A Flexible Stretchable Hydrogel Electrolyte for Healable All‐in‐One Configured Supercapacitors

The development of integrated high‐performance supercapacitors with all‐in‐one configuration, excellent flexibility and autonomously intrinsic self‐healability, and without the extra healable film layers, is still tremendously challenging. Compared to the sandwich‐like laminated structures of supercapacitors with augmented interfacial contact resistance, the flexible healable integrated supercapacitor with all‐in‐one structure could theoretically improve their interfacial contact resistance and energy densities, simplify the tedious device assembly process, prolong the lifetime, and avoid the displacement and delamination of multilayered configurations under deformations. Herein, a flexible healable all‐in‐one configured supercapacitor with excellent flexibility and reliable self‐healing ability by avoiding the extra healable film substrates and the postassembled sandwich‐like laminated structures is developed. The healable all‐in‐one configured supercapacitor is prepared from in situ polymerization and deposition of nanocomposites electrode materials onto the two‐sided faces of the self‐healing hydrogel electrolyte separator. The self‐healing hydrogel film is obtained from the physically crosslinked hydrogel with enormous hydrogen bonds, which can endow the healable capability through dynamic hydrogen bonding. The assembled all‐in‐one configured supercapacitor exhibits enhanced capacitive performance, good cycling stability, reliable self‐healing capability, and excellent flexibility. It holds broad prospects for obtaining various flexible healable all‐in‐one configured supercapacitors for working as portable energy storage devices in wearable electronics.     

Tough Self‐Healing Elastomers by Molecular Enforced Integration of Covalent and Reversible Networks

Self‐healing polymers crosslinked by solely reversible bonds are intrinsically weaker than common covalently crosslinked networks. Introducing covalent crosslinks into a reversible network would improve mechanical strength. It is challenging, however, to apply this concept to “dry” elastomers, largely because reversible crosslinks such as hydrogen bonds are often polar motifs, whereas covalent crosslinks are nonpolar motifs. These two types of bonds are intrinsically immiscible without cosolvents. Here, we design and fabricate a hybrid polymer network by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks. The randomly branched polymer links such two types of bonds and forces them to mix on the molecular level without cosolvents. This enables a hybrid “dry” elastomer that is very tough with fracture energy 13500 Jm^?2 comparable to that of natural rubber. Moreover, the elastomer can self‐heal at room temperature with a recovered tensile strength 4 MPa, which is 30% of its original value, yet comparable to the pristine strength of existing self‐healing polymers. The concept of forcing covalent and reversible bonds to mix at molecular scale to create a homogenous network is quite general and should enable development of tough, self‐healing polymers of practical usage.     

Skin‐Inspired Multifunctional Autonomic‐Intrinsic Conductive Self‐Healing Hydrogels with Pressure Sensitivity,Stretchability, and 3D Printability

The advent of conductive self‐healing (CSH) hydrogels, a class of novel materials mimicking human skin, may change the trajectory of the industrial process because of their potential applications in soft robots, biomimetic prostheses, and health‐monitoring systems. Here, the development of a mechanically and electrically self‐healing hydrogel based on physically and chemically cross‐linked networks is reported. The autonomous intrinsic self‐healing of the hydrogel is attained through dynamic ionic interactions between carboxylic groups of poly(acrylic acid) and ferric ions. A covalent cross‐linking is used to support the mechanical structure of the hydrogel. Establishing a fair balance between the chemical and physical cross‐linking networks together with the conductive nanostructure of polypyrrole networks leads to a double network hydrogel with bulk conductivity, mechanical and electrical self‐healing properties (100% mechanical recovery in 2 min), ultrastretchability (1500%), and pressure sensitivity. The practical potential of CSH hydrogels is further revealed by their application in human motion detection and their 3D‐printing performance.     

Self‐Healing Micellar Ion Gels Based on Multiple Hydrogen Bonding

Ion gels, composed of macromolecular networks filled by ionic liquids (ILs), are promising candidate soft solid electrolytes for use in wearable/flexible electronic devices. In this context, the introduction of a self‐healing function would significantly improve the long‐term durability of ion gels subject to mechanical loading. Nevertheless, compared to hydrogels and organogels, the self‐healing of ion gels has barely investigated been because of there being insufficient understanding of the interactions between polymers and ILs. Herein, a new class of supramolecular micellar ion gel composed of a diblock copolymer and a hydrophobic IL, which exhibits self‐healing at room temperature, is presented. The diblock copolymer has an IL‐phobic block and a hydrogen‐bonding block with hydrogen‐bond‐accepting and donating units. By combining the IL and the diblock copolymer, micellar ion gels are prepared in which the IL phobic blocks form a jammed micelle core, whereas coronal chains interact with each other via multiple hydrogen bonds. These hydrogen bonds between the coronal chains in the IL endow the ion gel with a high level of mechanical strength as well as rapid self‐healing at room temperature without the need for any external stimuli such as light or elevated temperatures.     

Tough,Self‐Healing Hydrogels Capable of Ultrafast Shape Changing

Achieving multifunctional shape‐changing hydrogels with synergistic and engineered material properties is highly desirable for their expanding applications, yet remains an ongoing challenge. The synergistic design of multiple dynamic chemistries enables new directions for the development of such materials. Herein, a molecular design strategy is proposed based on a hydrogel combining acid–ether hydrogen bonding and imine bonds. This approach utilizes simple and scalable chemistries to produce a doubly dynamic hydrogel network, which features high water uptake, high strength and toughness, excellent fatigue resistance, fast and efficient self‐healing, and superfast, programmable shape changing. Furthermore, deformed shapes can be memorized due to the large thermal hysteresis. This new type of shape‐changing hydrogel is expected to be a key component in future biomedical, tissue, and soft robotic device applications.     

Self‐Healing Hydrogels

Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self‐healing and self‐recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self‐healing hydrogels generally either possess mechanically robust or rapid self‐healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self‐healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self‐healing hydrogels are reviewed. Specifically, methods to test self‐healing efficiencies and recoveries, mechanisms of autonomous self‐healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self‐heal better also achieve self‐healing faster, as compared to gels that only partially self‐heal. Recommendations to guide future development of self‐healing hydrogels are offered and the potential relevance of self‐healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.     

Tough and Water‐Insensitive Self‐Healing Elastomer for Robust Electronic Skin

An electronic (e‐) skin is expected to experience significant wear and tear over time. Therefore, self‐healing stretchable materials that are simultaneously soft and with high fracture energy, that is high tolerance of damage or small cracks without propagating, are essential requirements for the realization of robust e‐skin. However, previously reported elastomers and especially self‐healing polymers are mostly viscoelastic and lack high mechanical toughness. Here, a new class of polymeric material crosslinked through rationally designed multistrength hydrogen bonding interactions is reported. The resultant supramolecular network in polymer film realizes exceptional mechanical properties such as notch‐insensitive high stretchability (1200%), high toughness of 12 000 J m^?2, and autonomous self‐healing even in artificial sweat. The tough self‐healing materials enable the wafer‐scale fabrication of robust and stretchable self‐healing e‐skin devices, which will provide new directions for future soft robotics and skin prosthetics.     

Hydrogen‐Bonded Molecular Networks of Melamine and Cyanuric Acid on Thin Films of NaCl on Au(111)

Self‐assembly of organized molecular structures on insulators is technologically very relevant, but in general rather challenging to achieve due to the comparatively weak molecule–substrate interactions. Here the self‐assembly of a bimolecular hydrogen‐bonded network formed by melamine (M) and cyanuric acid (CA) on ultrathin NaCl films grown on a Au(111) surface is reported. Using scanning tunneling microscopy under ultrahigh‐vacuum conditions it is demonstrated that it is possible to exploit strong intermolecular forces in the M–CA system, resulting from complementary triple hydrogen bonds, to grow 2D bimolecular networks on an ultrathin NaCl film that are stable at a relatively high temperature of ≈160 K and at a coverage below saturation of the first molecular monolayer. These hydrogen‐bonded structures on NaCl are identical to the self‐assembled structures observed for the M–CA system on Au(111), which indicates that the molecular self‐assembly is not significantly affected by the isolating NaCl substrate.     

Influence of the Thermodynamic and Kinetic Control of Self‐Assembly on the Microstructure Evolution of Silk‐Elastin‐Like Recombinamer Hydrogels

Complex recombinant biomaterials that merge the self‐assembling properties of different (poly)peptides provide a powerful tool for the achievement of specific structures, such as hydrogel networks, by tuning the thermodynamics and kinetics of the system through a tailored molecular design. In this work, elastin‐like (EL) and silk‐like (SL) polypeptides are combined to obtain a silk‐elastin‐like recombinamer (SELR) with dual self‐assembly. First, EL domains force the molecule to undergo a phase transition above a precise temperature, which is driven by entropy and occurs very fast. Then, SL motifs interact through the slow formation of β‐sheets, stabilized by H‐bonds, creating an energy barrier that opposes phase separation. Both events lead to the development of a dynamic microstructure that evolves over time (until a pore size of 49.9 ± 12.7 µm) and to a delayed hydrogel formation (obtained after 2.6 h). Eventually, the network is arrested due to an increase in β‐sheet secondary structures (up to 71.8 ± 0.8%) within SL motifs. This gives a high bond strength that prevents the complete segregation of the SELR from water, which results in a fixed metastable microarchitecture. These porous hydrogels are preliminarily tested as biomimetic niches for the isolation of cells in 3D cultures.     

Healable and Mechanically Super‐Strong Polymeric Composites Derived from Hydrogen‐Bonded Polymeric Complexes

It is challenging to fabricate mechanically super‐strong polymer composites with excellent healing capacity because of the significantly limited mobility of polymer chains. The fabrication of mechanically super‐strong polymer composites with excellent healing capacity by complexing polyacrylic acid (PAA) with polyvinylpyrrolidone (PVPON) in aqueous solution followed by molding into desired shapes is presented. The coiled PVPON can complex with PAA in water via hydrogen‐bonding interactions to produce transparent PAA–PVPON composites homogenously dispersed with nanoparticles of PAA–PVPON complexes. As healable materials, the PAA–PVPON composite materials with a glass transition temperature of ≈107.9 °C exhibit a super‐high mechanical strength, with a tensile strength of ≈81 MPa and a Young's modulus of ≈4.5 GPa. The PAA–PVPON composites are stable in water because of the hydrophobic interactions among pyrrolidone groups. The super‐high mechanical strength of the PAA–PVPON composite materials originates from the highly dense hydrogen bonds between PAA and PVPON and the reinforcement of in situ formed PAA–PVPON nanoparticles. The reversibility of the relatively weak but dense hydrogen bonds enables convenient healing of the mechanically strong PAA–PVPON composite materials from physical damage to restore their original mechanical strength.     

Modular Molecular Self‐Assembly for Diversified Chiroptical Systems

Bottom‐up multicomponent molecular self‐assembly is an efficient approach to fabricate and manipulate chiral nanostructures and their chiroptical activities such as the Cotton effect and circular polarized luminescence (CPL). However, the integrated coassembly suffers from spontaneous and inherent systematic pathway complexity with low yield and poor fidelity. Consequently, a rational design of chiral self‐assembled systems with more than two components remains a significant challenge. Herein, a modularized, ternary molecular self‐assembly strategy that generates chiroptically active materials at diverse hierarchical levels is reported. N‐terminated aromatic amino acids appended with binding sites for charge transfer and multiple hydrogen bonds undergo the evolution of supramolecular chirality with unique handedness and luminescent color, generating abundant CPL emission with high luminescence dissymmetry factor values in precisely controlled modalities. Ternary coassembly facilitates high‐water‐content hydrogel formation constituted by super‐helical nanostructures, demonstrating a helix to toroid topological transition. This discovery would shed light on developing complicated multicomponent systems in mimicking biological coassembly events.     

Tough Supramolecular Polymer Networks with Extreme Stretchability and Fast Room‐Temperature Self‐Healing

Recent progress on highly tough and stretchable polymer networks has highlighted the potential of wearable electronic devices and structural biomaterials such as cartilage. For some given applications, a combination of desirable mechanical properties including stiffness, strength, toughness, damping, fatigue resistance, and self‐healing ability is required. However, integrating such a rigorous set of requirements imposes substantial complexity and difficulty in the design and fabrication of these polymer networks, and has rarely been realized. Here, we describe the construction of supramolecular polymer networks through an in situ copolymerization of acrylamide and functional monomers, which are dynamically complexed with the host molecule cucurbit[8]uril (CB[8]). High molecular weight, thus sufficient chain entanglement, combined with a small‐amount dynamic CB[8]‐mediated non‐covalent crosslinking (2.5 mol%), yields extremely stretchable and tough supramolecular polymer networks, exhibiting remarkable self‐healing capability at room temperature. These supramolecular polymer networks can be stretched more than 100× their original length and are able to lift objects 2000× their weight. The reversible association/dissociation of the host–guest complexes bestows the networks with remarkable energy dissipation capability, but also facile complete self‐healing at room temperature. In addition to their outstanding mechanical properties, the networks are ionically conductive and transparent. The CB[8]‐based supramolecular networks are synthetically accessible in large scale and exhibit outstanding mechanical properties. They could readily lead to the promising use as wearable and self‐healable electronic devices, sensors and structural biomaterials.     

An Elastic Autonomous Self‐Healing Capacitive Sensor Based on a Dynamic Dual Crosslinked Chemical System

Adopting self‐healing, robust, and stretchable materials is a promising method to enable next‐generation wearable electronic devices, touch screens, and soft robotics. Both elasticity and self‐healing are important qualities for substrate materials as they comprise the majority of device components. However, most autonomous self‐healing materials reported to date have poor elastic properties, i.e., they possess only modest mechanical strength and recoverability. Here, a substrate material designed is reported based on a combination of dynamic metal‐coordinated bonds (β‐diketone–europium interaction) and hydrogen bonds together in a multiphase separated network. Importantly, this material is able to undergo self‐healing and exhibits excellent elasticity. The polymer network forms a microphase‐separated structure and exhibits a high stress at break (≈1.8 MPa) and high fracture strain (≈900%). Additionally, it is observed that the substrate can achieve up to 98% self‐healing efficiency after 48 h at 25 °C, without the need of any external stimuli. A stretchable and self‐healable dielectric layer is fabricated with a dual‐dynamic bonding polymer system and self‐healable conductive layers are created using polymer as a matrix for a silver composite. These materials are employed to prepare capacitive sensors to demonstrate a stretchable and self‐healable touch pad.     

Microfluidics‐Assisted Assembly of Injectable Photonic Hydrogels toward Reflective Cooling

Development of fast curing and easy modeling of colloidal photonic crystals is highly desirable for various applications. Here, a novel type of injectable photonic hydrogel (IPH) is proposed to achieve self‐healable structural color by integrating microfluidics‐derived photonic supraballs with supramolecular hydrogels. The supramolecular hydrogel is engineered via incorporating β‐cyclodextrin/poly(2‐hydroxypropyl acrylate‐co‐N‐vinylimidazole) (CD/poly(HPA‐co‐VI)) with methacrylated gelatin (GelMA), and serves as a scaffold for colloidal crystal arrays. The photonic supraballs derived from the microfluidics techniques, exhibit excellent compatibility with the hydrogel scaffolds, leading to enhanced assembly efficiency. By virtue of hydrogen bonds and host–guest interactions, a series of self‐healable photonic hydrogels (linear, planar, and spiral assemblies) can be facilely assembled. It is demonstrated that the spherical symmetry of the photonic supraballs endows them with identical optical responses independent of viewing angles. In addition, by taking the advantage of angle independent spectrum characteristics, the IPH presents beneficial effects in reflective cooling, which can achieve up to 17.4 °C in passive solar reflective cooling. The strategy represents an easy‐to‐perform platform for the construction of IPH, providing novel insights into macroscopic self‐assembly toward thermal management applications.     

Carbon Dots as Fillers Inducing Healing/Self‐Healing and Anticorrosion Properties in Polymers

Self‐healing is the way by which nature repairs damage and prolongs the life of bio entities. A variety of practical applications require self‐healing materials in general and self‐healing polymers in particular. Different (complex) methods provide the rebonding of broken bonds, suppressing crack, or local damage propagation. Here, a simple, versatile, and cost‐effective methodology is reported for initiating healing in bulk polymers and self‐healing and anticorrosion properties in polymer coatings: introduction of carbon dots (CDs), 5 nm sized carbon nanocrystallites, into the polymer matrix forming a composite. The CDs are blended into polymethacrylate, polyurethane, and other common polymers. The healing/self‐healing process is initiated by interfacial bonding (covalent, hydrogen, and van der Waals bonding) between the CDs and the polymer matrix and can be optimized by modifying the functional groups which terminate the CDs. The healing properties of the bulk polymer–CD composites are evaluated by comparing the tensile strength of pristine (bulk and coatings) composites to those of fractured composites that are healed and by following the self‐healing of scratches intentionally introduced to polymer–CD composite coatings. The composite coatings not only possess self‐healing properties but also have superior anticorrosion properties compared to those of the pure polymer coatings.     

Advanced Materials for Use in Soft Self‐Healing Devices

Devices integrated with self‐healing ability can benefit from long‐term use as well as enhanced reliability, maintenance and durability. This progress report reviews the developments in the field of self‐healing polymers/composites and wearable devices thereof. One part of the progress report presents and discusses several aspects of the self‐healing materials chemistry (from non‐covalent to reversible covalent‐based mechanisms), as well as the required main approaches used for functionalizing the composites to enhance their electrical conductivity, magnetic, dielectric, electroactive and/or photoactive properties. The second and complementary part of the progress report links the self‐healing materials with partially or fully self‐healing device technologies, including wearable sensors, supercapacitors, solar cells and fabrics. Some of the strong and weak points in the development of each self‐healing device are clearly highlighted and criticized, respectively. Several ideas regarding further improvement of soft self‐healing devices are proposed.     

Direct Imaging of the Induced‐Fit Effect in Molecular Self‐Assembly

Molecular recognition is a crucial driving force for molecular self‐assembly. In many cases molecules arrange in the lowest energy configuration following a lock‐and‐key principle. When molecular flexibility comes into play, the induced‐fit effect may govern the self‐assembly. Here, the self‐assembly of dicyanovinyl‐hexathiophene (DCV6T) molecules, a prototype specie for highly efficient organic solar cells, on Au(111) by using low‐temperature scanning tunneling microscopy and atomic force microscopy is investigated. DCV6T molecules assemble on the surface forming either islands or chains. In the islands the molecules are straight—the lowest energy configuration in gas phase—and expose the dicyano moieties to form hydrogen bonds with neighbor molecules. In contrast, the structure of DCV6T molecules in the chain assemblies deviates significantly from their gas‐phase analogues. The seemingly energetically unfavorable bent geometry is enforced by hydrogen‐bonding intermolecular interactions. Density functional theory calculations of molecular dimers quantitatively demonstrate that the deformation of individual molecules optimizes the intermolecular bonding structure. The intermolecular bonding energy thus drives the chain structure formation, which is an expression of the induced‐fit effect.     

Self‐Template‐Directed Metal–Organic Frameworks Network and the Derived Honeycomb‐Like Carbon Flakes via Confinement Pyrolysis

Metal–organic frameworks (MOFs) have become a research hotspot since they have been explored as convenient precursors for preparing various multifunctional nanomaterials. However, the preparation of MOF networks with controllable flake morphology in large scale is not realized yet. Herein, a self‐template strategy is developed to prepare MOF networks. In this work, layered double‐metal hydroxide (LDH) and other layered metal hydroxides are used not only as a scaffold but also as a self‐sacrificed metal source. After capturing the abundant metal cations identically from the LDH by the organic linkers, MOF networks are in situ formed. It is interesting that the MOF network‐derived carbon materials retain the flake morphology and exhibit a unique honeycomb‐like macroporous structure due to the confined shrinkage of the polyhedral facets. The overall properties of the carbon networks are adjustable according to the tailored metal compositions in LDH and the derived MOFs, which are desirable for target‐oriented applications as exemplified by the electrochemical application in supercapacitors.     

Cysteine–Ag Cluster Hydrogel Confirmed by Experimental and Numerical Studies

The native cysteine (Cys)‐Ag₃ cluster hydrogel is approved for the first time by both experimental and theoretical studies. From the detailed molecular structure and energy information, three factors are found to ensure the self‐assembly of Cys and Ag₃, and result in the hydrogel. First, the Ag–S bonds make Cys and Ag₃ form Cys‐Ag₃‐Cys monomer. Second, intermolecular hydrogen bonds between carboxyl groups of adjacent monomer push them self‐assembled. Third, more monomer precisely self‐assemble to produce the –[Cys‐Ag₃‐Cys]_n multimer, e.g., a single molecular chain with the left‐handed helix conformation, via a benign thermodynamic process. These multimers entangle together to form micro‐network to trap water and produce hydorgel in situ. The hydrogen bonds of hydrogel are sensitive to thermal and proton stimuli, and the hydrogel presents lysosome targeting properties via fluorescent imaging with biocompatibility.     

Colorless,Transparent, Robust,and Fast Scratch‐Self‐Healing Elastomers via a Phase‐Locked Dynamic Bonds Design

Robust self‐healing thermoplastic elastomers are expected to have repeated healing capability, remarkable mechanical properties, transparency, and superior toughness. The phase‐locked design in this work provides excellent tensile mechanical properties and efficient healability at a moderate temperature due to the dynamic disulfide bonds embedded in the hard segments and mainly being locked in the viscoelastic hard microphase region. The self‐healing elastomers exhibit a maximum tensile stress of 25 MPa and a fracture strain of over 1600%, which are quite prominent compared to previous reports. The nanoscale domains of the elastomer are smaller than the wavelength of visible light by microphase separation control resulting in colorless, nearly 100% transparency, and are as good as quartz glasses. The high dynamics of the phase‐locked disulfide bonds renders a high healing efficiency of scratches on the surface within 60 s at 70 °C. The rapid scratch healing and complete transparency recovery of the elastomers provide new avenues in the highly transparent surface or protective films which finds potential applications for precision optical lenses, flexible display screens, and automobile or aircraft lighting finishes.