3D‐Architected Soft Machines with Topologically Encoded Motion

The limited range of mechanical responses achievable by materials compatible with additive manufacturing hinders the 3D printing of continuum soft robots with programmed motion. This paper describes the rapid design and fabrication of low‐density, 3D‐architected soft machines (ASMs) by combining Voronoi tessellation and additive manufacturing. On tendon‐based actuation, ASMs deform according to the topologically encoded buckling of their structure to produce a wide range of motions (contraction, twisting, bending, and cyclic motion). ASMs exhibiting densities as low as 0.094 g cm^?3 (≈8% of bulk polymer) can be rapidly built by the stereolithographic 3D printing of flexible photopolymers or the injection molding of elastomers. The buckling of ASMs can be programmed by inducing gradients in the thickness of their flexible beams or by the localized enlargement of the Voronoi cells to generate complex motions such as multi‐finger gripping or quadrupedal locomotion. The topological architecture of these low‐density soft robots confers them with the stiffness necessary to recover their original shape even after ultrahigh compression (400%) and extension (500%). ASMs expand the range of mechanical properties currently achievable by 3D printed or molded materials to enable the fabrication of soft machines with auxetic mechanical metamaterial properties.     

Magnetic Actuation Methods in Bio/Soft Robotics

In recent years, magnetism has gained an enormous amount of interest among researchers for actuating different sizes and types of bio/soft robots, which can be via an electromagnetic-coil system, or a system of moving permanent magnets. Different actuation strategies are used in robots with magnetic actuation having a number of advantages in possible realization of microscale robots such as bioinspired microrobots, tetherless microrobots, cellular microrobots, or even normal size soft robots such as electromagnetic soft robots and medical robots. This review provides a summary of recent research in magnetically actuated bio/soft robots, discussing fabrication processes and actuation methods together with relevant applications in biomedical area and discusses future prospects of this way of actuation for possible improvements in performance of different types of bio/soft robots.     

A Fast Autonomous Healing Magnetic Elastomer for Instantly Recoverable,Modularly Programmable,and Thermorecyclable Soft Robots

Intrinsically self-healing stretchable polymers have been intensively explored for soft robotic applications due to their mechanical compliance and damage resilience. However, their prevalent use in real-world robotic applications is currently hindered by various limitations such as low mechanical strength, long healing time, and external energy input requirements. Here, a self-healing supramolecular magnetic elastomer (SHSME), featuring a hierarchical dynamic polymer network with abundant reversible bonds, is introduced. The SHSME exhibits high mechanical strength (Young's modulus of 1.2 MPa, similar to silicone rubber) and fast self-healing capability (300% stretch strain after 5 s autonomous repair at ambient temperature). A few SHSME-based robotic demonstrations, namely, rapid amphibious function recovery, modular-assembling-prototyping soft robots with complex geometries and diverse functionalities, as well as a dismembering–navigation–assembly strategy for robotic tasking in confined spaces are showcased. Notably, the SHSME framework supports circular material design, as it is thermoreformable for recycling, demonstrates autorepair for extended lifespan, and is modularizable for customized constructs and functions.     

Rugged Soft Robots using Tough,Stretchable, and Self-Healable Adhesive Elastomers

Soft robots are susceptible to premature failure from physical damages incurred within dynamic environments. To address this, we report an elastomer with high toughness, room temperature self-healing, and strong adhesiveness, allowing both prevention of damages and recovery for soft robotics. By functionalizing polyurethane with hierarchical hydrogen bonds from ureido-4[1H]-pyrimidinone (UPy) and carboxyl groups, high toughness (74.85 MJ m⁻³), tensile strength (9.44 MPa), and strain (2340%) can be achieved. Furthermore, solvent-assisted self-healing at room temperature enables retention of high toughness (41.74 MJ m⁻³), tensile strength (5.57 MPa), and strain (1865%) within only 12 h. The elastomer possesses a high dielectric constant (≈9) that favors its utilization as a self-healing dielectric elastomer actuator (DEA) for soft robotics. Displaying high area strains of ≈31.4% and ≈19.3% after mechanical and electrical self-healing, respectively, the best performing self-healable DEA is achieved. With abundant hydrogen bonds, high adhesive strength without additional curing or heating is also realized. Having both actuation and adhesive properties, a “stick-on” strategy for the assembly of robust soft robots is realized, allowing soft robotic components to be easily reassembled or replaced upon severe damage. This study highlights the potential of soft robots with extreme ruggedness for different operating conditions.     

A New Strategy of Discretionarily Reconfigurable Actuators Based on Self-Healing Elastomers for Diverse Soft Robots

Actuators have shown great promise in many fields including soft robotics. Since reconfiguration allows actuators to change their actuation mode, it is considered a key characteristic for new-generation adaptive actuators. However, it remains a challenge to design simple and universal methods to fabricate actuators that can be reconfigured to allow diverse actuation modes. Here, a macroscopically discretionary healing-assembly strategy to fabricate reconfigurable soft actuators based on intrinsic self-healing poly(dimethylglyoxime-urethane) (PDOU) elastomers is developed. The PDOU elastomers with different degrees of crosslinking show different responsiveness to solvents, and are seamlessly healed. Crosslinked and non-crosslinked PDOU elastomers as building units are healing-assembled into actuators/robots with diverse actuation behaviors. Notably, the assembled actuators/robots are readily reprogrammed to exhibit multiple actuation modes by simply tailoring and reassembling without any external stimuli. This work paves a new, simple, powerful, and universal method to construct sophisticated soft robots.     

Highly Conductive MXene/PEDOT:PSS-Integrated Poly(N-Isopropylacrylamide) Hydrogels for Bioinspired Somatosensory Soft Actuators

Sophisticated sensing and actuation capabilities of many living organisms in nature have inspired scientists to develop biomimetic somatosensory soft robots. Herein, the design and fabrication of homogeneous and highly conductive hydrogels for bioinspired somatosensory soft actuators are reported. The conductive hydrogels are synthesized by in situ copolymerization of conductive surface-functionalized MXene/Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) ink with thermoresponsive poly(N-isopropylacrylamide) hydrogels. The resulting hydrogels are found to exhibit high conductivity (11.76 S m⁻¹), strain sensitivity (GF of 9.93), broad working strain range (≈560% strain), and high stability after over 300 loading–unloading cycles at 100% strain. Importantly, shape-programmable somatosensory hydrogel actuators with rapid response, light-driven remote control, and self-sensing capability are developed by chemically integrating the conductive hydrogels with a structurally colored polymer. As the proof-of-concept illustration, structurally colored hydrogel actuators are applied for devising light-driven programmable shape-morphing of an artificial octopus, an artificial fish, and a soft gripper that can simultaneously monitor their own motions via real-time resistance variation. This work is expected to offer new insights into the design of advanced somatosensory materials with self-sensing and actuation capabilities, and pave an avenue for the development of soft-matter-based self-regulatory intelligence via built-in feedback control that is of paramount significance for intelligent soft robotics and automated machines.     

Biomimetic Color Changing Anisotropic Soft Actuators with Integrated Metal Nanowire Percolation Network Transparent Heaters for Soft Robotics

To add more functionalities and overcome the limitation in conventional soft robots, highly anisotropic soft actuators with color shifting function during actuation is demonstrated for the first time. The electrothermally operating soft actuators with installed transparent metal nanowire percolation network heater allow easy programming of their actuation direction and instantaneous visualization of temperature changes through color change. Due to the unique direction dependent coefficient of thermal expansion mismatch, the suggested actuator demonstrates a highly anisotropic and reversible behavior with very large bending curvature (2.5 cm^?1) at considerably low temperature (≈40 °C) compared to the previously reported electrothermal soft actuators. The mild operating heat condition required for the maximum curvature enables the superior long‐term stability during more than 10 000 operating cycles. Also, the optical transparency of the polymer bilayer and metal nanowire percolation network heater allow the incorporation of the thermochromic pigments to fabricate color‐shifting actuators. As a proof‐of‐concept, various color‐shifting biomimetic soft robots such as color‐shifting blooming flower, fluttering butterfly, and color‐shifting twining tendril are demonstrated. The developed color‐shifting anisotropic soft actuator is expected to open new application fields and functionalities overcoming the limitation of current soft robots.     

3D Knitting for Pneumatic Soft Robotics

Soft robots adapt passively to complex environments due to their inherent compliance, allowing them to interact safely with fragile or irregular objects and traverse uneven terrain. The vast tunability and ubiquity of textiles has enabled new soft robotic capabilities, especially in the field of wearable robots, but existing textile processing techniques (e.g., cut-and-sew, thermal bonding) are limited in terms of rapid, additive, accessible, and waste-free manufacturing. While 3D knitting has the potential to address these limitations, an incomplete understanding of the impact of structure and material on knit-scale mechanical properties and macro-scale device performance has precluded the widespread adoption of knitted robots. In this work, the roles of knit structure and yarn material properties on textile mechanics spanning three regimes–unfolding, geometric rearrangement, and yarn stretching–are elucidated and shown to be tailorable across unique knit architectures and yarn materials. Based on this understanding, 3D knit soft actuators for extension, contraction, and bending are constructed. Combining these actuation primitives enables the monolithic fabrication of entire soft grippers and robots in a single-step additive manufacturing procedure suitable for a variety of applications. This approach represents a first step in seamlessly “printing” conformal, low-cost, customizable textile-based soft robots on-demand.     

Programmable Liquid Metal Microstructures for Multifunctional Soft Thermal Composites

Soft, elastically deformable composites can enable new generations of multifunctional materials for electronics, robotics, and reconfigurable structures. Liquid metal (LM) droplets dispersed in elastomer matrices represent an emerging material architecture that has shown unique combinations of soft mechanical response with exceptional electrical and thermal functionalities. These properties are strongly dependent on the material composition and microstructure. However, approaches to control LM microdroplet morphology to program mechanical and functional properties are lacking. Here, this limitation is overcome by thermo‐mechanically shaping LM droplets in soft composites to create programmable microstructures in stress‐free materials. This enables LM loadings up to 70% by volume with prescribed particle aspect ratios and orientation, enabling control of microstructure throughout the bulk of the material. Through this microstructural control in soft composites, a material which simultaneously achieves a thermal conductivity as high as 13.0 W m^?1 K^?1 (>70 × increase over polymer matrix) with low modulus (<1.0 MPa) and high stretchability (>750% strain) is demonstrated in stress‐free conditions. Such properties are required in applications that demand extreme mechanical flexibility with high thermal conductivity, which is demonstrated in soft electronics, wearable robotics, and electronics integrated into 3D printed materials.     

Electrically and Sunlight‐Driven Actuator with Versatile Biomimetic Motions Based on Rolled Carbon Nanotube Bilayer Composite

Designing multistimuli responsive soft actuators which can mimic advanced and sophisticated biological movements through simple configuration is highly demanded for the biomimetic robotics application. Here, inspired by the human's flick finger behavior which can release large force output, a soft jumping robot mimicking the gymnast's somersault is designed based on the rolled carbon nanotube/polymer bilayer composite actuator. This new type of rolled bilayer actuator with tubular shape is fabricated and shows electrically and sunlight‐induced actuation with remarkable performances including ultralarge deformation from tubular to flat (angel change >200° or curvature >2 cm^?1), fast response (<5 s), and low actuation voltage (≤10 V). Besides jumping, the uniquely reversible rolling–unrolling actuation can lead to other smart soft robots with versatile complex biomimetic motions, including light‐induced tumbler with cyclic wobbling, electrically/light‐induced crawling‐type walking robots and grippers, electrically induced mouth movement, and ambient‐sunlight‐induced blooming of a biomimetic flower. These results open the way for using one simple type of actuator structure for the construction of various soft robots and devices toward practical biomimetic applications.     

Elastic Energy Storage Enables Rapid and Programmable Actuation in Soft Machines

Storage of elastic energy is key to increasing the efficiency, speed, and power output of many biological systems. This paper describes a simple design strategy for the rapid fabrication of prestressed soft actuators (PSAs), exploiting elastic energy storage to enhance the capabilities of soft robots. The elastic energy that PSAs store in their prestressed elastomeric layer enables the fabrication of grippers capable of zero‐power holding up to 100 times their weight and perching upside down from angles of up to 116°. The direction and magnitude of the force used to prestress the elastomeric layer can be controlled not only to define the final shape of the PSA but also to program its actuation sequence. Additionally, the release of the elastic energy stored by PSAs causes their high‐speed recovery (≈50 ms), which significantly improves the actuation rates of soft pneumatic actuators, especially after motions requiring large deformations. Moreover, judicious prestressing of PSAs can also create bistable soft robotic systems, which use their stored elastic energy as a source of power amplification for rapid movements. These strategies serve as a basis for a new class of entirely soft robots capable of recreating bioinspired high‐powered and high‐speed motions using stored elastic energy.     

Fatigue-Resistant Conducting Polymer Hydrogels as Strain Sensor for Underwater Robotics

Conducting polymer hydrogels are widely used as strain sensors in light of their distinct skin-like softness, strain sensitivity, and environmental adaptiveness in the fields of wearable devices, soft robots, and human-machine interface. However, the mechanical and electrical properties of existing conducting polymer hydrogels, especially fatigue-resistance and sensing robustness during long-term application, are unsatisfactory, which severely hamper their practical utilities. Herein, a strategy to fabricate conducting polymer hydrogels with anisotropic structures and mechanics is presented through a combined freeze-casting and salting-out process. The as-fabricated conducting polymer hydrogels exhibit high fatigue threshold (>300 J m⁻²), low Young's modulus (≈100 kPa), as well as long-term strain sensing robustness (over 10 000 cycles). Such superior performance enables their application as strain sensors to monitor the real-time movement of underwater robotics. The design and fabrication strategy for conducting polymer hydrogels reported in this study may open up an enticing avenue for functional soft materials in soft electronics and robotics.     

Functionally Antagonistic Hybrid Electrode with Hollow Tubular Graphene Mesh and Nitrogen‐Doped Crumpled Graphene for High‐Performance Ionic Soft Actuators

Ionic soft actuators, which exhibit large mechanical deformations under low electrical stimuli, are attracting attention in recent years with the advent of soft and wearable electronics. However, a key challenge for making high‐performance ionic soft actuators with large bending deformation and fast actuation speed is to develop a stretchable and flexible electrode having high electrical conductivity and electrochemical capacitance. Here, a functionally antagonistic hybrid electrode with hollow tubular graphene meshes and nitrogen‐doped crumpled graphene is newly reported for superior ionic soft actuators. Three‐dimensional network of hollow tubular graphene mesh provides high electrical conductivity and mechanically resilient functionality on whole electrode domain. On the contrary, nitrogen‐doped wrinkled graphene supplies ultrahigh capacitance and stretchability, which are indispensably required for improving electrochemical activity in ionic soft actuators. Present results show that the functionally antagonistic hybrid electrode greatly enhances the actuation performances of ionic soft actuators, resulting in much larger bending deformation up to 620%, ten times faster rise time and much lower phase delay in a broad range of input frequencies. This outstanding enhancement mostly attributes to exceptional properties and synergistic effects between hollow tubular graphene mesh and nitrogen‐doped crumpled graphene, which have functionally antagonistic roles in charge transfer and charge injection, respectively.     

Micromachining‐Compatible,Facile Fabrication of Polymer Nanocomposite Spin Crossover Actuators

[Fe^II(Htrz)₂(trz)](BF₄) spin crossover particles of 85 nm mean size are dispersed in an SU‐8 polymer matrix and spray‐coated onto silicon microcantilevers. The subsequent photothermal treatment of the polymer resist leads to micrometer thick, smooth, and homogeneous coatings, which exhibit well‐reproducible actuation upon the thermally induced spin transition. The actuation amplitude as a function of temperature is accurately determined by combining integrated piezoresistive detection with external optical interferometry, which allows for the assessment of the associated actuation force (9.4 mN), stress (28 MPa), strain (1.0%), and work density (140 mJ cm^?3) through a stratified beam model. The dynamical mechanical characterization of the films evidences an increase of the resonance frequency and a concomitant decrease of the damping in the high‐temperature phase, which arises due to a combined effect of the thickness and mechanical property changes. The spray‐coating approach is also successfully extended to scale up the actuators for the centimeter range on a polymer substrate providing perspectives for biomimetic soft actuators.     

Soft Composite Gels with High Toughness and Low Thermal Resistance through Lengthening Polymer Strands and Controlling Filler

Soft gels with high toughness have drawn tremendous attention recently due to their potential applications in flexible electronic fields. The miniaturization and high-power density of electronic devices require soft gels with both high toughness and low thermal resistance; however, it is difficult to achieve these properties simultaneously. Herein, a simple design strategy is reported for constructing soft (high stretchability of 6.91 and low Young's modulus of 340 kPa), tough (4741.48 J m⁻²) and thermal conductive (low thermal resistance of 0.14 cm² K W⁻¹, under 10 psi pressure) polydimethylsiloxane/aluminum composite gel. This is realized by precisely lengthening polymer strands between the chemical cross-linked points and controlling the aluminum content in the composite gels. The symbiosis of this combination involves: lengthening the polymer strands facilitates its unfolding to increase the softness and intrinsic toughness; the thermally conductive spherical aluminum enables low thermal resistance and increases the intrinsic toughness and stress dissipation. By utilizing this gel as a thermal interface material, effective heat dissipation is demonstrated in electronic devices operating under high-power conditions over numerous cycles. These results demonstrate the application potential of composite gels in meeting the performance maintenance and heat dissipation, which are needed for modern electronic devices.     

Reconfiguration,Camouflage, and Color‐Shifting for Bioinspired Adaptive Hydrogel‐Based Millirobots

Nature provides much inspiration for developing soft millirobots. However, compared with smart and adaptations of lives in nature, these robotic systems still suffer from insufficiency of intelligence. Here, a new untethered soft millirobot with magnetic actuation in the head and function in the tail is presented via implementing control, actuation, and sensing directly in the materials, thereby endowing robots with multimodal locomotion and environment‐adaptive functions. Due to the soft and asymmetric structure, the millirobot not only shows robust multimodal locomotion, including controllable and transformable crawling, swinging and rolling, but also achieves an excellent capability of helical propulsion in water. Moreover, the robot also possesses outstanding obstacle‐crossing abilities, including helically propelling over obstacles (>2 body length), crawling within a 2 mm height tunnel and swinging through a 450 µm width channel. Furthermore, the robot can even squeeze its body to crawl through a tube easily via near‐infrared irradiation, which triggers the osmotic shrinking of its body. Notably, the robots also possess extraordinary environment‐adaptive functions, for example, leptocephali‐like optical camouflage in water, octopus‐like controllable delivery and variable appearance via visible color–shifting for interaction with the changing environment. These smart robotic systems would be of benefit in various fields via seamless integration of bioinspired design and smart materials.     

Magnetic Assembly of Soft Robots with Hard Components

This paper describes the modular magnetic assembly of reconfigurable, pneumatically actuated robots composed of soft and hard components and materials. The soft components of these hybrid robots are actuators fabricated from silicone elastomers using soft lithography, and the hard components are acrylonitrile–butadiene–styrene (ABS) structures made using 3D printing. Neodymium–iron–boron (NdFeB) ring magnets are embedded in these components to make and maintain the connections between components. The reversibility of these magnetic connections allows the rapid reconfiguration of these robots using components made of different materials (soft and hard) that also have different sizes, structures, and functions; in addition, it accelerates the testing of new designs, the exploration of new capabilities, and the repair or replacement of damaged parts. This method of assembling soft actuators to build soft machines addresses some limitations associated with using soft lithography for the direct molding of complex 3D pneumatic networks. Combining the self‐aligning property of magnets with pneumatic control makes it possible for a teleoperator to modify the structures and capabilities of these robots readily in response to the requirements of different tasks.     

Robotic Locomotion and Piezo1 Activity Controlled with Novel Liquid Marble-based Soft Actuators

A novel soft actuator is designed, fabricated, and optimized for applied use in soft robotics and biomedical applications. The soft actuator is powered by the expansion and contraction of a graphene-containing and encased liquid marble using the photothermal effect. Unfortunately, conventional liquid marbles are found to be too fragile and prone to cracking and failure for such applications. After experimentation, it is possible to remedy this problem by synthesizing liquid marbles encased with polymeric shells–polymerized in situ–for added mechanical strength and robustness. These marbles are shown to have intrinsic photothermal activity. They are then situated in bimorph-type soft actuators where one side of the actuator has a dramatically different Young's modulus than the other, leading to directional actuation which is successfully demonstrated in multistep walking soft robots. The soft actuators are shown to successfully activate the mechanosensitive Piezo protein in a transfected human cell line with high effectiveness and no toxicity. Overall, the liquid marble-powered soft actuators described here represent a new soft actuation methodology and a novel tool for mechanobiological studies, such as stem cell fate and organoid differentiation.     

A Biomimetic Soft Lens Controlled by Electrooculographic Signal

Thanks to many unique features, soft robots or soft machines have been recently explored intensively to work collaboratively with human beings. Most of the previously developed soft robots are either controlled manually or by prewritten programs. In the current work, a novel human–machine interface is developed to use electrooculographic signals generated by eye movements to control the motions and the change of focal length of a biomimetic soft lens. The motion and deformation of the soft lens are achieved by the actuation of different areas of dielectric elastomer films, mimicking the working mechanisms of the eyes of human and most mammals. The system developed in the current study has the potential to be used in visual prostheses, adjustable glasses, and remotely operated robotics in the future.     

Adaptive Magnetoactive Soft Composites for Modular and Reconfigurable Actuators

Magnetoactive soft materials, typically composed of magnetic particles dispersed in a soft polymer matrix, are finding many applications in soft robotics due to their reversible and remote shape transformations under magnetic fields. To achieve complex shape transformations, anisotropic, and heterogeneous magnetization profiles must be programmed in the material. However, once programmed and assembled, magnetic soft actuators cannot be easily reconfigured, repurposed, or repaired, which limits their application, their durability, and versatility in their design. Here, magnetoactive soft composites are developed from squid-derived biopolymers and NdFeB microparticles with tunable ferromagnetic and thermomechanical properties. By leveraging reversible crosslinking nanostructures in the biopolymer matrix, a healing-assisted assembly process is developed that allows for on-demand reconfiguration and magnetic reprogramming of magnetoactive composites. This concept in multi-material modular actuators is demonstrated with programmable deformation modes, self-healing properties to recover their function after mechanical damage, and shape-memory behavior to lock in their preferred configuration and un-actuated catch states. These dynamic magnetic soft composites can enable the modular design and assembly of new types of magnetic actuators, not only eliminating device vulnerabilities through healing and repair but also by providing adaptive mechanisms to reconfigure their function on demand.