Self-healing materials with microvascular networks

Self-healing behavior of superhard covalent bond materials

In recent years, superhard covalently bonded materials have drawn a great deal of attention due to their excellent mechanical properties and potential applications in various fields. This review focuses on the self-healing behavior of these materials, outlining state-of-the-art research results. In detail, we discuss current self-healing mechanisms of self-healing materials including extrinsic healing mechanisms (such as microencapsulation, oxidative healing, shape memory, etc.) and intrinsic healing (dynamic covalent bonding, supramolecular interactions, diffusion, defect-driven processes, etc.). We also provide an overview of the progress in the self-healing behavior of superhard covalently bonded materials and the mechanisms of permanent covalent bonding healing. Additionally, we analyze the factors that influence the healing properties of these materials. Finally, the main findings and an outlook on the future directions and challenges of this emerging field are summarized in the Conclusion section.

Self-Healing Behavior of Metallopolymers in Complex3D-Structures Obtained by DLP-Based 3D-Printing

This current study focusses on the investigation of the self-healing abilities of metallopolymers containing different kinds of metal complexes, which were processed by direct digital light processing (DLP) based three-dimensional (3D) printing. For this purpose, 2-phenoxyethyl acrylate is mixed with ligand-containing monomers either based on triphenylmethyl(trt)-histidine or terpyridine, respectively. Either zinc(II) or nickel(II) salts are successfully applied for a complexation of the ligand monomers in solution and, subsequently, photopolymerization is performed. The thermo-mechanical properties of the obtained metallopolymers were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) as well as dynamic mechanical thermal analysis (DMTA). Multiple damages with defined forces ranging from 20 to 1500 mN were introduced into the 3D-structures and successfully healed within 24 h at 70 °C or 120 °C, respectively without losing the structural integrity of the overall 3D-structures. Herein, excellent healing efficiencies up to 97 % were determined. Consequently, these hollow structures not only feature very good self-healing abilities but also excellent retention of the 3D-structure at and above the healing temperature.

Polyimide nanocomposites for next generation spacesuits

Polyimides have a long history of use in space missions, with Kapton® being the first polymer material to touch the surface of the Moon. Polyimides offer remarkable mechanical strength, superior thermal stability, and resistance to radiation, chemicals, and wear, and as such are often serve as a thermal barrier and a protective layer against extreme radiation and temperatures in multi-layer insulation systems. While the use of Kapton® in spacesuits dates back to the two aluminised Kapton® layers used in the spacesuits in the Apollo 11 mission, the potential uses of polyimides in the design of spacesuits remain underexplored, particularly considering the advancement made in the development of high-performance polyimide-based composites. This review explores the opportunities that emerge when the desirable properties of polyimides are combined with that of nanomaterials, specifically carbon nanomaterials, to produce strategic material combinations that promise to achieve enhanced thermal and mechanical properties, improved resistance to abrasion and puncture, and potentially reduced weight compared to traditional spacesuit materials. In turn, these advancements will contribute to the development of next-generation spacesuits that offer superior comfort, protection, and astronaut mobility during extravehicular activities.

Dual-Scale Collaborative Optimization of Microtubule Self-Healing Composites Based on Variable-Angle Fiber Design

To enhance the mechanics and self-healing properties of the self-healing composite, this study introduces an innovative optimization method for variable-angle fiber-reinforced self-healing composites with microtubule network carriers. The study aims to minimize macroscopic structural compliance and carrier head loss. Firstly, a topological description function (TDF) for the self-healing composite was introduced, taking into account the configuration and geometry of the macroscopic structure and microtubule network carrier as design variables. Secondly, the relationship between the fiber laying angle and component spindle direction was established. An element stiffness matrix for variable-angle fibers was derived to determine the compliance of the self-healing composite. Then, the microtubule network head loss was calculated based on the Hardy Cross method. Finally, by integrating the Moving Morphable Component (MMC) method and the enumeration method, a dual-scale collaborative optimization framework was developed. The set of double-objective Pareto non-inferior solutions of the self-healing composite was obtained by iteration. Numerical examples show that (1) under the same optimization conditions, the non-inferior solution set of variable-angle fiber design is superior to those of fixed-angle fiber designs (0°, 45°, and 90°). (2) Compared with single-objective (compliance) optimization of the carrier-free composite, the Pareto solution set of the variable-angle dual-scale collaborative optimization can provide a better compliance optimization solution, and the maximum compliance solution of the solution set is only 10.64% higher. This paper proposes a method combining variable-angle and dual-scale collaborative optimization, which provides a useful reference for the topology design of a self-healing composite.

Functional hydrogel empowering 3D printing titanium alloys

Titanium alloys are widely used in the manufacture of orthopedic prosthesis given their excellent mechanical properties and biocompatibility. However, the primary drawbacks of traditional titanium alloy prosthesis are their much higher elastic modulus than cancellous bone and poor interfacial adhesion, which lead to poor osseointegration. 3D-printed porous titanium alloys can partly address these issues, but their bio-inertness still requires modifications to adapt to different physiological and pathological microenvironments. Hydrogels composed of three-dimensional networks of hydrophilic polymers can effectively simulate the extracellular matrix of natural bone and are capable of loading bioactive molecules such as proteins, peptides, growths factors, polysaccharides, or nucleotides for localized release within the human body, by directly participating in biological processes. Combining 3D-printed porous titanium alloys with hydrogels to construct a bioactive composite system that regulates cellular adhesion, proliferation, migration, and differentiation in the local microenvironment is of great significance for enhancing the bioactivity of the prosthesis surface. In this review, we focus on three aspects of the bioactive composite system: (Ⅰ) strategies for constructing bioactive interfaces with hydrogels, and (Ⅱ) how bioactive composite systems regulate the microenvironment under different physiological and pathological conditions to enhance the osteointegration and bone regeneration capability of prostheses. Considering the current research status in this field, innovations in orthopedic prosthesis can be achieved through material optimization, personalized customization, and the development of multifunctional composite systems. These advancements provide essential references for the clinical translation of osseointegration and bone regeneration in various physiological and pathological microenvironments.

Self-Healing Elastomers and Coatings via Metal Coordination Bonds

Self-healing materials can recover the materials from physical damage, and extend the life of equipment. Metal coordination bonds are supramolecular interactions with tunable stability and sensitivity to external stimuli, which are crucial for developing self-healing materials. Incorporating metal coordination bonds into elastomers and coatings can enable materials to repair damage and enhance material performance. This review details the advance in self-healing elastomers and coatings. The structural characteristics, mechanical properties, and self-healing efficacy of these materials are discussed, and a perspective on the challenges and development directions is given.

Dragonfly wings-inspired, anti-freezing, ultra-stretchable, and transparent nano-structure sodium alginate-based hydrogel for non-delayed wearable sensing at low-temperatures

Conductive hydrogels are regarded as an optimal flexible electronic material. Nevertheless, simultaneously achieving excellent mechanical and conductive properties in hydrogels necessitates attention. The high mechanical properties of hydrogels were achieved by employing a strategy that involves constructing a nano-structure network inspired by the highly ordered structure of dragonfly wings. The conductivity and anti-freezing of the hydrogel were enhanced through the construction of a conductive mechanism, achieved by combining ions with nano-particles. The hydrogel exhibits outstanding properties, including anti-freezing, ultra-stretchable (6000 %), impressive conductivity (16.2 S m-1), a transparency level of up to 91.2 %, and excellent sensitivity in strain sensors. Regulation of the hydrogel matrix's topology and the formation of bionic nano-structures synergistically establish the hydrogel's ultra-stretching and energy dissipation mechanism. The high conductivity of the hydrogel is achieved by constructing a synergistic conduction pathway, which incorporates nano-particles and ions. Under the stretching-induced effect of hydrogel, it facilitates a more efficient path for conduction, thereby enhancing its conductivity and sensing sensitivity under significant strains. Subsequently, this hydrogel was successfully applied to wearable sensor technology, demonstrating surprisingly remarkably prompt non-delayed sensing performance even at low-temperatures. It presents abundant opportunities for expanding the application of hydrogels in flexible electronics.

Enhancing the Self-Healing Efficiency of Ti3AlC2 MAX Phase via Irradiation

Self-healing materials are highly desirable in the nuclear industry to ensure nuclear security. Although extensive efforts have been devoted to developing self-healing materials in the past half century, very limited successes have been reported for ceramics or metals. Here, we report an intrinsic self-healing material of Ti3AlC2 MAX phase, which exhibits both ceramic and metallic properties, and a strategy for further enhancing the self-healing via irradiation is proposed. Quantitative in situ transmission electron microscopy tensile testing reveals that the fracture strength of 1.58 GPa is achieved on thoroughly fractured Ti3AlC2, corresponding to the self-healing efficiency of 19.8%, which is increased to 28.1% after irradiation. In situ irradiation experiments, atomic-resolution characterizations, and molecular dynamics simulations reveal that spontaneous rebonding of partial atoms on fracture surfaces is responsible for the self-healing, and irradiation-enhanced atomic migration, interplanar spacing increment, and gap-filling contribute to the self-healing enhancement.

Formation of Nanofibrillar Self-Healing Hydrogels Using Antimicrobial Peptides

The rise of drug-resistant microorganisms has prompted the development of innovative strategies with the aim of addressing this challenge. Among the alternative approaches gaining increased attention are antimicrobial peptides (AMPs), a group of peptides with the ability to combat microbial pathogens. Here, we investigated a small peptide, KLVFF, derived from the Alzheimer's amyloid-β (Aβ) protein. While Aβ has been associated with the development of neurodegenerative diseases, the core part of the Aβ protein, namely the Aβ 16-20 fragment, has also been exploited to obtain highly functional biomaterials. In this study we found that KLVFF is capable of self-assembling into a fibrillar network to form a self-healing hydrogel. Moreover, this small peptide can undergo a transition from a gel to a liquid state following application of shear stress, in a reversible manner. As an AMP, this material exhibited both antibacterial and antifungal properties while remaining highly biocompatible and noncytotoxic toward mammalian cells. The propensity of the KLVFF hydrogel to rapidly assemble into highly ordered macroscopic structures makes it an ideal candidate for biomedical applications necessitating antimicrobial activity, such as wound healing.

Skin-Mountable Functional Electronic Materials for Bio-Integrated Devices

Skin-mountable electronic materials are being intensively evaluated for use in bio-integrated devices that can mutually interact with the human body. Over the past decade, functional electronic materials inspired by the skin are developed with new functionalities to address the limitations of traditional electronic materials for bio-integrated devices. Herein, the recent progress in skin-mountable functional electronic materials for skin-like electronics is introduced with a focus on five perspectives that entail essential functionalities: stretchability, self-healing ability, biocompatibility, breathability, and biodegradability. All functionalities are advanced with each strategy through rational material designs. The skin-mountable functional materials enable the fabrication of bio-integrated electronic devices, which can lead to new paradigms of electronics combining with the human body.

Self-Healing Polymers Coupling Shape Memory Effect

In recent years, shape memory polymers (SMPs) and self-healing polymers (SHPs) have been research hotspots in the field of smart polymers owing to their unique stimulus response mechanisms. Previous research on SHPs has primarily focused on contact repair. However, in instances where substantial cracks occur during practical use, autonomous closure becomes challenging, impeding effective repair. By integration of the shape memory effect (SME) with SHPs, physical wound closure can be achieved via the SME, facilitating subsequent chemical/physical repair processes and enhancing self-healing effectiveness. This article reviews key findings from previous research on shape memory-assisted self-healing (SMASH) materials and addresses the challenges and opportunities for future investigation.

Verification of the Self-Healing Ability of PP-co-HUPy Copolymers in Epoxy Systems

This work concerns the verification of the self-healing ability of PP-co-HUPy copolymers dispersed in epoxy systems. PP is the acronym for the Poly-PEGMA polymer, and HUPy refers to the HEMA-UPy copolymers based on ureidopyrimidinone (UPy) moieties. In particular, this work aims to verify whether this elastomer characterized by an intrinsic self-healing ability can activate supramolecular interactions among polymer chains of an epoxy resin, as in the elastomer alone. The elastomer includes a class of polyethylene glycol monomethyl ether methacrylate-based copolymers, with different percentages of urea-N-2-amino-4-hydroxy-6-methyl pyrimidine-N'-(hexamethylene-n-carboxyethyl methacrylate) (HEMA-UPy) co-monomers. The self-healing capability of these copolymers based on possible quadruple hydrogen bond interactions between polymer chains has been verified. The formulated epoxy samples did not show self-healing efficiency. This can be attributed to the formation of phase segregation that originates during the curing process of the samples, although the PP-co-HUPy copolymers are completely soluble in the liquid epoxy matrix EP. The morphological investigation highlighted the presence of crystals of PP-co-HUPy copolymers, which are in greater quantity in the sample containing the highest weight percentage (7.8 wt%) of HUPy units. Furthermore, the crystals act as promotors for increasing the curing degree (DC) of the epoxy systems containing HUPy units. DC goes from 91.6% for EP to 96.1% and 95.4% for the samples containing weight percentages of 2.5 and 7.8 wt% of HUPy units, respectively. Dynamic mechanical analysis (DMA) shows storage modulus values for epoxy systems containing PP-co-HUPy units lower than that of the unfilled resin EP. The values of maximum in Tan δ (Tg), representing the temperature at which the glass transition occurs, are 220 for the unfilled resin EP, 228 for the sample containing 2.5 wt% of HEMA-UPy units, and 211 for the sample containing 7.8 wt% of HEMA-UPy units.

Carbodiimide-Driven Toughening of Interpenetrated Polymer Networks

Recent work has demonstrated that temporary crosslinks in polymer networks generated by chemical "fuels" afford materials with large, transient changes in their mechanical properties. This can be accomplished in carboxylic-acid-functionalized polymer hydrogels using carbodiimides, which generate anhydride crosslinks with lifetimes on the order of minutes to hours. Here, the impact of the polymer network architecture on the mechanical properties of transiently crosslinked materials was explored. Single networks (SNs) were compared to interpenetrated networks (IPNs). Notably, semi-IPN precursors that give IPNs on treatment with carbodiimide give much higher fracture energies (i.e., resistance to fracture) and superior resistance to compressive strain compared to other network architectures. A precursor semi-IPN material featuring acrylic acid in only the free polymer chains yields, on treatment with carbodiimide, an IPN with a fracture energy of 2400 J/m2, a fourfold increase compared to an analogous semi-IPN precursor that yields a SN. This resistance to fracture enables the formation of macroscopic complex cut patterns, even at high strain, underscoring the pivotal role of polymer architecture in mechanical performance.

Development and characterization of smart composites reinforced with fibrillated cellulose and nickel-titanium alloy

The current study presents the synergistic effects of fibrillated cellulose (FC) and nickel-titanium (NiTi) alloy on the performance properties of smart composites. Epoxy resin was reinforced with loadings of 1 %, 3 %, and 5 % FC and 3 % NiTi. The composites were produced using the casting method. The morphological properties have been analyzed using scanning electron microscopy (SEM). For mechanical properties, yield strength, modulus of elasticity, hardness, and impact energy were determined. The corrosion rate was determined via electrochemical corrosion testing. The recovery test was used to measure the shape-memory of the composites. The self-healing of the artificial defect in the composites was observed using a thermal camera. The yield strength, modulus of elasticity, hardness, and impact energy of composites reinforced with 5 % FC and 3 % NiTi increased by 168.2 %, 290 %, 33.3 %, and 114.3 %, respectively, compared to pure epoxy resin. There has been a 56.3 % decrease in the corrosion rate. The percentage of composites that returned from the final state to the original state after a deformation was 4 %. Self-healing analysis revealed that the scratch defect in composites was healed after 24 h. It is concluded that smart composites can be used in the aviation and automotive industries.

Hierarchically core-shell structured nanocellulose/carbon nanotube hybrid aerogels for patternable, self-healing and flexible supercapacitors

The flexible and self-healing supercapacitors (SCs) are considered to be promising smart energy storage devices. Nevertheless, the SCs integrated with flexibility, lightweight, pattern editability, self-healing capabilities and desirable electrochemical properties remain a challenge. Herein, an all-in-one self-healing SC fabricated with the free-standing hybrid film (TCMP) composed of the 2,2,6,6-tetramethylpiperidin-1-yloxy-oxidized cellulose nanofibers (TOCNs) carried carbon nanotubes (CNTs), manganese dioxide (MnO2) and polyaniline (PANI) as the electrode, polyvinyl alcohol/sulfuric acid (PVA/H2SO4) gel as the electrolyte and dynamically cross-linked cellulose nanofibers/PVA/sodium tetraborate decahydrate (CNF/PB) hydrogel as the self-healing electrode matrix is developed. The TCMP film electrodes are fabricated through a facile in-situ polymerization of MnO2 and PANI in TOCNs-dispersed CNTs composite networks, exhibiting lightweight, high electrical conductivity, flexibility, pattern editability and excellent electrochemical properties. Benefited from the hierarchically porous structure and high mechanical properties of TOCNs, excellent electrical conductivity of CNTs and the desirable synergistic effect of pseudocapacitance induced by MnO2 and PANI, the assembled SC with an interdigital structure demonstrated a high areal capacitance of 1108 mF cm-2 at 2 mA cm-2, large areal energy density of 153.7 μWh cm-2 at 1101.7 μW cm-2. A satisfactory bending cycle performance (capacitance retention up to 95 % after 200 bending deformations) and self-healing characteristics (∼90 % capacitance retention after 10 cut/repair cycles) are demonstrated for the TCMP-based symmetric SC, delivering a feasible strategy for electrochemical energy storage devices with excellent performance, designable patterns and desirable safe lifespan.

3D Printing of Self-Healing Materials

This review article presents a comprehensive overview of the latest advances in the field of 3D printable structures with self-healing properties. Three-dimensional printing (3DP) is a versatile technology that enables the rapid manufacturing of complex geometric structures with precision and functionality not previously attainable. However, the application of 3DP technology is still limited by the availability of materials with customizable properties specifically designed for additive manufacturing. The addition of self-healing properties within 3D printed objects is of high interest as it can improve the performance and lifespan of structural components, and even enable the mimicking of living tissues for biomedical applications, such as organs printing. The review will discuss and analyze the most relevant results reported in recent years in the development of self-healing polymeric materials that can be processed via 3D printing. After introducing the chemical and physical self-healing mechanism that can be exploited, the literature review here reported will focus in particular on printability and repairing performances. At last, actual perspective and possible development field will be critically discussed.

Understanding the application of covalent adaptable networks in self-repair materials based on molecular simulation

Covalent adaptable networks (CANs) are widely used in the field of self-repair materials. They are a group of covalently cross-linked associative polymers that undergo reversible chemical reactions, and can be further divided into dissociative CANs (Diss-CANs) and associative CANs (Asso-CANs). Self-repair refers to the ability of a material to repair itself without external intervention, and can be classified into self-adhesion and self-healing according to the utilization of open stickers. Unlike conventional materials, the viscoelastic properties of CANs are influenced by both the molecular structure and reaction kinetics, ultimately affecting their repair performance. To gain deeper insight into the repair mechanism of CANs, we conducted simulations by using the hybrid MC/MD algorithm, as previously proposed in our research. Interestingly, we observed a significant correlation between reaction kinetics and repair behavior. Asso-CANs exhibited strong mechanical strength and high creep resistance, rendering them suitable as self-adhesion materials. On the other hand, Diss-CANs formed open stickers that facilitated local relaxation, aligning perfectly with self-healing processes. Moreover, the introduction of crosslinkers in the form of small molecules enhanced the repair efficiency. Theoretically, it was found that the repair timescale of Asso-CANs is slower than that of Diss-CANs with identical molecular structures. Our study not only clarifies the similarities and differences between Diss-CANs and Asso-CANs in terms of their self-repairing capabilities, but more importantly, it provides valuable insights guiding the effective utilization of CANs in the development of self-repair materials.

A Self-Healing System for Polydicyclopentadiene Thermosets

Self-healing offers promise for addressing structural failures, increasing lifespan, and improving durability in polymeric materials. Implementing self-healing in thermoset polymers faces significant manufacturing challenges, especially due to the elevated temperature requirements of thermoset processing. To introduce self-healing into structural thermosets, the self-healing system must be thermally stable and compatible with the thermoset chemistry. This article demonstrates a self-healing microcapsule-based system stable to frontal polymerization (FP), a rapid and energy-efficient manufacturing process with a self-propagating exothermic reaction (≈200 °C). A thermally latent Grubbs-type complex bearing two N-heterocyclic carbene ligands addresses limitations in conventional G2-based self-healing approaches. Under FP's elevated temperatures, the catalyst remains dormant until activated by a Cu(I) co-reagent, ensuring efficient polymerization of the dicyclopentadiene (DCPD) upon damage to the polyDCPD matrix. The two-part microcapsule system consists of one capsule containing the thermally latent Grubbs-type catalyst dissolved in the solvent, and another capsule containing a Cu(I) coagent blended with liquid DCPD monomer. Using the same chemistry for both matrix fabrication and healing results in strong interfaces as demonstrated by lap-shear tests. In an optimized system, the self-healing system restores the mechanical properties of the tough polyDCPD thermoset. Self-healing efficiencies greater than 90% via tapered double cantilever beam tests are observed.

Microfiber-Patterned Versatile Perfusable Vascular Networks

Rapid construction of versatile perfusable vascular networks in vitro with cylindrical channels still remains challenging. Here, a microfiber-patterned method is developed to precisely fabricate versatile well-controlled perfusable vascular networks with cylindrical channels. This method uses tensile microfibers as an easy-removable template to rapidly generate cylindrical-channel chips with one-dimensional, two-dimensional, three-dimensional and multilayered structures, enabling the independent and precise control over the vascular geometry. These perfusable and cytocompatible chips have great potential to mimic vascular networks. The inner surfaces of a three-dimensional vascular network are lined with the human umbilical vein endothelial cells (HUVECs) to imitate the endothelialization of a human blood vessel. The results show that HUVECs attach well on the inner surface of channels and form endothelial tubular lumens with great cell viability. The simple, rapid and low-cost technique for versatile perfusable vascular networks offers plenty of promising opportunities for microfluidics, tissue engineering, clinical medicine and drug development.

Self-healing polymers for surface scratch regeneration

Recently, there has been a significant increase in academic and industrial interest in self-healing polymers (SHPs) due to their remarkable ability to regenerate scratched surfaces and materials of astronomical significance. Scientists have been inspired by the magical repairing mechanism of the living world. They transformed the fiction of self-healing into reality by designing engrossing polymeric materials that could self-repair mechanical abrasions repeatedly. As a result, the durability of the materials is remarkably improved. Thus, the idea of studying SHPs passively upholds economic and environmental sustainability. However, the critical areas of self-healing (including healing efficiency, healing mechanism, and thermo-mechanical property changes during healing) are under continuous scientific improvisation. This review highlights recent notable advances of SHPs for application in regenerating scratched surfaces with various distinctive underlying mechanisms. The primary focus of the work is aimed at discussing the impact of SHPs on scratch-healing technology. Beyond that, insights regarding scratch testing, methods of investigating polymer surfaces, wound depths, the addition of healing fillers, and the environmental conditions maintained during the healing process are reviewed thoroughly. Finally, broader future perspectives on the challenges and prospects of SHPs in healing surface scratches are discussed.

A review on self-healing featured soft robotics

Soft robots are becoming more popular because they can solve issues stiff robots cannot. Soft component and system design have seen several innovations recently. Next-generation robot-human interactions will depend on soft robotics. Soft material technologies integrate safety at the material level, speeding its integration with biological systems. Soft robotic systems must be as resilient as biological systems in unexpected, uncontrolled situations. Self-healing materials, especially polymeric and elastomeric ones, are widely studied. Since most currently under-development soft robotic systems are composed of polymeric or elastomeric materials, this finding may provide immediate assistance to the community developing soft robots. Self-healing and damage-resilient systems are making their way into actuators, structures, and sensors, even if soft robotics remains in its infancy. In the future, self-repairing soft robotic systems composed of polymers might save both money and the environment. Over the last decade, academics and businesses have grown interested in soft robotics. Despite several literature evaluations of the soft robotics subject, there seems to be a lack of systematic research on its intellectual structure and development despite the rising number of articles. This article gives an in-depth overview of the existing knowledge base on damage resistance and self-healing materials' fundamental structure and classifications. Current uses, problems with future implementation, and solutions to those problems are all included in this overview. Also discussed are potential applications and future directions for self-repairing soft robots.

Synergetic Inhibition and Corrosion-Diagnosing Nanofiber Networks for Self-Healing Protective Coatings

Organic coatings lack durability in marine corrosive environments. Herein, we designed a self-healing coating with a novel nanofiber network filler for enhanced protection. Using electrospinning, we created a core-shell structure nanofiber network consisting of polyvinyl butyral (PVB) as the shell material and gallic acid (GA) and phenanthroline (Phen) as the core material. The PVB@GA-Phen nanofiber network, which includes synergistic corrosion inhibitors (GA-Phen), was embedded in an epoxy coating (PVB@GA-Phen/epoxy) and applied to carbon steel. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations demonstrated that the GA-Phen combination, through hydrogen bond interaction, facilitated inhibitor adsorption on the steel surface. The GA-Phen combination diagnosed corrosion and formed a protective film on the scratched areas. The sustained release of Phen-GA combination inhibitors for up to 240 h resulted in an 88.63% healing efficiency of the PVB@GA-Phen/epoxy (PGP/EP) coating. The long-term corrosion resistance tests confirmed the effective barrier performance of the PGP/EP coating in 3.5 wt % NaCl solution. Moreover, the incorporation of the nanofiber network in the epoxy coating provided passive barrier, corrosion-diagnosing, and anticorrosion properties for carbon steel protection. The designed coating has the potential to continuously monitor the coating/metal system and could serve as a foundation for developing new anticorrosion coatings.

Designing self-healing hydrogels for biomedical applications

Self-healing hydrogels have emerged as the most promising alternatives to conventional brittle hydrogels used in the biomedical field due to the features of long-term stability and durability. However, the incompatibility between the fast self-healing property and enough mechanical strength of hydrogels remains a challenge. Therefore, hydrogels that possess not only mechanical toughness but also autonomous self-healing capacity are sought after. This review presents a comprehensive summary of the latest self-healing mechanisms. Specifically, we review various systems based on dynamic bonds, ranging from dynamic covalent bonds to non-covalent bonds. Additionally, this review presents different characterization methods for self-healing hydrogels, and also highlights their potential applications in the biomedical field, such as tissue engineering, drug delivery, cell therapy, and wound dressing. Furthermore, this review aims to provide valuable guidance for constructing diverse self-healing hydrogels with tailored functions.

Improving the 3D Printability of Sugar Glass to Engineer Sacrificial Vascular Templates

A prominent obstacle in scaling up tissue engineering technologies for human applications is engineering an adequate supply of oxygen and nutrients throughout artificial tissues. Sugar glass has emerged as a promising 3D-printable, sacrificial material that can be used to embed perfusable networks within cell-laden matrices to improve mass transfer. To characterize and optimize a previously published sugar ink, we investigated the effects of sucrose, glucose, and dextran concentration on the glass transition temperature (Tg), printability, and stability of 3D-printed sugar glass constructs. We identified a sucrose ink formulation with a significantly higher Tg (40.0 ± 0.9°C) than the original formulation (sucrose-glucose blend, Tg = 26.2 ± 0.4°C), which demonstrated a pronounced improvement in printability, resistance to bending, and final print stability, all without changing dissolution kinetics and decomposition temperature. This formulation allowed printing of 10-cm-long horizontal cantilever filaments, which can enable the printing of complex vascular segments along the x-, y-, and z-axes without the need for supporting structures. Vascular templates with a single inlet and outlet branching into nine channels were 3D printed using the improved formulation and subsequently used to generate perfusable alginate constructs. The printed lattice showed high fidelity with respect to the input geometry, although with some channel deformation after alginate casting and gelation-likely due to alginate swelling. Compared with avascular controls, no significant acute cytotoxicity was noted when casting pancreatic beta cell-laden alginate constructs around improved ink filaments, whereas a significant decrease in cell viability was observed with the original ink. The improved formulation lends more flexibility to sugar glass 3D printing by facilitating the fabrication of larger, more complex, and more stable sacrificial networks. Rigorous characterization and optimization methods for improving sacrificial inks may facilitate the fabrication of functional cellular constructs for tissue engineering, cellular biology, and other biomedical applications.

Copolymer Brush Particle Hybrid Materials with "Recall-and-Repair" Capability

The effect of sequence structure on the self-healing and shape-memory properties of copolymer-tethered brush particle films was investigated and compared to linear copolymer analogs. Poly(n-butyl acrylate-co-methyl methacrylate), P(BA-co-MMA), and linear and brush analogs with controlled gradient and statistical sequence were synthesized by atom transfer radical polymerization (ATRP). The effect of sequence on self-healing in BA/MMA copolymer brush particle hybrids followed similar trends as for linear analogs. Most rapid restoration of mechanical properties was found for statistical copolymer sequence; an increase of the high Tg (MMA) component provided a path to raise the material's modulus while retaining self-heal ability. Creep testing revealed profound differences between linear and brush systems. While linear copolymers featured substantial viscous deformation when exposed to constant stress in the linear regime, brush analogs displayed minimal permanent deformation and featured shape restoration. The reduction of flow was interpreted to be a consequence of slow cooperative relaxation due to the complex microstructure of brush particle hybrids in which long-range motions are constrained through entanglements and slow-diffusing particle cores. The rubbery-like response imparts BA/MMA copolymer brush material systems concurrent "shape-memory" and "self-heal" capability. This ability to "recall-and-repair" could find application in the design of functional hybrid materials, for example, for soft robotics.

Experimental Investigation of Cumulative Damage and Self-Healing Properties of Smart Cementitious Composite under Continuous Compression Load

This study investigated the effect of sustained loading on the cumulative damage of a newly developed smart cement-based self-healing composite material (SMA-ECC). SMA-ECC is composed of engineered cementitious composite (ECC) and shape memory alloy (SMA) fibers. A uniaxial compressive test with five predefined loading levels (0%, 30%, 40%, 50%, and 60% of compressive strength) was conducted on SMA-ECC hollow-cylindrical specimens and ECC control hollow-cylindrical specimens. The cumulative damage was mainly determined by changes in the total water absorption of different groups of specimens during three different periods (not loaded, at a predefined loading level, and after unloading). A normalized water content index was proposed to couple the effects of self-healing, sustained loading, and cumulative damage. The test results indicate that the cumulative water absorption of SMA-ECC was 35% lower than that of ECC, which may indicate less irreparable damage. In addition, the self-healing ability of SMA-ECC specimens under different compression load levels was evaluated through normalized water content analysis. SMA-ECC exhibited a 100% repair rate at load levels of 30% and 40%. At a higher load level of 60%, the repair rate of SMA-ECC was 76%. These results collectively emphasize the significant impermeability and self-healing performance of SMA-ECC after unloading.

Adaptive Ion-Gel: Stimuli-Responsive, and Self-Healing Ion Gels

Ion gels are an emerging class of polymer gels in which a three-dimensional polymer network swells with an ionic liquid. Ion gels have drawn considerable attention in various fields such as energy and biotechnology owing to their excellent properties including nonvolatility, nonflammability, high ionic conductivity, and high thermal and electrochemical stability. Since the first report on ion gels (published ∼30 years ago), diverse functional ion gels exhibiting impressive physicochemical properties have been reported. In this review, recent developments in functional ion gels that can modulate their physical properties in response to environmental conditions are outlined. Stimuli-responsive ion gels that can adaptively undergo phase transitions in response to thermal and light stimuli are initially discussed, followed by an evaluation of diverse self-healing ion gels that can spontaneously mend mechanical damage through judiciously designed ion-gel networks.

Autonomous healing of fatigue cracks via cold welding

Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure1,2. Prevention of fatigue relies on implementation of large safety factors and inefficient overdesign3. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal4-9. Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration. The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments.

Biomimetic strain-stiffening in fully synthetic dynamic-covalent hydrogel networks

Mechanoresponsiveness is a ubiquitous feature of soft materials in nature; biological tissues exhibit both strain-stiffening and self-healing in order to prevent and repair deformation-induced damage. These features remain challenging to replicate in synthetic and flexible polymeric materials. In recreating both the mechanical and structural features of soft biological tissues, hydrogels have been often explored for a number of biological and biomedical applications. However, synthetic polymeric hydrogels rarely replicate the mechanoresponsive character of natural biological materials, failing to match both strain-stiffening and self-healing functionality. Here, strain-stiffening behavior is realized in fully synthetic ideal network hydrogels prepared from flexible 4-arm polyethylene glycol macromers via dynamic-covalent boronate ester crosslinks. Shear rheology reveals the strain-stiffening response in these networks as a function of polymer concentration, pH, and temperature. Across all three of these variables, hydrogels of lower stiffness exhibit higher degrees of stiffening, as quantified by the stiffening index. The reversibility and self-healing nature of this strain-stiffening response is also evident upon strain-cycling. The mechanism underlying this unusual stiffening response is attributed to a combination of entropic and enthalpic elasticity in these crosslink-dominant networks, contrasting with natural biopolymers that primarily strain-stiffen due to a strain-induced reduction in conformational entropy of entangled fibrillar structures. This work thus offers key insights into crosslink-driven strain-stiffening in dynamic-covalent phenylboronic acid-diol hydrogels as a function of experimental and environmental parameters. Moreover, the biomimetic mechano- and chemoresponsive nature of this simple ideal-network hydrogel offers a promising platform for future applications.

Recent Advancements in Physiological, Biochemical, and Multimodal Sensors Based on Flexible Substrates: Strategies, Technologies, and Integrations

Flexible wearable devices have been widely used in biomedical applications, the Internet of Things, and other fields, attracting the attention of many researchers. The physiological and biochemical information on the human body reflects various health states, providing essential data for human health examination and personalized medical treatment. Meanwhile, physiological and biochemical information reveals the moving state and position of the human body, and it is the data basis for realizing human-computer interactions. Flexible wearable physiological and biochemical sensors provide real-time, human-friendly monitoring because of their light weight, wearability, and high flexibility. This paper reviews the latest advancements, strategies, and technologies of flexibly wearable physiological and biochemical sensors (pressure, strain, humidity, saliva, sweat, and tears). Next, we systematically summarize the integration principles of flexible physiological and biochemical sensors with the current research progress. Finally, important directions and challenges of physiological, biochemical, and multimodal sensors are proposed to realize their potential applications for human movement, health monitoring, and personalized medicine.

Room-Temperature Self-Healing Glassy Luminescent Hybrid Film

The self-healing of glassy polymer materials on site has always been a huge challenge due to their frozen polymer network. We herein report self-repairable glassy luminescent film by assembling a lanthanide-containing polymer with randomly hyperbranched polymers possessing multiple hydrogen (H) bonds. Because of multiple H bonds, the hybrid film exhibits enhanced mechanical strength, with high glass transition temperature (T_g) of 40.3 °C and high storage modulus of 3.52 GPa, meanwhile, dynamic exchange of multiple H bonds enables its rapid room-temperature self-healing ability. This research provides new insights in preparing mechanical robust yet repairable polymeric functional materials.

Recent advances in self-healing polyurethane based on dynamic covalent bonds combined with other self-healing methods

To meet more application requirements, improving mechanical properties and self-healing efficiency has become the focus of current research on self-healing PU. The competitive relationship between self-healing ability and mechanical properties cannot be avoided by a single self-healing method. To address this problem, a growing number of studies have combined dynamic covalent bonding with other self-healing methods to construct the PU structure. This review summarizes recent studies on PU materials that combine typical dynamic covalent bonds with other self-healing methods. It mainly includes four parts: hydrogen bonding, metal coordination bonding, nanofillers combined with dynamic covalent bonding and multiple dynamic covalent bond bonding. The advantages and disadvantages of different self-healing methods and their significant role in improving self-healing ability and mechanical properties in PU networks are analyzed. At the same time, the possible challenges and research directions of self-healing PU materials in the future are discussed.

Frontal Polymerizations: From Chemical Perspectives to Macroscopic Properties and Applications

The synthesis and processing of most thermoplastics and thermoset polymeric materials rely on energy-inefficient and environmentally burdensome manufacturing methods. Frontal polymerization is an attractive, scalable alternative due to its exploitation of polymerization heat that is generally wasted and unutilized. The only external energy needed for frontal polymerization is an initial thermal (or photo) stimulus that locally ignites the reaction. The subsequent reaction exothermicity provides local heating; the transport of this thermal energy to neighboring monomers in either a liquid or gel-like state results in a self-perpetuating reaction zone that provides fully cured thermosets and thermoplastics. Propagation of this polymerization front continues through the unreacted monomer media until either all reactants are consumed or sufficient heat loss stalls further reaction. Several different polymerization mechanisms support frontal processes, including free-radical, cat- or anionic, amine-cure epoxides, and ring-opening metathesis polymerization. The choice of monomer, initiator/catalyst, and additives dictates how fast the polymer front traverses the reactant medium, as well as the maximum temperature achievable. Numerous applications of frontally generated materials exist, ranging from porous substrate reinforcement to fabrication of patterned composites. In this review, we examine in detail the physical and chemical phenomena that govern frontal polymerization, as well as outline the existing applications.

Protocol to fabricate ionic hydrogel with ultra-stretchable and fast self-healing ability in cryogenic environments

Self-healing materials exhibit irreplaceable advantages in artificial electronics given their ability to repair from accidental damage, but the self-healing ability is temperature sensitive, limiting their applications in cryogenic environments. Here, we describe steps to fabricate a versatile ionic hydrogel with fast self-healing ability, ultra-stretchability, and stable conductivity, under the temperature ranging from -80°C to 30°C. We also detail steps for characterizing the polymer structure and interactions of the ionic hydrogel, as well as the mechanical, electrical, and self-healing properties. For complete details on the use and execution of this protocol, please refer to Wang et al. (2022).1.

Thermal and Electrical Characterization of Polyester Resins Suitable for Electric Motor Insulation

This paper undertakes the thermal and electrical characterization of three commercial unsaturated polyester imide resins (UPIR) to identify which among them could better perform the insulation function of electric motors (high-power induction motors fed by pulse-wide modulation (PWM) inverters). The process foreseen for the motor insulation using these resins is Vacuum Pressure Impregnation (VPI). The resin formulations were specially selected because they are one-component systems; hence, before the VPI process, they do not require mixing steps with external hardeners to activate the curing process. Furthermore, they are characterized by low viscosity and a thermal class higher than 180 °C and are Volatile Organic Compound (VOC)-free. Thermal investigations using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) techniques prove their excellent thermal resistance up to 320 °C. Moreover, impedance spectroscopy in the frequency range of 100 Hz–1 MHz was analyzed to compare the electromagnetic performance of the considered formulations. They manifest an electrical conductivity starting from 10−10 S/m, a relative permittivity around 3, and a loss tangent value lower than 0.02, which appears almost stable in the analyzed frequency range. These values confirm their usefulness as impregnating resins in secondary insulation material applications.

A rapid self-healing glassy polymer/metal-organic-framework hybrid membrane at room temperature

The development of repairable MOF-polymer hybrid materials will greatly extend their service life by repairing fractured parts on the spot; however, it is difficult for robust glassy polymers to self-heal below the glass transition temperature (T_g) as the polymer network is frozen. We herein report glassy polyMOF-RHP hybrid membranes by integrating lanthanide polyMOF (polyLnMOF) with randomly hyperbranched polymers (RHP) bearing a high density of hydrogen bonds. Since crystalline lanthanide MOFs act as multiconnected cross-linking agents and cross-link the interpenetrating polymer network, the obtained polyLnMOF-polymer membrane shows enhanced mechanical strength with a storage modulus of 3.09 GPa and a T_g up to 49 °C. Meanwhile, the high intersegment migration ability of the polyLnMOF-polymer network facilitates the exchange of hydrogen-bonded pairs even in the glassy state, leading to an instantaneous room-temperature self-healing ability. The polyLnMOF-polymer membranes inherit the ratiometric temperature-sensing behavior of pristine lanthanide MOFs, resulting in more processable temperature-sensing membranes. This work provides an appealing strategy for the design of mechanically robust, yet self-healing, MOF-polymer functional materials.

Synergistic Effect of Cation Composition Engineering of Hybrid Cs1-x FAx PbBr3 Nanocrystals for Self-Healing Electronics Application

Mixed-cation hybrid perovskite nanocrystal (HPNC) with high crystallinity, color purity, and tunable optical bandgap offers a practical pathway toward next-generation displays. Herein, a two-step modified hot-injection combined with cation compositional engineering and surface treatment to synthesize high-purity cesium/formamidinium lead bromide HPNCs(Cs_1-x FA_x PbBr₃ ) is presented. The optimized Cs_0.5 FA_0.5 PbBr₃ light-emitting devices (LEDs) exhibit uniform luminescence of 3500 cd m^-2 and a prominent current efficiency of 21.5 cd A^-1 . As a proof of concept, a self-healing polymer (SHP) integrated with white LED backlight and laser prototypes exhibited 4 h autonomous self-healing through the synergistic effect of weak reversible imine bonds and stronger H-bonds. First, the SHP-HPNCs-initial and SHP-HPNCs-cut possess high long-term stability and dramatically suppressed lead leakage as low as 0.6 ppm along with a low leakage rate of 1.11 × 10^-5 cm² and 3.36 × 10^-5 cm² even over 6 months in water. Second, the Cs_0.5 FA_0.5 PbBr₃ HPNCs and SHP-induced shattered-repaired perovskite glass substrate show the lowest lasing threshold values of 1.24 and 8.58 µJ cm^-2 , respectively. This work provides an integrative and in-depth approach to exploiting SHP with intrinsic and entropic self-healing capabilities combined with HPNCs to develop robust and reliable soft-electronic backlight and laser applications.

Self-Healing Polymer Electrolytes for Next-Generation Lithium Batteries

The integration of polymer materials with self-healing features into advanced lithium batteries is a promising and attractive approach to mitigate degradation and, thus, improve the performance and reliability of batteries. Polymeric materials with an ability to autonomously repair themselves after damage may compensate for the mechanical rupture of an electrolyte, prevent the cracking and pulverization of electrodes or stabilize a solid electrolyte interface (SEI), thus prolonging the cycling lifetime of a battery while simultaneously tackling financial and safety issues. This paper comprehensively reviews various categories of self-healing polymer materials for application as electrolytes and adaptive coatings for electrodes in lithium-ion (LIBs) and lithium metal batteries (LMBs). We discuss the opportunities and current challenges in the development of self-healable polymeric materials for lithium batteries in terms of their synthesis, characterization and underlying self-healing mechanism, as well as performance, validation and optimization.

NIR-Triggered High-Efficiency Self-Healable Protective Optical Coating for Vision Systems

Recently, self-healing materials have evolved to recover specific functions such as electronic, magnetic, acoustic, structural or hierarchical, and biological properties. In particular, the development of self-healing protection coatings that can be applied to lens components in vision systems such as augmented reality glasses, actuators, and image and time-of-flight sensors has received intensive attention from the industry. In the present study, we designed polythiourethane dynamic networks containing a photothermal N-butyl-substituted diimmonium borate dye to demonstrate their potential applications in self-healing protection coatings for the optical components of vision systems. The optimized self-healing coating exhibited a high transmittance (∼95% in the visible-light region), tunable refractive index (up to 1.6), a moderate Abbe number (∼35), and high surface hardness (>200 MPa). When subjected to near-infrared (NIR) radiation (1064 nm), the surface temperature of the coating increased to 75 °C via the photothermal effect and self-healing of the scratched coatings occurred via a dynamic thiourethane exchange reaction. The coating was applied to a lens protector, and its self-healing performance was demonstrated. The light signal distorted by the scratched surface of the coating was perfectly restored after NIR-induced self-healing. The photoinduced self-healing process can also autonomously occur under sunlight with low energy consumption.

Surface Hydrophobization Provides Hygroscopic Supramolecular Plastics Based on Polysaccharides with Damage-Specific Healability and Room-Temperature Recyclability

Supramolecular materials with room-temperature healability and recyclability are highly desired because they can extend materials lifetimes and reduce resources consumption. Most approaches toward healing and recycling rely on the dynamically reversible supramolecular interactions, such as hydrogen, ionic and coordinate bonds, which are hygroscopic and vulnerable to water. The general water-induced plasticization facilitates the healing and reprocessing process but cause a troubling problem of random self-adhesion. To address this issue, here it is reported that by modifying the hygroscopic surfaces with hydrophobic alkyl chains of dodecyltrimethoxysilane (DTMS), supramolecular plastic films based on commercial raw materials of sodium alginate (SA) and cetyltrimethylammonium bromide (CTAB) display extraordinary damage-specific healability. Owing to the hydrophobic surfaces, random self-adhesion is eliminated even under humid environment. When damage occurs, the fresh surfaces with ionic groups and hydroxyl groups expose exclusively at the damaged site. Thus, damage-specific healing can be readily facilitated by water-induced plasticization. Moreover, the films display excellent room-temperature recyclability. After multiple times of reprocessing and re-modifying with DTMS, the rejuvenated films exhibit fatigueless mechanical properties. It is anticipated that this approach to damage-specific healing and room-temperature recycling based on surface hydrophobization can be applied to design various of supramolecular plastic polysaccharides materials for building sustainable societies.

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.

Intrinsically Self-Healing Polymers: From Mechanistic Insight to Current Challenges

Self-healing materials open new prospects for more sustainable technologies with improved material performance and devices' longevity. We present an overview of the recent developments in the field of intrinsically self-healing polymers, the broad class of materials based mostly on polymers with dynamic covalent and noncovalent bonds. We describe the current models of self-healing mechanisms and discuss several examples of systems with different types of dynamic bonds, from various hydrogen bonds to dynamic covalent bonds. The recent advances indicate that the most intriguing results are obtained on the systems that have combined different types of dynamic bonds. These materials demonstrate high toughness along with a relatively fast self-healing rate. There is a clear trade-off relationship between the rate of self-healing and mechanical modulus of the materials, and we propose design principles of polymers toward surpassing this trade-off. We also discuss various applications of intrinsically self-healing polymers in different technologies and summarize the current challenges in the field. This review intends to provide guidance for the design of intrinsic self-healing polymers with required properties.

Multistimuli-Responsive PNIPAM-Based Double Cross-Linked Conductive Hydrogel with Self-Recovery Ability for Ionic Skin and Smart Sensor

Multistimuli-responsive conductive hydrogels have been appealing candidates for multifunctional ionic skin. However, the fabrication of the multistimuli-responsive conductive hydrogels with satisfactory mechanical property to meet the practical applications is still a great challenge. In this study, a novel poly(N-isopropylacrylamide-co-sodium acrylate)/alginate/hectorite clay Laponite XLS (PNIPAM-SA/ALG/XLS) double cross-linked hydrogel with excellent mechanical property, self-recovery ability, temperature/pH-responsive ability, and strain/temperature-sensitive conductivity was fabricated. The PNSAX hydrogel possessed a moderate tensile strength of 290 kPa at a large elongation rate of 1120% and an excellent compression strength of 2.72 MPa at 90%. The hydrogel also possessed excellent mechanical repeatability and self-recovery ability. Thus, the hydrogel could withstand repetitive deformations for long time periods. Additionally, the hydrogel could change its transparency and volume once at a temperature of 44 °C and change its volume at different pHs. Thus, the visual temperature/pH-responsive ability allowed the hydrogel to qualitatively harvest environmental information. Moreover, the hydrogel possessed an excellent conductivity of 0.43 S/m, and the hydrogel could transform large/subtle deformation and temperature information into electrical signal change. Thus, the ultrafast strain/temperature-sensitive conductivity allowed the hydrogel to quantitatively detect large/small-scale human motions as well as environmental temperature. A cytotoxicity test confirmed the good cytocompatibility. Taken together, the hydrogel was suitable for human motion detecting and environmental information harvesting for long time periods. Therefore, the hydrogel has a great application potential as a multifunctional ionic skin and smart sensor.

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.

New Building Blocks for Self-Healing Polymers

The healing efficiency in self-healing materials is bound by the ability to form blends between the prepolymer and curing agent. One of the problems in the development of self-healing polymers is the reduced affinity of the bismaleimide curing agent for the elastomeric furan-containing matrix. Even when stoichiometric amounts of both components are applied, incompatibility of components can significantly reduce the effectiveness of self-healing, and lead to undesirable side effects, such as crystallization of the curing agent, in the thickness and on the surface. This is exactly what we have seen in the development of linear and cross-linked PUs using BMI as a hardener. In this work, we present a new series of the di- and tetrafuranic isocyanate-related ureas-promising curing agents for the development of polyurethanes-like self-healing materials via the Diels-Alder reaction. The commonly used isocyanates (4,4'-Methylene diphenyl diisocyanate, MDI; 2,4-Tolylene diisocyanate, TDI; and Hexamethylene diisocyanate, HDI) and furfurylamine, difurfurylamine, and furfuryl alcohol (derived from biorenewables) as furanic compounds were utilized for synthesis. The remendable polyurethane for testing was synthesized from a maleimide-terminated prepolymer and one of the T-series urea. Self-healing properties were investigated by thermal analysis. Molecular mass was determined by gel permeation chromatography. The properties of the new polymer were compared with polyurethane from a furan-terminated analog. Visual tests showed that the obtained material has thermally induced self-healing abilities. Resulting polyurethane (PU) has a rather low fusing point and thus may be used as potential material for Fused Deposition Modeling (FDM) 3D printing.

A Comprehensive Review of Self-Healing Polymer, Metal, and Ceramic Matrix Composites and Their Modeling Aspects for Aerospace Applications

Composites can be divided into three groups based on their matrix materials, namely polymer, metal and ceramic. Composite materials fail due to micro cracks. Repairing is complex and almost impossible if cracks appear on the surface and interior, which minimizes reliability and material life. In order to save the material from failure and prolong its lifetime without compromising mechanical properties, self-healing is one of the emerging and best techniques. The studies to address the advantages and challenges of self-healing properties of different matrix materials are very limited; however, this review addresses all three different groups of composites. Self-healing composites are fabricated to heal cracks, prevent any obstructed failure, and improve the lifetime of structures. They can self-diagnose their structure after being affected by external forces and repair damages and cracks to a certain degree. This review aims to provide information on the recent developments and prospects of self-healing composites and their applications in various fields such as aerospace, automobiles etc. Fabrication and characterization techniques as well as intrinsic and extrinsic self-healing techniques are discussed based on the latest achievements, including microcapsule embedment, fibers embedment, and vascular networks self-healing.

Highly Self-Healable Polymeric Coating Materials with Enhanced Mechanical Properties Based on the Charge Transfer Complex

Polymeric coating materials (PCMs) are promising candidates for developing next-generation flexible displays. However, PCMs are frequently subjected to external stimuli, making them highly susceptible to repeated damage. Therefore, in this study, a highly self-healing PCM based on a charge transfer complex (CTC) was developed, and its thermal, self-healing, and mechanical properties were examined. The self-healing material demonstrated improved thermal stability, fast self-healing kinetics (1 min), and a high self-healing efficiency (98.1%) via CTC-induced multiple interactions between the polymeric chains. In addition, it eliminated the trade-off between the mechanical strength and self-healing capability that is experienced by typical self-healing materials. The developed PCM achieved excellent self-healing and superior bulk (in-plane) and surface (out-of-plane) mechanical strengths compared to those of conventional engineering plastics such as polyether ether ketone (PEEK), polysulfone (PSU), and polyethersulfone (PES). These remarkable properties are attributed to the unique intermolecular structure resulting from strong CTC interactions. A mechanism for the improved self-healing and mechanical properties was also proposed by comparing the CTC-based self-healing PCMs with a non-CTC-based PCM.

Mussel-Inspired Reversible Molecular Adhesion for Fabricating Self-Healing Materials

Nature offers inspiration for the development of high-performance synthetic materials. Extensive studies on the universal adhesion and self-healing behavior of mussel byssus reveal that a series of reversible molecular interactions occurring in byssal plaques and threads play an essential role, and the mussel-inspired chemistry can serve as a versatile platform for the design of self-healing materials. In this Perspective, we provide an overview of the recent progress in the detection, quantification, and utilization of mussel-inspired reversible molecular interactions, which includes the elucidation of their binding mechanisms via force-measuring techniques and the development of self-healing materials based on these dynamic interactions. Both conventional catechol-medicated interactions and newly discovered chemistry beyond the catechol groups are discussed, providing insights into the design strategies of advanced self-healing materials via mussel-inspired chemistry.