Transparent, Healable Elastomers with High Mechanical Strength and Elasticity Derived from Hydrogen-Bonded Polymer Complexes

Transparent, mechanically robust, conductive, self-healable, and recyclable ionogels for flexible strain sensors and electroluminescent devices

A mechanically robust, self-healable, and recyclable PVP-based ionogel was achieved through a simple one-pot photoinitiated polymerization process. This ionogel exhibits a combination of excellent properties, including transparency, high mechanical strength, good ionic conductivity, self healability, and recyclability. A wearable resistive strain sensor based on the ionogel is successfully assembled and demonstrated accurate response to human motion. Moreover, a flexible electroluminescent device has been fabricated based on our ionogel, which can maintain optimal luminescence functionality even when subjected to bending. Considering the simple preparation method and excellent applications, we believe that our PVP-based ionogel has promising applications in many fields such as in wearable devices, electronic skin, implantable materials, robotics and human-machine interfaces.

Ion transport mechanisms in covalent organic frameworks: implications for technology

Covalent organic frameworks (COFs) have emerged as promising materials for ion conduction due to their highly tunable structures and excellent electrochemical stability. This review paper explores the mechanisms of ion conduction in COFs, focusing on how these materials facilitate ion transport across their ordered structures, which is crucial for applications such as solid electrolytes in batteries and fuel cells. We discuss the design strategies employed to enhance ion conductivity, including pore size optimization, functionalization with ionic groups, and the incorporation of solvent molecules and salts. Additionally, we examine the various applications of ion-conductive COFs, particularly in energy storage and conversion technologies, highlighting recent advancements and future directions in this field. This review paper aims to provide a comprehensive overview of the current state of research on ion-conductive COFs, offering insights into their potential to design highly ion-conductive COFs considering not only fundamental studies but also practical perspectives for advanced electrochemical devices.

Dual Dynamic Cross-Linked Epoxy Vitrimers Used for Strong, Detachable, and Reworkable Adhesives

Novel reprocessable thermosetting adhesives (RTAs), which combine high adhesive strength, reusability, disassembly, and recyclability features, have attracted increasing attention. However, developing RTAs with a rapidly adhesive rate while ensuring high adhesive strength and self-healing ability is still a significant challenge. Here, we prepared a novel vitrimer called DAx-DTSAy, which can be used as an RTA. First, by adjusting the ratio of rigid and flexible segments, maximum tensile strength reached 35.92 MPa. Second, the combined effect of dynamic hydroxyl ester bonds and dynamic disulfide bonds resulted in a rapid stress relaxation behavior, with a complete relaxation time 13.6 times shorter than a vitrimer only cross-linked with hydroxy ester bonds. This feature endowed its good self-healing and reprocessing capabilities. After self-healing at 180 °C, the maximum healing rate of mechanical properties was 91.8%. After three reprocesses, the maximum recovery rate of tensile strength was 120.2%. Furthermore, the combination of rigid and flexible segments and the synergistic effect of dual dynamic covalent bonds made DAx-DTSAy capable of use as a high-performance RTA. The lap shear strength of a DAx-DTSAy film on stainless steel reached 18.18 MPa after 15 min, with a recovery rate of 91.9% after 5 rebonding cycles. Additionally, DAx-DTSAy can be disassembled in chemical agents and exhibited better insulation properties compared to traditional epoxy resins. DAx-DTSAy can be employed as a novel high-performance adhesive in applications such as electronic devices and transportation, contributing to the development of thermosetting adhesives toward recyclability and sustainability.

High strength, self-healing sensitive ionogel sensor based on MXene/ionic liquid synergistic conductive network for human-motion detection

Ionogels with both high strength and high conductivity for wearable strain and pressure dual-mode sensors are needed for human motion and health monitoring. Here, multiple hydrogen bonds are introduced through imidazolidinyl urea (IU) as a chain extender to provide high mechanical and self-healing properties for the water-borne polyurethane (WPU). The MXene/ionic liquids synergistic conductive network provides excellent conductivity and also reduces the relative content of ionic liquids to maintain the mechanical properties of the ionogels. The mechanical strength of this ionogel reached 1.81-2.24 MPa and elongation at break reached 570-624%. It also has excellent conductivity (22.7-37.5 mS m-1), gauge factor (GF) (as a strain sensor, GF = 1.8), sensitivity (S) (as a press sensor, S1 = 29.8 kPa-1, S2 = 1.3 kPa-1), and fast response time (as a strain sensor = 185 ms; as a press sensor = 204 ms). The ionogel also exhibits rapid photothermal self-healing capabilities due to the inherent photothermal behavior of MXene. It can maintain good elasticity and conductivity at low temperatures. In addition, this ionogel is able to stretch for 1200 cycles without significant change in the relative change of resistance. The ionogel can be assembled as a strain sensor for monitoring human motion and as a pressure sensor array for obtaining pressure magnitude and position information.

High-Performance Branched Polymer Elastomer Based on a Topological Network Structure and Dynamic Bonding

High performance has always been the research focus of elastomers. However, there are inherent conflicts among properties of elastomers, such as strength and toughness, strength and damping performance, strength and self-healing ability, etc. Herein, first, we synthesized a unique structure of the dangling chain containing proton donors and receptors. Then, we design and fabricate a kind of high-performance elastomer with a gradient distribution of a dangling chain and a dynamic bond structure. The dangling chains of different lengths intertwine with each other and self-assemble to form a "dense accumulation" structure driven by hydrogen bonds, and the elastomer exhibits special micro/nano scale aggregated states and microphase separation. The "dense accumulation" structure plays a vital role in the increase of mechanical properties. Meanwhile, under the joint action of a dangling chain and a dynamic bond, the damping performance and self-healing performance of the elastomer are greatly enhanced. High strength (27.5 MPa), toughness (121.9 MJ·m-3), 94.8% healing efficiency and outstanding damping performance (tan δ ≥ 0.4, high damping temperature range up to 144 °C) are simultaneously achieved beyond the current state-of-the-art. This topoarchitected polymer with a gradient distribution of dangling chains successfully solves the defects of conventional branched polymers in deteriorating their mechanical properties. This material design provides a new strategy for the development of high-performance structural and functional integrated elastomers.

Ambient Environment Adaptive Elastomer Constructed by Microphase Separation and Segment Complexation of Triblock Copolymers

Elastomers with environmental adaption have attracted considerable attention for advanced applications in various areas. Here, we fabricate an ambient environment adaptive elastomer by assembling triblock copolymers polystyrene-b-poly(acrylic acid)-b-polystyrene (SAS) and polystyrene-b-poly(ethylene oxide)-b-polystyrene (SES). Owing to the microphase separation of triblock polymers and hydrogen-bonding complexation of their middle segments, the SAS/SES complex presents dichotomy of vitrified hard PS domains and soft PAA/PEO domains, which presents major relaxation transition in the temperature zone 10-30 °C and relative humidity (RH) 40-60%. The SAS/SES elastomer presents quick adaption to the ambient environment change with temperature and humidity coupling. Moreover, after a loading-unloading cycle training, the SAS/SES elastomer exhibits domain orientation, low energy dissipation, high recovery ratio, and distinct strain stiffening compared with the pristine complex. The SAS/SES elastomer has potential to be used as a sensing and adaption component for complicated intelligent systems.

Gradient H-Bonding Supports Highly Adaptable and Rapidly Self-Healing Composite Binders with High Ionic Conductivity for Silicon Anodes in Lithium-Ion Batteries

An ideal binder for high-energy-density lithium-ion batteries (LIBs) should effectively inhibit volume effects, exhibit specific functional properties (e.g., self-repair capabilities and high ionic conductivity), and require low-cost, environmentally friendly mass production processes. This study adopts a synergistic strategy involving gradient (strong-weak) hydrogen bonding to construct a hard/soft polymer composite binder with self-healing abilities and high battery cell environments adaptability in LIBs. The meticulously designed 3D network structure comprising continuous electron transport pathways buffers the mechanical stresses caused by changes in silicon volume and improves the overall stability of the solid electrolyte interphase film. The Si-based anode with a polymer composite binder poly(acrylic acid-g-ureido pyrimidinone_5% )/polyethylene oxide (Si/PAA-UPy_5% /PEO) achieves a reversible capacity of 1245 mAh g^-1 after 200 cycles at 0.5 C, which is 6.6 times higher than that of the Si/PAA anode. After 200 cycles at 0.2 A g^-1 , a half-cell comprising Si/C anode with a polymer composite binder (Si/C/PAA-UPy_5% /PEO) has a remaining specific capacity of 420 mAh g^-1 and a capacity retention rate of 79%. The corresponding full cell with a Li-based cathode (LiFePO₄ /Si/C/PAA-UPy_5% /PEO) has an initial area capacity of 0.96 mAh cm^-2 and retains an area capacity of 0.90 mAh cm^-2 (capacity retention rate = 93%) after 100 cycles at 0.2 A g^-1 .

Self-Healing Polymeric Soft Actuators

Natural evolution has provided multicellular organisms with sophisticated functionalities and repair mechanisms for surviving and preserve their functions after an injury and/or infection. In this context, biological systems have inspired material scientists over decades to design and fabricate both self-healing polymeric materials and soft actuators with remarkable performance. The latter are capable of modifying their shape in response to environmental changes, such as temperature, pH, light, electrical/magnetic field, chemical additives, etc. In this review, we focus on the fusion of both types of materials, affording new systems with the potential to revolutionize almost every aspect of our modern life, from healthcare to environmental remediation and energy. The integration of stimuli-triggered self-healing properties into polymeric soft actuators endow environmental friendliness, cost-saving, enhanced safety, and lifespan of functional materials. We discuss the details of the most remarkable examples of self-healing soft actuators that display a macroscopic movement under specific stimuli. The discussion includes key experimental data, potential limitations, and mechanistic insights. Finally, we include a general table providing at first glance information about the nature of the external stimuli, conditions for self-healing and actuation, key information about the driving forces behind both phenomena, and the most important features of the achieved movement.

Optical mapping of the evolution of water content during the swelling of hydrophilic polymers

The water content of hydrophilic polymers is a fundamental property that regulates their performance. Herein, we report a new technique for optically imaging the water content of hydrophilic polymers both in static and dynamic evolution during swelling, based on mapping the interfacial refractive index of hydrophilic polymers with label-free total internal reflection microscopy.

Dynamic Bonds: Adaptable Timescales for Responsive Materials

Dynamic bonds introduce unique properties such as self-healing, recyclability, shape memory, and malleability to polymers. Significant efforts have been made to synthesize a variety of dynamic linkers, creating a diverse library of materials. In addition to the development of new dynamic chemistries, fine-tuning of dynamic bonds has emerged as a technique to modulate dynamic properties. This Review highlights approaches for controlling the timescales of dynamic bonds in polymers. Particularly, eight dynamic bonds are considered, including urea/urethanes, boronic esters, Thiol-Michael exchange, Diels-Alder adducts, transesterification, imine bonds, coordination bonds, and hydrogen bonding. This Review emphasizes how structural modifications and external factors have been used as tools to tune the dynamic character of materials. Finally, this Review proposes strategies for tailoring the timescales of dynamic bonds in polymer materials through both kinetic effects and modulating bond thermodynamics.

Self-Healing and Shape-Editable Wearable Supercapacitors Based on Highly Stretchable Hydrogel Electrolytes

Shape editability combined with a self-healing capability and long-term cycling durability are highly desirable properties for wearable supercapacitors. Most wearable supercapacitors have rigid architecture and lack the capacity for editability into desirable shapes. Through sandwiching hydrogel electrolytes between two electrodes, a suite of wearable supercapacitors that integrate desirable properties namely: repeated shape editability, excellent self-healing capability, and long-term cycling durability is demonstrated. A strategy is proposed to enhance the long-term cycling durability by utilizing hydrogel electrolytes with unique cross-linking structures. The dynamic crosslinking sites are formed by quadruple H bonds and hydrophobic association, stabilizing the supercapacitors from inorganic ion disruption during charge-discharge processes. The fabricated supercapacitors result in the capacitance retention rates of 99.6% and 95.8% after 5000 and 10 000 charge-discharge cycles, respectively, which are much higher than others reported in the literature. Furthermore, the supercapacitor sheets can be repeatedly processed into various shapes without any capacitance loss. The supercapacitors exhibit a 95% capacitance retention rate after five cutting/self-healing cycles, indicative of their excellent self-healing performance. To demonstrate real-life applicability, the wearable supercapacitors are successfully used to power a light-emitting diode and an electronic watch.

Skeletal Muscle Fibers Inspired Polymeric Actuator by Assembly of Triblock Polymers

Inspired by the striated structure of skeletal muscle fibers, a polymeric actuator by assembling two symmetric triblock copolymers, namely, polystyrene-b-poly(acrylic acid)-b-polystyrene (SAS) and polystyrene-b-poly(ethylene oxide)-b-polystyrene (SES) is developed. Owing to the microphase separation of the triblock copolymers and hydrogen-bonding complexation of their middle segments, the SAS/SES assembly forms a lamellar structure with alternating vitrified S and hydrogen-bonded A/E association layers. The SAS/SES strip can be actuated and operate in response to environmental pH. The contraction ratio and working density of the SAS/SES actuator are approximately 50% and 90 kJ m-3 , respectively; these values are higher than those of skeletal muscle fibers. In addition, the SAS/SES actuator shows a "catch-state", that is, it can maintain force without energy consumption, which is a feature of mollusc muscle but not skeletal muscle. This study provides a biomimetic approach for the development of artificial polymeric actuators with outstanding performance.

Super Tough and Spontaneous Water-Assisted Autonomous Self-Healing Elastomer for Underwater Wearable Electronics

Self-healing soft electronic material composition is crucial to sustain the device long-term durability. The fabrication of self-healing soft electronics exposed to high moisture environment is a significant challenge that has yet to be fully achieved. This paper presents the novel concept of a water-assisted room-temperature autonomous self-healing mechanism based on synergistically dynamic covalent Schiff-based imine bonds with hydrogen bonds. The supramolecular water-assisted self-healing polymer (WASHP) films possess rapid self-healing kinetic behavior and high stretchability due to a reversible dissociation-association process. In comparison with the pristine room-temperature self-healing polymer, the WASHP demonstrates favorable mechanical performance at room temperature and a short self-healing time of 1 h; furthermore, it achieves a tensile strain of 9050%, self-healing efficiency of 95%, and toughness of 144.2 MJ m-3 . As a proof of concept, a versatile WASHP-based light-emitting touch-responsive device (WASHP-LETD) and perovskite quantum dot (PeQD)-based white LED backlight are designed. The WASHP-LETD has favorable mechanical deformation performance under pressure, bending, and strain, whereas the WASHP-PeQDs exhibit outstanding long-term stability even over a period exceeding one year in a boiling water environment. This paper provides a mechanically robust approach for producing eco-friendly, economical, and waterproof e-skin device components.

Stretchable optical diffraction grating from poly(acrylic acid)/polyethylene oxide stereocomplex

Advances in optical materials, which were initially static elements, have enabled dynamically tunable optical diffraction gratings to be designed. One common tuning strategy relies on mechanical deformation of the grating pitch to modify the diffraction pattern. In the present work, we demonstrate an all-polymer tunable diffraction grating fabricated using a modified replica molding process. The poly(acrylic acid) (PAA)/polyethylene oxide (PEO) polymer stereocomplex films exhibit optical transmittance at or above 80% from 500 nm to 1400 nm and stretchability over 800% strain with reversibility under 70% strain. The imprinted gratings are characterized at 633 nm and 1064 nm under a range of strain conditions. The measured tunability agrees with finite element method modeling.

Laser-Induced Remote Healing of Stretchable Diselenide-Containing Conductive Composites

Remotely controlled on-demand functional healing is vital to components that are difficult to access and repair in distance such as satellites and unmanned cruising aircrafts. Compared with other stimuli, a blue laser is a better choice to input energy to the damaged area in distance because of its high energy density and low dissipation through the air. Herein, diselenide-containing polyurethane (PUSe) is first employed to fabricate visible light-responsive stretchable conductive composites with multiwalled carbon nanotubes (MWCNTs). Then, laser-induced remote healing was realized based on the characteristics of long-distance propagation of lasers and the dynamic properties of diselenide bonds. Moreover, the PUSe/MWCNT composite film can be used to transfer an electrical signal in the circuit containing a signal generator. This laser-induced remote healing of conductivity paves the way for developing healing conductors which are difficult to access and repair.

Peptidoglycan-inspired autonomous ultrafast self-healing bio-friendly elastomers for bio-integrated electronics

Elastomers are essential for stretchable electronics, which have become more and more important in bio-integrated devices. To ensure high compliance with the application environment, elastomers are expected to resist, and even self-repair, mechanical damage, while being friendly to the human body. Herein, inspired by peptidoglycan, we designed the first room-temperature autonomous self-healing biodegradable and biocompatible elastomers, poly(sebacoyl 1,6-hexamethylenedicarbamate diglyceride) (PSeHCD) elastomers. The unique structure including alternating ester-urethane moieties and bionic hybrid crosslinking endowed PSeHCD elastomers superior properties including ultrafast self-healing, tunable biomimetic mechanical properties, facile reprocessability, as well as good biocompatibility and biodegradability. The potential of the PSeHCD elastomers was demonstrated as a super-fast self-healing stretchable conductor (21 s) and motion sensor (2 min). This work provides a new design and synthetic principle of elastomers for applications in bio-integrated electronics.

Degradable Poly(vinyl alcohol)-Based Supramolecular Plastics with High Mechanical Strength in a Watery Environment

It is challenging to fabricate degradable poly(vinyl alcohol) (PVA)-based plastics that can be used in watery environments because PVA is soluble in water. In this study, PVA-based supramolecular plastics with excellent degradability in soil and high mechanical strength in watery environments are fabricated by the complexation of vanillin-grafted PVA (VPVA), hydrophobic humic acid (HA), and Fe³⁺ ions (hereafter denoted as VPVA-HA-Fe complexes). Large-area PVA-based plastics can be easily prepared from a solution of VPVA-HA-Fe complexes using a blade-coating method. The high-density of hydrogen bonds and coordination interactions, as well as the reinforcement of self-assembled Fe³⁺ -chelated HA nanoparticles, facilitate the fabrication of PVA-based plastics with a breaking strength of ≈85.0 MPa. After immersion in water at room temperature for 7 d, the PVA-based plastics exhibit a breaking strength of ≈26.2 MPa, which is similar to that of polyethylene in its dry state. Furthermore, owing to the reversibility of the hydrogen bonds and coordination interactions, the VPVA-HA-Fe plastics are recyclable and can be conveniently processed into plastic products with desired shapes. After being placed under soil for ≈108 d, the PVA-based plastics are completely degraded into nontoxic species without requiring manual interference.

An Extremely Stretchable and Self-Healable Supramolecular Polymer Network

The construction of a single polymer network with extreme stretchability, relatively high mechanical strength, and fast and facile autonomous room-temperature self-healing capability still remains a challenge. Herein, supramolecular polymer networks are fabricated by synergistically incorporating metal-ligand and hydrogen bonds in poly(propylene glycol) (PPG). The representative specimen, PPG-Im-MDA-1.5-0.25-Cu, shows a combination of notable mechanical properties involving an extreme stretching ratio of 346 ± 14× and a Young's modulus of 2.10 ± 0.14 MPa, which are superior to the previously reported extremely stretchable polymeric materials. Notably, the destroyed specimen can fully recover mechanical performances within 1 h. The tunability of mechanical properties and self-healing capability has been actualized by merely tailoring the content of a chain extender. The application of the as-prepared supramolecular PPG network in constructing a flexible and self-healable conductor has been demonstrated. This strategy provides some insights for preparing extremely stretchable and self-healable polymeric materials.

Synergy between dynamic covalent boronic ester and boron-nitrogen coordination: strategy for self-healing polyurethane elastomers at room temperature with unprecedented mechanical properties

Achieving mechanical robustness and highly efficient self-healing simultaneously at room temperature is always a formidable challenge for polymeric materials. Herein, a series of novel supramolecular polyurethane elastomers (SPUEs) are developed by incorporating dynamic covalent boronic ester and boron-nitrogen (B-N) coordination. The SPUEs demonstrate the highest tensile toughness (∼182.2 MJ m^-3) to date for room-temperature self-healable polymers, as well as an excellent ultimate tensile strength (∼10.5 MPa) and ultra-high fracture energy (∼72 100 J m^-2), respectively, owing to a synergetic quadruple dynamic mechanism. It is revealed that the B-N coordination not only facilitates the formation and dissociation of boronic ester at room temperature but also dramatically enhances the mechanical properties by the intermolecular coordinated chain crosslinking and intramolecular coordinated chain folding. Meanwhile, the B-N coordination and urethane hydrogen interaction also serve as sacrificial bonds, which rupture during stretching to dissipate energy and recover after release, leading to superior notch insensitiveness and recoverability. The SPUEs restore their mechanical robustness after self-healing at room temperature and the self-healing efficiency can be dramatically accelerated by surface wetting.

Healable, Recyclable, and Mechanically Tough Polyurethane Elastomers with Exceptional Damage Tolerance

There is a huge requirement of elastomers for use in tires, seals, and shock absorbers every year worldwide. In view of a sustainable society, the next generation of elastomers is expected to combine outstanding healing, recycling, and damage-tolerant capacities with high strength, elasticity, and toughness. However, it remains challenging to fabricate such elastomers because the mechanisms for the properties mentioned above are mutually exclusive. Herein, the fabrication of healable, recyclable, and mechanically tough polyurethane (PU) elastomers with outstanding damage tolerance by coordination of multiblock polymers of poly(dimethylsiloxane) (PDMS)/polycaprolactone (PCL) containing hydrogen and coordination bonding motifs with Zn²⁺ ions is reported. The organization of bipyridine groups coordinated with Zn²⁺ ions, carbamate groups cross-linked with hydrogen bonds, and crystallized PCL segments generates phase-separated dynamic hierarchical domains. Serving as rigid nanofillers capable of deformation and disintegration under an external force, the dynamic hierarchical domains can strengthen the elastomers and significantly enhance their toughness and fracture energy. As a result, the elastomers exhibit a tensile strength of ≈52.4 MPa, a toughness of ≈363.8 MJ m^-3 , and an exceptional fracture energy of ≈192.9 kJ m^-2 . Furthermore, the elastomers can be conveniently healed and recycled to regain their original mechanical properties and integrity under heating.

Basic Approaches to the Design of Intrinsic Self-Healing Polymers for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) as a revolutionary system for harvesting mechanical energy have demonstrated high vitality and great advantage, which open up great prospects for their application in various areas of the society of the future. The past few years have seen exponential growth in many new classes of self-healing polymers (SHPs) for TENGs. This review presents and evaluates the SHP range for TENGs, and also attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Among the most widely used SHPs for TENGs, the analysis of non-covalent (hydrogen bond, metal-ligand bond), covalent (imine bond, disulfide bond, borate bond) and multiple bond-based SHPs in TENGs has been performed. Particular attention is paid to the use of SHPs with shape memory as components of TENGs. Finally, the problems and prospects for the development of SHPs for TENGs are outlined.

A Dielectric Elastomer Actuator That Can Self-Heal Integrally

Dielectric actuators are prone to be worn or partially damaged when operating at high electric fields. The introduction of self-healing features into dielectric actuators is favorable for extending its life span and security. Although many attempts have been made to produce self-healing dielectric actuators, most of them focus on the healing of either the electrodes or the dielectric layers. A dielectric actuator that exhibits integral self-healing is still unprecedented. Meanwhile, realizing integral self-healing in dielectric actuator is highly challenging because both the electrode and the dielectric layer need to be healed while the interface between the electrode and the dielectric layer should remain unaffected during the healing process. In this paper, we synthesized self-healing polydimethylsiloxane (PDMS) polymers containing different amounts of polyaniline (PANI) (denoted as PDMS-PANI_n, where n represents the weight percentage of PANI) as the dielectric layer and electrode, respectively. PDMS-PANI_2.5 polymer exhibits good dielectric properties (ε = 11.11 at 50 Hz) and was used as the dielectric layer, while PDMS-PANI₂₀ polymer having a high conductivity of 4.5 × 10^-5 S/cm was used as the electrode. As both of them have excellent self-healing ability and are compatible and diffusible to each other, the entire actuator device can still cause actuated strain after cutting and healing at room temperature for 48 h. Our strategy for realizing integral self-healing of actuator is also applicable to other electronic devices.

Extremely Tough, Puncture-Resistant, Transparent, and Photoluminescent Polyurethane Elastomers for Crack Self-Diagnose and Healing Tracking

Ensuring material performance reliability and lifetime is crucial for practical operations. Small cracks on the material surface are often detrimental to its safe operation. This study describes the development of a hydrogen bond-rich puncture-resistant polyurethane elastomer with supertoughness. The as-prepared polyurethane transparent films feature high tensile break strength (57.4 MPa) and great toughness (228 MJ m^-3). Additionally, a facile, low-cost, crack self-diagnostic approach through photoluminescence using a small luminous pen is reported. The materials efficiently achieved self-healing at 90 °C after the crack formation. The change of fluorescence intensity on the crack can be used to track the self-healing process. Therefore, this work provides a guideline for the material design of supertough, puncture-resistant, transparent, and healable elastomers and a crack self-diagnosis and healing approach.

Remalleable, Healable, and Highly Sustainable Supramolecular Polymeric Materials Combining Superhigh Strength and Ultrahigh Toughness

To build a sustainable society, it is of significant importance but highly challenging to develop remalleable, healable, and biodegradable polymeric materials with integrated high strength and high toughness. Here, we report a superstrong and ultratough sustainable supramolecular polymeric material with a toughness of ca. 282.3 J g^-1 (395.2 MJ m^-3) in combination with a tensile strength as high as ca. 104.2 MPa and a Young's modulus of ca. 3.53 GPa. The toughness is even higher than that of the toughest spider silk (ca. 354 MJ m^-3) ever found in the world, while the material also exhibits a superior tensile strength over most engineering plastics. This material is fabricated by topological confinement of the biodegradable linear polymer of poly(vinyl alcohol) (PVA) via the naturally occurring dendritic molecules of tannic acid (TA) based on high-density hydrogen bonds. Simply blending TA and PVA in aqueous solutions at acidic conditions leads to the formation of TA-PVA complexes as precipitates, which can be processed into dry TA-PVA composite products with desired shapes via the compression molding method. Compared to the conventional solution casting method for the fabrication of PVA-based thin films, the as-developed strategy allows large-scale production of bulk TA-PVA composites. The TA-PVA composites consist of interpenetrating three-dimensional supramolecular TA-PVA clusters. Such a structural feature, revealed by computational simulations, is crucial for the integrated superhigh strength and ultrahigh toughness of the material. The biodegradable TA-PVA composites are remalleable for multiple generations of recycling and healable after break, at room temperature, by the assistance of water to activate the reversibility of the hydrogen bonds. The TA-PVA composites show high promise as sustainable substitutes for conventional plastics because of their remalleability, healability, and biodegradability. The integrated superhigh strength and ultrahigh toughness of the TA-PVA composites ensure their high reliability and broad applicability.

Preparation, characterization and properties of intrinsic self-healing elastomers

Significant advances have been made in the development of self-healing synthetic polymer materials in recent years. This review article discusses the recent progress in preparation, characterization and properties of different kinds of intrinsic self-healing elastomers based on reversible covalent bonds and dynamic supramolecular chemistry. Healing conditions, mechanical property recovery and healing efficiency are the main discussion topics. Potential applications, challenges and future prospects in self-healing elastomer fields are also discussed in the last part of this review.

Water-Enabled Room-Temperature Self-Healing and Recyclable Polyurea Materials with Super-Strong Strength, Toughness, and Large Stretchability

The synthesis of polymeric materials that simultaneously possess multiple excellent mechanical properties and high-efficient self-healability at room temperature is always a huge challenge. Here, we report the synthesis of a transparent polyurea material that can self-heal at room temperature with the aid of water and, meanwhile, has multiple remarkable mechanical performances, including super-high strength, excellent toughness, and large stretchability. Thanks to the synergistic enhancement of both dynamic imine bonds and hierarchical hydrogen bonds within the networks, the resulting polyureas have a world-record tensile strength of 41.2 MPa when compared with other polyurethanes that can self-heal at room temperature and, at the same time, a large breaking strain of 823.0% and a superior toughness of 127.2 MJ/m³. Besides the influence of imine bonds, the mechanical properties of the polyureas are also strongly related to the density and strength of the hierarchical hydrogen bonds within the polyurea networks, and these two factors could be finely controlled by adjusting the mass ratio of the soft segments with different chain lengths and the types of diisocyanates used for polyurea synthesis, respectively. More importantly, the highly dynamic characteristic of both imine bonds and hierarchical hydrogen bonds within the polyureas endows the materials with repeated water-enabled room-temperature self-healing capacity with a high healing efficiency of 92.2%. Moreover, the polyureas can also be recycled or remolded under mild conditions by the hot-pressing or dissolution/casting process. The synthesized polyureas also show great potential in damping applications with a loss factor larger than 0.3 over the temperature range from 12 to 75 °C. It is believed that polyureas with super-high and well-tunable mechanical properties and high-efficient room-temperature self-healing ability have great potential to substitute traditional irreparable polymers in diverse practical applications.

Highly Stretchable and Fast Self-Healing Luminescent Materials

Nowadays, the flourishing exploitation of multifunction luminescent materials with fast self-healing and superior mechanical features greatly broadens the scope for wide applications in optical and display devices, but this is still a formidably challenging task. Herein, we realize color-tunable luminescent materials functionalized with lanthanide ions (Ln³⁺) and terpyridine ligand coordination complexes that show highly stretchable and rapid self-healing performance, simultaneously broadening their application prospects both optically and mechanically. The multiple color emission, including visible and near-infrared luminescence, can be achieved by energy transfer from the coordinating terpyridine unit to Ln³⁺ via the so-called "antenna effect". The dynamic Ln-N coordination exhibits extreme stretchability and fast self-healing under ambient conditions. Of particular interest is that the healing process is not significantly affected by surface aging and atmospheric moisture. The multifunction materials open up a new pathway for future development of the next-generation wearable electronics including flexible and self-healable conductors.

Tough Ordered Mesoporous Elastomeric Biomaterials Formed at Ambient Conditions

Synthetic dry elastomers are randomly cross-linked polymeric networks with isotropic and unordered higher-level structural features. However, their growing use as soft-tissue biomaterials has demanded the need for an ordered and anisotropic nano-micro (or) mesoarchitecture, which is crucial for imparting specific properties such as hierarchical toughening, anisotropic mechanics, sustained drug delivery, and directed tissue growth. High processing cost, poor control in 3D, and compromised mechanical properties have made it difficult to synthesize tough and dry macroscopic elastomers with well-organized nano-microstructures. Inspired from biological design principles, we report a tough ordered mesoporous elastomer formed via bottom-up lyotropic self-assembly of noncytotoxic, polymerizable amphiphilic triblock copolymers and hydrophobic polymers. The elastomer is cross-linked using covalent cross-links and physical hydrophobic entanglements that are organized in a periodic manner at the nanoscale. This transforms into a well-ordered hexagonal arrangement of nanofibrils that are highly oriented at the micron scale, further organized as 3D macroscale objects. The ordered nano-microstructure and molecular multinetwork endows the elastomer with hierarchical toughening while possessing excellent stiffness and elongation comparable to engineering elastomers like silicone and vulcanized rubber. Processing of the elastomer is performed at ambient conditions using 3D printing and photo-cross-linking, which is fast and energy efficient and enables production of complex 3D objects with tailorable sub-millimeter features such as macroporosity. Furthermore, the periodic and amphiphilic nanostructure permits functionalization of the elastomer with secondary components such as inorganic nanoparticles or drug molecules, enabling complementary mechanical properties such as high stiffness and functional capabilities such as in localized drug delivery applications.

Self-healing and shape memory metallopolymers: state-of-the-art and future perspectives

Recent achievements and problems associated with the use of metallopolymers as self-healing and shape memory materials are presented and evaluated.

A self-healing polyurethane elastomer with excellent mechanical properties based on phase-locked dynamic imine bonds

The rigidity and the dynamic nature of the CN double bond ensure the effectiveness of the phase-locking strategy for robust self-healing materials.

Scalable Spider-Silk-Like Supertough Fibers using a Pseudoprotein Polymer

Spider silks are tougher than almost all other materials in the world and thus are considered ideal materials by scientists and the industry. Although there have been tremendous attempts to prepare fibers from genetically engineered spider-silk proteins, it is still a very large challenge to artificially produce materials with a very high fracture energy, not to mention the high scaling-up requirements because of the extremely low productivity and high cost levels. Here, a facile spider-silk-mimicking strategy is first reported for preparing scalable supertough fibers using the chemical synthesis route. Supertoughness (≈387 MJ m^-3 ), more than twice the reported value of common spider dragline silk and comparable to the value of the toughest spider silk, the aciniform silk of Argiope trifasciata, is achieved by introducing β-sheet crystals and α-helical peptides simultaneously in a pseudoprotein polymer. The process opens up a very promising avenue for obtaining excellent spider fibers.