Tannin‐Tethered Gelatin Hydrogels with Considerable Self‐Healing and Adhesive Performances

Hydrogels, especially the ones with self‐recovery and adhesive performances, have attracted more and more attention owing to their wide practical potential in the biomedical field involving cell delivery, wound filling, and tissue engineering. Tannic acid (TA), a nature‐derived gallol‐rich polyphenol, exhibits not only unique chelating properties with transition metal cations but also desirable anti‐oxidation properties and strong bonding capability to proteins and gelatin. Thus, taking advantage of the versatility of TA, a one‐pot method is proposed herein to produce TA‐modified gelatin hydrogels with the aid of NaIO₄ under basic conditions. By changing the amount of NaIO₄ used, the obtained hydrogels are covalently cross‐linked to different degrees and consequently exhibit diversity in their self‐healing and adhesive properties. The gelling time, viscoelasticity, and morphology of hydrogels are investigated, and when the feed molar ratio of NaIO₄ to TA is adjusted to 15:1, the fabricated hydrogel shows optimum self‐healing efficiency of 73% and adhesive strength of 36 kPa. Additionally, considering the completely natural origin of TA and gelatin, this study offers an original way for the fabrication of biocompatible self‐healing and adhesive materials.     

Flexible Sandwich Structural Strain Sensor Based on Silver Nanowires Decorated with Self‐Healing Substrate

Flexible and stretchable conducting composites that can sense stress or strain are needed for several emerging fields including human motion detection and personalized health monitoring. Silver nanowires (AgNWs) have already been used as conductive networks. However, once a traditional polymer is broken, the conductive network is subsequently destroyed. Integrating high pressure sensitivity and repeatable self‐healing capability into flexible strain sensors represents new advances for high performance strain sensing. Herein, superflexible 3D architectures are fabricated by sandwiching a layer of AgNWs decorated self‐healing polymer between two layers of polydimethylsiloxane, which exhibit good stability, self‐healability, and stretchability. For better mechanical properties, the self‐healing polymer is reinforced with carbon fibers (CFs). The sensors based on self‐healing polymer and AgNWs conductive network show high conductivity and excellent ability to repair both mechanical and electrical damage. They can detect different human motions accurately such as bending and recovering of the forearm and shank, the changes of palm, fist, and fingers. The fracture tensile stress of the reinforced self‐healing polymer (9 wt% CFs) is increased to 10.3 MPa with the elongation at break of 8%. The stretch/release responses under static and dynamic loads of the sensor have a high sensitivity, large sensing range, excellent reliability, and remarkable stability.     

Self‐Detecting and Self‐Healing Reinforce Elastomer Doped with Aggregation‐Induced Emission Molecules

Most of elastomers for fabrication of comfortable epidermal devices and smart actuators produce responsive signals by the stimuli‐induced deformation. Herein, a dynamic visualization of external stimuli rather than the deformation through synthesis of a self‐healing poly(dimethylsiloxane) (PDMS)‐based elastomer doped with aggregation‐induced emission (AIE) molecules is reported. The self‐healing PDMS‐based elastomer is designed and synthesized through molecule integration of reversible multi‐strength H‐bonds and permanent covalent crosslink sites. The adjustment of the weight ratio of elastic cross‐linker offers tunable mechanical properties of the resultant elastomer. After doping such an elastomer with AIE molecules of 1,1,2,2‐tetrakis(4‐nitrophenyl)ethane, the elastomer composite displays strong on–off fluorescence depending upon mechanical damage and temperatures, which can be used to detect the breaking and self‐healing performances, as well as the temperature change. The strategy described here provides another way to develop smart polymeric elastomers for practical applications.     

High‐Performance Flexible Pressure and Temperature Sensors with Complex Leather Structure

The ability of the skin to be pressure‐sensitive has prompted scientists to develop materials and equipment to simulate this function. Recently, flexible and stretchable artificial electronic skin has received increasing attention with its unique ability to detect subtle pressure changes. Pressure sensing is one of the key functions of electronic skin devices. Here, a stretchy and highly sensitive pressure sensor is developed that used a polydimethylsiloxane (PDMS) film with leather composite layer as flexible part. These features enable the sensor to accurately detect a variety of human activities, such as small finger movements and bending, pulse and so on. The sensor is found to have a good sensing signal for temperature. This feature provides great promise for sensors to detect temperature.     

Evaluation of Norbornene‐Based Adhesives to Amine‐Cured Epoxy for Self‐Healing Applications

High adhesive strengths are essential in self‐healing polymers. In these novel materials, healing is triggered by crack propagation through embedded microcapsules in an epoxy matrix, which then release the liquid healing agent into the crack plane. Subsequent exposure of the healing agent to an embedded chemical initiator triggers ring‐opening metathesis polymerization (ROMP), bonding the crack faces closed. In order to improve self‐healing efficiencies in these systems, it is necessary to improve the adhesion of the polymerized healing agent with the epoxy matrix. In this study, the adhesive shear strength between different norbornene‐based healing agents and an amine‐cured epoxy resin was evaluated using single lap shear specimens. The healing agents tested include endo‐dicyclopentadiene (DCPD), 5‐ethylidene‐2‐norbornene (ENB) and DCPD/ENB blends. 5‐Norbornene‐2‐methanol (NBM) and 5‐norbornene‐2‐exo,3‐exo‐dimethanol (NBDM) were used as adhesion promoters because they contain hydroxyl groups which can form hydrogen bonds with the amine‐cured epoxy adherend. A custom synthesized norbornene‐based crosslinking agent was also added to improve the adhesion of the polymerized ENB by increasing its crosslink density after ROMP. The effects of catalyst loading, polymerization time and cure temperature on the adhesive bond strength are studied in detail.

     

A Facile Strategy for Preparing Tough,Self‐Healing Double‐Network Hyaluronic Acid Hydrogels Inspired by Mussel Cuticles

Compared with hydrogel‐like biological tissues such as cartilage, muscles, and blood vessels, current hyaluronic acid hydrogels often suffer from poor toughness and limited self‐healing properties. Herein, a facile and generalizable strategy inspired by mussel cuticles is presented to fabricate tough and self‐healing double‐network hyaluronic acid hydrogels. These hydrogels are composed of ductile, reversible Fe³⁺‐catechol interaction primary networks, and secondarily formed brittle, irreversible covalent networks. Based on this design strategy, the hyaluronic acid hydrogels are demonstrated to exhibit reinforced mechanical strength while maintaining a rapid self‐healing property. In addition, by simply regulating pH or UV irradiation time, the mechanical properties of the hydrogels can be regulated conveniently through variations between the primary and secondary networks.     

Nanoclay Reinforced Self‐Cross‐Linking Poly(N‐Hydroxyethyl Acrylamide) Hydrogels with Integrated High Performances

Despite recent significant progress in fabricating tough hydrogels, it is still a challenge to realize high strength, large stretchability, high toughness, rapid recoverability, and good self‐healing simultaneously in a single hydrogel. Herein, Laponite reinforced self‐cross‐linking poly(N‐hydroxyethyl acrylamide) (PHEAA) hydrogels (i.e., PHEAA/Laponite nanocomposite [NC] gels) with dual physically cross‐linked network structures, where PHEAA chains can be self‐cross‐linked by themselves and also cross‐linked by Laponite nanoplatelets, demonstrate integrated high performances. At optimal conditions, PHEAA/Laponite NC gels exhibit high tensile strength of 1.31 MPa, ultrahigh tensile strain of 52.23 mm mm^?1, high toughness of 2238 J m^?2, rapid self‐recoverability (toughness recovery of 79% and stiffness recovery of 74% at room temperature for 2 min recovery without any external stimuli), and good self‐healing properties (strain healing efficiency of 42%). The work provides a promising and simple strategy for the fabrication of dual physically cross‐linked NC gels with integrated high performances, and helps to expand the fundamentals and applications of NC gels.     

Flexible Polysaccharide Hydrogel with pH‐Regulated Recovery of Self‐Healing and Mechanical Properties

A self‐healable hydrogel with recoverable self‐healing and mechanical properties is reported. The hydrogel (coded as ACSH) crosslinked by Schiff base linkage contains two polysaccharides of acrylamide‐modified chitosan (AMCS) and oxidized alginate (ADA). Self‐healing and mechanical properties are heavily influenced by the crosslinking time. The hydrogel crosslinked for 2 h possesses better mechanical and self‐healing properties than hydrogel crosslinked for 24 h. Macroscopic test shows that hydrogel without self‐healing ability can recover the self‐repair and mechanical properties by adjusting the pHs. The recovery of self‐healing and mechanical properties relies on the pH sensitivity of the Schiff base linkage. Adjusting the pH to acid, the Schiff base linkage becomes unstable and breaks. Regulating the pH to neutral, reconstruction of Schiff base linkage leads to recovery of the self‐repair and mechanical properties. The recoverable self‐healing property can be cycled once breakage and reconstruction of the Schiff base linkage can be conducted. In addition, this study demonstrates that the hydrogel can be remodeled into different shapes based on self‐healing property of the hydrogel. It is anticipated that this self‐healable hydrogel with recoverable self‐healing and mechanical properties may open a new way to investigate self‐healing hydrogel and find potential applications in different biomedical fields.     

Highly Flexible,Tough, and Self‐Healable Hydrogels Enabled by Dual Cross‐Linking of Triblock Copolymer Micelles and Ionic Interactions

Development of artificial soft materials that have good mechanical performances and autonomous healing ability is a longstanding pursuit but remains challenging. This work reports a kind of highly flexible, tough, and self‐healable poly(acrylic acid)/Fe(III) (PAA/Fe(III)) hydrogels. The hydrogels are dually cross‐linked by triblock copolymer micelles and ionic interaction between Fe(III) and carboxyl groups. Due to the coexistence of these two cross‐linking points, the resulting PAA/Fe(III) hydrogels are tough and can be flexibly stretched, bent, knotted, and twisted. The hydrogels can withstand a deformation of 600% and an ultimate stress as high as 250 kPa. Moreover, the dynamic ionic interaction also endows the hydrogels self‐healing properties. By varying the ratio of Fe(III)/AA, a compromised healing efficiency of 73% and an ultimate stress of 200 kPa are obtained.

     

Durable,Sensitive, and Wide‐Range Wearable Pressure Sensors Based on Wavy‐Structured Flexible Conductive Composite Film

Flexible pressure sensors have potential applications in human motion monitoring and electronic skins. To satisfy the practical applications, pressure sensors with a high sensitivity, a low detection limit, a broad response range, and an excellent stability are highly needed. Here, a piezoresistive pressure sensor based on wavy‐structured single‐walled carbon nanotube/graphite flake/thermoplastic polyurethane (SWCNT/GF/TPU) composite film is fabricated by a prestretching process. Due to the random wavy structure, high conductivity, and good flexibility, the prepared sensor displays a low detection limit of 2 Pa, a wide sensing range of 0–60 kPa, and a high sensitivity of 5.49 kPa^?1 for 0–50 Pa. Furthermore, the sensor shows a remarkable repeatability of over 1.1 × 10⁴, 9.0 × 10³, and 2.0 × 10³ pressure loading/unloading cycles at 50 Pa, 500 Pa, and 30 kPa, respectively, and a fast responsibility of 100–150 ms of loading response time and 400–600 ms of relaxation time. Therefore, the pressure sensor is successfully adopted to monitor both the large‐scale human activities (e.g., walk and jump) and the small‐scale signals (e.g., wrist pulse). Furthermore, a sensor array is assembled to map the weight and shape of an object, indicating its various potential applications including human–machine interactions, human health monitoring, and other wearable electronics.     

Microwave‐Assisted Reversible Coordination‐Mediated Polymerization for Self‐Healing Hybrid Materials: RGO@PDA Simultaneous as Catalyst and Nanocomposites in One‐Pot

In this article, polydopamine (PDA) is efficiently adhered on the surface of graphene oxide (GO) by mussel‐inspired chemistry. The obtained reduced GO/PDA (RGO@PDA) nanocomposites are used for catalyzing reversible coordination‐mediated polymerization under microwave radiation. Well‐defined and iodine‐terminated polyacrylonitrile‐co‐poly(n‐butyl acrylate) (PAN‐co‐PnBA) is successfully fabricated by using RGO@PDA nanocomposites as catalysts. Importantly, green and novel strategy of PAN‐co‐PnBA‐type self‐healing nanocomposite materials is further fabricated with RGO@PDA as additive after polymerization as catalyst in one‐pot. As a reinforcement agent, RGO@PDA can also improve the mechanical and self‐healing properties of hybrid materials, which opens up a novel and green methodology for the preparation of self‐healing hybrid materials.     

Highly Stretchable,Transparent, and Bio‐Friendly Strain Sensor Based on Self‐Recovery Ionic‐Covalent Hydrogels for Human Motion Monitoring

Stretchable, flexible, and strain‐sensitive hydrogels have gained tremendous attention due to their potential application in health monitoring devices and artificial intelligence. Nevertheless, it is still a huge challenge to develop an integrated strain sensor with excellent mechanical properties, broad sensing range, high transparency, biocompatibility, and self‐recovery. Herein, a simple paradigm of stretchable strain sensor based on multifunctional hydrogels is prepared by constructing synergistic effects among polyacrylamide (PAM), biocompatible macromolecule sodium alginate (SA), and Ca ion in covalently and ionically crosslinked networks. Under large deformation, the dynamic SA‐Ca²⁺ bonds effectively dissipate energy, serving as sacrificial bonds, while the PAM chains bridge the crack and stabilize the network, endowing hydrogels with outstanding mechanical performances, for instance, high stretchability and compressibility, as well as excellent self‐recovery performance. The hydrogel is assembled to be a transparent and wearable strain sensor, which has good sensitivity and very wide sensing range (0–1700%), and can precisely detect dynamic strains, including both low and high strains (20–800% strain). It also exhibits fast response time (800 ms) and long‐time stability (200 cycles). The sensor can monitor and distinguish complicated human motions, opening up a new route for broad potential applications of eco‐friendly flexible strain‐sensing devices.     

Self‐Healing and Shape‐Memory Superconducting Devices

Intelligent materials possess the function of self‐judgment and self‐optimization while sensing external stimuli such as stress, temperature, moisture, pH, electric or magnetic fields, or light. Besides, they often require self‐healing—the ability to repair damage spontaneously—or shape‐memory—the ability to return from a deformed state to their original shape induced by an external stimulus. Introducing such intelligence into superconducting (SC) devices is highly desirable to meet the critical requirement of maintenance‐free performance. Here, self‐healing and shape‐memory functions are realized in liquid metal based SC devices using smart packaging polymers. Without deteriorating their superconductivity, the SC devices can repair themselves by simply raising the temperature, without any other treatment. Beyond the specific functions achieved here, this work sheds new light on future SC devices with advanced functions such as self‐diagnosis, self‐adjusting, and sensing.     

Transparent Surfactant/Epoxy Composite Coatings with Self‐Healing and Superhydrophilic Properties

In this paper, highly transparent, robust, and superhydrophilic polyethylene glycol tert‐octylphenyl ether nonionic surfactant/epoxy (Triton X‐100/epoxy, TXE) composite coatings are successfully prepared with a facile, one‐step drop‐casting method by mixing Triton X‐100 with an epoxy resin and an amine curing agent. The hydrogen bond reaction between the hydroxyl group of Triton X‐100 and the ether group of the epoxy resin improves the compatibility and reduces the glass transition temperature (T_g) of the TXE composite coatings. The free Triton X‐100 surfactant easily accumulates on the surface of the TXE composite coatings, which improves the hydrophilicity of the TXE composite coatings. The TXE composite coatings are self‐healable because of their low T_g and the migration of Triton X‐100 small molecule surfactant. Any damage arising from denting, cutting, or wiping by tetrahydrofuran can be healed, and the composite coating can regain its superhydrophilic properties through a heating process. The TXE composite coatings demonstrate excellent acid, alkali, salt, high temperature, and ultrasonic‐resistant properties. This facile preparation technique has the potential to be applied in the scalable fabrication of multifunctional coatings in anti‐fogging, oil–water separation, and optical–electric devices.     

A Self‐Healing PAM/CMHPG System for Unconventional Reservoir Stimulation

A hybrid chemically and physically linked polyacrylamide (PAM)/carboxymethyl hydroxypropyl guar gum (CMHPG) system is prepared via a fast and controllable one‐pot strategy. Due to the synergetic effect of the non‐covalent interactions between chains, these systems show improved, balanced mechanical properties. The apparent morphology, storage modulus G′, and loss modulus G″ show that these systems have rapid and almost full recovery ability (the self‐healing efficiency can reach 95%) with several hydrogen‐bonding interactions between two networks. This self‐healing property can cover the shortage of G′, G″, and viscosity loss at high shear force, which will help the system keep enough viscosity to create fractures or carry proppants during the whole fracturing process. Meanwhile, the self‐healing fracturing fluid can be broken easily and flow back to surface with little damage to the fracture conductivity, indicating great potential in unconventional reservoir which is sensitive to the fracturing fluid damage.     

Chamber/Capsule‐Integrated Self‐Healing Coating on Glass for Preventing Crack Propagation

A transparent self‐healing coating incorporating chambers and capsules capable of preventing the propagation of cracks in glass is presented. The main features simultaneously satisfy the requirements of high transmittance (≈90% in the visible region) and the ability to heal random and large‐area cracks in coated‐glass materials (up to 6 cm long, 20 µm wide, and 1 mm deep per chamber). Additionally, the polymerized hydrogel used as the healing agent can stop crack propagation because of its high mechanical strength and good adhesion to glass. Remarkably, the healed glass can withstand a force approximately four times greater than what can be withstood by the unhealed glass after cracking.