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Stimuli‐responsive patterned photonic actuators, characterized by their patterned nano/microscale structures and capacity to demonstrate synergistic color changes and shape morphing in response to external stimuli, have attracted intense scientific attention. However, traditional patterned photonic actuator systems still face limitations such as cumbersome and time‐consuming preparation processes and small‐scale deformations. Herein, we introduce a facile approach involving an athermal embossing technique to rapidly fabricate patterned photonic actuators based on near‐infrared (NIR) light‐responsive liquid crystal elastomers. The resulting patterned photonic actuators demonstrate remarkable features, including brilliant angle‐dependent structural color, complex three‐dimensional actuation, and good color durability under NIR light stimulation. As illustrative demonstrations of the proof‐of‐concept, we fabricate two light‐fuelled patterned photonic soft actuators: a butterfly‐inspired actuator that can produce wing‐flapping dynamic changes in structural color, and an origami crane‐shaped actuator with shape memory, structural color information storage, and dynamic display properties. This strategy provides distinct insights into the design and fabrication of various patterned photonic soft robotic devices and intelligent actuators. [ABSTRACT FROM AUTHOR]

Soft actuators belong to a type of actuators made of soft materials which are capable of converting applied energy to mechanical motion. They have been utilized in several fields due to their flexibility, low weight, inexpensiveness and simple fabrication. In this work, iota‐carrageenan (푖C) was chosen as the starting material for a hydrogel‐based actuator. The 푖C hydrogels were fabricated via a simple solvent‐casting technique at various concentrations: 2.4% (v/v), 2.8% (v/v) and 3.2% (v/v). All 푖C hydrogels were characterized for their chemical, thermal, rheological and morphological properties as well as the actuation performances under applied electric field. The 푖C hydrogels showed monotonic increases in the static bending distance and dielectrophoretic force with increasing electric field strength. Above the critical electrical field strengths, the ribbon‐like 푖C hydrogels oscillated back and forth due to the competition between the dielectrophoresis force, the resisting elastic force, the weight and the inertia force. Stability diagrams were constructed for the first time separating static bending from oscillation behavior under constant applied electric fields. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The synthesis of MXene‐cobalt hybrid (MX‐Co) is presented utilizing a molten salt approach, targeting the application in artificial muscle technology. Mxenes possess exceptional electronic conductivity and surface chemistry, making them ideal candidates for electrochemical applications. Cobalt, known for its ferromagnetic qualities, is a good match for MXenes and enhances artificial muscles' mechanical performance. By circumventing hazardous hydrofluoric (HF) acid, a facile and scalable synthesis process for MX‐Co hybrids is demonstrated. Their structural and electrochemical characteristics are revealed through characterization using cutting‐edge spectroscopic and microscopic techniques. When compared to typical PEDOT: PSS electrodes, electrochemical experiments show that MX‐Co electrodes have higher electroactive performance, with enhanced bending deformation under various input conditions. MX‐Co hybrids exhibit a specific capacitance of 77.34 F g−1, 1.6 times higher than PEDOT: PSS, and achieve a substantial enhancement of electrochemical bending displacement, up to 11.72 mm under a low input voltage of 1 V, showcasing their potential for soft actuator applications. [ABSTRACT FROM AUTHOR]

In this paper, electrically responsive liquid crystal network (LCN) based soft actuators are presented that can achieve large deformations under an alternating current (AC) electric field. These LCN actuators are prepared by photopolymerization of liquid crystal acrylate monomers with polar end groups, which form polar side chains in the networks. Actuation is initiated by applying a high‐frequency and low‐voltage electric field. When this AC field is applied, the LC mesogens, especially the polar side chains, can oscillate, decreasing the molecular order, and creating free volume in the LCNs, which further results in anisotropic deformation. The formed shapes range from bending to bulging, depending on the programmed molecular alignment. The actuation proceeds fast within 5 s both for activation and for the relaxation to the initial state upon switching the power on and off. This LCN soft actuator exhibits fast response, low power consumption, and high precision, making it a promising candidate for applications in soft robotics, microfluidics, and biomimetic muscles. [ABSTRACT FROM AUTHOR]

Tardigrades are the most resilient biospecies on Earth, capable of surviving extreme conditions including high temperatures, pressures, air deprivation, and exposure to noxious chemicals and radiation. The study here undertakes biomimicry of the remarkable adaptability of tardigrades by designing biomorph soft actuators (BSAs) that can endure these harsh environments. Unlike previous tardigrade‐inspired materials, which lacked a naturalistic interaction with their surroundings, the BSAs replicate the anatomical macrostructures and the non‐monotonic environmental resilience of tardigrades, especially their ability to adapt via dehydration and rehydration. Dual‐layer hydrogel spheres are employed with embedded fluid bubbles, creating cohesive yet non‐monolithic smart BSA structures. These structures exhibit high resilience to compressive, thermal, and radiation stimuli, achieved through thermoresponsive shape morphing driven by fluid balance. Their advanced capabilities are also demonstrated, such as driving a McKibben‐type artificial muscle and rapidly regenerating themselves from a state exposed to hazardous chemicals. Such versatile actuating biomorphs hold great promise for various autonomous applications, including soft robotic operations in aqueous effluents, deserts, polar regions, and outer space. [ABSTRACT FROM AUTHOR]

Electro‐ionic artificial muscles, consisting of a configuration where an electrolyte membrane is flanked by two active electrodes, have emerged as transformative components in the field of soft robotics. Despite this, the current actuation performance falls short for many practical applications, because most existing electrode materials exhibit limitations in terms of their properties. Here, a multifunctional active electrode material is reported for an electro‐ionic artificial muscle, employing a triazine framework that incorporates 6,6′‐Dicyano‐2,2′‐bipyridyl (DCB‐TF). The multifunctional DCB‐TF boasts fully conjugated bonds, facilitating fast electron transfer, high porosity for ion accommodation, a substantial surface area of 1800 m2 g−1 for charge storage, numerous active sites for ion interactions, and complete aromatic rings contributing to stability. The application of DCB‐TF to the active electrodes in the electro‐ionic artificial muscles yields remarkable actuation performance, including a substantial bending displacement of 24 mm at 0.5 V and 0.2 Hz, a rapid response time of 2 s, and outstanding durability sustained over 3.4 million continuous cycles. Consequently, these soft actuators have enabled a dragonfly demonstration as a form of kinetic art. [ABSTRACT FROM AUTHOR]

Actuators based on soft elastomers offer significant advantages to the field of robotics, providing greater adaptability, improving collision resilience, and enabling shape‐morphing. Thus, soft fluidic actuators have seen an expansion in their fields of application. Closed‐cycle hydraulic systems are pressure agnostic, enabling their deployment in extremely high‐pressure conditions, such as deep‐sea environments. However, soft actuators have not been widely adopted on unmanned underwater vehicle control surfaces for deep‐sea exploration due to their unpredictable hydrodynamic behavior when camber‐morphing is applied. This study presents the design and characterization of a soft wing and investigates its feasibility for integration into an underwater glider. It is found that the morphing wing enables the glider to adjust the lift‐to‐drag ratio to adapt to different flow conditions. At the operational angle of attack of 12.5°, the lift‐to‐drag ratio ranges from −70% to +10% compared to a rigid version. Furthermore, it reduces the need for internal moving parts and increases maneuverability. The findings lay the groundwork for the real‐world deployment of soft robotic principles capable of outperforming existing rigid systems. With the herein‐described methods, soft morphing capabilities can be enabled on other vehicles. [ABSTRACT FROM AUTHOR]

Actuators utilizing snap‐through instabilities are widely investigated for high‐performance fast actuators and shape reconfigurable structures owing to their rapid response and limited reliance on continuous energy input. However, prevailing approaches typically involve a combination of multiple bistable actuator units and achieving multistability within a single actuator unit still remains an open challenge. Here, a soft actuator is presented that uses shape memory alloy (SMA) and mixed‐mode elastic instabilities to achieve intrinsically multistable shape reconfiguration. The multistable actuator unit consists of six stable states, including two pure bending states and four bend‐twist states. The actuator is composed of a pre‐stretched elastic membrane placed between two elastomeric frames embedded with SMA coils. By controlling the sequence and duration of SMA activation, the actuator is capable of rapid transition between all six stable states within hundreds of milliseconds. Principles of energy minimization are used to identify actuation sequences for various types of stable state transitions. Bending and twisting angles corresponding to various prestretch ratios are recorded based on parameterizations of the actuator's geometry. To demonstrate its application in practical conditions, the multistable actuator is used to perform visual inspection in a confined space, light source tracking during photovoltaic energy harvesting, and agile crawling. [ABSTRACT FROM AUTHOR]

The hygroscopic motion of plants has inspired the development of moisture‐activated soft actuators. These actuators driven by ambient moisture sources are of great research interest in robotics and self‐regulating textiles. However, these actuators often have slow motion and can only perform bending and twisting motions. Herein, a cellulose film‐based fast‐morphing and motion‐programmable soft actuator is presented that can generate caterpillar‐like movement. The cellophane films reported here bend almost instantaneously under changing humidity, with a large bending curvature, high repeatability, and negligible hysteresis. Different actuation modes are studied using both coated and uncoated cellophane films. The uncoated cellophane film can continuously move on a moist substrate through autonomous bending–rolling–flipping (or oscillating) cycles. A facile strategy is used here to control the rolling direction and facilitate the flipping motion by offsetting its center of gravity during deformation by adding appropriate weights on the end of the actuator. The coated cellophane film is used to fabricate motion‐programmable actuators through heat‐laminating. Several actuator structures are designed and fabricated and their diverse moisture‐induced motions are demonstrated. [ABSTRACT FROM AUTHOR]

Soft actuators with unique mechanics have gained significant interests for unique capabilities and versatile applications. However, their actuation mechanisms (usually driven by light, heat, or chemical reactions) result in long actuation times. Reported magnetically actuated soft actuators can produce rapid and precise motions, yet their complex manufacturing processes may constrain their range of applications. Here, the “bone‐in‐flesh” is proposed that constructs combining rigid magnetic structures encapsulated within soft polymers to create untethered magnetic soft actuators. This approach enables these soft, impact‐resistant, agile actuators with a significantly simplified fabrication process. As demonstration examples, multiple soft actuators are fabricated and tested, including actuators for auxetic properties, 2D–3D transformations, and multi‐stable states. As such, this work offers a promising solution to challenges associated with soft actuators to potentially expand their applications in various domains. [ABSTRACT FROM AUTHOR]

A porous actuator is prepared using a liquid crystal elastomer (LCE) loaded with metal‐organic framework (MOF) nanoparticles (MIL‐88A). While the swellable MOF additive endows the LCE actuator with nanoscale pores, after its removal by chemical etching, macroporous LCE actuator is obtained. This LCE‐MOF actuator displays several interesting features. 1) Selective etching allows the actuator in water to curl in one direction and then reverse the curling direction owing to differential water absorption of the nano‐ and macroporous layers. 2) The stretching‐induced alignment of mesogens in the actuator is little affected by the presence of MOF and substantially retained after water uptake, so that an actuation deformation can be generated either by water absorption or thermally induced order‐disorder phase transition. 3) Assisted by the UV irradiation used for polymer cross‐linking, magnetic iron oxide FeO appears to be formed after chemical etching, which allows the actuator to gain the ability to move on water surface guided by a magnet. 4) The in situ formation of magnetic iron oxide in the macroporous actuator also provides an enhanced photothermal effect, making light‐driven locomotion of the actuator more effective. The use of active porogen like MOF opens a new way to explore porous LCE actuators. [ABSTRACT FROM AUTHOR]

Soft robots require soft actuators for mobility and functionality. To integrate multiple functions in a limited space, researchers are developing multifunctional soft actuators with several functions integrated in one device. This study successfully demonstrates an electroluminescent (EL) soft actuator, a single device with both light‐emitting and actuating capabilities, using liquid dielectric and uniformly dispersed EL phosphor particles. EL phosphor particles are copper‐doped zinc sulfide (ZnS) particles doped with copper. The work is able to disperse the ZnS particles uniformly in the oil by coating the ZnS particles with silica, ensuring consistent luminescence across the device's active area. The performance of the soft actuator is notable, with a strain of 25% and a maximum EL intensity of 23 cd m−2 for a single actuator. When stacking multiple actuators, the intensity exceeds 29 cd m−2. The findings suggest that EL actuator devices will be valuable smart components for soft robots and interactive sensors. They can effectively represent external stimuli through color signals, expanding the capabilities of these systems. [ABSTRACT FROM AUTHOR]

In this review, 4D printing (4DP) is delved into through fused filament fabrication (FFF) and its implications for human–material interaction (HMI). FFF 4DP's emergence in HMI represents a nascent and evolving concept worthy of deeper exploration. In this article, FFF 4DP's fundamental principles, methodologies, materials, and associated benefits and challenges are introduced. Herein, the primary focus is the intersection between FFF 4DP and HMI, investigating the potential of employing FFF 4D‐printed objects as interactive interfaces. Various HMI scenarios are examined, including applications in soft actuators, smart toys, household devices, smart consumer products, 4D textiles, and customizable wood‐based items. Moreover, in this article, the current state of the art and development in the field are discussed, highlighting notable projects that integrate FFF 4DP into HMI to advance environmental sustainability. Also, key challenges/limitations requiring attention for the widespread adoption of 4DP in HMI applications are identified. In this work, an in‐depth analysis of FFF 4DP within the HMI context is offered, underscoring its potential to transform human interactions with machines and smart devices. Innovative features for dynamic and adaptable interfaces are introduced, promising to revolutionize user experiences. The article serves as a valuable resource for researchers, practitioners, and designers interested in exploring the exciting possibilities of FFF 4DP in the realm of HMI. [ABSTRACT FROM AUTHOR]

Liquid crystal actuators conventionally undergo shape changes across an order‐disorder phase transition between liquid crystal (LC) and isotropic phases. In this study, we introduce an innovative Liquid Crystal Polymer (LCP) actuator harnessing an order‐order LC phase transition mechanism. The LCP film is easily stretchable within the LC phase, facilitated by the π–π stacking of phenyl groups serving as robust physical crosslinking points, and thereby transforms to a stable monodomain structure. The resultant monodomain LCP actuator shows a distinctive reversible dynamic shape change, exhibiting extension followed by contraction along the LC director on cooling. The extension is propelled by the reversible smectic C to smectic A phase transition, and the contraction is attributed to the re‐entry to the smectic C phase from smectic A phase. Thermal annealing temperature determines this peculiar dynamic shape change, which occurs during both heating and cooling processes. This pivotal attribute finds manifestation in gripper and flower‐shaped actuators, adeptly executing grabbing and releasing as well as blooming and closure motions within a single thermal stimulation. In essence, our study introduces an innovative approach to the realm of LCP actuators, ushering in a new avenue for the design and fabrication of versatile and dynamically responsive LCP actuators. [ABSTRACT FROM AUTHOR]

Stiffness variable materials have aroused extensive research interest in smart devices, especially in soft actuators. However, achieving materials with high stiffness switch range remains challenging. Here, a novel three‐dimensional (3D) lightweight Field's metal (FM) foam was developed. Meanwhile, the polymer composite (SUFF) with superior stiffness switchable capacity was fabricated by embedding FM foam into a kind of designed stiffness variable polymer. The SUFF shows outstanding conductivity under relatively low FM volume fraction of 20.6%. Impressively, because of the extremely high modulus and fast transition of FM foam, the stiffness switch ratio of the SUFF are able to reach an ultra‐high value of 6987.5‐folds. Apart from its exceptional stiffness switchable capacity, the SUFF also possesses remarkable shape memory and self‐healing characteristics. Next, the SUFF was then fastened to a soft actuator as the stiffness changing units. The obtained actuator was able to exhibit a short heating–cooling cycle time of 44 s while using 10 A of current and 4°C water for cooling. Moreover, the actuator can reach remarkable values of 973 mN/mm and 4729 mN, respectively, for its stiffness and net force. Then, a soft robot gripper made up of three obtained actuators mounted on a base demonstrates its excellent load and stiffness switchable ability. It can lift a variety of objects with various forms with weights up to more than 3 kg. This study might provide a reference for application of stiffness variable materials in soft actuators. Highlights: The FM foam were designed and synthetized by lost‐wax casting method.The polymer composite exhibits large stiffness switching range.The polymer composite achieves 6987.5‐folds rigid/soft stiffness ratio.A 3D‐printing soft actuator was fabricated using obtained polymer composite.The assembled robotic gripper can lift weights up to more than 3 kg. [ABSTRACT FROM AUTHOR]

Pneumatic soft actuators possess relatively fast response, inherent high flexibility, and achieve extraordinary shape morphing under large deformations. Conventionally, the entire body of soft pneumatic robots needs to be designed for specific applications. Herein, a soft pneumatic actuator design with structured fabrics as actuator skins, which has high bending stiffness variation that can accomplish multiple tasks and different deformation modes in a single body, is proposed. By adjusting the structured skin, the developed soft actuator can be tailored to achieve various deformations. It is experimentally shown that the bending stiffness of the actuator can be adjusted from 108 to 5654 N m−1. The blocking force of the actuator in bending is comparable with that of conventional fabric‐reinforced pneumatic actuators, while the actuator skins are reusable and programmable. In application, the actuators are used to construct a bionic soft gripper with multiple degrees of freedom. By switching between three grasping modes, the gripper successfully fulfills a series of tasks including lifting weights up to 1 kg and grasping objects ranging from a grain of grape to a large iron basin. This work opens up an avenue for designing structured skins for pneumatic robots with programmable deformation modes and versatile functions. [ABSTRACT FROM AUTHOR]

Soft pneumatic biomimetic robotic systems excel at the specific application they are designed for, often to interact or navigate unstructured environments safely. However, redeployment to new purposes requires substantial resources, from redesign to revalidation. Despite most pneumatic artificial muscles surpassing the power and contraction performance of natural muscles, natural muscles largely remain unmatched in terms of their versatility and complex performance. This is likely due to artificial muscle's low effective strain and high radial expansion, limiting parallel operating efficiencies. To address these challenges, a class of compact versatile pneumatic actuators, called multilayer artificial muscle (MAM), that are capable of deployment to different applications through configurable modularity, is presented. The MAMs are biomimetically inspired by the sarcomere, the building block for natural muscle architecture. Similarly, MAM can extend and contract as well as be rearranged to mimic muscle‐like actions and functions, such as a caterpillar locomotion robot and an entire robotic arm. The MAMs are fabricated through multilayer, multimaterial, low‐cost additive manufacturing, which offers certain advantages such as higher extension, contraction force, and durability. MAMs have the potential to provide a crucial fundamental building block toward future versatile reconfigurable architecture. [ABSTRACT FROM AUTHOR]

Shape‐changing polymeric materials have gained significant attention in the field of bioinspired soft robotics. However, challenges remain in versatilizing the shape‐morphing process to suit different tasks and environments, and in designing systems that combine reversible actuation and self‐healing ability. Here, we report halogen‐bonded liquid crystal elastomers (LCEs) that can be arbitrarily shape‐programmed and that self‐heal under mild thermal or photothermal stimulation. We incorporate halogen‐bond‐donating diiodotetrafluorobenzene molecules as dynamic supramolecular crosslinks into the LCEs and show that these relatively weak crosslinks are pertinent for their mechanical programming and self‐healing. Utilizing the halogen‐bonded LCEs, we demonstrate proof‐of‐concept soft robotic motions such as crawling and rolling with programmed velocities. Our results showcase halogen bonding as a promising, yet unexplored tool for the preparation of smart supramolecular constructs for the development of advanced soft actuators. [ABSTRACT FROM AUTHOR]

Smart actuators that can convert external energy stimuli into mechanical energy output have great potential in industrial, biomedical, and military applications. However, the existed disadvantage such as complex fabrication process, single stimulus source, and the requirement of artificial energy restrict their further development. Herein, a MXene/polyethylene (PE)‐based soft actuator with multistimulus response and the ability to be driven by natural sunlight and human humidity is proposed through a simple method. Owing to the excellent electrical conductivity, high photothermal conversion capability, and surface hydrophilicity of MXene, the MXene/PE actuator exhibits rapid and large bending deformation in response to external multistimuli such as light, electricity, heat, and humidity. Owing to the simple preparation, and anisotropic, tailorable and programmable properties of the MXene/PE actuator, a soft robot that can crawl directionally under light conditions is constructed. In addition, based on the high sensitivity response of the actuator to light and humidity, smart clothing that can generate reversible bending deformation under natural sunlight as well as sweat conditions is developed. These results provide a new inspiration for the design of high‐performance soft actuators with multistimulus response, and demonstrate the potential applications of the MXene/PE actuators in smart devices, bionic robots, and wearable clothing. [ABSTRACT FROM AUTHOR]

Additive manufacturing of lattice structures provides materials with enhanced strength, stiffness, and lightweight properties. While most research focuses on stiff, low-stretch materials like metals and acrylonitrile butadiene styrene, herein, the tensile behavior of soft, elastomeric lattice structures is explored. Softmaterial 3D-printing advancements have enabled increased usage of directly printed soft robots. Traditional fluidic elastic actuators, however, face limitations due to the ballooning effect of soft polymers, causing potential explosions or leakages. To mitigate this, the study proposes using a soft lattice structure to reinforce soft inflatable robots, thereby reducing the ballooning effect and increasing design freedom. Herein, soft lattices are fabricated using Agilus30 in a Stratasys J735 printer and their behaviors under compression and stretching are compared. It is indicated in the results that lattice reinforcement maintains the soft robot's shape under higher pressure and allows tunability of stiffness with variable internal pressure. The implementation of this method in non-convex soft robots successfully demonstrates its anti-ballooning effect. [ABSTRACT FROM AUTHOR]

Soft pneumatic gripping strategies are often based on pressurized actuation of structures made of soft elastomeric materials, which limits designs in terms of size, weight, achievable forces, and ease of fabrication. In contrast, fabric‐based inflatable structures offer high stiffness‐to‐weight ratio solutions for soft robotics, but their actuation has been little explored. Herein, a new class of pneumatic soft grippers is presented that exploits the in‐plane overcurvature effect of inextensible fabric flat balloons upon inflation. A star‐shaped gripper contracts radially under pressure producing a gripping force on the object whose intensity can be modulated by the pressure input. First, the kinematics and mechanics of a single V‐shaped actuator are studied through experiments, finite element simulations, and analytical models. Then, these results are leveraged to predict the mechanical response of the entire star, optimize its geometry, and maximize contraction and stiffness. It is shown that the gripping performance can be improved by stacking several stars with silicon‐coated corners. It is expected that the flexibility, robustness, scalability, and ease of fabrication of this methodology will lead to a new generation of lighter and larger actuators capable of developing higher forces and moving delicate and irregularly shaped objects while maintaining reasonable complexity. [ABSTRACT FROM AUTHOR]

Smart materials that can actively tune their stiffness are of great interest to many fields, including the construction industry, medical devices, industrial machines, and soft robotics. However, developing a material that can offer a large range of stiffness change and rapid tuning remains a challenge. Herein, a liquid metal variable stiffness material (LMVSM) that can actively and rapidly tune its stiffness by applying an external magnetic field or by changing the temperature is developed. The LMVSM is composed of three layers: a gallium-iron magnetorheological fluid (Ga-Fe MRF) layer for providing variable stiffness, a nickel-chromium wire layer for Joule heating, and a soft heat dissipation layer for accelerating heating and rapid cooling. The stiffness can be rapidly increased by 4 times upon the application of a magnetic field or 10 times by solidifying the Ga-Fe MRF. Finally, the LMVSM is attached to a pneumatically controlled soft robotic gripper to actively tune its load capacity, demonstrating its potential to be further developed into smart components that can be widely adopted by smart devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Covalent adaptable networks (CANs) are reprocessable polymers whose structural arrangement is based on the recombination of dynamic covalent bonds. Composite materials prepared by incorporating magnetic particles into CANs attract much attention due to their remote and precise control, fast response speed, high biological safety and strong penetration of magnetic stimuli. These properties often involve magnetothermal effect and direct magnetic‐field guidance. Besides, some of them can also respond to light, electricity or pH values. Thus, they are favorable for soft actuators since various functions are achieved such as magnetic‐assisted self‐healing (heating or at ambient temperature), welding (on land or under water), shape‐morphing, and so on. Although magnetic CANs just start to be studied in recent two years, their advances are promised to expand the practical applications in both cutting‐edge academic and engineering fields. This review aims to summarize recent progress in magnetic‐responsive CANs, including their design, synthesis and application. [ABSTRACT FROM AUTHOR]

Balloon‐type actuators have attracted scientific attention because they allow easy control of the output intensity and a high degree‐of‐freedom regarding shape and movement. However, they require bulky external pumps and electric power suppliers. This makes miniaturization and wearable device fabrication difficult. Herein, a balloon soft actuator that does not require a pneumatic pump or electric power supplier, and that uses a finger‐operated pump based on a fluidic circuit and catalytic reaction, is proposed. This device can be driven without electric power multiple times by applying a vent valve system to exhaust the generated gas. Further, it is applied to two different types of applications—soft robots and wearable devices—by optimizing their structure and material. In conclusion, the proposed device is expected to lead to the development of a broad range of soft actuators for stand‐alone robots and wearable devices in the future. [ABSTRACT FROM AUTHOR]

As a typical behavior of releasing energy in a short time, catapulting is a way for organisms to adapt to complex and changeable environments, such as crossing terrain obstacles and spreading seeds. The essence of catapulting behavior is that plants and animals use their structural characteristics to control elastic strain energy locking, triggering, and releasing under external stimulation. At present, bistable or multistable structures are attractive for optimizing the system energy and improving the performance of liquid crystal elastomer (LCE) soft actuators. However, the overelaborate designation of such structures makes it a great challenge to achieve fast morphing LCE soft actuators. Here, a light‐driven azobenzene liquid crystal elastomer (azo‐LCE) soft actuator mimicking the catapulting behavior of fern sporangia is reported. 2D azo‐LCE monoliths are simply folded to construct V‐shaped structures as 3D catapults, which exhibit higher morphing velocity upon UV light, and the morphing velocity is related to the aspect ratio of films. Furthermore, asymmetric morphing behavior occurs by constructing localized UV irradiation conditions, which greatly improves the morphing velocity. It is envisioned that the origami‐inspired azo‐LCE catapults can be further designed as the throwing component in fast‐morphing soft robots for the remote delivery of microcargoes. [ABSTRACT FROM AUTHOR]

With the increasing requirements of underwater missions and the rapid development of soft robotics technologies, soft underwater swimming robots have become a hot topic of research due to their low noise, high flexibility, and high environmental adaptability. In the past 10 years, research into soft underwater robots based on artificial muscle actuation has made considerable progress. Herein, a comprehensive survey on recent advances in soft underwater swimming robots based on different actuation methods is reviewed systematically, including pressure actuation, intelligent material actuation, and biomaterial actuation. First, for each type of actuation, the actuating principle, structural design, and swimming performance of soft underwater robots are introduced in detail. Then, according to the different swimming modes of underwater organisms, the aforementioned soft underwater robots are classified and compared. The results show that for different swimming tasks and application scenarios, the robot needs to realize the optimal design by reasonably selecting the actuating method and the swimming mode. This review summarizes the advanced information and critical technology in designing high‐performance soft underwater robots in the aspect of structural design, actuating methods, and swimming modes and offers an insightful outlook for the future development of soft robots. [ABSTRACT FROM AUTHOR]

Poly(N‐isopropylacrylamide) (PNIPAm) is widely implemented in responsive soft actuators. However, there are still defects of low brittleness and poor mechanical properties. Moreover, little attention has been paid to diameter shrinkage deformation of tubular PNIPAm hydrogels. In this study, physical crosslinking between Ca2+ cations and sodium alginate (SA) was introduced to form an interpenetrating network with chemically crosslinked PNIPAm, and then Ca–alginate/PNIPAm hydrogels were prepared. Molecular structure, surface morphology, swelling properties and mechanical properties were characterized. The results indicated that the pure PNIPAm hydrogel obtained using thermal initiation polymerization had better swelling and temperature‐responsive properties (with a maximum swelling ratio of 1134.65% and a fastest decrease rate of 318.45% min−1 in swelling ratio) compared to the hydrogel using ultraviolet polymerization. The mechanical properties the Ca/PNIPAm hydrogel were enhanced until the SA concentration exceeded 8 wt%. The compressive modulus of the hydrogel with SA concentration of 8 wt% (16.61 kPa) was increased by 10 times as compared with the pure PNIPAm hydrogel (1.42 kPa), and its corresponding elastic modulus increased by 47%. Moreover, a model soft actuator was prepared based on annular and tubular hydrogels. It had reversible diameter shrinkage behavior at 50 °C, and excellent temperature‐responsive property. The results reported herein provide valuable insight into the engineering application of temperature‐responsive PNIPAm‐based hydrogels. © 2022 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

The emergence of soft actuators that exhibit large, complex, programmable, and reversible shape deformation is of fundamental interest having potential applications in optics, medicals, and robotics fields. However, existing soft actuators are generally driven by only few given external stimuli such as temperature, humidity, or light which limit their interactions with their surroundings. Here, biomimetic soft actuators that respond to a variety of solvent vapors via programmable motion studied by Finite Element Modeling (FEM) are presented. A versatile micromachining process is used to fabricate these biomimetic soft actuators able to bend, curve, and twist in different manners according to their designs mimicking stamen, seed pots, and petals of Bauhinia variegate and Dendrobium orchids. The kinetic parameters of the transient response and recovery actuation are taken as the input feature in principal component analysis (PCA) to discriminate analyte molecules. Finally, to broaden the accessible 3D motions and thus functions of these smart actuators, an origami approach is employed to provide further flexibility and novel controlled structural changes in continuum structures such as snake‐like soft actuators, walkers, and grippers. [ABSTRACT FROM AUTHOR]

The realization of bidirectional deformation function is an important symbol of most natural creatures and intelligent flexible robots. Currently, most soft actuators are developed on the basis of transition between two different states, which means difficulties of control during the whole movement. In this work, variable distribution positions of hard magnetorheological elastomers (H‐MREs) in the matrix are used to achieve different magnetic force distributions. The programmable force distribution promotes different deformations of the magnetic actuators, which enlarges the deformation range by 51.69% under the same magnetic field. Pre‐magnetizing the H‐MREs makes them have a certain residual magnetization. Due to the residual magnetization property of H‐MREs, the magnetized actuator can not only be attracted but also be repelled by the applied magnetic field. This bidirectional deformation capability gives the actuators a wider deformation range and greater clamping force, such as the smart gripper for pinching up object. In addition, the actuators are integrated with a flexible sensing layer with high resolution and strong stability for self‐sensing. This kind of force distribution programmable technology and self‐sensing performance have the potential to broaden the application of actuators in medical equipment requiring high control accuracy. [ABSTRACT FROM AUTHOR]

To allow a linear one‐way shape‐memory alloy (SMA) wire to have a deterministic curvilinear two‐way actuation, the SMA wire can be bonded on a curved substrate or prestrained soft materials to create mismatched SMA‐wire composites. These composites have recently been applied to soft robots to achieve rapid periodic untethered locomotion. Herein, by knitting bare SMA wires on scattered holes, it is shown that the substrate‐free knitted SMA wires can periodically ride robots forward, where a deterministic spatial curvilinear actuation can be achieved in which its in‐between heated configuration and the final stable pattern is sensitive to the prescribed hole constraints. By arranging "knitting‐constraints," the 3D‐printed and origami robots with a pair of SMA wires, respectively, are ridden. The SMA wires have an angle parameter with a variation range of 30° for the 3D‐printed robot and that of 8° for the origami robot, where the angle parameter is defined to indicate the performance of the knitted SMAs. Both the robots can displace up to 5 mm in one motion cycle with an average speed of 20 and 15 mm min−1, respectively. The motion efficiencies of the two robots are close to 1 when taking the possible backward movement in one forward‐moving cycle into consideration. [ABSTRACT FROM AUTHOR]

Light induced soft actuators have broad application prospects where non‐contact stimulation and remote control are required. However, such soft actuators cannot achieve uniform contraction easily due to the weak penetration of light. Here, with the aid of vertical distribution of Sm2O3, Yb2O3, and Nd2O3 as selectively photothermal fillers along film thickness, a near‐infrared (NIR) light (1064, 980, and 808 nm) induced soft actuator based on shape‐memory polymer composites, which has a large thickness up to 2 mm is reported. The results show that tri‐layer films present uniform contraction and could lift a weight of 101.44 g by 8 mm under simultaneous irradiations of three NIR light beams. It is believed that the vertical distribution of selectively photothermal fillers provides a new strategy to create light induced soft actuators that can present uniform shape reconfiguration and high pulling force, further filling the gap between material concept and engineering applications. [ABSTRACT FROM AUTHOR]

A porous liquid‐crystalline network (LCN), prepared by using a template method, was found to exhibit peculiar actuation functions. The creation of porosity makes the initially hydrophobic LCN behave like a hydrogel, capable of absorbing a large volume of water (up to ten times the sample size of LCN). When the amount of absorbed water is relatively small (about 100 % swelling ratio), the porous LCN displays anisotropic swelling in water and, in the same time, the retained uniaxial alignment of mesogens ensures a thermally induced shape change associated with a LC‐isotropic phase transition. Combining the characteristic actuation mechanisms of LCN (order–disorder transition of mesogens) and hydrogel (water absorption), such porous LCNs can be explored for versatile stimuli‐triggered shape transformations. Moreover, the porosity enables loading/removal/reloading of functional fillers such as ionic liquids, photothermal dyes and fluorophores, which imparts the porous LCN actuator with reconfigurable functions such as ionic conductivity, light‐driven locomotion, and emissive color. [ABSTRACT FROM AUTHOR]

Beyond a traditional stimuli‐responsive soft actuator that shows a single motion by a stimulus, multidirectional actuation reversal with a single stimulus is highly required in applications such as shape morphing sensors and soft robotics. Liquid crystal elastomers (LCEs) are one of the most attractive candidates for the soft actuator due to their capability of stimuli‐responsive shape changing in 3D, which is programmable with local orientation of LC mesogens. Here, a simple but effective method to fabricate monolithic LCE actuators that are capable of reversible curvature reversal in bending and twisting deformation by a single stimulus—heat—is reported. The curvature reversal of the LCE film can be programmed by means of asymmetric crosslinking density along the thickness and the orientation of the LC mesogens. The curvature reversal of the monolithic LCE film exhibits highly reversible (more than 100 times) and fast actuation (≈3–5 s) by heating and cooling, allowing new concept of a practical application using LCE material: a self‐regulated smart valve that is capable of qualitatively sorting liquids by temperature. It is believed that this system is potentially applied to a self‐regulated sorting platform for various endothermic and exothermic chemical or biological reactions [ABSTRACT FROM AUTHOR]

As a research of human arm activities, the research of soft actuator is one of the important topics in the field of robotics. This article is concerned with the robust passive tracking control for an uncertain soft actuator by robust right coprime factorization (RRCF). First, applying the recursive least squares identification algorithm, the identification of the actuator modeling is studied by which the parameter of radius is estimated by using the experimental data. Second, the passivity of the soft actuator with inflatable rubber tube is discussed; meanwhile, the robustness of the soft actuator is ensured by the designed robust controllers. Third, by combining the RRCF and integral sliding mode control methods, the tracking performance is improved, for the soft actuator with time‐varying radius. Finally, the proposed methods are confirmed by the simulation with experimental data. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fabrication and assembly of flexible sensors and soft actuators play important roles in improving the performance of wearable electronics and soft robots. Traditional manufacturing techniques have limitations in controlling the geometry and architecture of many soft actuation and sensing systems, which compromise their performance as well as applications. With the emergence of 3D printing, directly transforming 3D models into real objects becomes possible. In particular, vat photopolymerization techniques, represented by stereolithography, are capable of printing all‐in‐one and lab‐on‐a‐chip devices with fast speed and high accuracy. Novel polymer formulations, including functional resins, hydrogels, elastomers, polymer blends, composites, and biological materials, have been developed for vat photopolymerization 3D printing to produce highly stable architectures, which prompts a remarkable revolution in mechanics and materials for soft electronics. This review looks into the recent developments of vat photopolymerization 3D printing technology for lightweight engineering, personalized electronics, and soft robots. [ABSTRACT FROM AUTHOR]

Liquid crystalline elastomers (LCEs) have been actively investigated as stimuli‐controlled actuators and soft robots. The basis of these applications is the ability of LCEs to undergo a reversible shape change upon a liquid crystalline (LC)‐isotropic phase transition. Herein, we report the synthesis of a novel LCE based on a side‐chain liquid crystalline polymer (SCLCP). In contrast to known LCEs, this LCE exhibits a striking anomalous shape change. Subjecting a mechanically stretched monodomain strip to LC‐disorder phase transition, both the length and width of the strip contract in isotropic phase, and both elongate in LC phase. This thermally induced behaviour is the result of a subtle interplay between the relaxation of polymer main chain oriented along the stretching direction and the disordering of side‐group mesogens oriented perpendicularly to the stretching direction. This finding points out potential design of LCEs of this peculiar type and possible applications to exploit. [ABSTRACT FROM AUTHOR]

Magnetic Fe3O4 nanoparticles are employed to develop digital light processing 3D printing resin, which is used to fabricate arbitrary-shape soft actuators with multimaterials printing in a free assembly manner. Various mechanical properties and printed morphology of curing resin with different Fe3O4 nanoparticles content are explored to demonstrate the feasibility and precision. By using magnetic and nonmagnetic resins as the magnetic and nonmagnetic segments, mulitple magnetic devices and actuators are prepared by digital light processing (DLP) 3D printing technology. Moreover, the interfacial binding strength between magnetic and nonmagnetic segments and deflection with different diameters of printed lattices and content of Fe3O4 nanoparticles are investigated. DLP 3D printing enables the free assembly manufacturing of actuators with complicated architectures to achieve bending, deformation, cargo transportation, and so on. As proof-of-concept, a flexible gripper is printed through integrating magnetic responsive and nonresponsive materials into one body. This approach with special material will be promising to extend the capability of 3D printing for applications in controllable delivery with remote magnetic control in biological, medical, and robotic fields. [ABSTRACT FROM AUTHOR]

Light triggered soft actuator in aqueous media has applications in operating underwater objects, creating liquid flow, and adjusting reaction velocity, etc. Here, composites prepared from commercial materials, poly[ethylene- ran-(vinyl acetate)] (EVA) and aniline black (AB), are reported as one cost efficient material for preparing such actuator, where EVA and AB work respectively as shape-memory polymer matrix and near-infrared light triggered photothermal filler. Upon irradiation, the temperature of the composites increases greatly with light power density and AB content. Light-induced shape-memory effect (SME) with recovery ratio >98%, temperature-memory effect (TME), and reversible bidirectional shape-memory effect (rbSME) of the prepared composites in air are realized. Higher light power density is required to trigger the shape recovery in aqueous media, while good SME, TME, and rbSME are also achieved. Releasing device and gripper are used to indicate the feasibility of the composites as light triggered soft underwater actuators. [ABSTRACT FROM AUTHOR]

Many pneumatic actuators have been developed to be lightweight with high output for decreasing the impact force. However, for pneumatic actuators it is difficult to maintain exact control because these actuators have constraints. In this study, we developed model predictive control (MPC) that can accommodate these constraints when applied to the pneumatic actuator we developed. As described here, we compared and evaluated the control performance using MPC and proportional-integral-derivative (PID) control with an anti-windup control system. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Stimuli responsive elastic instabilities provide opportunities for controlling the structures and properties of polymer surfaces, offering a range of potential applications. Here, a surface actuator based on a temperature and electrically responsive poly( N-isopropyl acrylamide-co-sodium acrylate) hydrogel that undergoes a two-step delamination and buckling instability triggered using micropatterned electrodes is described. The electrically actuated structures entail large out-of-plane displacements that take place on time-scales of less than 1 s, in response to modest triggering voltages (−3-6 V). Alongside these experimental observations, finite element simulations are conducted to better understand the two-step nature of the instability. In the first step, hydrogel films undergo delamination and formation of blisters, facilitated by electrochemical reduction of the thiol groups anchoring the film to the electrodes. Subsequently, at larger reducing potentials, the electrolytic current is sufficient to nucleate a gas bubble between the electrode and the gel, causing the delaminated region to adopt a straight-sided blister shape. Finally, thermally induced deswelling of the gel allows the film to be returned to its flat state and readhered to the electrode, thereby allowing for repeated actuation. [ABSTRACT FROM AUTHOR]

ABSTRACT Research in the field of liquid crystalline polymers has recently witnessed the introduction of liquid crystalline hydrogels. Here, we report the synthesis and characterization of a new liquid crystalline network featuring elastomeric softness, water-swelling and shape memory characteristics. By comparing with a nonmesogenic network prepared using the same procedure, we reveal structure-property relationships of the liquid crystalline and crystalline polymer networks. Wide angle and small angle X-ray scattering studies were used to examine the liquid crystalline ordering in both dry and hydrated states. Such ordering was found to be related to the observed shape memory and actuation (two-way shape memory) properties and these phenomena are highlighted with demonstrations of shape change in response to heat and water stimuli. This study provides insight into the mechanisms affecting the shape evolution of water activated anisotropic liquid crystalline hydrogels and enables the future design of materials or devices for a variety of applications such as biomaterials interacting with body fluids in a hydrated state. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 38-52 [ABSTRACT FROM AUTHOR]

The authors comment on the fabrication and the geometric designs of the cellular actuating structures. The topics discussed include the methods of actuating the honeycombs, the prediction of honeycombs' actuation capacity, and its cellular structures. Moreover, it cites the honeycomb's volume expansion.

Ionic polymer-metal composites (IPMC) are promising materials in biomedical actuators and sensors, as they are soft and flexible, thus assuring the safety of the device itself. The purpose of this study is to investigate the biocompatibility of IPMC in in vitro experiments in order to evaluate their applicability in biomedical fields. In addition to an IPMC specimen prepared by the conventional “impregnation-reduction method” using cationic gold complexes and reducing agents, two specimens were prepared by additional processes: one specimen was reduced in Na2SO3 solution and the other was cleaned in H2O2 solution. A colony-forming test using Chinese hamster V79 cells showed high cytotoxicity for all IPMC specimens. Examination by direct inlet mass spectrometry (DI-MS) revealed that the peak intensity of the gold complex (particularly, m/z=180) was different from that of Nafion film. Monitoring the peak at m/z=180 showed a remnant with the structure of phenanthroline in IPMC specimens that were not cleaned in H2O2 solution. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 93(1): 1–8, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10239 [ABSTRACT FROM AUTHOR]

As promising candidates in the field of artificial muscles, ionic‐polymer–metal composites (IPMCs) still cannot simultaneously provide large deformations and fast responses, which has limited their practical applications. In this study, to overcome this issue, a Nafion‐based IPMC with high‐quality metal electrodes is fabricated via novel isopropanol‐assisted electroless plating. The IPMC exhibits a large tip displacement (35.3 mm, 102.3°) under a low direct‐current driving voltage and ultrafast response (>10 Hz) under an alternating‐current (AC) voltage. Furthermore, the simultaneous integration of a large deformation and fast response can be achieved by the IPMC under a high‐frequency (19 Hz) AC voltage, where the largest bending amplitude is 5.9 mm and the highest bending speed reaches 224.2 mm s−1 (596.2° s−1). Additionally, the lightweight IPMC exhibits a decent load capacity and can lift objects 20 times heavier. The outstanding performances of the Nafion IPMC are demonstrated by mimicking biological motions such as petal opening/closing, tendril coiling/uncoiling, and high‐frequency wing flapping. This study paves the way for the fabrication of lightweight actuators with simultaneous large displacements and fast responses for promising applications in biomedical devices and bioinspired robotics. [ABSTRACT FROM AUTHOR]

Active materials and surfaces that are less intrusive and more compatible with humans and their environment are critical for robotic applications. Humidity‐ and water‐responsive materials are emerging as versatile alternatives to commonly used actuators in robotic systems, due to ease of actuation with humidity gradients and pervasiveness of water in the environment. However, these materials exhibit relatively low work densities and slow responses, and they are degraded when placed in direct contact with water. Recent work has shown that as a humidity‐responsive material, Bacillus spores exhibit high work density actuation. Here, spore‐based actuators containing water‐resistant UV‐curable adhesives are reported. These adhesives improve the work and power density of spore‐based actuators, allow patterning of actuators with lithographic approaches and, importantly, provide water resistance to the resulting actuators. As a result, it is possible to demonstrate spore‐based actuators driven directly with liquid water, which increase the actuation speed and power by nearly 100‐fold. These developments might facilitate broader use of humidity‐ and water‐driven actuators in robotics and related applications. [ABSTRACT FROM AUTHOR]

This paper introduces a fabrication method and properties of newly developed Twisted and Coiled soft Actuator (TCA) from nylon and spandex. The TCA, a thermally driven actuator, is one of the promising soft actuators that shows considerable strain compared to the others. Typically, TCA is fabricated from single polymer fiber such as the spandex and nylon. However, TCA from each material shows some limits. The spandex TCA (STCA) shows siginificant strain more than 45%. However, since the spandex is non‐conductive material, the STCA requires additional heat source such as heat gun. On the other hand, since the nylon TCA (NTCA) is fabricated from silver‐coated nylon, it is capable of Joule heating. However, the strain is considerably smaller than that of the STCA. Newly developed TCA, Double helix TCA (DTCA), is composed of both of them. As a result, the DTCA inherits the properties of the STCA and the NTCA. It is capable of Joule heating showing high strain over 40%. Since, DTCA is very soft, light, and cheap, it has various applications in the field of robots including artificial limbs. An artificial muscle fabricated from nylon and spandex is introduced. As the spandex is ultra‐stretchable, it is very soft and shows significantly large strain compared to the other soft actuators. Since the nylon is coated by silver, it is capable of Joule heating. It results in compact system without any other heat source such as heat gun. [ABSTRACT FROM AUTHOR]

Soft, 3D elastomeric structures and composite structures are easy to fabricate using click-e-bricks, and the internal architecture of these structures together with the capabilities built into the bricks themselves provide mechanical, optical, electrical, and fluidic functions., Chemistry and Chemical Biology