Foldable mechanical metamaterials can toggle between multiple folding states with distinct properties. Each state differs in arrangement of elements and contact points, which change how mechanical signals and stresses distribute and propagate. Similarly, such folding states may influence how chemical signals travel, which may open new functional capabilities of these materials. Herein, we investigate how autocatalytic chemical waves propagate across metamaterial structures prepared from double network hydrogels with different geometry, hydrogel composition, and signaling chemistry. As folding states change, so do the signaling patterns; hinges and elements create new contact points that determine chemical signals’ pathways. Dynamically flipping between folding states modulates chemical signal propagation in both modeling and experiments, including structure-aided transport where chemical signals hop across large distances. Structuring chemical signal transport through foldable geometries, instead of propagation through the bulk, opens up unprecedented possibilities for user-defined control over spatiotemporal signal distribution in life-like materials.

Dynamic control over optical whiteness is promising for applications ranging from energy-efficient coatings to adaptive displays. However, current approaches rely on macroscopic structural transformations or externally imposed refractive-index contrasts, offering limited tunability and scalability. Here, we introduce a liquid crystal network (LCN) that undergoes reversible whitening through solvent-triggered disruption of supramolecular interactions. Exposure to polar protic solvents breaks hydrogen bonds and drives nanoscale phase segregation, generating domains that efficiently scatter visible light. This whitening mechanism enables rapid, robust, and fatigue-resistant switching, with scattering efficiencies exceeding 90% in 100 μm LCN films. By tailoring the molecular design, incorporating halogen-bonding dopants, and post-treatment with acid or base, the optical contrast and switching kinetics can be tuned. We demonstrate potential applications in biometric pattern recognition, underwater visibility enhancement, and solvent discrimination, establishing a materials platform towards dynamic scattering materials. Dynamic control over optical whiteness is promising for applications ranging from energy-efficient coatings to adaptive displays but current approaches offer limited tunability and scalability. Here the authors introduce a liquid crystal network that undergoes reversible whitening through solvent-triggered disruption of supramolecular interactions.

Natural anisotropic tissues, such as tendons and cartilages, achieve remarkable mechanical properties and various biofunctions through oriented hierarchical structures. Inspired from organisms, we develop a synergistic molecular and structural engineering technique based on the thermodynamically reversible reconfiguration of hydrogen bonds to achieve high-performance anisotropic supramolecular hydrogels by quenching pre-stretched polymer networks. Multiple inherent hydrogen bonds gradually dissociate under high-temperature processing to allow the good alignment of the polymer chains by uniaxial pre-stretching. The oriented polymer chains are then fixed on-site by rapid quenching-mediated hydrogen bond reconstruction at low temperatures (e.g., ice bath). This process merely relies on the inherent hydrogen bonds of polymer chains instead of traditional salting-out, metal ionic coordination and solvent effects. The optimal anisotropic hydrogel shows a tensile strength of 19.4 ± 0.7 MPa and toughness of 53.8 ± 5.2 MJ m-3 along the pre-stretching direction, which are 2.6- and 1.7-times higher than that of the unquenched isotropic hydrogels, respectively. This general strategy is applicable to different strong hydrogen bonding supramolecular hydrogel systems. Furthermore, we fabricate anisotropic hydrogel fibers as damping materials. This general approach for the preparation of anisotropic supramolecular hydrogels shows great potential for various engineering applications, such as in the fabrication protective and cushioning materials, flexible optoelectronics, and mechano-functional scaffolds.

Natural organisms use sensory feedback to adaptively regulate their behavior, but replicating such feedback mechanisms in synthetic materials remains a major challenge. It is believed that achieving complex feedback mechanisms in responsive materials will pave the way toward autonomous, intelligent structures and actuation without complex electronics. Inspired by biological systems, we present a general strategy for embedding feedback loops into light-responsive materials. We introduce a baffle-actuator system that enables programmed positive or negative feedback by adjusting the baffle's position relative to incident light. This allows self-regulated control of actuation behavior. Using this approach, we transform a light-bending strip into a switchable, multi-stable structure controlled by light intensity. Leveraging negative feedback, we further demonstrate two autonomous soft robots-a walker and a swimmer-with self-regulated motion. Our results highlight the ubiquity and potential of feedback mechanisms in optically responsive materials, opening new avenues for intelligent, electronics-free soft robotics.

Hydrogels, renowned for their remarkable water absorption capacity, have emerged as promising materials for oil-water separation. Nevertheless, the widespread application of traditional hydrogels remains challenging owing to their insufficient mechanical robustness, particularly in the hydrated and swollen state. In addition, hydrogels that simultaneously exhibit high strength, strong adhesion, excellent swelling capacity, and self-healing ability remain relatively rare. Herein, we present an "all-in-one" polyacrylonitrile (PAN) nanofibrous hydrogel through a "from-nanofibers-to-gel" strategy by controlling the alkaline hydrolysis time of PAN nanofibers. The resulting hydrogel exhibits exceptional mechanical strength and toughness (over 3.36 MPa at a strain of 1230%), adhesion (greater than 520 kPa), self-healing capability, and particularly outstanding swelling performance (more than 3600%). Notably, the hydrogels that have reached swelling equilibrium still remain good mechanical properties and can return to their original state with minimal shrinkage (<5% volume loss) after dehydration, enabling cyclic use. Furthermore, by integrating the thermoresponsive polymer PNIPAm and the photothermal material MXene into a PAN nanofibrous hydrogel, a photothermal-responsive PAN/MXene/PNIPAm hydrogel (PMP hydrogel) were obtained which demonstrates high efficiency in separating dye-contaminated oil/water mixtures. Additionally, as a solar-driven water evaporator, the PMP hydrogel effectively evaporates and degrades dye solutions, enabling the recovery of clean water. Benefiting from the hydrogel's exceptional mechanical strength and swelling capacity, the PMP hydrogel evaporator maintains 99.9% photodegradation efficiency for dyes and an 85.3% water recovery rate after 20 hydration-dehydration cycles.

Many biological tissues are mechanically strong and stiff but can still heal from damage. By contrast, synthetic hydrogels have not shown comparable combinations of properties, as current stiffening approaches inevitably suppress the required chain/bond dynamics for self-healing. Here we show a stiff and self-healing hydrogel with a modulus of 50 MPa and tensile strength up to 4.2 MPa by polymer entanglements in co-planar nanoconfinement. This is realized by polymerizing a highly concentrated monomer solution within a scaffold of fully delaminated synthetic hectorite nanosheets, shear oriented into a macroscopic monodomain. The resultant physical gels show self-healing efficiency up to 100% despite the high modulus, and high adhesion shear strength on a broad range of substrates. This nanoconfinement approach allows the incorporation of novel functionalities by embedding colloidal materials such as MXenes and can be generalized to other polymers and solvents to fabricate stiff and self-healing gels for soft robotics, additive manufacturing and biomedical applications.

Stimuli-responsive hydrogels with thermal phase transitions serve as pivotal components in advancing biomedical and soft robotics applications. In contrast to widely studied LCST-type thermo-responsive hydrogels, UCST-type hydrogels provide reverse thermo-responses. However, conventional UCST-type hydrogels suffer from weak mechanical properties and fixed phase transition kinetics. Here, we present polyzwitterionic UCST-type hydrogels under coplanar nanoconfinement by large aspect ratio hectorite nanosheets. The nanoconfinement significantly enhances the strength and stiffness of the hydrogels. In addition, the nanosheets serve as kinetic barriers for water diffusion. This regulates the swelling and shrinking kinetics of the polyzwitterionic hydrogels and thus allows for tunable phase transitions dependent on the thermal history of the hydrogels. Furthermore, we demonstrate that the incorporation of gold nanoparticles allows precise control of the optical properties of the hydrogel through photothermal means. These findings pave the way for engineering both the mechanical and thermoresponsive properties in polyzwitterionic hydrogels, thus broadening their applications in smart soft materials.

Electrostatic flocking, traditionally used in decoration, has recently found emerging applications in diverse fields such as sensors, tissue engineering, evaporators and thermal management. By attaching high aspect ratio fibers onto a substrate through electrostatic flocking, it enables large‐scale control of fiber orientation, resulting in fibrous, porous, or furry structures with several benefits, including enhanced microforce detection sensitivity, large specific surface area, improved reflection/absorption, increased surface roughness, anisotropic surfaces, and strengthened mechanical properties. While challenges remain in achieving highly customized pattern for functional materials, electrostatic flocking holds promise in replicating natural fluffy structures, such as villi and cilia, which could lead to superior performance in biomimetic and functional applications. Despite recent significant progress, a comprehensive review on this technology for cutting‐edge applications is still lacking. This review aims to provide an in‐depth analysis of electrostatic flocking's broader applications and investigates the potential future of electrostatic flocking at the forefront of functional materials by examining the relationship between structure and performance in advanced materials. It begins with an overview of the technology's principles, followed by an exploration of its applications and morphological advantages, and concludes with a discussion of challenges, material selection, structural design, and future directions for this innovative technology.

Biological tissues, such as tendons or cartilage, possess high strength and toughness with very low plastic deformations. In contrast, current strategies to prepare tough hydrogels commonly utilize energy dissipation mechanisms based on physical bonds that lead to irreversible large plastic deformations, thus limiting their load-bearing applications. This article reports a strategy to toughen hydrogels using fibrillar connected double networks (fc-DN), which consist of two distinct but chemically interconnected polymer networks, that is, a polyacrylamide network and an acrylated agarose fibril network. The fc-DN design allows efficient stress transfer between the two networks and high fibril alignment during deformation, both contributing to high strength and toughness, while the chemical crosslinking ensures low plastic deformations after undergoing high strains. The mechanical properties of the fc-DN network can be readily tuned to reach an ultimate tensile strength of 8 MPa and a toughness of above 55 MJ m-3, which is 3 and 3.5 times more than that of fibrillar double network hydrogels without chemical connections, respectively. The application potential of the fc-DN hydrogel is demonstrated as load-bearing damping material for a jointed robotic lander. The fc-DN design provides a new toughening mechanism for hydrogels that can be used for soft robotics or bioelectronic applications.

The ability to switch adhesion strength is a highly desirable property for adhesives applied in a wet environment. The major challenges involve the presence of a water layer between the substrate and adhesive, and the incorporation of efficient switching mechanisms. Despite the recent progresses in devising such systems, there exist several intrinsic limitations in the current strategies, such as high residual adhesion, the use of solid-liquid transition, or thin film configurations. Herein, a channeled poly(N-isopropylacrylamide) (PNIPAm) hydrogel containing bio-inspired dopamine-comonomers is reported, which undergoes temperature-controlled reversible switching of underwater adhesion on both hydrophilic and hydrophobic surfaces. The introduction of microscopic channels inside the hydrogel, achieved by removing a sacrificial agarose network, greatly facilitates water removal from the interface and thus promotes underwater adhesive strength. On glass, the maximum adhesive stress of the channeled hydrogel can reach six times that of hydrogels without channels. Additionally, high switching efficiency and low residual adhesion can be achieved by the thermal phase transition of the PNIPAm network, also demonstrated by the capture and release of lightweight, irregular, fragile, and biological objects using the hydrogel. The channeling strategy provides implications for designing future underwater adhesive systems for, e.g., soft robotics or biomedical applications.

Light‐fueled self‐oscillators based on stimuli‐responsive soft materials have been explored toward the realization of a myriad of nonequilibrium robotic functions, such as adaptation, autonomous locomotion, and energy conversion. However, the high energy density and unidirectionality of the light field, together with the unscalable design of the existing demonstrations, hinder their further implementation. Herein, a light‐responsive lampshade‐like smart material assembly as a new self‐oscillator model that is unfettered by the abovementioned challenges, is introduced. Liquid crystal elastomer with low phase transition temperature is used as the photomechanical component to provide twisting movement under low‐intensity incoherent light field. A spiral lampshade frame ensures an equal amount of light being shadowed as negative feedback to sustain the oscillation upon constant light field from omnidirectional excitation (0°–360° azimuth and 20°–90° zenith). Different‐sized oscillators with 6, 15, and 50 mm in diameter are fabricated to prove the possibility of scaling up and down the concept. The results provide a viewpoint on the fast‐growing topic of self‐oscillation in soft matter and new implications for self‐sustained soft robots.

Bright white color is often achieved in nature by the combination of polydisperse scattering structures and high refractive index contrast between the scatterer and the surrounding medium. Similarly, synthetic systems have commonly utilized inorganic materials as the scattering centers to achieve white color, which, however, lacks the ability to switch the optical properties. While hydrogels capable of scattering light are utilized in applications such as smart windows, their reflection properties have remained limited due to the low refractive index contrast between the polymer and water. As a result, thick layers in the millimeter range are often required to achieve reasonable whiteness. Here a hydrogel consisting of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAm) and chemically modified agarose used as a chemical macro-crosslinker is presented. The hydrogel exhibits high whiteness at temperatures above the phase transition (approximate to 31 degrees C). The reflectance at 800 nm is four times as high as for standard PNIPAm, and a change in transmittance can be induced by laser pulses as short as 30 ms. The macro-crosslinked structure of this hydrogel provides superior reflectance at a lower thickness compared to reported hydrogel systems, enabling a variety of potential applications including smart windows, responsive displays, optical switches, and camouflage. Macro-crosslinked hydrogels consisting of poly(N-isopropylacrylamide) (PNIPAm) and acrylated agarose are prepared. The hydrogels demonstrate significantly enhanced switchable whiteness compared to previously reported hydrogel systems. The efficient switching and scattering of visible light can be used for optical applications such as camouflage or smart windows.image

The commercialized lithium-ion battery separators are mass-produced by mixing ultra-high molecular weight polyethylene (UHMWPE) and paraffin oil (PO). The dissipative particle dynamics method is utilized to investigate the extrinsic factors (shear rate and cooling rate) and the intrinsic factors (the molecular chain length) on the microstructure of the UHMWPE-PO mixture. For the mixture with UHMWPE possessing the same chain length, the high shear rate promoted a lower porosity (similar to 28%) and smaller pores. In contrast, the slow shearing led to a high porosity (similar to 40%) and larger pores. For the mixture with UHMWPE possessing short and long chains, the shear rate hardly affects the porosity and the pore size: the porosity was kept at similar to 30%, and the pore size was reduced by similar to 35% compared to the model with the same-chain-length UHMWPE. The cooling rate after shearing is the dominant factor in determining the porosity and pore size: the fast cooling raised the porosity by similar to 33% but hardly increased the pore size, while the slow cooling raised the porosity by similar to 74%, and the pore size by similar to 105%. The current study provided a deep understanding of the pore structure evolution in separator processing. Highlights The effects of processing parameters on the pore structures are numerically illustrated. MD simulation and rheometer measurement assist DPD interaction parameters calibration for UHMWPE and PO. The low shear rate leads to a higher porosity and pore size. At the high shear rate, short UHMWPE chains reduce porosity but do not increase pore size. The fast-cooling process slightly increases the porosity while keeping the pore size.

Inspired by biological systems, trainable responsive materials have received burgeoning research interests for future adaptive and intelligent material systems. However, the trainable materials to date typically cannot perform active work, and the training allows only one direction of functionality change. Here, we demonstrate thermally trainable hydrogel systems consisting of two thermoresponsive polymers, where the volumetric response of the system upon phase transitions enhances or decreases through a training process above certain threshold temperature. Positive or negative training of the thermally induced deformations can be achieved, depending on the network design. Importantly, softening, stiffening, or toughening of the hydrogel can be achieved by the training process. We demonstrate trainable hydrogel actuators capable of performing increased active work or implementing an initially impossible task. The reported dual network hydrogels provide a new training strategy that can be leveraged for bio-inspired soft systems such as adaptive artificial muscles or soft robotics.

Imitating the self-regulated motions of natural species allows for novel applications in inanimate material systems. These applications include autonomous robotic systems, adaptive devices, and auto-energy harvesting. However, significant challenges exist in accurately controlling stimulus-induced deformations and establishing a reliable relationship between external energy fields and material deformations. In this study, we demonstrate that a simple light-triggered bending actuation in smart material systems based on liquid crystal elastomers is influenced by an opto-mechano-optical feedback mechanism. The pre-curved geometry enables enhance of light absorption upon photothermally induced deformation (from bent to flat), followed by a reduce of energy absorption upon further deformation (from flattening to bending toward the light). This strong nonlinearity in stimulus-induced deformability is governed by positive and negative feedback, and we experimentally verified these mechanisms using a thermal camera. Our results reveal the ubiquitous feedback nature of most light-active polymer systems.

Self-healing of hydrogels has attracted intensive research based on dynamically exchangeable bonds. However, this typically leads to decreased elasticity and increased energy dissipation during mechanical deformations, which is not desirable in, for example, soft robotic applications. Thus, there exists an unmet demand for low hysteresis, that is, resilient, materials to quickly recover the mechanical properties after damage. Here, we show low-hysteresis chemically cross-linked hydrogels with on-demand local light-triggered fast self-adhesion, with time-dependent adhesion strength controlled by the duration of irradiation. Low mechanical hysteresis is achieved by swelling of the loosely cross-linked poly(N-isopropylacrylamide) network. Rapid self-adhesion is followed by localized photothermal heating of embedded gold nanoparticles, causing collapse and promoting local entanglements of the thermoresponsive poly(N-isopropylacrylamide) chains. This provides 95.7% initial recovery of the original mechanical properties, while the interface undergoes gradual rehydration and disentanglement depending on the irradiation details, leading to a decrease of the adhesive strength to zero within 7 h. The concept can be combined with conventional slow self-healing that is allowed by additional clay nanoplatelets for long-standing healing. The application potential is demonstrated by oscillations, time-programmed release of the adhered object, and on-demand assembly of designed hydrogel shapes. The proposed mechanism with facile, efficient, and light-controlled temporal profiles that are time-programmed can be applied to soft robotics, biomedical applications, and flexible electronics.

Light-fueled self-oscillators based on soft actuating materials have triggered novel designs for small-scale robotic constructs that self-sustain their motion at non-equilibrium states and possess bioinspired autonomy and adaptive functions. However, the motions of most self-oscillators are reciprocal, which hinders their use in sophisticated biomimetic functions such as fluidic transportation. Here, an optically powered soft material strip that can perform nonreciprocal, cilia-like, self-sustained oscillation under water is reported. The actuator is made of planar-aligned liquid crystal elastomer responding to visible light. Two laser beams from orthogonal directions allow for piecewise control over the strip deformation, enabling two self-shadowing effects coupled in one single material to yield nonreciprocal strokes. The nonreciprocity, stroke pattern and handedness are connected to the fluidic pumping efficiency, which can be controlled by the excitation conditions. Autonomous microfluidic pumping in clockwise and anticlockwise directions, translocation of a micro-object by liquid propulsion, and coupling between two oscillating strips through liquid medium interaction are demonstrated. The results offer new concepts for non-equilibrium soft actuators that can perform bio-like functions under water.

Driving systems out of equilibrium under feedback control is characteristic for living systems, where homeostasis and dissipative signal transduction facilitate complex responses. This feature not only inspires dissipative dynamic functionalities in synthetic systems but also poses great challenges in designing novel pathways. Here we report feedback-controlled systems comprising two coupled hydrogels driven by constant light, where the system can be tuned to undergo stable homeostatic self-oscillations or damped steady states of temperature. We demonstrate that stable temperature oscillations can be utilized for dynamic colours and cargo transport, whereas damped steady states enable signal transduction pathways. Here mechanical triggers cause temperature changes that lead to responses such as bending motions inspired by the single-touch mechanoresponse in Mimosa pudica and the frequency-gated snapping motion inspired by the plant arithmetic in the Venus flytrap. The proposed concepts suggest generalizable feedback pathways for dissipative dynamic materials and interactive soft robotics.