Cyclodextrin Nano-Assemblies Enabled Robust,Highly Stretchable,and Healable Elastomers with Dynamic Physical Network

Artificial materials with biomimic self-healing ability are fascinating, however, the balance between mechanical properties and self-healing performance is always a challenge. Here, a robust, highly stretchable self-healing elastomer with dynamic reversible multi-networks based on polyurethane matrix and cyclodextrin-assembled nanosheets is proposed. The introduction of cyclodextrin nano-assemblies with abundant surface hydroxyl groups not only forms multiple interfacial hydrogen bonding but also enables a strain-induced reversible crystalline physical network owing to the special nanoconfined effect. The formation and dissociation of a dynamic crystalline physical network under stretching–releasing cycles skillfully balance the contradiction between mechanical robustness and self-healing ability. The resulting nanocomposites exhibit ultra-robust tensile strength (40.5 MPa), super toughness (274.7 MJ m⁻³), high stretchability (1696%), and desired healing efficiency (95.5%), which can lift a weight ≈ 100 000 times their own weight. This study provides a new approach to the development of mechanically robust self-healing materials for engineering applications such as artificial muscles and healable robots.     

Multiple Structure Reconstruction by Dual Dynamic Crosslinking Strategy Inducing Self-Reinforcing and Toughening the Polyurethane/Nanocellulose Elastomers

High-performance elastomers are expected to possess excellent healing and recycling ability, damage resistance in conjunction with high strength and toughness. Herein, a dual dynamic crosslinking strategy is implemented by multiple hydrogen and disulfide bonds to obtain a novel amorphous and transparent polyurethane/nanocellulose elastomer with excellent self-healing, self-reinforcing and toughening performance. First, hydrogen bonds are introduced in TEMPO-oxidized cellulose nanofibers (TCNF) by modification with 2-ureido-4[1H]-pyrimidone (UTCNF), while disulfide bonds (SS) are introduced in the polyurethane (PU) main chain, leading to the formation of dual dynamic cross-linking networks. The PU-SS-UTCNF elastomer can fully self-heal within 4.0 h at 50 °C. Surprisingly, for the first time, the PU-SS-UTCNF elastomer also self-strengthens and self-toughens after multiple hot-pressing, with tensile strength and toughness that increase by up to 401% and 257% compared to original elastomer samples, up to 50.0 MPa and 132.5 MJ m^-3. The self-strength and self-toughening effects are attributed to 1) reconstruction of dual dynamic networks that increase the cross-linking degree during the multiple hot-pressing processes; 2) multiple hydrogen bonds in the system are beneficial to the orientation of highly crystallized UTCNF, as a replacement of stress-induced process in deformation under external tensile force.     

Multiple H-Bonding Chain Extender-Based Ultrastiff Thermoplastic Polyurethanes with Autonomous Self-Healability,Solvent-Free Adhesiveness,and AIE Fluorescence

Developing an autonomous room temperature self-healing supramolecular polyurethane (PU) with toughness and stiffness remains a great challenge. Herein, a novel concept that utilizes a T-shaped chain extender with double amide hydrogen bonds in a side chain to extend PU prepolymers to construct highly stiff and tough supramolecular PU with integrated functions is reported. Mobile side-chain H-bonds afford a large flexibility to modulate the stiffness of the PUs ranging from highly stiff and tough elastomer (105.87 MPa Young's modulus, 27 kJ m⁻² tearing energy), to solvent-free hot-melt adhesive, and coating. The dynamic side-chain multiple H-bonds afford an autonomous self-healability at room temperature (25  ° C). Due to the rapid reconstruction of hydrogen bonds, this PU adhesive demonstrates a high adhesion strength, fast curing, reusability, long-term adhesion, and excellent low-temperature resistance. Intriguingly, the PU emits intrinsic blue fluorescence presumably owing to the aggregation-induced emission of tertiary amine domains induced by side-chain H-bonds. The PU is explored as a counterfeit ink coated on the predesigned pattern, which is visible-light invisible and UV-light visible. This work represents a universal and facile approach to fabricate supertough supramolecular PU with tailorable functions by chain extension of PU prepolymers with multiple H-bonding chain extenders.     

Self-Healing,Robust, and Stretchable Electrode by Direct Printing on Dynamic Polyurea Surface at Slightly Elevated Temperature

Printed electronics on elastomer substrates have found wide applications in wearable devices and soft robotics. For everyday usage, additional requirements exist for the robustness of the printed flexible electrodes, such as the ability to resist scratching and damage. Therefore, highly robust electrodes with self-healing, and good mechanical strength and stretchability are highly required and challenging. In this paper, a cross-linking polyurea using polydimethylsiloxane as the soft segment and dynamic urea bonds is prepared and serves as a self-healing elastomer substrate for coating and printing of silver nanowires (AgNWs). Due to the dynamic exchangeable urea bond at 60 °C, the elastomer exhibits dynamic exchange of the cross-linking network while retaining the macroscopic shape. As a result, the AgNWs are partially embedded in the surface of the elastomer substrate when coated or printed at 60 °C, forming strong interfacial adhesion. As a result, the obtained stretchable electrode exhibits high mechanical strength and stretchability, the ability to resist scratching and sonication, and self-healing. This strategy can be applied to a variety of different conducting electrode materials including AgNWs, silver particles, and liquid metal, which provides a new way to prepare robust and self-healing printed electronics.     

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.     

Photonic Vitrimer Elastomer with Self-Healing,High Toughness,Mechanochromism, and Excellent Durability based on Dynamic Covalent Bond

Vitrimers, with their unique dynamic covalent bonds, possess attractive self-healability and mechanical robustness, providing an intriguing opportunity to construct functional soft materials. However, their potential for function recovery, especially optical function, is underexplored. Harnessing the synergistic effect of photonic crystals and vitrimers, a novel photonic vitrimer with light regulating and self-healing capabilities is presented. The resulting photonic vitrimer exhibits a large tensile strain (>1000%), high toughness (21.2 kJ m⁻³), bright structural color, and mechanochromism. Notably, the structural color remains constant even after 10 000 stretching/releasing cycles, showing superior mechanical stability, creep-resistance, and excellent durability. More importantly, the exchange of dynamic covalent bonds imparts the photonic vitrimer with a self-healing ability (>95% efficiency), enabling the recovery of its optical function. Benefiting from the above merits, the photonic vitrimer has been successfully used as a sensor for human motion detection, which demonstrates visualized interactive sensibility even after self-repairing. This material design provides a general strategy for optical functionalization of vitrimers. The photonic vitrimer elastomers present great potential as resilient functional soft materials for diverse flexible devices and a novel optical platform for soft robotics, smart wearable devices, and human-machine interaction.     

Strong,Compressible, and Ultrafast Self-Recovery Organogel with In Situ Electrical Conductivity Improvement

Coordination complexes are widely used to tune the mechanical behaviors of polymer materials, including tensile strength, stretchability, self-healing, and toughness. However, integrating multivalent functions into one material system via solely coordination complexes is challenging, even using combinations of metal ions and polymer ligands. Herein, a single-step process is described using silver-based coordination complexes as cross-linkers to enable high compressibility (>85%). The resultant organogel displays a high compressive strength (>1 MPa) with a low energy loss coefficient (<0.1 at 50% strain). Remarkably, it demonstrates an instant self-recovery at room temperature with a speed >1200 mm s⁻¹, potentially being utilized for designing high-frequency-responsive soft materials (>100 Hz). Importantly, in situ silver nanoparticles are formed, effectively endowing the organogel with high conductivity (550 S cm⁻¹). Given the synthetic simplification to achieve multi-valued properties in a single material system using metal-based coordination complexes, such organogels hold significant potential for wearable electronics, tissue-device interfaces, and soft robot applications.     

Inorganic Ionic Oligomers Induced Organic-Inorganic Synergistic Toughening Enabling Mechanical Robust and Recyclable Nanocomposite Hydrogels

Mechanical robust hydrogels are ideal for applications in energy, environment, biomedicine, and structural engineering materials fields. However, high strength and high toughness are usually in conflict with each other, and simultaneously achieving both of them within a hydrogel has been challenging. Herein an organic-inorganic synergistic toughening strategy is reported via in-situ inorganic ionic polymerization of calcium phosphate oligomers within polymer composite networks composed of polyvinyl alcohol chains and aramid nanofibers. The composite hydrogels are provided with a prestress-induced hierarchically fibrous structure through the assembly, which resulted in the mechanical strength and toughness up to 24.15 ± 1.12 MPa and 15.68 ± 1.78 MJ m⁻³, respectively, surpassing most toughened hydrogels. Through lamination and crosslinking, bulk hydrogels with controllable mechanical anisotropy and significant energy absorption/dissipation ability are produced. Moreover, the recycling and regeneration of the hydrogels are easily realized owing to the physically crosslinked network and acid-induced dissolution of the inorganic units of the hydrogels, which lays a foundation for the sustainable large-scale production and application of the hydrogels. This study provides an alternative approach for the development of mechanical robust and recyclable nanocomposite hydrogels for various applications including soft body armor, flexible electronics, soft robotics, etc.     

Highly Stretchable,Resilient, Adhesive,and Self-Healing Ionic Hydrogels for Thermoelectric Application

Harvesting low-grade waste heat from the natural environment with thermoelectric materials is considered as a promising solution for the sustainable energy supply for wearable electronic devices. For practical applications, it is desirable to endow the thermoelectric materials with excellent mechanical and self-healing properties, which remains a great challenge. Herein, the design and characterization of a series of high-performance ionic hydrogels for soft thermoelectric generator applications are reported. Composed of a physically cross-linked network of polyacrylic acid (PAA) and polyethylene glycol (PEO) doped with sodium chloride, the resulting PAA-PEO-NaCl ionic hydrogels demonstrates impressive mechanical strength (breaking stress >1.3 MPa), stretchability (>1100%), and toughness (up to 7.34 MJ m⁻³). Moreover, the reversible hydrogen bonding interaction and chain entanglement render the ionic hydrogels with excellent mechanical resilience, adhesion properties, and self-healing properties. At ambient conditions, the electrochemical and thermoelectric performance of the ionic hydrogels can be restored immediately from physical damage such as cutting, and the mechanical healing can be completely restored within 24 h. At the optimized composition, the Seebeck coefficient of the ionic hydrogels can reach 3.26 mV K⁻¹ with a low thermal conductivity of 0.321 W m⁻¹ K⁻¹. Considering the excellent mechanical properties and thermoelectric performance, it is believed that the ionic hydrogels are widely applicable in ionic thermoelectric capacitors to convert low-grade heat into electricity for soft electronic devices.     

Reversible Elastomer–Fluid Transitions for Metamorphosic Robots

Endowing robots with reversible phase transition ability, especially between elastomer and fluid states, can significantly broaden their functionality and applicability. Limited attempts have been made to realize the reversible elastomer–fluid transition. Existing phase transition materials in robotics have over-hard (≈4 GPa) or over-soft (≈4 kPa) stiffness in the solid states, which should be further investigated to perform more compliant motions. To address these challenges, a reversible elastomer–fluid transition mechanism  enabled by magnetically induced hot melt materials (MIMMs) is presented. The transition principle is explained and material characterizations are conducted. MIMMs-based metamorphosic robots endow self-metamorphosing abilities, such as self-healing, spatial reshaping, self-division/assembly, and additive manufacturability. When interacting with external environments, MIMMs-based robots can perform further multifunctional abilities, such as collaborations for structure repairs, swimming by symbiosis with external objects, flowing through a narrow terrain by transiting to fluid, and working with elastomeric structures for stiffness-variable fluid soft actuators. The proposed elastomer–fluid transitions open a new path for robots to generate more flexible and metamorphosic motions, thereby addressing the cross-phase transformation challenges that soft robots face.     

A Universal Interfacial Strategy Enabling Ultra-Robust Gel Hybrids for Extreme Epidermal Bio-Monitoring

A seamless and tough interface to integrate incompatible/immiscible soft materials is highly desired for flexible/wearable electronics and many soft devices with multi-layer structures. Here, a surfactant-mediated interfacial chemistry is introduced to achieve seamless and tough interfaces in soft multi-layer structures, with an ultra-high interfacial toughness up to ≈1300 J m⁻² for the architectural gel hybrid (AGH). The reversible noncovalent interfacial interactions efficiently dissipate energy at the interface, thereby providing excellent durability. The interfacial toughness only decreases by ≈6.9% after 10 000 tensile cycles. This strategy can be universally applied to hybrid systems with various interfaces between an interior hydrogel (PAA, PVA, PAAm, and gelatin) and an exterior hydrophobic soft matter (ionogel, lipogel and elastomer). The AGH-based mechano-sensor presents high robustness and stability in a wide range of conditions, including open air, underwater, and various solvents and temperatures. Epidermal bio-monitoring, tactile trajectory, and facial expression recognition are demonstrated using the AGH sensors in various environments. A rich set of electrophysiological signals of high quality are acquired.     

Block Copolymer-Based Supramolecular Ionogels for Accurate On-Skin Motion Monitoring

Interest in wearable and stretchable on-skin motion sensors has grown rapidly in recent years. To expand their applicability, the sensing element must accurately detect external stimuli; however, weak adhesiveness of the sensor to a target object has been a major challenge in developing such practical and versatile devices. In this study, freestanding, stretchable, and self-adhesive ionogel conductors are demonstrated which are composed of an associating polymer network and ionic liquid that enable conformal contact between the sensor and skin even during dynamic movement. The network of ionogel is formed by noncovalent association of two diblock copolymers, where phase-separated micellar clusters are interconnected via hydrogen bonds between corona blocks. The resulting ionogels exhibit superior adhesive characteristics, including a very high lift-off force of 93.3 N m⁻¹, as well as excellent elasticity (strain at break ≈ 720%), toughness ( ≈ 2479 kJ m⁻³), thermal stability ( ≈ 150  ° C), and high ionic conductivity ( ≈ 17.8 mS cm⁻¹ at 150  ° C). These adhesive ionogels are successfully applied to stretchable on-skin strain sensors as sensing elements. The resulting devices accurately monitor the movement of body parts such as the wrist, finger, ankle, and neck while maintaining intimate contact with the skin, which was not previously possible with conventional non-adhesive ionogels.     

In Situ Synthesis of Mechanically Robust,Transparent Nanofiber-Reinforced Hydrogels for Highly Sensitive Multiple Sensing

Hydrogels that are both highly conductive and mechanically robust have demonstrated great potential in various applications ranging from healthcare to soft robotics; however, the creation of such materials remains an enormous challenge. This study presents an in situ synthesis strategy for developing bioinspired chemically integrated silica-nanofiber-reinforced hydrogels (SFRHs) with robust mechanical and electronic performance. The strategy is to synthesize soft hydrogel matrices from acrylamide monomers in the presence of well-dispersed silica nanofibers and vinyl silane, which generates homogenous SFRHs with innovative interfacial chemical bonds. The resultant SFRHs exhibit excellent mechanical properties including high mechanical strength of 0.3 MPa at a fracture strain of 1400%, high Young's modulus of 0.11 MPa (comparable to human skin), and superelasticity over 1000 tensile cycles without plastic deformation, while maintaining high transmittance (≥83%). In parallel, the SFRHs show enhanced ionic conductivity (3.93 S m⁻¹) and can monitor multiple stimuli (stretching, compressing, and bending) with high sensitivity (gauge factor of 2.67) and ultra-durability (10 000 cycles). This work may shed light on the design and development of tough and stretchable hydrogels for various applications.     

A Fully Self-Healing and Highly Stretchable Liquid-Free Ionic Conductive Elastomer for Soft Ionotronics

Soft ionic conductors hold great potential for soft ionotronics, such as ionic skin, human–machine interface and soft luminescent device. However, most hydrogel and ionogel-based soft ionic conductors suffer from freezing, evaporation and liquid leakage problems, which limit their use in complex environments. Herein, a class of liquid-free ionic conductive elastomers (ICEs) is reported as an alternative soft ionic conductor in soft ionotronics. These liquid-free ICEs offer a combination of desirable properties, including extraordinary stretchability (up to 1913%), toughness (up to 1.08 MJ cm⁻³), Young's modulus (up to 0.67 MPa), rapid fully self-healing capability at room temperature, and good conductivity (up to 1.01 × 10⁻⁵ S cm⁻¹). The application of these ICEs is demonstrated by creating a wearable sensor that can detect and discriminate minimal deformations and human body movements, such as finger or elbow joint flexion, walking, running, etc. In addition, self-healing soft ionotronic devices are demonstrated to confront mechanical breakdown, such as an ionic skin and an alternating-current electroluminescent device that can reuse from damage. It is believed that these liquid-free ICEs hold great promises for applications in wearable devices and soft ionotronics.     

Tunable Optical Modulator by Coupling a Triboelectric Nanogenerator and a Dielectric Elastomer

A conjunction system based on triboelectric nanogenerator (TENG) and dielectric elastomer actuator (DEA) is a promising demonstration for the application of TENG in the field of electronic skin and soft robotics. In this paper, a triboelectric tunable smart optical modulator (SOM) has been proposed based on this TENG‐DEA system. The SOM has a very simple structure of an elastomer film and electrodes made of dispersed silver nanowires. Owing to the voltage induced rippling of the elastomer, the output of the TENG for a contact‐separation motion at a velocity ranging from 0.5 to 10 cm s^?1 can decrease the SOM's transmittance from 72% to 40%, which is enough for realizing the function of privacy protection. Meanwhile, an effective operation method is also proposed for this SOM. By serially connecting an accessory DEA to the SOM, an external bias voltage can be applied on the SOM to tune its “threshold” voltage and the output from TENG can smoothly regulate the transmittance on the basis of the bias. The proposed operation method has excellent applicability for all DEA‐based devices, which can promote the practical study of TENG‐DEA system in the field of micro‐electro‐mechanical system and human–robots interaction.     

Leveraging Bioinspired Structural Constraints for Tunable and Programmable Snapping Dynamics in High-Speed Soft Actuators

Creating high-speed soft actuators will have broad engineering and technological applications. Snapping provides a power-amplified mechanism to achieve rapid movements in soft actuators that typically show slow movements. However, precise control of snapping dynamics (e.g., speed and direction of launching or jumping) remains a daunting challenge. Here, a bioinspired design principle is presented that harnesses a reconfigurable constraint structure integrated into a photoactive liquid crystal elastomer actuator to enable tunable and programmable control over its snapping dynamics. By reconfiguring constrained fin-array-shaped structure, the snapping dynamics of the structured actuator, such as launching or jumping angle and height, motion speed, and release force can be on-demand tuned, thus enabling controllable catapult motion and programmable jumping. Moreover, the structured actuators exhibit a unique combination of ultrafast moving speed (up to 2.5 m s⁻¹ in launching and 0.22 m s⁻¹ in jumping), powerful ejection (long ejection distance of ≈20 cm, 35 mg ball), and high jumping height (≈8 cm, 40 times body lengths), which few other soft actuators can achieve. This study provides a new universal design paradigm for realizing controllable rapid movements and high-power motions in soft matter, which are useful for building high-performance soft robotics and actuation devices.     

Ultra-High Toughness Fibers Using Controlled Disorder of Assembled Aramid Nanofibers

Assembling nanoscale building blocks with reduced defects has emerged as a promising approach to exploit nanomaterials in the fabrication of simultaneously strong and tough architectures at larger scales. Aramid nanofibers (ANFs), a type of organic nanobuilding block, have been spotlighted due to their superior mechanical properties and thermal stability. However, no breakthrough research has been conducted on the high mechanical properties of a structure composed of ANFs. Here, assembling ANFs into macroscale fiber using a simultaneous protonation and wet-spinning process is studied to reduce defects and control disorder. The ANF-assembled fibers consist of hierarchically aligned nanofibers that behave as a defective law structure, making it possible to reach a Young's modulus of 53.15 ± 8.98 GPa, a tensile strength of 1,353.64 ± 92.98 MPa, and toughness of 128.66 ± 14.13 MJ m⁻³. Compared to commercial aramid fibers, the fibers exhibit ≈1.6 times greater toughness while also providing specific energy to break as 93 J g⁻¹. Furthermore, this shows recyclability of the ANF assembly by retaining ≈94% of the initial mechanical properties. This study demonstrates a facile process to produce high stiffness and strength fibers composed of ANFs that possess significantly greater toughness than commercial synthetic fibers.     

A Stiff yet Rapidly Self-Healable Elastomer in Harsh Aqueous Environments

Rapid underwater self-healing elastomers with high mechanical strength at ambient temperature are highly desirable for dangerous underwater operations. However, current room temperature self-healing materials have shortcomings, such as low healing strength (below megapascal), long healing time (hours), and decay of healing functions in harsh environments (salty, acidic, and basic solutions), limiting their practical applications. Herein, it is introduced water-stable Debye forces and high-density nano-sized physical crosslinking into one network to achieve a stiff yet rapid self-healing elastomer that can work in harsh aqueous environments. The obtained elastomer possesses a high Young's modulus of 48 MPa (24 times than that of natural elastomer), and it can achieve 90% of maximum mechanical strength healing for 10 s at ambient temperature in all types of harsh aqueous conditions, outperforming three orders of magnitudes in healing speed of reported room-temperature self-healing elastomers with Young's modulus over 10 MPa. The new stiff yet rapidly healable elastomers have great potential in emergent repair in urgent and dangerous cases.     

Stimulating Acrylic Elastomers by a Triboelectric Nanogenerator – Toward Self‐Powered Electronic Skin and Artificial Muscle

Dielectric elastomers are a type of actuator materials that exhibit excellent performance as artificial muscles, but a high driving voltage is required for their operation. By using the amazingly high output voltage generated from a triboelectric nanogenerator (TENG), a thin film dielectric elastomer actuator (DEA) can be directly driven by the contact‐separation motion of TENG, demonstrating a self‐powered actuation system. A TENG with a tribo surface area of 100 cm² can induce an expansion strain of 14.5% for the DEA samples (electrode diameter of 0.6 cm) when the system works stably within the contact‐separation velocity ranging from 0.1 to 10 cm s^?1. Finally, two simple prototypes of an intelligent switch and a self‐powered clamper based on the TENG and DEA are demonstrated. These results prove that the dielectric elastomer is an ideal material to work together with TENG and thereby the fabricated actuation system can potentially be applied to the field of electronic skin and soft robotics.     

A Biologically Muscle-Inspired Polyurethane with Super-Tough,Thermal Reparable and Self-Healing Capabilities for Stretchable Electronics

Polymeric elastomers play an increasingly important role in the development of stretchable electronics. A highly demanded elastic matrix is preferred to own not only excellent mechanical properties, but also additional features like high toughness and fast self-healing. Here, a polyurethane (DA-PU) is synthesized with donor and acceptor groups alternately distributed along the main chain to achieve both intra-chain and inter-chain donor-acceptor self-assembly, which endow the polyurethane with toughness, self-healing, and, more interestingly, thermal repair, like human muscle. In detail, DA-PU exhibits an amazing mechanical performance with elongation at break of 1900% and toughness of 175.9 MJ m⁻³. Moreover, it shows remarkable anti-fatigue and anti-stress relaxation properties as manifested by cyclic tensile and stress relaxation tests, respectively. Even in case of large strain deformation or long-time stretch, it can almost completely restore to original length by thermal repair at 60 °C in 60 s. The self-healing speed of DA-PU is gradually enhanced with the increasing temperature, and can be 1.0–6.15 µm min⁻¹ from 60 to 80 °C. At last, a stretchable and self-healable capacitive sensor is constructed and evaluated to prove that DA-PU matrix can ensure the stability of electronics even after critical deformation and cut off.