Recent Advances in Wearable Healthcare Devices: From Material to Application

In recent years, the proliferation of wearable healthcare devices has marked a revolutionary shift in the personal health monitoring and management paradigm. These devices, ranging from fitness trackers to advanced biosensors, have not only made healthcare more accessible, but have also transformed the way individuals engage with their health data. By continuously monitoring health signs, from physical-based to biochemical-based such as heart rate and blood glucose levels, wearable technology offers insights into human health, enabling a proactive rather than a reactive approach to healthcare. This shift towards personalized health monitoring empowers individuals with the knowledge and tools to make informed decisions about their lifestyle and medical care, potentially leading to the earlier detection of health issues and more tailored treatment plans. This review presents the fabrication methods of flexible wearable healthcare devices and their applications in medical care. The potential challenges and future prospectives are also discussed.

Environment Endurable, Self-Healing, Super-Adhesive, and Mechanically Strong Ionogels for Reliable Sensing

Ionogels possess high conductivity, stretchability, and adhesion, making them promising as flexible sensors. However, it remains challenging to fabricate an ionogel which integrates excellent environment endurance, superior mechanical strength, high self-healing efficiency, and super adhesion. Herein, a supramolecular ionic liquid is synthesized using calcium chloride and 1-butyl-3-methylimidazolium chloride. An advanced ionogel based on this supramolecular ionic liquid is conveniently constructed by a one-pot method with acrylamide and acrylic acid as monomers. The supramolecular cross-linking network, formed by affluent coordination interactions, hydrogen bonds, and electrostatic interactions, provides the ionogel with ideal mechanical strength (tensile strength up to 1.7 MPa), high self-healing efficiency (up to 149%), super adhesion (up to 358 kPa on aluminum), excellent solvent tolerance (less than 10% weight increase, high mechanical and sensing performance retention after being soaked in organic solvents), and low-temperature endurance (breaking elongation can reach 87% at -30 °C). The supramolecular ionogels can function as multi-mode sensors, capable of monitoring strain and different amplitudes of human movements in real-time. Moreover, the sensing performance of ionogels remains unaffected even after being self-healed or exposure to organic solvents. It is expected that this study could offer valuable design ideas to construct advanced gel materials applicable in complicated environment.

Healable Ionic Conductors with Extremely Low-Hysteresis and High Mechanical Strength Enabled by Hydrophobic Domain-Locked Reversible Interactions

Extremely low hysteresis, high mechanical strength, superior toughness, and excellent healability are essential for stretchable ionic conductors to enhance their reliability and meet for cutting-edge applications. However, the fabrication of stretchable ionic conductors with such mutually exclusive properties remains challenging. Herein, extremely low-hysteresis and healable ionic conductors with a tensile strength of ≈8.9 MPa and toughness of ≈23.2 MJ m-3 are fabricated through the complexation of 4-carboxybenzaldehyde (CBA) grafted poly(vinyl alcohol) (PVA) (denoted as PVA-CBA) and poly (allylamine hydrochloride) (PAH) followed by acidification and ion-loading steps. The acidification step generates the PVA-CBA/PAH ionic conductors with in situ formed dynamic hydrophobic domains that lock and stabilize noncovalent interactions. This significantly minimizes the energy dissipation of the ionic conductors during cyclic mechanical loading (≤200% strain), resulting in ionic conductors with extremely low hysteresis (≈5%). The fractured ionic conductors can be healed at 60 °C to restore their original properties. Because of the extremely low hysteresis, the PVA-CBA/PAH ionic conductors show a highly stable and reproducible electrical response over 5000 uninterrupted loading-unloading cycles at a strain of 200%. The ionic conductor based sensors exhibit a high sensitivity to a wide range of strains (1-500%).

Multi-stimulus Response Behavior of Biomimetic Autocrine Waxy Materials for Potential Self-Constructing Surface Microstructures

Many functions of terrestrial plant leaves rely on the regenerable epidermal wax layer. Biomimetic autocrine waxy materials (AWMs) inspired by renewable epidermal waxes are attracting increasing attention. However, the growth properties of the wax layer remain unclear, limiting the development of this promising material. This work focuses on the stimulated growth characteristics and microstructural regulation methods of the waxy layers. It is found that the wax layers exhibit a corresponding behavior of changing their surface micromorphology under force, heat, solvents, and other stimuli during the self-growth process, and as a result of which, various types of fine surface microstructures such as grids, rings, stripes, pattern copying, and printing can be self-built on their surfaces. The composition of the surface autocrine wax layer changes with the autocrine time, and this finding may be useful for the separation and purification of alkane mixtures. In addition, the surface wax layer possesses the ability to self-heal and strengthen itself at the damage site after being stimulated by injury, similar to the damage-response behavior of a bark surface. Such multi-stimulus response behavior described here provides a platform for the discovery of more functional materials and microstructural self-construction techniques and can also serve as a basis for their applications.

An Ultrahighly Stretchable and Recyclable Starch-Based Gel with Multiple Functions

With the development of various gel-based flexible sensors, novel gels with multiple integrated and efficient properties, particularly recyclability, have been developed. Herein, a starch-based ADM (amylopectin (AP)-poly(3-[dimethyl-[2-(2-methylprop-2- enoyloxy)ethyl]azaniumyl]propane-1-sulfonate) (PDMAPS)-MXene) gel is prepared by a facile "cooking" strategy accompanying the gelatinization of AP and polymerization reaction of zwitterionic monomers. Reversible crosslinking in the gel occurs through hydrogen bonding and electrostatic interactions. The ADM gel exhibits high stretchability (≈2700%, after one month), swift self-healing performance, self-adhesive properties, favorable freezing resistance, and satisfactory moisturizing properties (≥30 days). Interestingly, the ADM gel can be recycled and reused by a "kneading" method and "dissolution-dialysis" process, respectively. Furthermore, the ADM gel can be assembled as a strain sensor with a broad working strain range (≈800%) and quick response time (response time 211 ms and recovery time 253 ms, under 10% strain) to detect various macro- and micro-human-motions, even under harsh conditions such as pronunciation and handwriting. The ADM gel can also be used as a humidity sensor to investigate humidity and human respiratory status, suggesting its practical application in personal health management. This study provides a novel strategy for the preparation of high-performance recycled gels and flexible sensors.

Synthesis of Self-healing and Light-, Thermal-, and Humidity-induced Deformative Polyurethane Actuator

Intelligent actuating materials have drawn enormous attention because of their potential applications in soft robots, smart sensors, bionics, etc. Aiming to integrate light, thermal, and humidity stimuli deformations and self-healing function into a single polymer, a smart actuating polyurethane material CPPU-50 is designed and successfully synthesized through co-polymerization of azobenzene-containing Azo-C12 , polyethylene glycol 200 (PEG200), and 4,4'-diphenylmethane diisocyanate (MDI) at a ratio of 1:1:2. The obtained polyurethane CPPU-50 exhibits good photoinduced bending, thermal responsive shape memory effect, humidity triggered deflections and self-healing properties. Furthermore, an actuator combining light and thermal stimuli is created and the self-healing CPPU-50 film can withstand the object of 1800 times without tearing. This work can pave a way for further development of long-lived multi-stimuli-responsive actuating devices and intelligent materials.

Molecular Dynamics Simulation of Polymer Nanocomposites with Supramolecular Network Constructed via Functionalized Polymer End-Grafted Nanoparticles

Since the proposal of self-healing materials, numerous researchers have focused on exploring their potential applications in flexible sensors, bionic robots, satellites, etc. However, there have been few studies on the relationship between the morphology of the dynamic crosslink network and the comprehensive properties of self-healing polymer nanocomposites (PNCs). In this study, we designed a series of modified nanoparticles with different sphericity (η) to establish a supramolecular network, which provide the self-healing ability to PNCs. We analyzed the relationship between the morphology of the supramolecular network and the mechanical performance and self-healing behavior. We observed that as η increased, the distribution of the supramolecular network became more uniform in most cases. Examination of the segment dynamics of polymer chains showed that the completeness of the supramolecular network significantly hindered the mobility of polymer matrix chains. The mechanical performance and self-healing behavior of the PNCs showed that the supramolecular network mainly contributed to the mechanical performance, while the self-healing efficiency was dominated by the variation of η. We observed that appropriate grafting density is the proper way to effectively enhance the mechanical and self-healing performance of PNCs. This study provides a unique guideline for designing and fabricating self-healing PNCs with modified Nanoparticles (NPs).

Repair mechanism and application of self-healing materials for food preservation

The traditional packaging concept has reached its limits when it comes to ensuring the quality of food and extending its shelf life. Compared to traditional packaging materials, food packaging with self-healing function is becoming more and more popular. This is because they can automatically repair the damaged area, restore the original properties and prevent the decline of food quality and loss of nutrients. Materials based on various self-healing mechanisms have been developed and used on a laboratory scale in the form of coatings and films for food packaging. However, more efforts are needed for the commercial application of these new self-healing packaging materials. Understanding the self-healing mechanism of these packaging materials is very important for their commercial application. This article first discusses the self-healing mechanism of different packaging materials and compares the self-healing efficiency of self-healing materials under different conditions. Then, the application potential of self-healing coatings and films in the food industry is systematically analyzed. Finally, we give an outlook on the application of self-healing materials in the field of food packaging.

Complexation of Sulfonate-Containing Polyurethane and Polyacrylic Acid Enables Fabrication of Self-Healing Hydrogel Membranes with High Mechanical Strength and Excellent Elasticity

Artificial hydrogel membranes with good biocompatibility are strongly needed in biological fields. The preparation of biocompatible hydrogel membranes simultaneously possessing high mechanical strength, excellent elasticity, and satisfactory self-healing properties remains a challenge. Herein, we demonstrate the preparation of such hydrogel membranes by complexation of sulfonate-containing polyurethane (SPU) and poly(acrylic acid) (PAA) in the presence of Zn²⁺ ions followed by swelling in water (denoted as SPU-PAA/Zn). Originating from the synergy of the coordination and hydrogen-bonding interactions and the reinforcement effect of the in situ formed hydrophobic domains, the SPU-PAA/Zn hydrogel membrane exhibits a high tensile strength of ∼7.1 MPa and a toughness of ∼30.4 MJ m^-3. Moreover, the hydrogel membrane is highly elastic, which can restore to its initial state from an ∼500% strain within 40 min rest at room temperature without any external assistance. The dynamic noncovalent interactions and hydrophobic domains allow the fractured hydrogel membrane to heal and completely regain its original integrity and mechanical properties at room temperature. Both in vitro and in vivo tests confirm that the hydrogel membrane exhibits satisfactory biocompatibility and could be potentially used as a biological barrier membrane in surgical operations or artificial organs.

Self-Adhesive Self-Healing Thermochromic Ionogels for Smart Windows with Excellent Environmental and Mechanical Stability, Solar Modulation, and Antifogging Capabilities

Current thermochromic materials used in smart windows still face challenges, such as poor mechanical and environmental stability, unsatisfactory solar modulation capacity, and low transparency. Herein, the first self-adhesive self-healing thermochromic ionogels with excellent mechanical and environmental stability, antifogging capability, transparency, and solar modulation capability by loading binary ionic liquids (ILs) into rational-designed self-healing poly(urethaneurea) with acylsemicarbazide (ASCZ) moieties that have reversible and multiple hydrogen bonds are reported and their feasibility as smart windows with reliability and long service life is demonstrated. The self-healing thermochromic ionogels can switch between transparent and opaque without leakage or shrinkage, by the constrained reversible phase separation of ILs within the ionogels. The ionogels have the highest transparency and solar modulation capability among reported thermochromic materials and such excellent solar modulation capability can be well maintained after undergoing 1000 transitions, stretches, and bends, and storage at -30 °C, 60 °C, 90% RH, and vacuum environment for 2 months. The formation of high-density hydrogen bonds among the ASCZ moieties contributes to the excellent mechanical strength of the ionogels and allows the thermochromic ionogels to spontaneously heal their damages and be fully recycled at room temperature without the loss of thermochromic capabilities.

Highly Elastic, Healable, and Durable Anhydrous High-Temperature Proton Exchange Membranes Cross-Linked with Highly Dense Hydrogen Bonds

Proton exchange membranes (PEMs) with excellent durability and working stability are important for PEM fuel cells with extended service life and enhanced reliability. In this study, highly elastic, healable, and durable electrolyte membranes are fabricated by the complexation of poly(urea-urethane), ionic liquids (ILs), and MXene nanosheets (denoted as PU-IL-MX). The resulting PU-IL-MX electrolyte membranes have a tensile strength of ≈3.86 MPa and a strain at break of ≈281.89%. The PU-IL-MX electrolyte membranes can act as high temperature PEMs to conduct protons under an anhydrous condition of the temperatures above 100 °C. Importantly, the ultrahigh density of hydrogen-bond-cross-linked network renders PU-IL-MX membranes excellent IL retention properties. The membranes can maintain more than ≈98% of their original weight and show no decline of proton conductivity after being placed under highly humid conditions of ≈80 °C and relative humidity of ≈85% for 10 days. Moreover, due to the reversibility of hydrogen bonds, the membranes can heal damage under the working conditions of fuel cells to restore their original mechanical properties, proton conductivities, and cell performances.

Self-Healing of Polymers and Polymer Composites

This review is devoted to the description of methods for the self-healing of polymers, polymer composites, and coatings. The self-healing of damages that occur during the operation of the corresponding structures makes it possible to extend the service life of the latter, and in this case, the problem of saving non-renewable resources is simultaneously solved. Two strategies are considered: (a) creating reversible crosslinks in the thermoplastic and (b) introducing a healing agent into cracks. Bond exchange reactions in network polymers (a) proceed as a dissociative process, in which crosslinks are split into their constituent reactive fragments with subsequent regeneration, or as an associative process, the limiting stage of which is the interaction of the reactive end group and the crosslink. The latter process is implemented in vitrimers. Strategy (b) is associated with the use of containers (hollow glass fibers, capsules, microvessels) that burst under the action of a crack. Particular attention is paid to self-healing processes in metallopolymer systems.

A Review of Lightweight Self-Healing Concrete

Cementitious composites often crack because of their low tensile strength. The ability of self-healing cementitious composite to automatically repair cracks has attracted widespread attention. Lightweight aggregate (LWA) has a low density and a high porosity which can provide storage space for a healing agent. The healing mechanisms and healing compositions of lightweight self-healing concrete (LWSHC) have been summarized in this research. The workability, compressive strength, crack repairing, and durability of LWSHC performance is also illustrated. A LWA with interconnected pores and a high strength should be integrated into LWSHC to increase the crack closure rate and mechanical properties. Expanded perlite is the most suitable LWA carrier for bioremediation. The chemical healing agents are better than the biological healing agents at present since the biological healing agents have more negative effects. A sodium silicate solution is a good choice as a chemical healing agent. Vacuum conditions, high-temperature processing, and the use of coating technologies on LWAs can improve the healing effect of LWSHC. The addition of fibers also enhance the self-healing ability of LWSHC. Further, the use of numerical simulation supports the healing performance of LWSHC. The goal of this research is to investigate the most appropriate component of LWSHC to ensure a high crack closure rate, strength healing ratio, and great durability while being lightweight. It can then be adopted in high-rise and large-span concrete structures to extend the service life.

Tough, Self-Healing, and Conductive Elastomer ─Ionic PEGgel

Ionically conductive elastomers are necessary for realizing human-machine interfaces, bioelectronic applications, or durable wearable sensors. Current design strategies, however, often suffer from solvent leakage and evaporation, or from poor mechanical properties. Here, we report a strategy to fabricate ionic elastomers (IHPs) demonstrating high conductivity (0.04 S m-1), excellent electrochemical stability (>60,000 cycles), ultra-stretchability (up to 1400%), high toughness (7.16 MJ m-3), and fast self-healing properties, enabling the restoration of ionic conductivity within seconds, as well as no solvent leakage. The ionic elastomer is composed of in situ formed physically cross-linked poly(2-hydroxyethyl methacrylate) networks and poly(ethylene glycol) (PEG). The long molecular chains of PEG serve as a solvent for dissolving electrolytes, improve its long-term stability, reduce solvent leakage, and ensure the outstanding mechanical properties of the IHP. Surprisingly, the incorporation of ions into PEG simultaneously enhances the strength and toughness of the elastomer. The strengthening and toughening mechanisms were further revealed by molecular simulation. We demonstrate an application of the IHPs as (a) flexible sensors for strain or temperature sensing, (b) skin electrodes for recording electrocardiograms, and (c) a tough and sensing material for pneumatic artificial muscles. The proposed strategy is simple and easily scalable and can further inspire the design of novel ionic elastomers for ionotronics applications.

The Final Frontier of Sustainable Materials: Current Developments in Self-Healing Elastomers

It is impossible to describe the recent progress of our society without considering the role of polymers; however, for a broad audience, "polymer" is usually related to environmental pollution. The poor disposal and management of polymeric waste has led to an important environmental crisis, and, within polymers, plastics have attracted bad press despite being easily reprocessable. Nonetheless, there is a group of polymeric materials that is particularly more complex to reprocess, rubbers. These macromolecules are formed by irreversible crosslinked networks that give them their characteristic elastic behavior, but at the same time avoid their reprocessing. Conferring them a self-healing capacity stands out as a decisive approach for overcoming this limitation. By this mean, rubbers would be able to repair or restore their damage automatically, autonomously, or by applying an external stimulus, increasing their lifetime, and making them compatible with the circular economy model. Spain is a reference country in the implementation of this strategy in rubbery materials, achieving successful self-healable elastomers with high healing efficiency and outstanding mechanical performance. This article presents an exhaustive summary of the developments reported in the previous 10 years, which demonstrates that this property is the last frontier in search of truly sustainable materials.

Self-Healable and Stretchable Ionic-Liquid-Based Thermoelectric Composites with High Ionic Seebeck Coefficient

The advancement of wearable electronics, particularly self-powered wearable electronic devices, necessitates the development of efficient energy conversion technologies with flexible mechanical properties. Recently, ionic thermoelectric (TE) materials have attracted great attention because of their enormous thermopower, which can operate capacitors or supercapacitors by harvesting low-grade heat. This study presents self-healable, stretchable, and flexible ionic TE composites comprising an ionic liquid (IL), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM:OTf); a polymer matrix, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP); and a fluoro-surfactant (FS). The self-healability of the IL-based composites originates from dynamic ion-dipole interactions between the IL, the PVDF-HFP, and the FS. The composites demonstrate excellent ionic TE properties with an ionic Seebeck coefficient (S_i ) of ≈38.3 mV K^-1 and an ionic figure of merit of ZT_i  = 2.34 at 90% relative humidity, which are higher than the values reported for other IL-based TE materials. The IL-based ionic TE composites developed in this study can maintain excellent ionic TE properties under harsh conditions, including severe strain (75%) and multiple cutting-healing cycles.

Highly Transparent and Self-Healable Solar Thermal Anti-/Deicing Surfaces: When Ultrathin MXene Multilayers Marry a Solid Slippery Self-Cleaning Coating

Solar anti-/deicing can solve icing problems by converting sunlight into heat. One of the biggest problems, which has long been plaguing the design of solar anti-/deicing surfaces, is that photothermal materials are always lightproof and appear black, because of the mutual exclusiveness between generating heat and retaining transparency. Herein, a highly transparent and scalable solar anti-/deicing surface is reported, which enables the coated glass to exhibit high transparency (>77% transmittance at 550 nm) and meanwhile causes a >30 °C surface temperature increase relative to the ambient environment under 1.0 sun illumination. Such a transparent anti-/deicing surface can be fabricated onto a large class of substrates (e.g., glass, ceramics, metals, plastics), by applying a solid omniphobic slippery coating onto layer-by-layer-assembled ultrathin MXene multilayers. Hence, the surface possesses a self-cleaning ability to shed waterborne and oil-based liquids thanks to residue-free slipping motion. Passive anti-icing and active deicing capabilities are, respectively, obtained on the solar thermal surface, which effectively prevents water from freezing and simultaneously melts pre-formed ice and thick frost. The self-cleaning effect enables residue-free removal of unfrozen water and interfacially melted ice/frost to boost the anti-/deicing efficiency. Importantly, the surface is capable of self-healing under illumination to repair physical damage and chemical degradation.

Tough, Transparent, 3D-Printable, and Self-Healing Poly(ethylene glycol)-Gel (PEGgel)

Polymer gels, such as hydrogels, have been widely used in biomedical applications, flexible electronics, and soft machines. Polymer network design and its contribution to the performance of gels has been extensively studied. In this study, the critical influence of the solvent nature on the mechanical properties and performance of soft polymer gels is demonstrated. A polymer gel platform based on poly(ethylene glycol) (PEG) as solvent is reported (PEGgel). Compared to the corresponding hydrogel or ethylene glycol gel, the PEGgel with physically cross-linked poly(hydroxyethyl methacrylate-co-acrylic acid) demonstrates high stretchability and toughness, rapid self-healing, and long-term stability. Depending on the molecular weight and fraction of PEG, the tensile strength of the PEGgels varies from 0.22 to 41.3 MPa, fracture strain from 12% to 4336%, modulus from 0.08 to 352 MPa, and toughness from 2.89 to 56.23 MJ m^-3 . Finally, rapid self-healing of the PEGgel is demonstrated and a self-healing pneumatic actuator is fabricated by 3D-printing. The enhanced mechanical properties of the PEGgel system may be extended to other polymer networks (both chemically and physically cross-linked). Such a simple 3D-printable, self-healing, and tough soft material holds promise for broad applications in wearable electronics, soft actuators and robotics.

Self-Healing Materials for Electronics Applications

Self-healing materials have been attracting the attention of the scientists over the past few decades because of their effectiveness in detecting damage and their autonomic healing response. Self-healing materials are an evolving and intriguing field of study that could lead to a substantial increase in the lifespan of materials, improve the reliability of materials, increase product safety, and lower product replacement costs. Within the past few years, various autonomic and non-autonomic self-healing systems have been developed using various approaches for a variety of applications. The inclusion of appropriate functionalities into these materials by various chemistries has enhanced their repair mechanisms activated by crack formation. This review article summarizes various self-healing techniques that are currently being explored and the associated chemistries that are involved in the preparation of self-healing composite materials. This paper further surveys the electronic applications of self-healing materials in the fields of energy harvesting devices, energy storage devices, and sensors. We expect this article to provide the reader with a far deeper understanding of self-healing materials and their healing mechanisms in various electronics applications.

Highly Stiff and Stretchable DNA Liquid Crystalline Organogels with Super Plasticity, Ultrafast Self-Healing, and Magnetic Response Behaviors

DNA-based gels are attractive materials as they allow intuitive rational design, respond to external physicochemical stimuli, and show great potential for biomedical applications. However, their relatively poor mechanical properties currently limit their technological application considerably as the latter requires mechanical integrity and tunability. With this work, a DNA organogel is reported that gels through supramolecular interactions, which induce mesophase ordering, and that exhibits exceptional stretchability, deformability, plasticity, and biocompatibility. Moreover, the nature of the supramolecular bond enables complete self-healing within 3 s. Most importantly, the DNA-based liquid crystalline organogels exhibit impressive ultimate tensile strengths above 1 MPa, stiffness higher than 20 MPa, and toughness up to 18 MJ m^-3 , rendering these materials the strongest among reported DNA networks. In addition, the facile access is demonstrated to composite DNA materials by blending magnetic nanoparticles with the organogel matrix giving access to magnetic field induced actuation. It is believed that these findings contribute significantly to the advancement of DNA gels for their use in smart materials and biomedical applications.

Terpolymerization of Ethylene and Two Different Methoxyaryl-Substituted Propylenes by Scandium Catalyst Makes Tough and Fast Self-Healing Elastomers

The terpolymerization of a non-polar olefin (such as ethylene) and two different polar functional olefins in a controlled fashion is of great interest and importance but has hardly been explored to date. We report for the first time the terpolymerization of ethylene (E) and two different methoxyaryl-substituted propylenes (A^R1 P=hexylanisyl propylene; A^R2 P=methoxynaphthyl propylene or methoxypyrenyl propylene) by a half-sandwich scandium catalyst. The terpolymerization took place in a sequence-controlled fashion, affording unique multi-block copolymers composed of two different ethylene-alt-methoxyarylpropylene sequences E-alt-A^R1 P (soft segments) and E-alt-A^R2 P (hard segments) and relatively short ethylene-ethylene (EE) blocks (crystalline segments). The terpolymers exhibited excellent elasticity and unprecedented self-healing as a result of microphase separation of nanodomains of the crystalline EE segments and the hard amorphous E-alt-A^R2 P segments from a very flexible E-alt-A^R1 P matrix, demonstrating unique synergy of the three different components.

A Transparent, Highly Stretchable, Solvent-Resistant, Recyclable Multifunctional Ionogel with Underwater Self-Healing and Adhesion for Reliable Strain Sensors

Ionogels have gained increasing attentions as a flexible conductive material. However, it remains a big challenge to integrate multiple functions into one gel that can be widely applied in various complex scenes. Herein, a kind of multifunctional ionogels with a combination of desirable properties, including transparency, high stretchability, solvent and temperature resistance, recyclability, high conductivity, underwater self-healing ability, and underwater adhesiveness is reported. The ionogels are prepared via one-step photoinitiated polymerization of 2,2,2-trifluoroethyl acrylate and acrylamide in a hydrophobic ionic liquid. The abundant noncovalent interactions including hydrogen bonding and ion-dipole interactions endow the ionogels with excellent mechanical strength, resilience, and rapid self-healing capability at room temperature, while the fluorine-rich polymeric matrix brings in high tolerance against water and various organic solvents, as well as tough underwater adhesion on different substrates. Wearable strain sensors based on the ionogels can sensitively detect and differentiate large body motions, such as bending of limbs, walking and jumping, as well as subtle muscle movements, such as pronunciation and pulse. It is believed that the designed ionogels will show great promises in wearable devices and ionotronics.

Acid-Resistance and Self-Repairing Supramolecular Nanoparticle Membranes via Hydrogen-Bonding for Sustainable Molecules Separation

Functional membranes generally wear out when applying in harsh conditions such as a strong acidic environment. In this work, high acid-resistance, long-lasting, and low-cost functional membranes are prepared from engineered hydrogen-bonding and pH-responsive supramolecular nanoparticle materials. As a proof of concept, the prepared membranes for dehydration of alcohols are utilized. The synthesized membranes have achieved a separation factor of 3000 when changing the feed solution pH from 7 to 1. No previous reports have demonstrated such unprecedentedly high-record separation performance (pervaporation separation index is around 1.1 × 107  g m-2  h-1 ). More importantly, the engineered smart membrane possesses fast self-repairing ability (48 h) that is inherited from the dynamic hydrogen bonds between the hydroxyl groups of polyacrylic acid and carbonyl groups of polyvinylpyrrolidone. To this end, the designed supramolecular materials offer the membrane community a new material type for preparing high acid resistance and long-lasting membranes for harsh environmental cleaning applications.

Healable and Recyclable Elastomers with Record-High Mechanical Robustness, Unprecedented Crack Tolerance, and Superhigh Elastic Restorability

Spider silk is one of the most robust natural materials, which has extremely high strength in combination with great toughness and good elasticity. Inspired by spider silk but beyond it, a healable and recyclable supramolecular elastomer, possessing superhigh true stress at break (1.21 GPa) and ultrahigh toughness (390.2 MJ m^-3 ), which are, respectively, comparable to and ≈2.4 times higher than those of typical spider silk, is developed. The elastomer has the highest tensile strength (ultimate engineering stress, 75.6 MPa) ever recorded for polymeric elastomers, rendering it the strongest and toughest healable elastomer thus far. The hyper-robust elastomer exhibits superb crack tolerance with unprecedentedly high fracture energy (215.2 kJ m^-2 ) that even exceeds that of metals and alloys, and superhigh elastic restorability allowing dimensional recovery from elongation over 12 times. These extraordinary mechanical performances mainly originate from the meticulously engineered hydrogen-bonding segments, consisting of multiple acylsemicarbazide and urethane moieties linked with flexible alicyclic hexatomic spacers. Such hydrogen-bonding segments, incorporated between extensible polymer chains, aggregate to form geometrically confined hydrogen-bond arrays resembling those in spider silk. The hydrogen-bond arrays act as firm but reversible crosslinks and sacrificial bonds for enormous energy dissipation, conferring exceptional mechanical robustness, healability, and recyclability on the elastomer.

Heat- and Light-Responsive Materials Through Pairing Dynamic Thiol-Michael and Coumarin Chemistry

Covalent adaptable networks (CANs) based on the thiol-Michael (TM) linkages can be thermal and pH responsive. Here, a new vinyl-sulfone-based thiol-Michael crosslinker is synthesized and incorporated into acrylate-based CANs to achieve stable materials with dynamic properties. Because of the reversible TM linkages, excellent temperature-responsive re-healing and malleability properties are achieved. In addition, for the first time, a photoresponsive coumarin moiety is incorporated with TM-based CANs to introduce light-mediated reconfigureability and postpolymerization crosslinking. Overall, these materials can be on demand dynamic in response to heat and light but can retain mechanical stability at ambient condition.

Progress and Roadmap for Intelligent Self-Healing Materials in Autonomous Robotics

Robots are increasingly assisting humans in performing various tasks. Like special agents with elite skills, they can venture to distant locations and adverse environments, such as the deep sea and outer space. Micro/nanobots can also act as intrabody agents for healthcare applications. Self-healing materials that can autonomously perform repair functions are useful to address the unpredictability of the environment and the increasing drive toward the autonomous operation. Having self-healable robotic materials can potentially reduce costs, electronic wastes, and improve a robot endowed with such materials longevity. This review aims to serve as a roadmap driven by past advances and inspire future cross-disciplinary research in robotic materials and electronics. By first charting the history of self-healing materials, new avenues are provided to classify the various self-healing materials proposed over several decades. The materials and strategies for self-healing in robotics and stretchable electronics are also reviewed and discussed. It is believed that this article encourages further innovation in this exciting and emerging branch in robotics interfacing with material science and electronics.

Rapid and Local Self-Healing Ability of Polyurethane Nanocomposites Using Photothermal Polydopamine-Coated Graphene Oxide Triggered by Near-Infrared Laser

In this study, we report the self-healing ability of polyurethane (PU) nanocomposites based on the photothermal effect of polydopamine-coated graphene oxide (PDA-rGO). Polydopamine (PDA) was coated on the graphene oxide (GO) surface, while simultaneously reducing GO by the oxidation of dopamine hydrochloride in an alkaline aqueous solution. The PDA-rGO was characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy-energy-dispersive X-ray analysis. PDA-rGO/PU nanocomposites with nanofiller contents of 0.1, 0.5 and 1 wt% were prepared by ex situ mixing method. The photothermal effect of the PDA-rGO in the PU matrix was investigated at 0.1 W/cm2 using an 808 nm near-infrared (NIR) laser. The photothermal properties of the PDA-rGO/PU nanocomposites were superior to those of the GO/PU nanocomposites, owing to an increase in the local surface plasmon resonance effect by coating with PDA. Subsequently, the self-healing efficiency was confirmed by recovering the tensile stress of the damaged nanocomposites using the thermal energy generated by the NIR laser.

Dental Restorative Materials for Elderly Populations

The incidence of dental caries, especially root caries, has risen in elderly populations in recent years. Specialized restorative materials are needed due to the specific site of root caries and the age-related changes in general and oral health in the elderly. Unfortunately, the restorative materials commonly used clinically cannot fully meet the requirements in this population. Specifically, the antibacterial, adhesive, remineralization, mechanical, and anti-aging properties of the materials need to be significantly improved for dental caries in the elderly. This review mainly discusses the strengths and weaknesses of currently available materials, including amalgam, glass ionomer cement, and light-cured composite resin, for root caries. It also reviews the studies on novel anti-caries materials divided into three groups, antimicrobial, remineralization, and self-healing materials, and explores their potential in the clinical use for caries in the elderly. Therefore, specific restorative materials for caries in the elderly, especially for root caries, need to be further developed and applied in clinical practice.

Dually Crosslinked Polymer Networks Incorporating Dynamic Covalent Bonds

Covalent adaptable networks (CANs) are polymeric networks containing covalent crosslinks that are dynamic under specific conditions. In addition to possessing the malleability of thermoplastics and the dimensional stability of thermosets, CANs exhibit a unique combination of physical properties, including adaptability, self-healing, shape-memory, stimuli-responsiveness, and enhanced recyclability. The physical properties and the service conditions (such as temperature, pH, and humidity) of CANs are defined by the nature of their constituent dynamic covalent bonds (DCBs). In response to the increasing demand for more sophisticated and adaptable materials, the scientific community has identified dual dynamic networks (DDNs) as a promising new class of polymeric materials. By combining two (or more) distinct crosslinkers in one system, a material with tailored thermal, rheological, and mechanical properties can be designed. One remarkable ability of DDNs is their capacity to combine dimensional stability, bond dynamicity, and multi-responsiveness. This review aims to give an overview of the advances in the emerging field of DDNs with a special emphasis on their design, structure-property relationships, and applications. This review illustrates how DDNs offer many prospects that single (dynamic) networks cannot provide and highlights the challenges associated with their synthesis and characterization.

Novel Biobased Self-Healing Ionomers Derived from Itaconic Acid Derivates

This article presents novel biobased ionomers featuring self-healing abilities. These smart materials are synthesized from itaconic acid derivates. Large quantities of itaconic acid can be produced from diverse biomass like corn, rice, and others. This study presents a comprehensive investigation of their thermal and mechanical properties via differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and FT-Raman and FT-IR measurements as well as dynamic mechanic analysis. Within all these measurements, different kinds of structure-property relationships could be derived from these measurements. For example, the proportion of ionic groups enormously influences the self-healing efficiency. The investigation of the self-healing abilities reveals healing efficiencies up to 99% in 2 h at 90 °C for the itaconic acid based ionomer with the lowest ionic content.

Polymeric Complex-Based Transparent and Healable Ionogels with High Mechanical Strength and Ionic Conductivity as Reliable Strain Sensors

Transparent and healable ionogels with very high mechanical strength, ionic conductivity, and resilience were fabricated for use as strain sensors with satisfactory reliability. The ionogels were fabricated by casting an aqueous solution of poly(vinyl alcohol) (PVA)-poly(vinylpyrrolidone) (PVP) complexes and 1-ethyl-3-methylimidazolium dicyanamide ([EMIm][DCA]), followed by evaporation of water at room temperature. The use of [EMIm][DCA] endowed the resulting ionogels with ionic conductivity at room temperature as high as 19.7 mS cm^-1. Owing to the synergy between the abundant number of hydrogen bonds between PVA and PVP and the crystallized PVA segments that served as nanofillers, the resulting ionogels had good mechanical properties with a tensile stress of 7.7 MPa, a strain of 821%, and good resilience. In addition, the resulting ionogels showed rapid and repeatable sensing signals over a wide strain range (0.1-400%). This enabled them to detect both vigorous muscle movements, such as walking and jumping, and subtle muscle movements, such as pulse. Moreover, owing to the reversibility of hydrogen bonds, physically damaged mechanical properties, conductivity, and sensing ability of the ionogels could be conveniently healed with the assistance of water.

Mechanically Robust, Elastic, and Healable Ionogels for Highly Sensitive Ultra-Durable Ionic Skins

The fabrication of highly durable skin-mimicking sensors remains challenging because of the unavoidable fatigue and physical damage that sensors are subjected to in practical applications. In this study, ultra-durable ionic skins (I-skins) with excellent healability and high sensitivity are fabricated by impregnating ionic liquids (ILs) into a mechanically robust poly(urea-urethane) (PU) network. The PU network is composed of crystallized poly(ε-caprolactone) and flexible poly(ethylene glycol) that are dynamically cross-linked with hindered urea bonds and hydrogen bonds. Such a design endows the resultant ionogels with high mechanical strength, good elasticity, Young's modulus similar to that of natural skin, and excellent healability. The ionogel-based I-skins exhibit a high sensitivity to a wide range of strains (0.1-300%) and pressures (0.1-20 kPa). Importantly, the I-skins show a highly reproducible electrical response over 10 000 uninterrupted strain cycles. The sensing performance of the I-skins stored in open air for 200 days is almost the same as that of the freshly prepared I-skin. The fractured I-skins can be easily healed by heating at 65 °C that restores their original ultra-durable sensing performance. The long-term durability of the I-skins is attributed to the combination of non-volatility of the ILs, excellent healability, and well-designed mechanical properties.

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.

Mechanically Robust, Self-Healing, Polymer Blends and Polymer/Small Molecule Blend Materials with High Antibacterial Activity

There is a growing demand for antibacterial materials around the world in recent years because they can be used for preventing pathogen infection, which is one of the major threats to human health. However, the mechanical damage of the antibacterial materials may weaken their protective effect since bacteria can invade through the cracks of the material. Therefore, antibacterial materials with self-healing ability, in which the mechanical damage can be spontaneously healed, exhibit better reliability and a longer lifespan. In this article, we prepared a series of low-cost antibacterial polymer blends and polymer/small molecule blend materials with excellent self-healing ability and high mechanical strength by a one-pot reaction under mild conditions. These materials were facilely obtained by blending a tiny amount of commercialized cationic antibacterial chemicals, poly(ethylene imine) (PEI) or cetyltrimethylammonium bromide (CTAB), into a self-healing, mechanically robust polymer, poly(ether-thioureas) (PETU). It can be found that they can effectively kill Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) on their surface. Meanwhile, the distinguished advantages of PETU, including self-healing property, excellent mechanical robustness, recyclability, and transparency, were perfectively maintained. Furthermore, it was shown that their cytotoxicity was satisfactory and their hemolytic activity was insignificant. The above advantages of the blend materials suggested their potential applications in health care, food industry, and environmental hygiene.

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.

Additive Manufacturing for Self-Healing Soft Robots

The field of self-healing soft robots was initiated a few years ago. A healing ability can be integrated in soft robots by manufacturing their soft membranes out of synthetic self-healing polymers, more specifically elastomeric Diels-Alder (DA) networks. As such they can recover completely from macroscopic damage, including scratches, cuts, and ruptures. Before this research, these robots were manufactured using a technique named "shaping-through-folding-and-self-healing." This technique requires extensive manual labor, is relatively slow, and does not allow for complex shapes. In this article, an additive manufacturing methodology, fused filament fabrication, is developed for the thermoreversible DA polymers, and the approach is validated on a soft robotic gripper. The reversibility of their network permits manufacturing these flexible self-healing polymers through reactive printing into the complex shapes required in soft robotics. The degree of freedom in the design of soft robotics that this new manufacturing technique offers is illustrated through the construction of adaptive DHAS gripper fingers, based on the design by FESTO. Being constructed out of self-healing soft flexible polymer, the fingers can recover entirely from large cuts, tears, and punctures. This is highlighted through various damage-heal cycles.

Self-Healable Solid Polymeric Electrolytes for Stable and Flexible Lithium Metal Batteries

The key issue holding back the application of solid polymeric electrolytes in high-energy density lithium metal batteries is the contradictory requirements of high ion conductivity and mechanical stability. In this work, self-healable solid polymeric electrolytes (SHSPEs) with rigid-flexible backbones and high ion conductivity are synthesized by a facile condensation polymerization approach. The all-solid Li metal full batteries based on the SHSPEs possess freely bending flexibility and stable cycling performance as a result of the more disciplined metal Li plating/stripping, which have great implications as long-lifespan energy sources compatible with other wearable devices.

Superhydrophobic Foams with Chemical- and Mechanical-Damage-Healing Abilities Enabled by Self-Healing Polymers

The fabrication of superhydrophobic materials capable of spontaneously healing both chemical and mechanical damages at ambient conditions has been a great challenge but highly desired. In this study, we propose that a self-healing hydrophobic polymer can be used to induce self-healing in a superhydrophobic material. As a demonstration, stable and porous self-healing superhydrophobic foams are fabricated by casting a mixture of healable poly(dimethylsiloxane) (PDMS)-based polyurea, multiwalled carbon nanotubes (MCNTs), and table salt, followed by solvent evaporation and removal of the salt template. The PDMS-based polyurea is able to heal mechanical damage by reforming hydrogen bonds and can also reverse chemical damage through surface reorganization. Thus, the chemically and mechanically damaged foams can spontaneously restore their superhydrophobicity and structural integrity at ambient conditions. Moreover, because of the satisfactory photothermal conversion of MCNTs, the temperature of the self-healing superhydrophobic foams can rapidly reach 60 °C under sunlight, which greatly increases the healing speed and healing efficiency of the foam.

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.

Facile Fabrication of Room-Temperature Self-Healing, Mechanically Robust, Highly Stretchable, and Tough Polymers Using Dual Dynamic Cross-Linked Polymer Complexes

The development of polymeric materials with a combination of excellent mechanical performance and room-temperature self-healing property is still a huge challenge. Here, we report a facile method for the fabrication of dual dynamic cross-linked polymer complexes that simultaneously possess multiple remarkable mechanical properties and room-temperature self-healability by simply mixing polymers that have complementary interactions in solutions. Thanks to the synergistic effects of electrostatic and hydrogen-bonding interactions within their networks, the complexes obtained a superhigh tensile strength of 27.4 MPa and toughness of 110.0 MJ/m³ when compared with other polymers that can self-heal at room temperature. More importantly, the complexes can repair a physical cut in an ∼90% relative humid environment at room temperature with a high healing efficiency of ∼96% because of the dynamic nature of the noncovalent interactions. This method is a simple, low-cost, and widely applicable strategy for the large-scale fabrication of room-temperature self-healing materials that possess superior and controllable mechanical performances.

Self-Healing and Recyclable Hydrogels Reinforced with in Situ-Formed Organic Nanofibrils Exhibit Simultaneously Enhanced Mechanical Strength and Stretchability

In this work, self-healing and recyclable polymer hydrogels with simultaneously enhanced mechanical strength and stretchability are fabricated through the complexation of poly(acrylic acid) (PAA) with complexes of branched poly(ethylenimine) and 1-pyrenybutyric acid (PEI-PYA) to generate PAA/PEI-PYA complexes, which are further molded, dried, and rehydrated. The in situ-formed PYA nanofibrils with aggregated structures during the complexation process enable the simultaneous enhancement of the tensile strength and stretchability of the PAA/PEI-PYA hydrogels. The PAA/PEI-PYA hydrogels have a tensile strength of 1.13 ± 0.04 MPa and stretchability of 2970 ± 154%, which are 2.2 and 2.1 times higher than those of the PAA/PEI hydrogels. Meanwhile, the damaged PAA/PEI-PYA hydrogels can be efficiently healed or recycled at room temperature to regain their original mechanical strength and integrity because the dynamic nature of hydrogen-bonding and electrostatic interactions among PAA, PEI, and PYA endows the hydrogels with excellent healing and recycling capacity. This strategy of using aggregated nanofibrils to simultaneously enhance the tensile strength and stretchability of hydrogels can be extended to PAA/PEI hydrogels reinforced with aggregated nanofibrils of 9-anthracenecarboxylic acid and N,N'-di(propanoic acid)-perylene-3,4,9,10-tetracarboxylic diimide, demonstrating its generality for fabricating hydrogels with enhanced mechanical properties.

Self-Healable Polyelectrolytes with Mechanical Enhancement for Flexible and Durable Supercapacitors

The practical application of advanced personalized electronics is inseparable from flexible, durable, and even self-healable energy storage devices. However, the mechanical and self-healing performance of supercapacitors is still limited at present. Herein, highly transparent, stretchable, and self-healable poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA)/poly(vinyl alcohol) (PVA)/LiCl polyelectrolytes were facilely prepared by one-step radical polymerization. The cooperation of PAMPSA and PVA significantly increased the mechanical and self-healing capacity of the polyelectrolyte, which exhibited superior stretchability of 938 %, stress of 112.68 kPa, good electrical performance (ionic conductivity up to 20.6 mS cm^-1 ), and high healing efficiency of 92.68 % after 24 h. After assembly with polypyrrole-coated single-walled carbon nanotubes, the resulting as-prepared supercapacitor had excellent electrochemical properties with high areal capacitance of 297 mF cm^-2 at 0.5 mA cm^-2 and good rate capability (218 mF cm^-2 at 5 mA cm^-2 ). Besides, after cutting in two the supercapacitor recovered 99.2 % of its original specific capacitance after healing for 24 h at room temperature. The results also showed negligible change in the interior contact resistance of the supercapacitor after ten cutting/healing cycles. The present work provides a possible solution for the development of smart and durable energy storage devices with low cost for next-generation intelligent electronics.

Healable, Highly Conductive, Flexible, and Nonflammable Supramolecular Ionogel Electrolytes for Lithium-Ion Batteries

High-performance solid-state electrolytes with healability to repair mechanical damages are important for the fabrication of Li-ion batteries (LIBs) with enhanced safety and prolonged service life. In this study, we present the fabrication of healable, highly conductive, flexible, and nonflammable ionogel electrolytes for use in LIBs by loading ionic liquids and Li salts within a hydrogen-bonded supramolecular poly(ionic liquid) copolymer network. The ionogel electrolytes exhibit ionic conductivities as high as 10^-3 S/cm, which is comparable to the conventional liquid electrolytes. The Li/LiFePO₄ battery assembled with the ionogel membrane exhibits excellent cycling performance and delivers a steady high discharge capacity of 147.5 mA h g^-1 and Coulombic efficiency of 99.7% after 120 cycles at the charge/discharge rate of 0.2 C. Importantly, the ionogel membranes can heal damages outside or inside a battery because of the reversible nature of the supramolecular interactions between the components. The damaged ionogel membranes after being healed can effectively restore the original performance of the LIBs.

Facile Fabrication of Self-Healable and Antibacterial Soy Protein-Based Films with High Mechanical Strength

Soy protein isolate (SPI), a ubiquitous and readily available biopolymer, has drawn increasing attention because of its sustainability, abundance, and low price. However, the poor mechanical properties, tedious performance adjustments, irreversible damage, and weak microorganism resistance have limited its applications. In this study, a facile but delicate strategy is proposed to fabricate an excellently self-healable and remarkably antibacterial SPI-based material with high mechanical strength by integrating polyethyleneimine (PEI) and metal ions (Cu(II) or Zn(II)). The tensile strengths of the SPI/PEI-Cu-0.750 and SPI/PEI-Zn-0.750 films reach up to 10.46 ± 0.50 and 9.06 ± 0.62 MPa, which is 367.06 and 306.28% strength increase compared to that of neat SPI film, respectively. Due to abundant non-covalent bonds and low glass transition temperature of the network, both SPI/PEI-Cu and SPI/PEI-Zn films exhibit a satisfactory self-healing behavior even at room temperature. Furthermore, SPI/PEI-Cu and SPI/PEI-Zn films demonstrate high bacterial resistance against Escherichia coli and Staphylococcus aureus. This facile strategy of establishing dynamic networks in a biomaterial with numerous excellent properties will enormously expand the scope of its applications, especially in the field of recyclable and durable materials.

Nitrogen-Coordinated Boroxines Enable the Fabrication of Mechanically Robust Supramolecular Thermosets Capable of Healing and Recycling under Mild Conditions

The fabrication of mechanically robust polymeric materials capable of self-healing and recycling remains challenging because the mobility of polymer chains in such polymers is very limited. In this work, mechanically robust supramolecular thermosets capable of healing physical damages and recycling under mild conditions are fabricated by trimerization of bi-( ortho-aminomethyl-phenylboronic acid)- and tri-( ortho-aminomethyl-phenylboronic acid)-terminated poly(propylene glycol) oligomers (denoted as Bi-PBA-PPG and Tri-PBA-PPG, respectively). The resultant supramolecular thermosets are cross-linked by dynamic covalent bonds of nitrogen-coordinated boroxines. The mechanical properties of the supramolecular thermosets can be systematically tailored by varying the ratios between Tri-PBA-PPG and Bi-PBA-PPG, which changes the cross-linking density of nitrogen-coordinated boroxines and the topology of the supramolecular thermosets. The mechanically strongest supramolecular thermosets with a molar ratio of Tri-PBA-PPG to Bi-PBA-PPG being 1:2 have a glass transition temperature of ∼36 °C, a tensile strength of ∼31.96 MPa, and a Young's modulus of ∼298.5 MPa. The high reversibility of nitrogen-coordinated boroxines and the flexibility of poly(propylene glycol) chains enable the supramolecular thermosets with the strongest mechanical strength to be highly efficiently healed at 55 °C and recycled under a pressure of 4 MPa at 60 °C to regain their original mechanical strength and integrity.

Thermally and Near-Infrared Light-Induced Shape Memory Polymers Capable of Healing Mechanical Damage and Fatigued Shape Memory Function

The fabrication of shape memory polymers that are mechanically robust and capable of being induced by near-infrared (NIR) light and healing mechanical damage and the fatigued shape memory function remains a challenge. In this study, thermally and NIR-light-induced shape memory polymers with self-healing ability and satisfactory mechanical robustness are fabricated by dispersing poly(acrylic acid) (PAA)-grafted graphene oxide (GO) (PAA-GO) into poly(vinyl alcohol) (PVA) matrix. The PVA/PAA-GO_3% films with a PAA-GO content of 3.0 wt % have a fracture stress of ∼70.4 MPa and a Young's modulus of ∼2.8 GPa. The PVA/PAA-GO_3% films exhibit an excellent shape memory performance because PVA and PAA-GO form a stable network through hydrogen-bonding interaction between them. Meanwhile, the PVA/PAA-GO_3% films are capable of recovering from temporary shape to permanent shape under NIR light irradiation because of excellent photothermal conversion property of the GO nanosheets. More importantly, benefiting from the reversibility of hydrogen-bonding interactions between PVA and PAA-GO nanosheets, the shape memory PVA/PAA-GO_3% films are capable of healing physical damage and the fatigued shape memory function with the assistance of water, which greatly enhance their reliability as shape memory materials and prolong their service life.

Self-Healing Polymeric Hydrogel Formed by Metal-Ligand Coordination Assembly: Design, Fabrication, and Biomedical Applications

Self-healing hydrogels based on metal-ligand coordination chemistry provide new and exciting properties that improve injectability, rheological behaviors, and even biological functionalities. The inherent reversibility of coordination bonds improves on the covalent cross-linking employed previously, allowing for the preparation of completely self-healing hydrogels. In this article, recent advances in the development of this class of hydrogels are summarized and their applications in biology and medicine are discussed. Various chelating ligands such as bisphosphonate, catechol, histidine, thiolate, carboxylate, pyridines (including bipyridine and terpyridine), and iminodiacetate conjugated onto polymeric backbones, as well as the chelated metal ions and metal ions containing inorganic particles, which are used to form dynamic networks, are highlighted. This article provides general ideas and methods for the design of self-healing hydrogel biomaterials based on coordination chemistry.

Advanced Materials for Next-Generation Spacecraft

Spacecraft are expected to traverse enormous distances over long periods of time without an opportunity for maintenance, re-fueling, or repair, and, for interplanetary probes, no on-board crew to actively control the spacecraft configuration or flight path. Nevertheless, space technology has reached the stage when mining of space resources, space travel, and even colonization of other celestial bodies such as Mars and the Moon are being seriously considered. These ambitious aims call for spacecraft capable of self-controlled, self-adapting, and self-healing behavior. It is a tough challenge to address using traditional materials and approaches for their assembly. True interplanetary advances may only be attained using novel self-assembled and self-healing materials, which would allow for realization of next-generation spacecraft, where the concepts of adaptation and healing are at the core of every level of spacecraft design. Herein, recent achievements are captured and future directions in materials-driven development of space technology outlined.

Towards Dynamic but Supertough Healable Polymers through Biomimetic Hierarchical Hydrogen-Bonding Interactions

A biomimetic (titin protein molecular structure) strategy is reported for preparing transparent and healable elastomers featuring supertoughness (345 MJ m^-3 ) and high tensile strength (44 MPa) after self-healing enabled by hierarchical (single, double, and quadruple) hydrogen-bonding moieties in the polymer backbone. The rigid domain containing hierarchical H-bonds formed with urethane, urea, and 2-ureido-4[1H]-pyrimidinone groups leads to a durable network structure that has enhanced mechanical properties and is also dynamic for rapid self-healing. Healable polymers with hierarchical hydrogen-bonding interactions show excellent recoverability and high energy dissipation owing to the durable interaction between polymer chains. This biomimetic strategy of using hierarchical hydrogen bonds as building blocks is an alternative approach for obtaining dynamic, strong, yet smart self-healing polymers for heavy-duty protection materials and wearable electronics.

Mechanically Robust Atomic Oxygen-Resistant Coatings Capable of Autonomously Healing Damage in Low Earth Orbit Space Environment

Polymeric materials used in spacecraft require to be protected with an atomic oxygen (AO)-resistant layer because AO can degrade these polymers when spacecraft serves in low earth orbit (LEO) environment. However, mechanical damage on AO-resistant coatings can expose the underlying polymers to AO erosion, shortening their service life. In this study, the fabrication of durable AO-resistant coatings that are capable of autonomously healing mechanical damage under LEO environment is presented. The self-healing AO-resistant coatings are comprised of 2-ureido-4[1H]-pyrimidinone (UPy)-functionalized polyhedral oligomeric silsesquioxane (POSS) (denoted as UPy-POSS) that forms hydrogen-bonded three-dimensional supramolecular polymers. The UPy-POSS supramolecular polymers can be conveniently deposited on polyimides by a hot pressing process. The UPy-POSS polymeric coatings are mechanically robust, thermally stable, and transparent and have a strong adhesion toward polyimides to endure repeated bending/unbending treatments and thermal cycling. The UPy-POSS polymeric coatings exhibit excellent AO attack resistance because of the formation of epidermal SiO2 layer after AO exposure. Due to the reversibility of the quadruple hydrogen bonds between UPy motifs, the UPy-POSS polymeric coatings can rapidly heal mechanical damage such as cracks at 80 °C or under LEO environment to restore their original AO-resistant function.