MXene-Enabled Pneumatic Multiscale Shape Morphing for Adaptive, Programmable and Multimodal Radar-infrared Compatible Camouflage

Achieving radar-infrared compatible camouflage with dynamic adaptability has been a long-sought goal, but faces significant challenges owing to the limited dispersion relations of conventional material systems operating in different wavelength ranges. Here, this work proposes the concept of pneumatic multiscale shape morphing and design a periodically arranged pneumatic unit consisting of MXene-based morphable conductors and intake platforms. During gas actuation, the morphable conductor transforms centimeter-scale 2D flat sheets into 3D balloon shapes to enhance microwave absorption behavior, and also reconfigures micrometer-scale MXene wrinkles into smooth planes in combination with cavity-induced low heat transfer to minimize infrared (IR) signatures. Through theory-guided reverse engineering, the final pneumatic matrix shows remarkable frequency tunability (2.64-18.0 GHz), moderate IR emissivity regulation (0.14 at 7-16.5 µm), rapid responsiveness (≈30 ms), wide-angle operation (>45°), and excellent environmental tolerance. Additionally, the multiplexed pneumatic matrix enables over 14 programmable coding sequences that independently alter thermal radiation without compromising radar stealth, and allows multimodal camouflage switching between three distinct compatible states. The approach may facilitate the evolution of camouflage techniques and electromagnetic functional materials toward multispectral, adaptability and intelligence.

Engineering Kirigami Frameworks Toward Real-World Applications

The surge in advanced manufacturing techniques has led to a paradigm shift in the realm of material design from developing completely new chemistry to tailoring geometry within existing materials. Kirigami, evolved from a traditional cultural and artistic craft of cutting and folding, has emerged as a powerful framework that endows simple 2D sheets with unique mechanical, thermal, optical, and acoustic properties, as well as shape-shifting capabilities. Given its flexibility, versatility, and ease of fabrication, there are significant efforts in developing kirigami algorithms to create various architectured materials for a wide range of applications. This review summarizes the fundamental mechanisms that govern the transformation of kirigami structures and elucidates how these mechanisms contribute to their distinctive properties, including high stretchability and adaptability, tunable surface topography, programmable shape morphing, and characteristics of bistability and multistability. It then highlights several promising applications enabled by the unique kirigami designs and concludes with an outlook on the future challenges and perspectives of kirigami-inspired metamaterials toward real-world applications.

Encoded sewing soft textile robots

Incorporating soft actuation with soft yet durable textiles could effectively endow the latter with active and flexible shape morphing and motion like mollusks and plants. However, creating highly programmable and customizable soft robots based on textiles faces a longstanding design and manufacturing challenge. Here, we report a methodology of encoded sewing constraints for efficiently constructing three-dimensional (3D) soft textile robots through a simple 2D sewing process. By encoding heterogeneous stretching properties into three spatial seams of the sewed 3D textile shells, nonlinear inflation of the inner bladder can be guided to follow the predefined spatial shape and actuation sequence, for example, tendril-like shape morphing, tentacle-like sequential manipulation, and bioinspired locomotion only controlled by single pressure source. Such flexible, efficient, scalable, and low-cost design and formation methodology will accelerate the development and iteration of soft robots and also open up more opportunities for safe human-robot interactions, tailored wearable devices, and health care.

Embedded shape morphing for morphologically adaptive robots

Shape-morphing robots can change their morphology to fulfill different tasks in varying environments, but existing shape-morphing capability is not embedded in a robot's body, requiring bulky supporting equipment. Here, we report an embedded shape-morphing scheme with the shape actuation, sensing, and locking, all embedded in a robot's body. We showcase this embedded scheme using three morphing robotic systems: 1) self-sensing shape-morphing grippers that can adapt to objects for adaptive grasping; 2) a quadrupedal robot that can morph its body shape for different terrestrial locomotion modes (walk, crawl, or horizontal climb); 3) an untethered robot that can morph its limbs' shape for amphibious locomotion. We also create a library of embedded morphing modules to demonstrate the versatile programmable shapes (e.g., torsion, 3D bending, surface morphing, etc.). Our embedded morphing scheme offers a promising avenue for robots to reconfigure their morphology in an embedded manner that can adapt to different environments on demand.

Programming hydrogel adhesion with engineered polymer network topology

Hydrogel adhesion that can be easily modulated in magnitude, space, and time is desirable in many emerging applications ranging from tissue engineering and soft robotics to wearable devices. In synthetic materials, these complex adhesion behaviors are often achieved individually with mechanisms and apparatus that are difficult to integrate. Here, we report a universal strategy to embody multifaceted adhesion programmability in synthetic hydrogels. By designing the surface network topology of a hydrogel, supramolecular linkages that result in contrasting adhesion behaviors are formed on the hydrogel interface. The incorporation of different topological linkages leads to dynamically tunable adhesion with high-resolution spatial programmability without alteration of bulk mechanics and chemistry. Further, the association of linkages enables stable and tunable adhesion kinetics that can be tailored to suit different applications. We rationalize the physics of polymer chain slippage, rupture, and diffusion at play in the emergence of the programmable behaviors. With the understanding, we design and fabricate various soft devices such as smart wound patches, fluidic channels, drug-eluting devices, and reconfigurable soft robotics. Our study presents a simple and robust platform in which adhesion controllability in multiple aspects can be easily integrated into a single design of a hydrogel network.

Mechanochemically assisted morphing of shape shifting polymers

Morphing in creatures has inspired various synthetic polymer materials that are capable of shape shifting. The morphing of polymers generally relies on stimuli-active (typically heat and light active) units that fix the shape after a mechanical load-based shape programming. Herein, we report a strategy that uses a mechanochemically active 2,2'-bis(2-phenylindan-1,3-dione) (BPID) mechanophore as a switching unit for mechanochemical morphing. The mechanical load on the polymer triggers the dissociation of the BPID moiety into stable 2-phenylindan-1,3-dione (PID) radicals, whose subsequent spontaneous dimerization regenerates BPID and fixes the temporary shapes that can be effectively recovered to the permanent shapes by heating. A greater extent of BPID activation, through a higher BPID content or mechanical load, leads to higher mechanochemical shape fixity. By contrast, a relatively mechanochemically less active hexaarylbiimidazole (HABI) mechanophore shows a lower fixing efficiency when subjected to the same programing conditions. Another control system without a mechanophore shows a low fixing efficiency comparable to the HABI system. Additionally, the introduction of the BPID moiety also manifests remarkable mechanochromic behavior during the shape programing process, offering a visualizable indicator for the pre-evaluation of morphing efficiency. Unlike conventional mechanical mechanisms that simultaneously induce morphing, such as strain-induced plastic deformation or crystallization, our mechanochemical method allows for shape programming after the mechanical treatment. Our concept has potential for the design of mechanochemically programmable and mechanoresponsive shape shifting polymers.

Pneumatic cells toward absolute Gaussian morphing

On a flat map of the Earth, continents are inevitably distorted. Reciprocally, curving a plate simultaneously in two directions requires a modification of in-plane distances, as Gauss stated in his seminal theorem. Although emerging architectured materials with programmed in-plane distortions are capable of such shape morphing, an additional control of local bending is required to precisely set the final shape of the resulting three-dimensional surface. Inspired by bulliform cells in leaves of monocotyledon plants, we show how the internal structure of flat panels can be designed to program bending and in-plane distortions simultaneously when pressurized, leading to a targeted shell shape. These surfaces with controlled stiffness and fast actuation are manufactured using consumer-grade materials and open a route to large-scale shape-morphing robotics applications.

A multifunctional soft robotic shape display with high-speed actuation, sensing, and control

Shape displays which actively manipulate surface geometry are an expanding robotics domain with applications to haptics, manufacturing, aerodynamics, and more. However, existing displays often lack high-fidelity shape morphing, high-speed deformation, and embedded state sensing, limiting their potential uses. Here, we demonstrate a multifunctional soft shape display driven by a 10 × 10 array of scalable cellular units which combine high-speed electrohydraulic soft actuation, magnetic-based sensing, and control circuitry. We report high-performance reversible shape morphing up to 50 Hz, sensing of surface deformations with 0.1 mm sensitivity and external forces with 50 mN sensitivity in each cell, which we demonstrate across a multitude of applications including user interaction, image display, sensing of object mass, and dynamic manipulation of solids and liquids. This work showcases the rich multifunctionality and high-performance capabilities that arise from tightly-integrating large numbers of electrohydraulic actuators, soft sensors, and controllers at a previously undemonstrated scale in soft robotics.

Passively addressed robotic morphing surface (PARMS) based on machine learning

Reconfigurable morphing surfaces provide new opportunities for advanced human-machine interfaces and bio-inspired robotics. Morphing into arbitrary surfaces on demand requires a device with a sufficiently large number of actuators and an inverse control strategy. Developing compact, efficient control interfaces and algorithms is vital for broader adoption. In this work, we describe a passively addressed robotic morphing surface (PARMS) composed of matrix-arranged ionic actuators. To reduce the complexity of the physical control interface, we introduce passive matrix addressing. Matrix addressing allows the control of N2 independent actuators using only 2N control inputs, which is substantially lower than traditional direct addressing (N2 control inputs). Using machine learning with finite element simulations for training, our control algorithm enables real-time, high-precision forward and inverse control, allowing PARMS to dynamically morph into arbitrary achievable predefined surfaces on demand. These innovations may enable the future implementation of PARMS in wearables, haptics, and augmented reality/virtual reality.

A modular strategy for distributed, embodied control of electronics-free soft robots

Robots typically interact with their environments via feedback loops consisting of electronic sensors, microcontrollers, and actuators, which can be bulky and complex. Researchers have sought new strategies for achieving autonomous sensing and control in next-generation soft robots. We describe here an electronics-free approach for autonomous control of soft robots, whose compositional and structural features embody the sensing, control, and actuation feedback loop of their soft bodies. Specifically, we design multiple modular control units that are regulated by responsive materials such as liquid crystal elastomers. These modules enable the robot to sense and respond to different external stimuli (light, heat, and solvents), causing autonomous changes to the robot's trajectory. By combining multiple types of control modules, complex responses can be achieved, such as logical evaluations that require multiple events to occur in the environment before an action is performed. This framework for embodied control offers a new strategy toward autonomous soft robots that operate in uncertain or dynamic environments.

Polymorphic display and texture integrated systems controlled by capillarity

Soft robotics offer unusual bioinspired solutions to challenging engineering problems. Colorful display and morphing appendages are vital signaling modalities used by natural creatures to camouflage, attract mates, or deter predators. Engineering these display capabilities using traditional light emitting devices is energy expensive and bulky and requires rigid substrates. Here, we use capillary-controlled robotic flapping fins to create switchable visual contrast and produce state-persistent, multipixel displays that are 1000- and 10-fold more energy efficient than light emitting devices and electronic paper, respectively. We reveal the bimorphic ability of these fins, whereby they switch between straight or bent stable equilibria. By controlling the droplets temperature across the fins, the multifunctional cells simultaneously exhibit infrared signals decoupled from the optical signals for multispectral display. The ultralow power, scalability, and mechanical compliance make them suitable for curvilinear and soft machines.

Programming 3D curved mesosurfaces using microlattice designs

Cellular microstructures form naturally in many living organisms (e.g., flowers and leaves) to provide vital functions in synthesis, transport of nutrients, and regulation of growth. Although heterogeneous cellular microstructures are believed to play pivotal roles in their three-dimensional (3D) shape formation, programming 3D curved mesosurfaces with cellular designs remains elusive in man-made systems. We report a rational microlattice design that allows transformation of 2D films into programmable 3D curved mesosurfaces through mechanically guided assembly. Analytical modeling and a machine learning-based computational approach serve as the basis for shape programming and determine the heterogeneous 2D microlattice patterns required for target 3D curved surfaces. About 30 geometries are presented, including both regular and biological mesosurfaces. Demonstrations include a conformable cardiac electronic device, a stingray-like dual mode actuator, and a 3D electronic cell scaffold.

Turing pattern-based design and fabrication of inflatable shape-morphing structures

Turing patterns are self-organizing stripes or spots widely found in biological systems and nature. Although inspiring, their applications are limited. Inflatable shape-morphing structures have attracted substantial research attention. Traditional inflatable structures use isotropic materials with geometrical features to achieve shape morphing. Recently, gradient-based optimization methods have been used to design these structures. These methods assume anisotropic materials whose orientation can vary freely. However, this assumption makes fabrication a considerable challenge by methods such as additive manufacturing, which print isotropic materials. Here, we present a methodology of using Turing patterns to bridge this gap. Specifically, we use Turing patterns to convert a design with distributed anisotropic materials to a distribution with two materials, which can be fabricated by grayscale digital light processing 3D printing. This work suggests that it is possible to apply patterns in biological systems and nature to engineering composites and offers new concepts for future material design.

Regulating Aggregated Structures in Organohydrogels for On-Demand Information Encryption

As one of the most promising candidates for dynamic information storage, intelligent gels with tunable optical properties under external stimuli have received great attention. The implementation of transparency variation for information display is a favorable and versatile strategy but still faces the challenge of on-demand encryption-decryption. Herein, an optical tunable organohydrogel is prepared, which has interpenetrating heterogeneous networks consisting of hydrophilic poly(N,N-dimethylacrylamide) (PDMA) and hydrophobic polyoctadecyl methacrylate (PSMA). The long alkane side chains of PSMA endow the organohydrogel with the capacity of crystallization-melting transitions under the stimulus of heat, accompanied by transparent-opaque switching. In addition, the variations of transparency can also be achieved by water-induced hydrophobic association and microphase separation, resulting from the unique heterogeneous networks of the organohydrogel. Based on the abovementioned two aggregated structures, various pieces of information can be loaded on the organohydrogel by light writing or water printing with the assistance of masks. The coded information can be encrypted and decrypted by solvent replacement and temperature switching. This elaborately designed organohydrogel can act as an effective communication platform with an improved security level and ignite the sparks of developing novel information storage materials.

Bio-Inspired Transparent Soft Jellyfish Robot

Jellyfish are among the widely distributed nature creatures that can effectively control the fluidic flow around their transparent soft body, thus achieving movements in the water and camouflage in the surrounding environments. Till now, it remains a challenge to replicate both transparent appearance and functionalities of nature jellyfish in synthetic systems due to the lack of transparent actuators. In this work, a fully transparent soft jellyfish robot is developed to possess both transparency and bio-inspired omni motions in water. This robot is driven by transparent dielectric elastomer actuators (DEAs) using hybrid silver nanowire networks and conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/waterborne polyurethane as compliant electrodes. The electrode exhibits large stretchability, low stiffness, high transmittance, and excellent conductivity at large strains. Consequently, the highly transparent DEA based on this hybrid electrode, with Very-High-Bond membranes as dielectric layers and polydimethylsiloxane as top coating, can achieve a maximum area strain of 146% with only 3% hysteresis loss. Driven by this transparent DEA, the soft jellyfish robot can achieve vertical and horizontal movements in water, by mimicking the actual pulsating rhythm of an Aurelia aurita. The bio-inspired robot can serve multiple functions as an underwater soft robot. The hybrid electrodes and bio-inspired design approach are potentially useful in a variety of soft robots and flexible devices.

A Stretchable Fiber with Tunable Stiffness for Programmable Shape Change of Soft Robots

All soft robots require the same functionality, that is, controlling the shape of a structure made from soft materials. However, existing approaches for shape control of soft robots are primarily dominated by modular pneumatic actuators, which require multichambers and complex flow control components. Nature shows exciting examples of manipulation (shape change) in animals, such as worms, using a single-chambered soft body and programmable stiffness changes in the skin; controlling the spatial distribution of changes in stiffness enables achieving complex shape evolutions. However, such stiffness control requires a drastic membrane stiffness contrast between stiffened and nonstiffened states. Generally, this is extremely challenging to accomplish in stretchable materials. Inspired by longitudinal muscle fibers in the skin of worms, we developed a new concept for fabricating a hybrid fiber with tunable stiffness, that is, a fiber comprising both stiff and soft parts connected in a series. A substantial change in membrane stiffness was then observed by the locking/unlocking of the soft part. Our proposed hybrid fiber cyclically produced a membrane stiffness contrast of more than 100 × in less than 6 s using an input power of 3 W. A network of these hybrid fibers with tunable stiffness could manipulate a single-chambered soft body in multiple directions and transform it into a complex shape by selectively varying the stiffness at different locations.

A mechanics-based approach to realize high–force capacity electroadhesives for robots

Materials with electroprogrammable stiffness and adhesion can enhance the performance of robotic systems, but achieving large changes in stiffness and adhesive forces in real time is an ongoing challenge. Electroadhesive clutches can rapidly adhere high stiffness elements, although their low force capacities and high activation voltages have limited their applications. A major challenge in realizing stronger electroadhesive clutches is that current parallel plate models poorly predict clutch force capacity and cannot be used to design better devices. Here, we use a fracture mechanics framework to understand the relationship between clutch design and force capacity. We demonstrate and verify a mechanics-based model that predicts clutch performance across multiple geometries and applied voltages. On the basis of this approach, we build a clutch with 63 times the force capacity per unit electrostatic force of state-of-the-art electroadhesive clutches. Last, we demonstrate the ability of our electroadhesives to increase the load capacity of a soft, pneumatic finger by a factor of 27 times compared with a finger without an electroadhesive.

Shape-morphing into 3D curved surfaces with nacre-like composite architectures

Inhomogeneous in-plane deformation of soft materials or cutting and folding of inextensible flat sheets enables shape-morphing from two dimensional (2D) to three-dimensional (3D), while the resulting structures often have weakened mechanical strength. Shells like nacre are known for the superior fracture toughness due to the "brick and mortar" composite layers, enabling stress redistribution and crack stopping. Here, we report an optimal and universal cutting and stacking strategy that transforms composite plies into 3D doubly curved shapes with nacre-like architectures. The multilayered laminate exhibits staggered cut distributions, while the interlaminar shear mitigates the cut-induced mechanical weakness. The experimentally consolidated hemispherical shells exhibit, on average, 37 and 69% increases of compression peak forces, versus those with random cut distributions, when compressed in different directions. Our approach opens a previously unidentified paradigm for shape-conforming arbitrarily curved surfaces while achieving high mechanical performance.

Chiral topographic instability in shrinking spheres

Many biological structures exhibit intriguing morphological patterns adapted to environmental cues, which contribute to their important biological functions and also inspire material designs. Here, we report a chiral wrinkling topography in shrinking core-shell spheres, as observed in excessively dehydrated passion fruit and experimentally demonstrated in silicon core-shells under air extraction. Upon shrinkage deformation, the surface initially buckles into a buckyball pattern (periodic hexagons and pentagons) and then transforms into a chiral mode. The neighbouring chiral cellular patterns can further interact with each other, resulting in secondary symmetry breaking and the formation of two types of topological network. We develop a core-shell model and derive a universal scaling law to understand the underlying morphoelastic mechanism and to effectively describe and predict such chiral symmetry breaking far beyond the critical instability threshold. Moreover, we show experimentally that the chiral characteristic adapted to local perturbation can be harnessed to effectively and stably grasp small-sized objects of various shapes and made of different stiff and soft materials. Our results not only reveal chiral instability topographies, providing fundamental insights into the surface morphogenesis of the deformed core-shell spheres that are ubiquitous in the real world, but also demonstrate potential applications of adaptive grasping based on delicate chiral localization.

Soft shape-programmable surfaces by fast electromagnetic actuation of liquid metal networks

Low modulus materials that can shape-morph into different three-dimensional (3D) configurations in response to external stimuli have wide-ranging applications in flexible/stretchable electronics, surgical instruments, soft machines and soft robotics. This paper reports a shape-programmable system that exploits liquid metal microfluidic networks embedded in an elastomer matrix, with electromagnetic forms of actuation, to achieve a unique set of properties. Specifically, this materials structure is capable of fast, continuous morphing into a diverse set of continuous, complex 3D surfaces starting from a two-dimensional (2D) planar configuration, with fully reversible operation. Computational, multi-physics modeling methods and advanced 3D imaging techniques enable rapid, real-time transformations between target shapes. The liquid-solid phase transition of the liquid metal allows for shape fixation and reprogramming on demand. An unusual vibration insensitive, dynamic 3D display screen serves as an application example of this type of morphable surface.

Low modulus materials that can change shape in response to external stimuli are promising for a wide range of applications. The authors here introduce a shape-reprogrammable construct, based on liquid metal microfluidic networks and electromagnetic actuation, that supports a unique collection of capabilities.

A dynamically reprogrammable surface with self-evolving shape morphing

Dynamic shape-morphing soft materials systems are ubiquitous in living organisms; they are also of rapidly increasing relevance to emerging technologies in soft machines^1-3, flexible electronics^4,5 and smart medicines⁶. Soft matter equipped with responsive components can switch between designed shapes or structures, but cannot support the types of dynamic morphing capabilities needed to reproduce natural, continuous processes of interest for many applications^7-24. Challenges lie in the development of schemes to reprogram target shapes after fabrication, especially when complexities associated with the operating physics and disturbances from the environment can stop the use of deterministic theoretical models to guide inverse design and control strategies^25-30. Here we present a mechanical metasurface constructed from a matrix of filamentary metal traces, driven by reprogrammable, distributed Lorentz forces that follow from the passage of electrical currents in the presence of a static magnetic field. The resulting system demonstrates complex, dynamic morphing capabilities with response times within 0.1 second. Implementing an in situ stereo-imaging feedback strategy with a digitally controlled actuation scheme guided by an optimization algorithm yields surfaces that can follow a self-evolving inverse design to morph into a wide range of three-dimensional target shapes with high precision, including an ability to morph against extrinsic or intrinsic perturbations. These concepts support a data-driven approach to the design of dynamic soft matter, with many unique characteristics.

Compact Multilayer Extension Actuators for Reconfigurable Soft Robots

Soft robotic pneumatic actuators generally excel in the specific application they were designed for but lack the versatility to be redeployed to other applications. This study presents a novel and versatile soft compact multilayer extension actuator (MEA) to overcome this limitation. We use the MEA linear output in different hybrid configurations to achieve this versatility. The unique design and fabrication of the MEA allow for a compact elastomeric actuator with innate tension, capable of reverting to its initial state without the need for external stimulus. The MEA is made from alternating elastomers with different Young's modulus, bestowing the MEA with high durability, force, and extension capabilities. In addition, the MEA is lightweight at 4 g, capable of a high force-to-weight ratio of 1000 and an extension ratio of 525%. We also explored varying the MEA parameters, such as its material and dimension, which further enhance its properties. Subsequently, we showed four different design configurations encompassing the MEA to produce four basic motions, that is, push, pull, bend, and twist. Finally, we demonstrated three possible hybrid configurations for manipulation, locomotion, and assistive applications that highlight the versatility, manipulability, and modularity of the MEA.

Wrinkling and restabilization of a hyperelastic PDMS membrane at finite strain

Wrinkles are commonly observed in uniaxially stretched hyperelastic membranes and eventually disappear with the increase of stretching. The widely used scheme at present assumes the material parameters to be empirical values and straightforwardly considers some constitutive models to explore the wrinkling and restabilization behavior. However, this simple treatment may cause deviation from experiment by ignoring the applicability of the models and the authenticity of the input parameters, prompting us to report based on realistic material parameters. This paper presents an experimental, theoretical and numerical investigation on the wrinkling and restabilization behavior of hyperelastic materials. By fitting experimental stress-strain curves of PDMS films, we confirm that the 3-term Ogden model bears a closer resemblance to the experimental data than the widely used neo-Hookean, Mooney-Rivlin, and Arruda-Boyce models under certain circumstances. The simulation results indicate that different constitutive models quantitatively affect the critical buckling strain, wrinkling amplitudes, and restabilization points. Furthermore, the isolated central bifurcation point solved by Koiter stability theory agrees well with the simulation and experimental results. A 3D phase diagram of stability boundaries was established to gain a comprehensive insight into the effects of geometric parameters (length, width, and thickness) on wrinkling.

Mechanics of tension-induced film wrinkling and restabilization: a review

Wrinkling of thin films under tension is omnipresent in nature and modern industry, a phenomenon which has aroused considerable attention during the past two decades because of its intricate nonlinear behaviours and intriguing morphology changes. Here, we review recent advancements in the mechanics of tension-induced film wrinkling and restabilization, by identifying three major stages of its progress: small-strain (less than 5 % ) wrinkling of stiff sheets, finite-strain (up to 30 % ) wrinkling and restabilization (isola-centre bifurcation) of soft films, and the effects of curved configurations and material properties on pattern formation. Growing demand for fundamental understanding, quantitative prediction and precise tracking of secondary bifurcation transitions in morphological evolution of thin films helps to advance finite-strain plate/shell theories and sophisticated modelling methods. This progress not only promotes our insightful understanding of complex instability behaviour but also reveals novel phenomena and sheds light on developing wrinkle-tunable membrane structures and functional surfaces.

Formation of Pixelated Elastic Films via Capillary Suction of Curable Elastomers in Templated Hele-Shaw Cells

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

Multistable shape programming of variable-stiffness electromagnetic devices

Programmable shape morphing enables soft machines to safely and effectively interact with the environment. Stimuli-responsive materials can transform 2D sheets into 3D geometries. However, most solutions cannot hold their shape at zero power, are limited to predetermined configurations, or lack sufficient mechanical stiffness to manipulate common objects. We demonstrate here segmented soft electromagnetic actuators integrated with shape memory polymer (SMP) films, capable of deforming and latching into a broad range of configurations. The device consists of liquid metal (LM) coils in an elastomer shell, laminated between two SMP films. The coils are linked by narrow joints, on which stretchable heaters are patterned. Heating the SMP greatly reduces its stiffness. Driving current through an LM coil in the presence of a magnetic field then leads to large bending or twisting. Cooling the SMP locks in the shape, leading to load-bearing capacity. Complex shapes are obtained from an initially flat device.

Photomorphogenesis of Diverse Autonomous Traveling Waves in a Monolithic Soft Artificial Muscle

Biological organisms (e.g., batoid fish, etc.) possess the remarkable ability to morph their soft, sheet-like tissues into wavy morphologies and self-oscillate to make traveling waves, enabling myriad functionalities in propulsion, locomotion, and transportation. In contrast, current manmade soft robotic systems cannot adaptively make wavy morphologies and concurrently achieve wave propagation because the controllable actuation of desired 3D morphologies in entirely soft materials is a formidable challenge due to their continuously deformable bodies that own a large number of actuable degrees of freedom. Here, we report a bioinspired robotic system that not only allows photomorphogenesis of on-demand 3D wavy morphologies but also enables autonomous wave propagation in a monolithic soft artificial muscle (MSAM). This system employs a conceptually different design strategy based on a combination of two principles derived from plant morphogenesis and the undulatory motion of ray fish. The former offers a shaping principle based on differential growth that enables morphing MSAM into target wavy configurations, while the latter inspires a driving principle that induces autonomous propagation of shaped waves by rhythmic motor patterns. This waving system can be used as adaptive "soft engines/motors" that enable directional locomotion, intelligent transportation of cargo, and autonomous propulsion. It even produces programmable, complex artificial peristaltic waves. Our design allows controllable formation of 3D wavy morphologies and autonomous wave behaviors in the soft robotic system that would be useful for broad applications in adaptive, self-regulated mechanical systems for advanced robotics, soft machines, and energy harvest.

3D Printing Soft Matters and Applications: A Review

The evolution of nature created delicate structures and organisms. With the advancement of technology, especially the rise of additive manufacturing, bionics has gradually become a popular research field. Recently, researchers have concentrated on soft robotics, which can mimic the complex movements of animals by allowing continuous and often responsive local deformations. These properties give soft robots advantages in terms of integration and control with human tissue. The rise of additive manufacturing technologies and soft matters makes the fabrication of soft robots with complex functions such as bending, twisting, intricate 3D motion, grasping, and stretching possible. In this paper, the advantages and disadvantages of the additive manufacturing process, including fused deposition modeling, direct ink writing, inkjet printing, stereolithography, and selective laser sintering, are discussed. The applications of 3D printed soft matter in bionics, soft robotics, flexible electronics, and biomedical engineering are reviewed.

Bioinspired Porous Anodic Alumina/Aluminum Flake Powder for Multiband Compatible Low Detectability

Continuous development and advancement in modern detection technologies have increased the demand for multiband (e.g., visual and infrared) compatible camouflage. However, challenges exist in the requirements of incompatible structure resulting from the adaptation to different camouflage effects. This study is inspired by the light absorption structure of butterfly wing scales and demonstrates a porous anodic alumina/aluminum flake powder material prepared by a microscopic powder anodic oxidation technique for visual and infrared camouflage. The fabricated structures manipulate a compromise condition for visual camouflage by low reflectance (R̅_400-800nm = 0.32) and dual-band infrared camouflage by low emission (ε̅_3-5μm = 0.081 and ε̅_8-14μm = 0.085). Further, the characteristic of short-range disorder in these bioinspired structures allows maintenance of the camouflage performance under omnidirectional detection (0-60°). This study provides new insight and a feasible method for coordinated manipulation of electromagnetic waves via bioinspired structural design and improved fabrication.

Shape morphing mechanical metamaterials through reversible plasticity

Biological organisms such as the octopus can reconfigure their shape and properties to perform diverse tasks. However, soft machines struggle to achieve complex configurations, morph into shape to support loads, and go between multiple states reversibly. Here, we introduce a multifunctional shape-morphing material with reversible and rapid polymorphic reconfigurability. We couple elastomeric kirigami with an unconventional reversible plasticity mechanism in metal alloys to rapidly (<0.1 seconds) morph flat sheets into complex, load-bearing shapes, with reversibility and self-healing through phase change. This kirigami composite overcomes trade-offs in deformability and load-bearing capacity and eliminates power requirements to sustain reconfigured shapes. We demonstrate this material through integration with onboard control, motors, and power to create a soft robotic morphing drone, which autonomously transforms from a ground to air vehicle and an underwater morphing machine, which can be reversibly deployed to collect cargo.

Electro-assembly of a dynamically adaptive molten fibril state for collagen

Collagen is a biological building block that is hierarchically assembled into diverse morphological structures that, in some cases, is dynamically adaptive in response to external cues and in other cases forms static terminal structures. Technically, there is limited capabilities to guide the emergence of collagen's hierarchical organization to recapitulate the richness of biological structure and function. Here, we report an electro-assembly pathway to create a dynamically adaptive intermediate molten fibril state for collagen. Structurally, this intermediate state is composed of partially aligned and reversibly associating fibrils with limited hierarchical structure. These molten fibrils can be reversibly reconfigured to offer dynamic properties such as stimuli-stiffening, stimuli-contracting, self-healing, and self-shaping. Also, molten fibrils can be guided to further assemble to recapitulate the characteristic hierarchical structural features of native collagen (e.g., aligned fibers with D-banding). We envision that the electro-assembly of collagen fibrils will provide previously unidentified opportunities for tailored collagen-based biomedical materials.

Stretchable Soft Composites with Strain-Induced Architectured Color

Colors enable interaction and communication between living species in a myriad of biological and artificial environments. While living organisms feature low-power mechanisms to dynamically control color in soft tissues, man-made color-changing devices remain predominantly rigid and energy intensive. Here, architectured composites that display striking color changes when stretched in selective directions under ambient light with minimum power input are reported. The orientation-dependent color change results from the rotation of reflective coated platelets that are embedded in a soft polymer matrix and pre-aligned in a well-defined architecture. The light reflected by the platelets generates structural color defined by the oxide coating on the platelet surface. By magnetically programming the initial orientation and spatial distribution of selected platelets within the soft matrix, composites with strain-modulated color-changing effects that cannot be achieved using state-of-the-art technologies are created. The proposed concept of strain-induced architectured color can be harnessed to develop low-power smart stretchable displays, tactile synthetic skins, and autonomous soft robotic devices that undergo fast and reversible color changes through the mechano-optic coupling programmed within their soft composite architecture.

3D-to-3D Microscale Shape-Morphing from Configurable Helices with Controlled Chirality

Tunable and reconfigurable materials with autonomic shape transformation in response to the environment have emerged as one of the most promising approaches for a variety of biomedical applications, such as tissue engineering, biosensing, and in vivo biomedical devices. Currently, it is still quite challenging to fabricate soft, microscaled 3D shape-reconfigurable structures due to either complicated microfabrication or limited microscale photopolymerization-based printing approaches to enable adaptive shape transformation. Here, a one-step photo-cross-linking approach has been demonstrated to obtain a 3D-to-3D morphological transformable microhelix from a self-rolled hydrogel microsheet, resulting in chirality conversion. It was enabled by a custom-designed "hard" stripe/"soft" groove topography on the microsheets for introducing, which introduced both in-planar and out-of-planar anisotropies. Both experiment and simulation confirmed that a stripe/groove geometry can effectively control the 3D transformation by activating in-planar or/and out-of-planar mismatch stress within the microsheets, resulting in switching of the rolling direction between perpendicular/parallel to the length of the stripe. Furthermore, versatile 3D microconstructs with the ability to transform between two distinct 3D configurations have been achieved based on controlled rolling of microhelices, demonstrated as "windmill"-to-"T-cross" and "cylinder"-to-"scroll" transformations and dynamic blossoming of biomimetic orchids. In contrast to conventional 2D-to-3D micro-origami, we have successfully demonstrated an approach for fabricating microscale, all-soft-material-based constructs with autonomic 3D-to-3D structural transformation, which presents an opportunity for designing more complex hydrogel-based microrobotics.

Bioinspired Nanostructured Superwetting Thin-Films in a Self-supported form Enabled "Miniature Umbrella" for Weather Monitoring and Water Rescue

An elastic, superhydrophobic and conductive thin film inspired by the natural self-supported superhydrophobic butterfly wings enabled by a controllable composite of assembled carbon nanotube and elastomer is fabricated. Through the adjustment of hydrophobic elastomeric coating, the surface wettability can be effectively controlled and still maintain superhydrophobic characteristics under the applied strain of 60%. The achieved film can function as a self-supported smart umbrella to sensitively monitor the day weather and perform water rescue.

ABSTRACT

Two-dimensional (2D) soft materials, especially in their self-supported forms, demonstrate attractive properties to realize biomimetic morphing and ultrasensitive sensing. Although extensive efforts on design of self-supported functional membranes and integrated systems have been devoted, there still remains an unexplored regime of the combination of mechanical, electrical and surface wetting properties for specific functions. Here, we report a self-supported film featured with elastic, thin, conductive and superhydrophobic characteristics. Through a well-defined surface modification strategy, the surface wettability and mechanical sensing can be effectively balanced. The resulted film can function as a smart umbrella to achieve real-time simulated raining with diverse frequencies and intensity. In addition, the integrated umbrella can even response sensitively to the sunlight and demonstrate a positively correlation of current signals with the intensity of sun illumination. Moreover, the superhydrophobic umbrella can be further employed to realize water rescue, which can take the underwater object onto water surface, load and rapidly transport the considerable weight. More importantly, the whole process of loaded objects and water flow velocity can be precisely detected. The self-supported smart umbrella can effectively monitor the weather and realize a smart water rescue, demonstrating significant potentials in multifunctional sensing and directional actuation in the presence of water. [Image: see text]

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-021-00775-4.

Dissecting Biological and Synthetic Soft-Hard Interfaces for Tissue-Like Systems

Soft and hard materials at interfaces exhibit mismatched behaviors, such as mismatched chemical or biochemical reactivity, mechanical response, and environmental adaptability. Leveraging or mitigating these differences can yield interfacial processes difficult to achieve, or inapplicable, in pure soft or pure hard phases. Exploration of interfacial mismatches and their associated (bio)chemical, mechanical, or other physical processes may yield numerous opportunities in both fundamental studies and applications, in a manner similar to that of semiconductor heterojunctions and their contribution to solid-state physics and the semiconductor industry over the past few decades. In this review, we explore the fundamental chemical roles and principles involved in designing these interfaces, such as the (bio)chemical evolution of adaptive or buffer zones. We discuss the spectroscopic, microscopic, (bio)chemical, and computational tools required to uncover the chemical processes in these confined or hidden soft-hard interfaces. We propose a soft-hard interaction framework and use it to discuss soft-hard interfacial processes in multiple systems and across several spatiotemporal scales, focusing on tissue-like materials and devices. We end this review by proposing several new scientific and engineering approaches to leveraging the soft-hard interfacial processes involved in biointerfacing composites and exploring new applications for these composites.

Pangolin-Inspired Stretchable, Microwave-Invisible Metascale

Microwave-invisible devices are emerging as a valuable technology in various applications, including soft robotics, shape-morphing structures, and textural camouflages, especially in electronic countermeasures. Unfortunately, conventional microwave-absorbing metastructures and bulk absorbers are stretching confined, limiting their application in deformable or special-shaped targets. To overcome such limitations, a conceptually novel soft-rigid-connection strategy, inspired by the pangolin, is proposed. Pangolin-inspired metascale (PIMS), which is a kind of stretchable metamaterial consisting of an electromagnetic dissipative scale (EMD-scale) and elastomer, is rationally designed. Such a device exhibits robust microwave-absorbing capacity under the interference of 50% stretching. Besides, profiting from the covering effect and size-confined effect of EMD-scale, the out-of-plane indentation failure force of PIMS is at least 5 times larger than conventional device. As a proof of concept, the proposed device is conformally pasted on nondevelopable surfaces. For a spherical dome surface, the maximum radar cross-section (RCS) reduction of PIMS is 6.3 dB larger than that of a conventional device, while for a saddle surface, the bandwidth of 10 dB RCS reduction exhibits an increase of 83%. In short, this work provides a conceptually novel platform to develop stretchable, nondevelopable surface conformable functional devices.

Organismal Design and Biomimetics: A Problem of Scale

Organisms and their features represent a complex system of solutions that can efficiently inspire the development of original and cutting-edge design applications: the related discipline is known as biomimetics. From the smallest to the largest, every species has developed and adapted different working principles based on their relative dimensional realm. In nature, size changes determine remarkable effects in organismal structures, functions, and evolutionary innovations. Similarly, size and scaling rules need to be considered in the biomimetic transfer of solutions to different dimensions, from nature to artefacts. The observation of principles that occur at very small scales, such as for nano- and microstructures, can often be seen and transferred to a macroscopic scale. However, this transfer is not always possible; numerous biological structures lose their functionality when applied to different scale dimensions. Hence, the evaluation of the effects and changes in scaling biological working principles to the final design dimension is crucial for the success of any biomimetic transfer process. This review intends to provide biologists and designers with an overview regarding scale-related principles in organismal design and their application to technical projects regarding mechanics, optics, electricity, and acoustics.

Multivalued Inverse Design: Multiple Surface Geometries from One Flat Sheet

Designing flat sheets that can be made to deform into three-dimensional shapes is an area of intense research with applications in micromachines, soft robotics, and medical implants. Thus far, such sheets were designed to adopt a single target shape. Here, we show that through anisotropic deformation applied inhomogeneously throughout a sheet, it is possible to design a single sheet that can deform into multiple surface geometries upon different actuations. The key to our approach is development of an analytical method for solving this multivalued inverse problem. Such sheets open the door to fabricating machines that can perform complex tasks through cyclic transitions between multiple shapes. As a proof of concept, we design a simple swimmer capable of moving through a fluid at low Reynolds numbers.

Materials with Electroprogrammable Stiffness

Stiffness is a mechanical property of vital importance to any material system and is typically considered a static quantity. Recent work, however, has shown that novel materials with programmable stiffness can enhance the performance and simplify the design of engineered systems, such as morphing wings, robotic grippers, and wearable exoskeletons. For many of these applications, the ability to program stiffness with electrical activation is advantageous because of the natural compatibility with electrical sensing, control, and power networks ubiquitous in autonomous machines and robots. The numerous applications for materials with electrically driven stiffness modulation has driven a rapid increase in the number of publications in this field. Here, a comprehensive review of the available materials that realize electroprogrammable stiffness is provided, showing that all current approaches can be categorized as using electrostatics or electrically activated phase changes, and summarizing the advantages, limitations, and applications of these materials. Finally, a perspective identifies state-of-the-art trends and an outlook of future opportunities for the development and use of materials with electroprogrammable stiffness.

Agile reversible shape-morphing of particle rafts

Materials that transform shapes responding to external stimuli can bring unprecedented innovations to soft matter physics, soft robotics, wearable electronics, and architecture. As most conventional soft actuation technologies induce large deformations only in a preprogrammed manner at designated locations, the material systems capable of agile reversible deformations without prescribed patterns are strongly desired for versatile mechanical morphing systems. Here we report a morphable liquid interface coated with dielectric particles, or a particle raft, which can reversibly change its topography under an external electric field. The rafts change from flat floors to towers within seconds, and the morphed structures are even capable of horizontal translation. Our experiments and theory show that the raft deformation is driven by electrostatic attraction between particles and electrodes, while being modulated by electric discharge. A broad range of materials serving as electrodes, e.g., human fingers and transparent polymers, suggests this system's diverse applications, including the human-machine interface and the three-dimensional physical display.

Recent progress of biomimetic motions-from microscopic micro/nanomotors to macroscopic actuators and soft robotics

Motion is a basic behavioral attribute of organisms, and it is a behavioral response of organisms to the external environment and internal state changes. Materials with switchable mechanical properties are widespread in living organisms and play crucial roles in the motion of organisms. Therefore, significant efforts have been made toward mimicking such architectures and motion behaviors by making full use of the properties of stimulus-responsive materials to design smart materials/machines with specific functions. In recent years, the biomimetic motions based on micro/nanomotors, actuators and soft robots constructed from smart response materials have been developed gradually. However, a comprehensive discussion on various categories of biomimetic motions in this field is still missing. This review aims to provide such a panoramic overview. From nano-to macroscales, we summarize various biomimetic motions based on micro/nanomotors, actuators and soft robotics. For each biomimetic motion, we discuss the driving modes and the key functions. The challenges and opportunities of biomimetic motions are also discussed. With rapidly increasing innovation, advanced, intelligent and multifunctional biomimetic motions based on micro/nanomotors, actuators and soft robotics will certainly bring profound impacts and changes for human life in the near future.

Biomimetic motions are derived from the many different functional materials and/or intricate and highly organized structure of the biological material from the molecular to the nanoscale, microscale and macroscale.

Bi-Shell Valve for Fast Actuation of Soft Pneumatic Actuators via Shell Snapping Interaction

Rapid motion in soft pneumatic robots is typically achieved through actuators that either use a fast volume input generated from pressure control, employ an integrated power source, such as chemical explosions, or are designed to embed elastic instabilities in the body of the robot. This paper presents a bi-shell valve that can fast actuate soft actuators neither relying on the fast volume input provided by pressure control strategies nor requiring modifications to the architecture of the actuator. The bi-shell valve consists of a spherical cap and an imperfect shell with a geometrically tuned defect that enables shell snapping interaction to convert a slowly dispensed volume input into a fast volume output. This function is beyond those of current valves capable to perform fluidic flow regulation. Validated through experiments, the analysis unveils that the spherical cap sets the threshold of the snapping pressure along with the upper bounds of volume and energy output, while the imperfect shell interacts with the cap to store and deliver the desired output for rapid actuation. Geometry variations of the bi-shell valve are provided to show that the concept is versatile. A final demonstration shows that the soft valve can quickly actuate a striker.

Static Modeling of the Fiber-Reinforced Soft Pneumatic Actuators Including Inner Compression: Bending in Free Space, Block Force, and Deflection upon Block Force

Fiber-reinforced soft pneumatic actuators (FR-SPAs) are among the most successful soft actuators in the soft robotics community considering their structural strength, motion range, and force output. Inspired by the pneumatic artificial muscle, the bending-type tubular SPAs have also been applied with fiber winding for body reinforcement and then utilized in many applications. Due to their superior utility and popularity, FR-SPAs have been extensively modeled using different methods. However, very little attention was given to the compression on the inner wall of the FR-SPAs by the compressed air. Furthermore, there is no unified modeling principle for bending, force output, and deflection of the FR-SPA. In this article, we take into account the inner compression and propose a static modeling approach based on the moment equilibrium for three important and frequently studied cases: free bending, block force, and deflection upon block force of the FR-SPA. Stress analysis of the material inside the fiber wall is conducted, which reveals the influence of radial compression by the input air. Then, the new stress expression is used in the moment equilibrium and results in the SPA models for the three aforementioned cases. The models are experimentally verified using SPAs featuring two profile designs and three different silicone rubbers. The results show that the placement of the fiber wall plays an important role in the SPA behavior. More importantly, the models successfully differentiate the two profiles and produce fairly accurate predictions of the bending angles, block forces, and deflections. The understanding of the compression effect offers a new variable in the FR-SPA design process, which can be used to tune the SPA properties for different applications.

Printing Multi-Material Organic Haptic Actuators

Haptic actuators generate touch sensations and provide realism and depth in human-machine interactions. A new generation of soft haptic interfaces is desired to produce the distributed signals over large areas that are required to mimic natural touch interactions. One promising approach is to combine the advantages of organic actuator materials and additive printing technologies. This powerful combination can lead to devices that are ergonomic, readily customizable, and economical for researchers to explore potential benefits and create new haptic applications. Here, an overview of emerging organic actuator materials and digital printing technologies for fabricating haptic actuators is provided. In particular, the focus is on the challenges and potential solutions associated with integration of multi-material actuators, with an eye toward improving the fidelity and robustness of the printing process. Then the progress in achieving compact, lightweight haptic actuators by using an open-source extrusion printer to integrate different polymers and composites in freeform designs is reported. Two haptic interfaces-a tactile surface and a kinesthetic glove-are demonstrated to show that printing with organic materials is a versatile approach for rapid prototyping of various types of haptic devices.

Recent Progress in Artificial Muscles for Interactive Soft Robotics

Artificial muscles are the core components of the smart and interactive soft robotic systems, providing the capabilities in shape morphing, manipulation, and mobility. Intense research efforts in the development of artificial muscles are based on the dielectric elastomer actuators, pneumatic actuators, electrochemical actuators, soft magnetic actuators, and stimulus responsive polymers. Recent progress has presented artificial muscles with impressive specific power output exceeding that of the natural muscles, dexterous shape morphing behavior that can be programmed and reconfigured, and exceptional high maneuverability to traverse surfaces with obstacles and different textures. Here, a succinct and critical summary is provided on the materials and strategies that have contributed to the important advancement of the artificial muscles in recent research. On that basis, the exciting opportunities are discussed in the integration of soft electronic devices with artificial muscles to enable smart and interactive soft robotic systems.

Transparent Soft Actuators/Sensors and Camouflage Skins for Imperceptible Soft Robotics

The advent of soft robotics has led to great advancements in robots, wearables, and even manufacturing processes by employing entirely soft-bodied systems that interact safely with any random surfaces while providing great mechanical compliance. Moreover, recent developments in soft robotics involve advances in transparent soft actuators and sensors that have made it possible to construct robots that can function in a visually and mechanically unobstructed manner, assisting the operations of robots and creating more applications in various fields. In this aspect, imperceptible soft robotics that mainly consist of optically transparent imperceptible hardware components is expected to constitute a new research focus in the forthcoming era of soft robotics. Here, the recent progress regarding extended imperceptible soft robotics is provided, including imperceptible transparent soft robotics (transparent soft actuators/sensors) and imperceptible nontransparent camouflage skins. Their principles, materials selections, and working mechanisms are discussed so that key challenges and perspectives in imperceptible soft robotic systems can be explored.

Robotic surfaces with reversible, spatiotemporal control for shape morphing and object manipulation

Continuous and controlled shape morphing is essential for soft machines to conform, grasp, and move while interacting safely with their surroundings. Shape morphing can be achieved with two-dimensional (2D) sheets that reconfigure into target 3D geometries, for example, using stimuli-responsive materials. However, most existing solutions lack the ability to reprogram their shape, face limitations on attainable geometries, or have insufficient mechanical stiffness to manipulate objects. Here, we develop a soft, robotic surface that allows for large, reprogrammable, and pliable shape morphing into smooth 3D geometries. The robotic surface consists of a layered design composed of two active networks serving as artificial muscles, one passive network serving as a skeleton, and cover scales serving as an artificial skin. The active network consists of a grid of strips made of heat-responsive liquid crystal elastomers (LCEs) containing stretchable heating coils. The magnitude and speed of contraction of the LCEs can be controlled by varying the input electric currents. The 1D contraction of the LCE strips activates in-plane and out-of-plane deformations; these deformations are both necessary to transform a flat surface into arbitrary 3D geometries. We characterize the fundamental deformation response of the layers and derive a control scheme for actuation. We demonstrate that the robotic surface provides sufficient mechanical stiffness and stability to manipulate other objects. This approach has potential to address the needs of a range of applications beyond shape changes, such as human-robot interactions and reconfigurable electronics.

Beyond the Visible: Bioinspired Infrared Adaptive Materials

Infrared (IR) adaptation phenomena are ubiquitous in nature and biological systems. Taking inspiration from natural creatures, researchers have devoted extensive efforts for developing advanced IR adaptive materials and exploring their applications in areas of smart camouflage, thermal energy management, biomedical science, and many other IR-related technological fields. Herein, an up-to-date review is provided on the recent advancements of bioinspired IR adaptive materials and their promising applications. First an overview of IR adaptation in nature and advanced artificial IR technologies is presented. Recent endeavors are then introduced toward developing bioinspired adaptive materials for IR camouflage and IR radiative cooling. According to the Stefan-Boltzmann law, IR camouflage can be realized by either emissivity engineering or thermal cloaks. IR radiative cooling can maximize the thermal radiation of an object through an IR atmospheric transparency window, and thus holds great potential for use in energy-efficient green buildings and smart personal thermal management systems. Recent advances in bioinspired adaptive materials for emerging near-IR (NIR) applications are also discussed, including NIR-triggered biological technologies, NIR light-fueled soft robotics, and NIR light-driven supramolecular nanosystems. This review concludes with a perspective on the challenges and opportunities for the future development of bioinspired IR adaptive materials.