A Highly-Adhesive and Self-Healing Elastomer for Bio-Interfacial Electrode

Stretchable electrodes are playing important roles in the measurement of bio-electrical signals especially in wearable electronic devices. These electrodes usually adopt commercial elastomers such as polydimethylsiloxane or polystyrene-ethylene-butylene-styrene as substrates, which result in poor stability and reliability due to weak interfacial adhesion between electrodes and human skin. Here, dopamine is introduced into the hydrogen bonding based elastomer as pendent groups. The elastomer shows both mechanical strength and adhesion strength at the same time. It exhibits high stress at break (1.9 MPa) and high fracture strain (5100%). Significantly, it exhibits a high adhesive strength (≈62 kPa) and underwater adhesive strength (≈16 kPa) with epithelial tissue. Thus, a stretchable bio-interfacial electrode is fabricated by spray-coating silver nanowires on the elastic substrate, which is stretchable, self-healable, and highly adhesive and suitable for electromyogram measurement.     

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

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

Stretchable Conductive Composites Based on Metal Wools for Use as Electrical Vias in Soft Devices

Soft devices can be bent, stretched, and compressed reversibly, but conventional wires are rigid. This work describes stretchable composites that are easily fabricated with simple tools and commodity materials, and that can provide a strategy for electrical wiring that meets certain needs of soft devices. These composites are made by combining metal wool and elastomeric polymers. Embedding fine (average fiber width ≈25 μm) steel wool (or other metal wools) in a silicone polymer creates an electrically conductive path through the nonconductive elastomer. This composite is flexible, stretchable, compressible, inexpensive, and simple to incorporate into the bodies of soft devices. It is also electrically anisotropic, and shows maximum conductivity along the majority axis of the fibers, but maximum extension perpendicular to this axis. The utility of this composite for creating an electrically conductive path through an elastomer was demonstrated in several devices, including: a soft, solderless breadboard, a soft touch sensor, and a soft strain gauge.     

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.     

Autonomous Self-Healing Elastomers with Unprecedented Adhesion Force

Self-healable elastomers are extremely attractive due to their ability to prolong product lifetime. An additional function that could further expand their applications is strong adhesion force to clean and dusty surfaces. This study reports a series of autonomous self-healable and highly adhesive elastomers (ASHA-Elastomer) that are fabricated via a simple, efficient, and scalable process. The obtained elastomers exhibit outstanding mechanical properties with elongation at break up to 2102% and toughness (modulus of toughness) of 1.73 MJ m^–3. The damaged ASHA-Elastomer can autonomously self-heal with full recovery of functionalities, and the healing process is not affected by the presence of water. The elastomers are found to possess an ultrahigh adhesion force up to 3488 N m⁻¹, greatly outperforming previously reported self-healing adhesive elastomers. Furthermore, the adhesion force of the ASHA-Elastomer is negligibly affected by dust on the surface, in stark contrast with regular adhesive polymers that have adhesion strengths extremely sensitive to dust. The successful development of high-toughness, autonomous self-healable, and ultra-adhesive elastomers will enable a wide range of applications with enhanced longevity and versatility, including their use in sealants, adhesives, and stretchable devices.     

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.     

Carbon Nanotube Optoelectronic Synapse Transistor Arrays with Ultra-Low Power Consumption for Stretchable Neuromorphic Vision Systems

High-performance stretchable optoelectronic synaptic transistor arrays are key units for constructing and mimicking simulated neuromorphic vision systems. In this study, ultra-low power consumption and low-operation-voltage stretchable all-carbon optoelectronic synaptic thin film transistors (TFTs) using sorted semiconducting single-walled carbon nanotubes (sc-SWCNTs) modified with CdSe/ZnS quantum dots as active layers on ionic liquid-based composite elastomer substrates are first reported. The resulting stretchable TFT devices show enhancement-mode characteristics with excellent electrical properties (such as the record on/off ratios up to 10⁵, negligible hysteresis, and small subthreshold swing), excellent mechanical tensile properties (such as the only 12.4% and 6.4% degradations of the carrier mobility after 20% vertical and horizontal strain stretching), and optoelectronic synaptic plasticity (for the recognition of Morse codes) with ultra-low power consumptions (15.38 aJ) at the operating voltage from −1 to 0.2 V. At the same time, the designed nonvolatile conductance of the stretchable SWCNT optoelectronic synapse thin film transistors (SSOSTFTs) stimulated by UV light and the bending angle are first used to simulate stretchable neuromorphic vision systems (including the functions of the crystalline lens and optic cone cells as bionic eyes) for detecting the atmospheric environment with a record accuracy of 95.1% as a bionic eye.     

A Highly Stretchable and Self‐Healing Supramolecular Elastomer Based on Sliding Crosslinks and Hydrogen Bonds

The long application life and stable performance of stretchable electronics have been putting forward requirements for both higher mechanical properties and better self‐healing ability of polymeric substrates. However, for self‐healing materials, simultaneously improving stretchability and robustness is still challenging. Here, by incorporating sliding crosslinker (polyrotaxanes) and hydrogen bonds into a polymer, a highly stretchable and self‐healable elastomer with good mechanical strength is achieved. The elastomer exhibits very high stretchability, such that it can be stretched to 2800% with a fracture strength of 1.05 MPa. Moreover, the elastomer can achieve nearly complete self‐healing (93%) at 55 °C. Next, tensile tests under different temperatures, step extension experiments, and in situ small angle X‐ray scattering confirm that the excellent stretchability is attributed to the combined effects of sliding cyclodextrins along guest chains and hydrogen bonds. Furthermore, a strain sensor by coating the single‐wall carbon nanotubes onto the surface of the elastic substrate is fabricated.     

Buckled Conductive Polymer Ribbons in Elastomer Channels as Stretchable Fiber Conductor

Conductors that can sustain large strains without change in resistance are highly needed for wearable electronic systems. Here, the fabrication of highly stretchable coaxial fiber conductors through self‐buckling of conductive polymer ribbons inside thermoplastic elastomer channels, using a “solution stretching–drying–buckling” process, is reported. The unique hierarchically buckled and conductive core in the axial direction makes the resistance of the fiber very stable, with less than 4% change when applying as much as 680% strain. These fibers can then be directly used as stretchable electrical interconnects or wearable heaters.     

Novel Sulfur-Containing Carbon Nanotubes with Graphene Nanoflaps for Stretchable Sensing,Joule Heating,and Electro-Thermal Actuating

Stretchable conductors based on nanopercolation networks have garnered great attention for versatile applications. Carbon nanotubes (CNTs) are well-suited for creating high-efficiency nanopercolation networks. However, the weak interfacial shear strength (IFSS) between CNTs and elastomer hardly dissipates the deformation energy and thus deteriorates the conductive network. Herein, a novel sulfur-containing CNTs attached with abundant graphene nanoflaps using a two-step sulfidation strategy are developed. The sulfur functionality creates a strong interfacial interaction with the elastomer polymer, while the graphene nanoflaps provide an enhanced, intertwined shear interface with elastomer that is capable of efficiently dissipating the deformation energy. As a result, the optimized nanocomposite significantly improves the IFSS between nanofiller and elastomer, displaying remarkable conductive robustness (ΔR/R₀≈1.8 under 200%), superior stretchability (> 450%), and excellent mechanical durability (≈30 000 cycles). Moreover, the nanocomposite demonstrates excellent Joule heating efficiency (≈150 °C in 12 V), stretchable heating conversion (≈200%), and long-term stability (> 24 h). To illustrate its capabilities, the nanocomposite is used to track human physiological signals and perform electric-thermal actuating as a set of soft tongs. It is believed that this innovative approach will provide value for the development of wearable/stretchable devices, as well as human-machine interaction, and bio-robotics in the future.     

MXene Composite and Coaxial Fibers with High Stretchability and Conductivity for Wearable Strain Sensing Textiles

The integration of nanomaterials with high conductivity into stretchable polymer fibers can achieve novel functionalities such as sensing physical deformations. With a metallic conductivity that exceeds other solution‐processed nanomaterials, 2D titanium carbide MXene is an attractive material to produce conducting and stretchable fibers. Here, a scalable wet‐spinning technique is used to produce Ti₃C₂T_x MXene/polyurethane (PU) composite fibers that show both conductivity and high stretchability. The conductivity at a very low percolation threshold of ≈1 wt% is demonstrated, which is lower than the previously reported values for MXene‐based polymer composites. When used as a strain sensor, the MXene/PU composite fibers show a high gauge factor of ≈12900 (≈238 at 50% strain) and a large sensing strain of ≈152%. The cyclic strain sensing performance is further improved by producing fibers with MXene/PU sheath and pure PU core using a coaxial wet‐spinning process. Using a commercial‐scale knitting machine, MXene/PU fibers are knitted into a one‐piece elbow sleeve, which can track various movements of the wearer's elbow. This study establishes fundamental insights into the behavior of MXene in elastomeric composites and presents strategies to achieve MXene‐based fibers and textiles with strain sensing properties suitable for applications in health, sports, and entertainment.     

Ionoskins: Nonvolatile,Highly Transparent,Ultrastretchable Ionic Sensory Platforms for Wearable Electronics

The primary technology of next‐generation wearable electronics pursues the development of highly deformable and stable systems. Here, nonvolatile, highly transparent, and ultrastretchable ionic conductors based on polymeric gelators [poly(methyl methacrylate‐ran‐butyl acrylate), PMMA‐r‐PBA] and ionic liquids (IL) are proposed. A crucial strategy in the molecular design of polymer gelators is copolymerization of PMMA and IL‐insoluble low glass transition temperature (T_g) polymers that can be deformed and effectively dissipate applied strains. Highly stretchable (elongation limit ≈850%), mechanically robust (elastic modulus ≈3.1 × 10⁵ Pa), and deformation durable (recovery ratio ≈96.1% after 500 stretching/releasing cycles) gels are obtained by judiciously adjusting the molecular characteristics of polymer gelators and gel composition. An extremely simple “ionic” strain sensory platform is fabricated by directly connecting the stretchable gel and a digital multimeter, exhibiting high sensitivity (gauge factor ≈2.73), stable operation (>13 000 cycles), and nonvolatility (>10 d in air). Moreover, the skin‐type strain sensor, referred to as ionoskin, is demonstrated. The gels are attached to a part of the body (e.g., finger, elbow, knee, or ankle) and various human movements are successfully monitored. The ionoskin renders the opportunity to achieve wearable ubiquitous electronics such as healthcare devices and smart textile systems.     

Strain-Tolerant,High-Detectivity,and Intrinsically Stretchable All-Polymer Photodiodes

A skin-like photodiode (PD) that is stretchable and skin-conformable is crucial to opening the next-generation wearable electronics for optical biometric monitoring, biomedical imaging, and others. To achieve reliable PD characteristics under large deformation, stretchable PDs with high detectivity and high mechanical stretchability must be developed. Herein, intrinsically stretchable polymer-based PDs (is-PPDs) comprising all-polymeric constituent layers are demonstrated. In particular, elastomeric photoactive layers consisting of an elastomer with p-/n-type semiconducting polymers and conducting polymer-based stretchable transparent electrodes with modulated work functions improve both the mechanical stability and the detectivity (D*) of is-PPDs. Accordingly, is-PPDs show excellent D* over 10¹³ Jones with a suppressed dark current density of 0.1 nA cm⁻² before and after 100% stretching. The proposed is-PPDs record high-quality and stable photoplethysmography signals at the wrist with outward extension.     

Controlled Nitrogen Doping in Crumpled Graphene for Improved Alkali Metal-Ion Storage under Low-Temperature Conditions

The significant performance decay in conventional graphite anodes under low-temperature conditions is attributed to the slow diffusion of alkali metal ions, requiring new strategies to enhance the charge storage kinetics at low temperatures. Here, nitrogen (N)-doped defective crumpled graphene (NCG) is employed as a promising anode to enable stable low-temperature operation of alkali metal-ion storage by exploiting the surface-controlled charge storage mechanisms. At a low temperature of −40 °C, the NCG anodes maintain high capacities of ≈172 mAh g⁻¹ for lithium (Li)-ion, ≈107 mAh g⁻¹ for sodium (Na)-ion, and ≈118 mAh g⁻¹ for potassium (K)-ion at 0.01 A g⁻¹ with outstanding rate-capability and cycling stability. A combination of density functional theory (DFT) and electrochemical analysis further reveals the role of the N-functional groups and defect sites in improving the utilization of the surface-controlled charge storage mechanisms. In addition, the full cell with the NCG anode and a LiFePO₄ cathode shows a high capacity of ≈73 mAh g⁻¹ at 0.5 °C even at −40 °C. The results highlight the importance of utilizing the surface-controlled charge storage mechanisms with controlled defect structures and functional groups on the carbon surface to improve the charge storage performance of alkali metal-ion under low-temperature conditions.     

Intrinsically Stretchable Light-Emitting Polymer Semiconductors with High Charge Mobility Through Micro-Crystalline Aggregation-Limited Morphology

Intrinsically stretchable light-emitting polymer semiconductors are essential building blocks for bioelectronics and display textiles. Stretchability is challenging for rigid conjugated polymers unless sacrificing charge mobility by introducing amorphous domains. High-performance light-emitting properties designed with twisted angle are undesirable for conductive materials. Hence, the concurrent strategies hardly satisfy the balance of stretchability, light-emitting and mobility. Herein, a morphology engineering is proposed by controlling micro-crystalline and limiting aggregation, that four intrinsically stretchable emissive polymers with good charge mobility based on indacenodithiophene (IDT) are obtained. Polymers reveal good emission properties with high photoluminescence quantum yields (PLQY) of about 20%, while stretchable modulus and charge mobility are tunable by backbone and weight. Specifically emphasizing, IDT-2T-H retains high performance of charge mobility and PLQY even at 100% strain. Therefore, organic light emitting diodes are fabricated based on it and showing the luminance of 176.2 cd cm⁻², which verifies the potential of technique to reconcile integration of stretchability, light-emitting, and mobility. This is the first attempt to integrate balanced mechanical, optical, and electrical properties through micro-crystalline aggregation-limited morphology in one polymer, offering a feasible approach to advanced integrated circuit and multi-functional electronics in the future.     

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.     

Stretchable,Transparent, and Thermally Stable Triboelectric Nanogenerators Based on Solvent‐Free Ion‐Conducting Elastomer Electrodes

The development of stretchable/soft electronics requires power sources that can match their stretchability. In this study, a highly stretchable, transparent, and environmentally stable triboelectric nanogenerator with ionic conductor electrodes (iTENG) is reported. The ion‐conducting elastomer (ICE) electrode, together with a dielectric elastomer electrification layer, allows the ICE‐iTENG to achieve a stretchability of 1036% and transmittance of 91.5%. Most importantly, the ICE is liquid solvent‐free and thermally stable up to 335 °C, avoiding the dehydration‐induced performance degradation of commonly used hydrogels. The ICE‐iTENG shows no decrease in electrical output even after storing at 100 °C for 15 h. Biomechanical motion energies are demonstrated to be harvested by the ICE‐iTENG for powering wearable electronics intermittently without extra power sources. An ICE‐iTENG‐based pressure sensor is also developed with sensitivity up to 2.87 kPa^?1. The stretchable ICE‐iTENG overcomes the strain‐induced performance degradation using percolated electrical conductors and liquid evaporation‐induced degradation using ion‐conducting hydrogels/ionogels, suggesting great promising applications in soft/stretchable electronics under a relatively wider temperature range.     

3D Printable One-Part Carbon Nanotube-Elastomer Ink for Health Monitoring Applications

3D printing of conductive elastomers is a promising route to personalized health monitoring applications due to its flexibility and biocompatibility. Here, a one-part, highly conductive, flexible, stretchable, 3D printable carbon nanotube (CNT)-silicone composite is developed and thoroughly characterized. The one-part nature of the inks: i) enables printing without prior mixing and cures under ambient conditions; ii) allows direct dispensing at ≈100 µm resolution printability on nonpolar and polar substrates; iii) forms both self-supporting and high-aspect-ratio structures, key aspects in additive biomanufacturing that eliminate the need for sacrificial layers; and iv) lends efficient, reproducible, and highly sensitive responses to various tensile and compressive stimuli. The high electrical and thermal conductivity of the CNT-silicone composite is further extended to facilitate use as a flexible and stretchable heating element, with applications in body temperature regulation, water distillation, and dual temperature sensing and Joule heating. Overall, the facile fabrication of this composite points to excellent synergy with direct ink writing and can be used to prepare patient-specific wearable electronics for motion detection and cardiac and respiratory monitoring devices and toward advanced personal health tracking and bionic skin applications.     

Photo-Patternable Stretchable Semi-Interpenetrating Polymer Semiconductor Network Using Thiol–Ene Chemistry for Field-Effect Transistors

Stretchable polymer semiconductors are an essential component for skin-inspired electronics. However, the lack of scalable patterning capability of stretchable polymer semiconductors limits the development of stretchable electronics. To address this issue, photo-curable stretchable polymer blends consisting of a high-mobility donor–acceptor conjugated polymer and an elastic rubber through thiol–ene chemistry are developed. The thiol–ene reaction can selectively cross-link the rubber with alkene or vinyl groups without damaging the electronic properties of the conjugated polymer. The conjugated polymer chains embedded in the elastic polymer matrix induce a semi-interpenetrating polymer network (SIPN). The thiol–ene-cross-linked network provides great solvent resistance and enhances stretchability for the embedded conjugated polymer. The well-defined patterned film with a feature size of ≈10 µm can be obtained using UV light at 365 nm through conventional photolithography processes. Furthermore, the SIPN-based transistors show increased mobilities from 0.61 to 1.18 cm² V⁻¹ s⁻¹ when applying the strain from 0% to 100%. Moreover, the hole mobility can still maintain at 0.87 cm² V⁻¹ s⁻¹ after 1000 strain-and-release cycles at the strain of 25%. This study sheds light on the molecular design of photo-curable polymer semiconductors for the mass production of stretchable circuits.     

Bio-Inspired Differential Capillary Migration of Aqueous Liquid Metal Ink for Rapid Fabrication of High-Precision Monolayer and Multilayer Circuits

Manipulating liquid metal inks to create conductive microstructures has attracted widespread interest as liquid metal microstructures are turning into influential components in flexible electronics. However, it is challenging to prevent the issues with low precision, low efficiency, and residue caused by sedimentation, free diffusion, and the Marangoni effect. Inspired by the water transport in plants, the wetting-induced assembly method based on the differential capillary effect for liquid metal ink is created to realize the facile and rapid manufacture of liquid metal conductive microstructures. The single-micron accuracy circuits with a minimum of ≈4 µm straight lines are fabricated to a centimeter scale. This method can also be extended to the preparation of multilayer circuits (minimum 5 µm through hole). The resulting entirely flexible stretchable circuits make it possible to construct highly stretchable devices, such as flexible transparent conductors and stretching sensors. Transparent conductors exhibit excellent mechanical (maximum ≈750% tensile rupture limit) and optoelectronic properties (the transmittance reaches ≈87% and the sheet resistance is ≈0.5 Ω/□)|making them suitable for optically-clear electromagnetic shielding. This study offers a fresh and plain approach to solving the assembly problem of liquid metal inks, paving the way for the creation of flexible electronic devices