystal elastomers (CLCEs) that combine rubbery elasticity with structural colour from self-assembled helical nanostructures are of paramount importance for diverse applications such as biomimetic skins, adaptive optics and soft robotics. Despite great advances, it is challenging to integrate electrical sensing and colour-changing characteristics in a single CLCE system. Here, we report the design and synthesis of an ionic conductive cholesteric liquid crystal elastomer (iCLCE) through in situ Michael addition and free-radical photopolymerization of CLCE precursors on silane-functionalized polymer ionic liquid networks, in which robust covalent chemical bonding was formed at the interface. Thanks to superior mechanochromism and ionic conductivity, the resulting iCLCEs exhibit dynamic colour-changing and electrical sensing functions in a wide range upon mechanical stretching, and can be used for biomechanical monitoring during joint bending. Importantly, a capacitive elastomeric sensor can be constructed through facilely stacking iCLCEs, where the optical and electrical dual-signal reporting performance allows intuitive visual localization of pressure intensity and distribution. Moreover, proof-of-concept application of the iCLCEs has been demonstrated with human-interactive systems. The research disclosed herein can provide new insights into the development of bioinspired somatosensory materials for emerging applications in diverse fields such as human-machine interaction, prostheses and intelligent robots.

Photo-Responsive Dynamic Organic Room-Temperature Phosphorescence Materials Based on a Functional Unit Combination Strategy

A rational molecular design strategy facilitates the development of a purely organic room-temperature phosphorescence (RTP) material system with precisely regulated luminescence properties, which surely promotes its functional integration and intelligent application. Here, a functional unit combination strategy is proposed to design novel RTP molecules combining a folding unit with diverse luminescent cores. The different luminescent cores are mainly responsible for tunable RTP properties, while the folding unit contributes to the spin-orbit coupling (SOC) enhancement, which makes the RTP material design as workable as the building block principle. By this strategy, a series of color/lifetime-tunable RTP materials is achieved with unique photo-responsive RTP enhancement when subjected to UV irradiation, which expands their application scenarios in reusable privacy tags, advanced "4D" encryption, and phase separation analysis of blended polymers. This work suggests a simple and effective strategy to design purely organic RTP materials with tunable color and lifetime, and also provides new application options for photo-responsive dynamic RTP materials.

4D Printing: The Development of Responsive Materials Using 3D-Printing Technology

Additive manufacturing, widely known as 3D printing, has revolutionized the production of biomaterials. While conventional 3D-printed structures are perceived as static, 4D printing introduces the ability to fabricate materials capable of self-transforming their configuration or function over time in response to external stimuli such as temperature, light, or electric field. This transformative technology has garnered significant attention in the field of biomedical engineering due to its potential to address limitations associated with traditional therapies. Here, we delve into an in-depth review of 4D-printing systems, exploring their diverse biomedical applications and meticulously evaluating their advantages and disadvantages. We emphasize the novelty of this review paper by highlighting the latest advancements and emerging trends in 4D-printing technology, particularly in the context of biomedical applications.

Shape-Programmable Liquid-Crystalline Polyurethane-Based Multimode Actuators Triggered by Light-Driven Molecular Motors

In recent years, light-driven soft actuators have been rapidly developed as enablers in the fabrication of artificial robots and biomimetic devices. However, it remains challenging to amplify molecular isomerization to multiple modes of macroscopic actuation with large amplitude and complex motions. Here, a strategy is reported to build a light-responsive liquid-crystalline polyurethane elastomer by phototriggered overcrowded alkene-based molecular motors. A trifunctional molecular motor modified with an ethylene glycol spacer on the rotor and stator functions as a crosslinker and unidirectional stirrer that amplifies molecular motion into macroscopic movement. The shape-programmable polymeric film presents superior mechanical properties and characteristic shape-memory effect. Furthermore, diverse modes of motions including bending, unwinding, and contracting with tunable actuation speed over a wide range are achieved. Such research is hoped to pave a new way for the design of advanced light-responsive soft actuators and robots.

Cold-programmed shape-morphing structures based on grayscale digital light processing 4D printing

Shape-morphing structures that can reconfigure their shape to adapt to diverse tasks are highly desirable for intelligent machines in many interdisciplinary fields. Shape memory polymers are one of the most widely used stimuli-responsive materials, especially in 3D/4D printing, for fabricating shape-morphing systems. They typically go through a hot-programming step to obtain the shape-morphing capability, which possesses limited freedom of reconfigurability. Cold-programming, which directly deforms the structure into a temporary shape without increasing the temperature, is simple and more versatile but has stringent requirements on material properties. Here, we introduce grayscale digital light processing (g-DLP) based 3D printing as a simple and effective platform for fabricating shape-morphing structures with cold-programming capabilities. With the multimaterial-like printing capability of g-DLP, we develop heterogeneous hinge modules that can be cold-programmed by simply stretching at room temperature. Different configurations can be encoded during 3D printing with the variable distribution and direction of the modular-designed hinges. The hinge module allows controllable independent morphing enabled by cold programming. By leveraging the multimaterial-like printing capability, multi-shape morphing structures are presented. The g-DLP printing with cold-programming morphing strategy demonstrates enormous potential in the design and fabrication of shape-morphing structures.

Möbius carbon nanobelts interacting with heavy metal nanoclusters

CONTEXT

The interaction between carbon nanostructures and heavy metal clusters is of great interest due to their potential applications as sensors and filters to remove the former from environment. In this work, we investigated the interaction between two types of carbon nanobelts (Möbius-type nanobelt and simple nanobelt) and nickel, cadmium, and lead nanoclusters. Our aim was to determine how both systems interact which would shed light on the potential applications of the carbon nanostructures as pollutant removal and detecting devices.

METHODS

To investigate the interaction between carbon nanostructures and heavy metal nanoclusters, we utilized the semiempirical tight binding framework provided by xTB software with the GFN2-xTB Hamiltonian. We performed calculations to determine the best interaction site, lowest energy geometries, complexes stability (using molecular dynamics at 298K), binding energy, and electronic properties. We also carried out a topological study to investigate the nature and intensity of the bonds formed between the metal nanoclusters and the nanobelts. Our results demonstrate that heavy metal nanoclusters have a favorable binding affinity towards both nanobelts, with the Möbius-type nanobelt having a stronger interaction. Additionally, our calculations reveal that the nickel nanocluster has the lowest binding energy, displaying the greatest charge transfer with the nanobelts, which was nearly twice that of the cadmium and lead nanoclusters. Our combined results lead to the conclusion that the nickel nanoclusters are chemisorbed, whereas cadmium and lead nanoclusters are physisorbed in both nanobelts. These findings have significant implications for the development of sensor and filtering devices based on carbon and heavy metal nanoclusters.

Liquid Crystalline Elastomer for Separate or Collective Sensing and Actuation Functions

A porous liquid crystalline elastomer actuator filled with an ionic liquid (PLCE-IL) is shown to exhibit the functions of two classes of materials: electrically responsive, deformable materials for sensing and soft active materials for stimuli-triggered actuation. On one hand, upon the order-disorder phase transition of aligned mesogens, PLCE-IL behaves like a typical actuator capable of reversible shape change and can be used to assemble light-fuelled soft robot. On the other hand, at temperatures below the phase transition, PLCE-IL is an elastomer that can sustain and sense large deformations of various modes as well as environmental condition changes by reporting the corresponding electrical resistance variation. The two distinguished functions can also be used collectively with PLCE-IL integrated in one device. This intelligent feature is demonstrated with an artificial arm. When the arm is manually powered to fold and unfold, the PLCE-IL strip serves as a deformation sensor; while when the manual power is not available, the role of the PLCE-IL strip is switched to an actuator that enables light-driven folding and unfolding of the arm. This study shows that electrically responsive LCEs are a potential materials platform that offers possibilities for merging deformable electronic and actuation applications.

Vibration of a Liquid Crystal Elastomer Spring Oscillator under Periodic Electrothermal Drive

The oscillations of electrically actuated thermally-responsive liquid crystal elastomer (LCE) microfibers under cyclic electric actuation have been discovered in recent experiments. Periodic electric actuation is a common method of active control with potential applications in the fields of micro-actuators. In this paper, the vibration behavior of LCE spring oscillator under periodic electrothermal drive is studied theoretically. Based on the dynamic LCE model, the dynamic governing equation of the LCE spring oscillator is established, and the time history curves of the vibration are obtained by numerical calculations. The results show that the periodic electrothermal drive can cause periodic vibration of the LCE spring oscillator. With the increase of time rate, the vibration amplitude increases first and then decreases. In a small damping system, there exist optimal sets of electrothermal drive period and electrothermal drive time rate to maximize the system amplitude. For the optimum periodic mode, the vibration amplitude of the spring oscillator is affected by the current heat, damping coefficient, gravital acceleration, spring constant and shrinkage coefficient, but not by the initial velocity. The application examples of LCE materials show that periodic electrothermally driven LCEs have promising applications. The results of this study are instructive for the design of soft robots and LCE-based electric locomotives.

Recent Advances in 4D Printing of Liquid Crystal Elastomers

Liquid crystal elastomers (LCEs) are renowned for their large, reversible, and anisotropic shape change in response to various external stimuli due to their lightly cross-linked polymer networks with an oriented mesogen direction, thus showing great potential for applications in robotics, bio-medics, electronics, optics, and energy. To fully take advantage of the anisotropic stimuli-responsive behaviors of LCEs, it is preferable to achieve a locally controlled mesogen alignment into monodomain orientations. In recent years, the application of 4D printing to LCEs opens new doors for simultaneously programming the mesogen alignment and the 3D geometry, offering more opportunities and higher feasibility for the fabrication of 4D-printed LCE objects with desirable stimuli-responsive properties. Here, the state-of-the-art advances in 4D printing of LCEs are reviewed, with emphasis on both the mechanisms and potential applications. First, the fundamental properties of LCEs and the working principles of the representative 4D printing techniques are briefly introduced. Then, the fabrication of LCEs by 4D printing techniques and the advantages over conventional manufacturing methods are demonstrated. Finally, perspectives on the current challenges and potential development trends toward the 4D printing of LCEs are discussed, which may shed light on future research directions in this new field.

Dandelion-Inspired, Wind-Dispersed Polymer-Assembly Controlled by Light

The rise of stimuli-responsive polymers has brought about a wealth of materials for small-scale, wirelessly controlled soft-bodied robots. Thinking beyond conventional robotic mobilities already demonstrated in synthetic systems, such as walking, swimming and jumping, flying in air by dispersal, gliding, or even hovering is a frontier yet to be explored by responsive materials. The demanding requirements for actuator's performance, lightweight, and effective aerodynamic design underlie the grand challenges. Here, a soft matter-based porous structure capable of wind-assisted dispersal and lift-off/landing action under the control of a light beam is reported. The design is inspired by the seed of dandelion, resembling several biomimetic features, i.e., high porosity, lightweight, and separated vortex ring generation under a steady wind flow. Superior to its natural counterparts, this artificial seed is equipped with a soft actuator made of light-responsive liquid crystalline elastomer, which induces reversible opening/closing actions of the bristles upon visible light excitation. This shape-morphing enables manual tuning of terminal velocity, drag coefficient, and wind threshold for dispersal. Optically controlled wind-assisted lift-off and landing actions, and a light-induced local accumulation in descending structures are demonstrated. The results offer novel approaches for wirelessly controlled, miniatured devices that can passively navigate over a large aerial space.

Three-dimensional liquid crystal polymer actuators assembled by athermal photo-welding

Photodeformable liquid crystal polymers (LCPs) exhibit shape changes of different modes like bending, twisting, and oscillation, which depend on the orientation of liquid crystals. However, it is challenging to create a three-dimensional (3D) actuator with distinct actuation modes due to the difficulty of local orientation in a complex bulk architecture. Here we propose a strategy based on athermal photo-welding to integrate different orientations into a single flexible actuator by the photofluidization of azobenzene-containing linear LCPs. Stretch-induced uniaxial films are cut in different directions and subsequently welded via local photofluidization, during which the LCP transitions from a high-modulus glassy state to a rubbery state upon photoisomerization of azobenzene at room temperature. As a consequence, a cucumber vine-like structure with the opposite handedness and a lifting gripper are constructed by such a cut-and-weld process, demonstrating diverse deformation modes of winding, unwinding, and curling. This strategy provides an athermal process for the fabrication of seamless 3D flexible actuators without structural defects, which have potential applications in micromechanical systems, soft robotics, and artificial muscles.

Luminescent Möbius Strip of a Flexible Halogen-Bonded Cocrystal Evolved from Ring and Helix

Luminescent Möbius strip microstructures have been created for the first time based on flexible organic single crystals via a template-free solution self-assembly. We herein demonstrated a rationally designed morphological evolution toward Möbius strips from rings and helixes. Our findings lay the foundation for the future construction of complex matters with predetermined morphologies and functions from crystal systems.

Meniscus-Climbing System Inspired 3D Printed Fully Soft Robotics with Highly Flexible Three-Dimensional Locomotion at the Liquid-Air Interface

Soft robotics locomotion at the liquid-air interface has become more and more important for an intelligent society. However, existing locomotion of soft robotics is limited to two dimensions. It remains a formidable challenge to realize three-dimensional locomotion (X, Y, and Z axes) at the liquid-air two-phase interface due to the unbalanced mechanical environment. Inspired by meniscus-climbing beetle larva Pyrrhalta, the mechanism of a three-phase (liquid-solid-air) contact line is here proposed to address the aforementioned challenge. A corresponding 3D printed fully soft robotics (named larvobot) based on photoresponsive liquid crystal elastomer/carbon nanotubes composites endowed repeatable programmable deformation and high degree-of-freedom locomotion. Three-dimensional locomotion at the liquid-air interface including twisting and rolling-up has been developed. The equation of motion is established by analyzing the mechanics along the solid-water surface of the larvobot. Meanwhile, ANSYS is used to calculate the stress distribution, which coincides with the speculation. Moreover, soft robotics is remotely driven by light in a precise spatiotemporal control, which provides a great advantage for applications. As an example, we demonstrate the controllable locomotion of the soft robotics inside closed tubes, which could be used for drug delivery and intelligent transportation.

Electrically driven liquid crystal network actuators

Soft actuators based on liquid crystal networks (LCNs) have aroused great scientific interest for use as stimuli-controlled shape-changing and moving components for robotic devices due to their fast, large, programmable and solvent-free actuation responses. Recently, various LCN actuators have been implemented in soft robotics using stimulus sources such as heat, light, humidity and chemical reactions. Among them, electrically driven LCN actuators allow easy modulation and programming of the input electrical signals (amplitude, phase, and frequency) as well as stimulation throughout the volume, rendering them promising actuators for practical applications. Herein, the progress of electrically driven LCN actuators regarding their construction, actuation mechanisms, actuation performance, actuation programmability and the design strategies for intelligent systems is elucidated. We also discuss new robotic functions and advanced actuation control. Finally, an outlook is provided, highlighting the research challenges faced with this type of actuator.

Healable, Recyclable, and Multifunctional Soft Electronics Based on Biopolymer Hydrogel and Patterned Liquid Metal

Recent years have witnessed the rapid development of sustainable materials. Along this line, developing biodegradable or recyclable soft electronics is challenging yet important due to their versatile applications in biomedical devices, soft robots, and wearables. Although some degradable bulk hydrogels are directly used as the soft electronics, the sensing performances are usually limited due to the absence of distributed conducting circuits. Here, sustainable hydrogel-based soft electronics (HSE) are reported that integrate sensing elements and patterned liquid metal (LM) in the gelatin-alginate hybrid hydrogel. The biopolymer hydrogel is transparent, robust, resilient, and recyclable. The HSE is multifunctional; it can sense strain, temperature, heart rate (electrocardiogram), and pH. The strain sensing is sufficiently sensitive to detect a human pulse. In addition, the device serves as a model system for iontophoretic drug delivery by using patterned LM as the soft conductor and electrode. Noncontact detection of nearby objects is also achieved based on electrostatic-field-induced voltage. The LM and biopolymer hydrogel are healable, recyclable, and degradable, favoring sustainable applications and reconstruction of the device with new functions. Such HSE with multiple functions and favorable attributes should open opportunities in next-generation electronic skins and hydrogel machines.

Twisting for soft intelligent autonomous robot in unstructured environments

SignificanceAutonomy is crucial for soft robotics that are constructed of soft materials. It remains challenging to create autonomous soft robots that can intelligently interact with and adapt to changing environments without external controls. To do so, it often requires an analogical soft "brain" that integrates on-board sensing, control, computation, and decision-making. Here, we report an autonomous soft robot embodied with physical intelligence for decision-making via adaptive soft body-environment interactions and snap-through instability, without integrated sensing and external controls. This study harnesses physical intelligence as a new paradigm for designing autonomous soft robots that can interact intelligently with their environments, thus potentially reducing the burdens on the conventional integrated sensing, control, computations, and decision-making systems in designing intelligent soft robots.

Design, Regulation, and Applications of Soft Actuators Based on Liquid-Crystalline Polymers and Their Composites

Soft actuators designed from stimuli-responsive polymers often possess a certain amount of bionic functionality because of their versatile deformation. Liquid-crystalline polymers (LCPs) and their composites are among the most fascinating materials for soft actuators due to their great advantages of flexible structure design and easy regulation. In this Spotlight on Applications, we mainly focus on our group's latest research progress in soft actuators based on LCPs and their composites. Some representative research findings from other groups are also included for a better understanding of this research field. Above all, the essential principles for the responsive behavior and reconfigurable performance of the soft actuators are discussed, from the perspective of material morphology and structure design. Further on, we analyze recent work on how to precisely regulate the responsive modes and quantify the operating parameters of soft actuators. Finally, some application examples are given to demonstrate well-designed soft actuators with different functions under varied working environments, which is expected to provide inspiration for future research in developing more intelligent and multifunctional integrated soft actuators.

Light-Fueled Polymer Film Capable of Directional Crawling, Friction-Controlled Climbing, and Self-Sustained Motion on a Human Hair

Recent efforts in stimuli-responsive soft materials have enabled wirelessly controlled actuation with increasing degrees of freedom, yielding miniature robots capable of various locomotion in open environments such as on a plane or inside fluids. However, grand challenges remain in harnessing photomechanical deformation to induce locomotion and control of friction during the movement, especially for robotic actuations within constrained spaces. Here, the authors report a centimeter-long polymer strip made of a liquid crystal network that is capable of versatile light-fueled motions along a human hair. The soft polymer robot can translocate directionally upon temporally modulated excitation and climb vertically through friction control with light. A self-oscillating strip is demonstrated to continuously translocate along the hair upon a constant light stimulus, and its gaiting is associated to the smoothness of the hair surface. The results offer new insights to small-scale photo-actuator, mechanical control, and automation in soft micro robotics.

Liquid Crystals: Versatile Self-Organized Smart Soft Materials

Smart soft materials are envisioned to be the building blocks of the next generation of advanced devices and digitally augmented technologies. In this context, liquid crystals (LCs) owing to their responsive and adaptive attributes could serve as promising smart soft materials. LCs played a critical role in revolutionizing the information display industry in the 20th century. However, in the turn of the 21st century, numerous beyond-display applications of LCs have been demonstrated, which elegantly exploit their controllable stimuli-responsive and adaptive characteristics. For these applications, new LC materials have been rationally designed and developed. In this Review, we present the recent developments in light driven chiral LCs, i.e., cholesteric and blue phases, LC based smart windows that control the entrance of heat and light from outdoor to the interior of buildings and built environments depending on the weather conditions, LC elastomers for bioinspired, biological, and actuator applications, LC based biosensors for detection of proteins, nucleic acids, and viruses, LC based porous membranes for the separation of ions, molecules, and microbes, living LCs, and LCs under macro- and nanoscopic confinement. The Review concludes with a summary and perspectives on the challenges and opportunities for LCs as smart soft materials. This Review is anticipated to stimulate eclectic ideas toward the implementation of the nature's delicate phase of matter in future generations of smart and augmented devices and beyond.

Ultrafast Digital Fabrication of Designable Architectured Liquid Crystalline Elastomer

The muscle-like activities of liquid crystalline elastomers (LCEs) offer great potential for designing future soft machines. Their motion complexity, however, relies on inflexible and cumbersome mesogen alignment techniques. Here, a digital photocuring method for ultrafast template-free fabrication of LCE artificial muscles capable of designable complex motions is reported. This method utilizes the intrinsic light attenuation in the through-plane direction to create mesogen alignment for reversible bending action. To turn this simple actuation into complex motions, the principles of muscles are borrowed which realize diverse motions through the cooperative actions of otherwise simple contraction/expansion of individual muscle bundles. Specifically, the spatiotemporal digital light is utilized to design LCE architectures composed of strategically arranged bending modules. As such, LCE capable of highly designable motions can be fabricated within 25 s light curing without employing any physical alignment templates, which offers an attractive option toward designing functionally diverse soft machines.

Light-Driven Linear Inchworm Motor Based on Liquid Crystal Elastomer Actuators Fabricated with Rubbing Overwriting

Linear displacement is used for positioning and scanning, e.g., in robotics at different scales or in scientific instrumentation. Most linear motors are either powered by rotary drives or are driven directly by pressure, electromagnetic forces or a shape change in a medium, such as piezoelectrics or shape-memory materials. Here, we present a centimeter-scale light-powered linear inchworm motor, driven by two liquid crystal elastomer (LCE) accordion-like actuators. The rubbing overwriting technique was used to fabricate the LCE actuators, made of elastomer film with patterned alignment. In the linear motor, a scanned green laser beam induces a sequence of travelling deformations in a pair of actuators that move a gripper, which couples to a shaft via friction moving it with an average speed in the order of millimeters per second. The prototype linear motor demonstrates how LCE light-driven actuators with a limited stroke can be used to drive more complex mechanisms, where large displacements can be achieved, defined only by the technical constrains (the shaft length in our case), and not by the limited strain of the material. Inchworm motors driven by LCE actuators may be scaled down to sub-millimeter size and can be used in applications where remote control and power supply with light, either delivered in free space beams or via fibers, is an advantage.

Light-Driven Self-Oscillating Actuators with Phototactic Locomotion Based on Black Phosphorus Heterostructure

Developing self-oscillating soft actuators that enable autonomous, continuous, and directional locomotion is significant in biomimetic soft robotics fields, but remains great challenging. Here, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed. Owing to the good photothermal effect of black phosphorus heterostructure and thermal deformation of the actuator components, the new actuator assembled by heterostructured black phosphorus, polymer and paper produces light-driven reversible deformation with fast and large response. By using this actuator as mechanical power and designing a robot configuration with self-feedback loop to generate self-oscillation, an inchworm-like actuator that can crawl autonomously towards the light source is constructed. Moreover, due to the anisotropy and tailorability of the actuator, an artificial crab robot that can simulate the sideways locomotion of crabs and simultaneously change color under light irradiation is also realized.