Self-healing Function Research Articles

Hierarchically Structured Carbon Nanofiber-Enabled Skin-Like Strain Sensors with Full-Range Human Motion Monitoring and Autonomous Self-Healing Capability

Flexible strain sensors that mimic the properties of human skin have recently attracted tremendous attention. However, integrating multiple functions of skin into one strain sensor, e.g., stretchability, full-range motion response, and self-healing capability, is still an enormous challenge. Herein, a skin-like strain sensor was presented by the construction of hierarchically structured carbon nanofibers (CNFs), followed by encapsulation of elastic self-healing polyurethane (PU). The hierarchical sensing structure was composed of diversified CNFs with orientations from highly aligned to randomly oriented, and their different fracture mechanisms enabled the resultant strain sensor to successfully integrate key sensing properties including high sensitivity (gauge factor of 90), wide sensing range (∼80% strain), and fast response (52 ms). These properties, combined with high stretchability (870%) and excellent stability (>2000 cycles), allowed the sensor to precisely detect full-range human motions from large joint motions to subtle physiological signals. Moreover, the strain sensor had spontaneous self-healing capability at room temperature with high healing efficiencies of 97.7%, while the healing process could substantially be accelerated by the natural sunlight (24 h → 0.5 h). The healed sensor possessed comparable stretchability, sensing performance, and accurate monitoring ability of subtle body signals with the original sensor. The biomimetic self-healing functionality along with skin-like sensing properties makes it attractive for next-generation wearable electronics.

Corrosion resistance and mechanisms of smart micro-arc oxidation/epoxy resin coatings on AZ31 Mg alloy: Strategic positioning of nanocontainers

Smart micro-arc oxidation (MAO)/epoxy resin (EP) composite coatings were formed on AZ31 magnesium (Mg) alloy. Mesoporous silica nanocontainers (MSN) encapsulated with sodium benzoate (SB) corrosion inhibitors were strategically incorporated in the MAO micropores and in the top EP layer. The influence of the strategic positioning of the nanocontainers on the corrosion protective performance of coating was investigated. The experimental results and analysis indicated that the superior corrosion resistance of the hybrid coating is ascribed to the protection mechanisms of the nanocontainers. This involves two phenomena: (1) the presence of the nanocontainers in the MAO micropores decreased the distance between MSN@SB and the substrate, demonstrating a low admittance value (∼ 5.18 × 10−8 Ω−1), and thus exhibiting significant corrosion inhibition and self-healing function; and (2) the addition of nanocontainers in the top EP layer densified the coating via sealing of the inherent defects, and hence the coating maintained higher resistance even after 90 days of immersion (1.13 × 1010 Ω cm2). However, the possibility of corrosion inhibitors located away from the substrate transport to the substrate is reduced, reducing its effective utilization rate. This work demonstrates the importance of the positioning of nanocontainers in the coating for enhanced corrosion resistance, and thereby providing a novel perspective for the design of smart protective coatings through regulating the distribution of nanocontainers in the coatings.

Achieving anti-corrosion and anti-biofouling dual-function self-healing coating by natural carrier attapulgite loading with 2-Undecylimidazoline

In the marine environment, the protective coatings face serious corrosion and biofouling problem, limitations, and challenges that made self-healing coatings unable to perform both anti-corrosion and anti-biofouling dual-function at the same time. Here we constructed the corrosion resistance and anti-biofouling self-healing coating by integrating nano-containers into the coating matrix, the 2-Undecylimidazoline (ULM) acted as a corrosion inhibitor and anti-biofouling dual-functional agent which was loaded on the natural container attapulgite (ATP). To obtain high healing efficiency, a fluidity-driven self-healing silicone oil coating was thickened by fibrous ATP to enhance its stability, which played a key role in the self-healing and long-term corrosion resistance. The self-healing time of ULM@ATP reinforced oil coating was 4 s at least in the air and up to 30 s in the 1 M HCl solution. Meanwhile, the ULM@ATP can significantly enhance the corrosion resistance of the self-healing coating, with the best effect achieved when the content of ULM@ATP was 5 wt.%. The impedance modulus of ULM@ATP-2 still reached 1.62 × 108 Ω cm2 after 480 immersion in 3.5 wt.% NaCl solution, which is 3 orders of magnitude high than pure Oil coating (2.17 × 105 Ω cm2). The restructure of the ATP network and the release of ULM could largely inhibit the corrosion of metal. The continuous open circuit potential of the composite coating performed the potentially infinite self-healing capacity. The self-healing performances of the composite coating in strong acid and base solutions exhibited high environmental suitability. This anti-corrosion and anti-biofouling (the surface coverage of adhered chlorella decreased 96.88%) dual-function strategy of self-healing coatings could be also realized by many other porous nano-materials or function modifications. The self-healing performances of the composite coating in strong acid and base solutions exhibited high environmental suitability. This anti-corrosion and anti-biofouling dual-function strategy of self-healing coatings could be also realized by many other porous nano-materials or function modifications. The rapid response self-healing coating possessed anti-biofouling and active self-healing functions and showed wide application under more service environments.

Master-slave strategy based in artificial intelligence for the fault section estimation in active distribution networks and microgrids

Fault location plays an essential role in the integration of self-healing functionalities in active distribution networks and microgrids. However, the fault location methods formulation presents great challenges for these types of networks because the operating changes that occur them, such as changes in topology, DER connection/disconnection and microgrids operating modes. Several fault location solutions have been proposed; nevertheless, these are strongly dependent on robust communication systems. This paper presents an artificial intelligence-based master–slave strategy for the estimation of the fault section in active distribution networks and microgrids using dispersed measurements. The strategy is composed by two stages. The master stage uses a genetic algorithm that determines the location and number of devices which maximize the faulted location e performance. The slave stage uses artificial neural networks to predict the fault section by using local voltage and current measurements trough an intelligent electronic device (IED). This approach is useful because it neglects the need of a robust communication systems and synchronization process between measurements. Here, each IED estimates the faulted section and then sends it through the single communication system to the distribution system operator control center. The presented method is validated on the modified IEEE 34-nodes test feeder where the accuracy of the strategy was 95%. The results obtained and its easy implementation indicate potential for real-life applications.

Combing experimental methods and molecular simulations to study self-healing behaviors of polyurethane elastomers containing multiple hydrogen bond networks and flexible blocks.

The preparation of polymers with high self-healing ability is conducive to environmental protection and resource conservation. In the present work, two kinds of polyurethane (PU) elastomers were prepared: the one containing flexible end blocks (polypropylene glycol) and the other containing flexible end blocks and 2-ureido-4[1H]-pyrimidinone (UPy) groups that can form reversible quadruple hydrogen bonds. Both of the two PU elastomers have self-healing ability. At low temperatures the PU without UPy groups exhibits stronger self-healing ability, while at high temperatures the PU with UPy groups has better self-healing function. The difference can be attributed to the combined effect of segmental mobility and reversible network strength. Based on molecular simulations, we further observed that the self-healing behaviors are affected by four factors: healing temperature, reversible interaction strength, reversible interaction site density and segment diffusion ability.

Preparation and properties of a photocrosslinked MCl n -doped PDMA-g-PSMA hydrogel.

To treat damaged joint areas, photocrosslinked hydrophobically associating PDMA-g-PSMA hydrogels can act as mild and easily regulated materials due to their rich pore structure, which have been widely applied in articular cartilage replacement research. In this study, the effects of ADS-MCl n (ADS-NaCl, ADS-MgCl2 and ADS-CaCl2) doping systems on the micro morphology, mechanical, self-healing, and friction properties and cytotoxicity of PDMA-g-PSMA hydrogels were studied. The results showed that the solubilization behavior of the ADS-MCl n ionic micelles affected the hydrophobic association stability, thereby changing the toughness, self-healing and friction properties of the hydrogel. Ca2+-doping resulted in the crystallization and precipitation of the anionic surfactants, destroying the solubilization ability of the ionic micelles for the hydrophobic units, and thus hydrogels with high hardness, low toughness and no self-healing function were obtained. Doping with Na+ greatly improved the dissolving power of the ADS micelles for SMA, yielding PDMA-g-PSMA hydrogels with good mechanical strength and good self-healing ability. However, in this case, a drawback is that the Na+-doped system will lose its components during the swelling process, leading to the degradation of its self-healing performance. Interestingly, Mg2+ doping resulted in the formation of highly stable ADS micellar aggregates, and then PDMA-g-PSMA hydrogels with a lower friction coefficient (0.023), less wear (35.0 mg), higher elongation at break and 100% self-healing efficiency were obtained. The hydrogel products obtained from the three doping systems all exhibited good biocompatibility. Our research provides important guidelines for the design and preparation of anti-friction artificial articular cartilage.

Biodegradable smart materials with self-healing and shape memory function for wound healing.

Notwithstanding the rapid development of suture elastomers to meet the needs of practical surgery, utilizing the elastomers' self-healing function as a surgical suture to facilitate the healing of wounds has not been addressed. Here, a biodegradable aliphatic polycarbonate smart elastomer, mPEG113-b-PMBC n , was synthesized from aliphatic polycarbonate monomer with methoxy polyethylene glycol (mPEG113, 5.0 kDa) as initiator, which exhibited excellent mechanical properties, highly efficient self-repairing, and remarkable shape memory behavior. The polymers possess outstanding self-healing ability for 150 min. Meanwhile, after 46.33 ± 1.18 s, the temporary shape of the obtained polymer had been recovered. The results of biocompatibility tests reveal that the polymers have excellent biocompatibility and can be regarded as good biomedical materials. Then, in vivo experiments were used to prove the self-healing knotting ability of the polymers and quickly close a wound surface using a programmed shape at physiological temperature. The results demonstrated that the injury wound can be effectively healed compared with traditional sutures, which will offer new study suggestions for subsequent healing areas.

Corrosion resistance and mechanisms of Nd(NO3)3 and polyvinyl alcohol organic-inorganic hybrid material incorporated MAO coatings on AZ31 Mg alloy.

This work reports the design and preparation of novel organic (polyvinyl alcohol, PVA)-inorganic (neodymium nitrate, Nd(NO3)3) hybrid coatings on micro-arc oxidation (MAO) coating for magnesium (Mg) alloy corrosion protection. X-ray diffractometer, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, field emission scanning electron microscope, Energy Dispersive X-ray spectrometer and surface roughness were applied to characterize the chemical composition and surface morphology of the coatings. The corrosion resistance of the coatings was evaluated by electrochemical and salt spray tests. The results suggested that the formation of PVA-Nd3+ and PVA-Mg2+ complexes promoted the enrichment of Nd3+ on the surface, and thereby improved the sealing quality and compactness of the coating. Interestingly, when the coating was damaged, the Nd3+ ions were transformed to their carbonates and covered the active sites, and thus exhibiting self-healing function. Further, the corrosion resistance of PVA-Nd3+ modified MAO composite coating on AZ31 Mg alloy was improved.

Legal Regulation of Internet Platform Banning Behaviors

There are frequent banning behaviors in the field of Internet platforms in China, which harm the interests of other operators, harm market innovation, and damage the rights and interests of consumers. The market self-healing function in traditional economics does not have a realistic basis and cannot play its practical effect. The regulation of the banning behavior not only will not produce economic damage, but also is conducive to reduce the damage of rights and interests in the competitive market, so it is urgent to regulate this behavior through the anti-monopoly law.The exsiting anti-monopoly law has the dilemma of insufficient explanation and limited application to the regulation of the banning behavior. It is feasible and necessary to introduce the ex ante supervision mode of the comparative law, namely the platform gatekeeper theory, which can effectively suppress the banning behavior of the platform. Therefore, the gatekeeper theory should be perfected from the aspects of gatekeeper’s definition standard, gatekeeper’s obligation and gatekeeper’s platform’s defense.This paper provides implications for improving the regulation of banning behaviors in China.

Self-healing and superhydrophobic dual-function composite coating for active protection of magnesium alloys

Anti-corrosion inorganic-organic hybrid coating with the self-healing feature is still scare for the Mg alloys. The adhesion between various compositions is one troublesome problem. On the other hand, the incorporation of corrosion inhibitor would destroy the feature of organic film leading to the inferior anti-corrosion performance. The hybrid coating, PEO/IN/QSE, with the self-healing feature is firstly fabricated on Mg alloys, in which the corrosion inhibitor of imidazolium-based ionic liquid (IN) is embedded in the plasma electrolytic oxidation (PEO) pores and the superhydrophobic film (QSE) is covered on the top. The IN embedded in the pores of PEO layer does not destroy the feature of QSE film and improve the anti-corrosion performance of PEO layer. And it affords the self-healing function, which is determined by the anti-corrosion test with the scratched samples. More important, it strengthens the adhesion between QSE and PEO coating as a bridge. This work provides a feasible strategy to prepare the inorganic-organic composite film with the promising applications for the anti-corrosion of the Mg alloys.

Self-Healing Superwetting Surfaces, Their Fabrications, and Properties.

The research on superwetting surfaces with a self-healing function against various damages has progressed rapidly in the recent decade. They are expected to be an effective approach to increasing the durability and application robustness of superwetting materials. Various methods and material systems have been developed to prepare self-healing superwetting surfaces, some of which mimic natural superwetting surfaces. However, they still face challenges, such as being workable only for specific damages, external stimulation to trigger the healing process, and poor self-healing ability in the water, marine, or biological systems. There is a lack of fundamental understanding as well. This article comprehensively reviews self-healing superwetting surfaces, including their fabrication strategies, essential rules for materials design, and self-healing properties. Self-healing triggered by different external stimuli is summarized. The potential applications of self-healing superwetting surfaces are highlighted. This article consists of four main sections: (1) the functional surfaces with various superwetting properties, (2) natural self-healing superwetting surfaces (i.e., plants, insects, and creatures) and their healing mechanism, (3) recent research development in various self-healing superwetting surfaces, their preparation, wetting properties in the air or liquid media, and healing mechanism, and (4) the prospects including existing challenges, our views and potential solutions to the challenges, and future research directions.

An anti-corrosion coating with self-healing function of polyurethane modified by lipoic acid

An anti-corrosion coating with self-healing function of polyurethane modified by lipoic acid

High-strength, fatigue-resistant, and fast self-healing antibacterial nanocomposite hydrogels for wound healing

The development of functional medical dressings with mechanical designability for complex wounds is crucial for the repair of tissue function. As one of the promising strategies in treating complex wounds, the unsatisfying mechanical properties and low-efficiency antimicrobial biofilm for liquid or gel dressings greatly limit their applications in many emergencies. Therefore, it is highly desirable to construct hydrogel dressings with high fatigue resistance, self-healing, and antibacterial biofilm properties. Here, we reported a strategy to build a nanocomposite hydrogel dressing to overcome these problems. The hydrogel dressings incorporated gold nanorods and Ca2+ into polyacrylic acid and polyvinyl alcohol, which endorsed the double network structure with good toughness (∼551 KJ/m3), and excellent fatigue resistance (efficiency ∼ 82.4 %). In addition, the hydrogel dressings have good biocompatibility. Significantly, the gold nanorods incorporated in the hydrogel network provide a practical photothermal effect to initiate the self-healing function (self-healing efficiency ∼ 88.2 %) and effectively eliminate various multi-bacterial biofilm (∼80 %). Furthermore, we showed that the hydrogel dressing could remove the wound bacterial biofilm and promote infected wound healing in vivo.

ZnAl-LDH@MXene modified by inhibitor as a nanofiller applied on Mg alloys coating protection

Recently, MXene/Epoxy coatings have attracted attention for its outstanding corrosion and wear resistance. However, the self-restacking tendency of MXene in epoxy resins affects the mechanical properties of coatings. Herein, ZnAl-LDH-NO3- nanosheets were grown on MXene by one-step hydrothermal method to inhibit its spontaneous aggregation, and then the ZnAl-LDH-NO3-@MXene mixed with epoxy resin was spun onto the pre-prepared Mg PEO coatings. ZnAl-LDH-NO3-@MXene nanocomposite had long-term dispersibility, resulting in a satisfactory sealing of the Mg PEO coatings. The lowest wear rate and corrosion current density of the final coating demonstrated that LDH and MXene nanosheets presented a good synergistic effect. Moreover, nitrate was simultaneously intercalated into the guest layer of the ZnAl-LDH providing a self-healing function. This work proposed a new strategy to solve the self-restacking of MXene and facilitate its anticorrosion/wear applications in epoxy coatings: that is MXene-based nanocomposite.

Designing an epoxy composite coating having dual-barrier-active self-healing anti-corrosion functions using a multi-functional GO/PDA/MO nano-hybrid

The graphene oxide, functionalized with polydopamine (PDA) bio-polymers and molybdate (MO) ions, was incorporated into the epoxy coating. The FT-IR, Raman, UV-visible, XRD, and FE-SEM/EDS analyses were utilized for the GO/PDA/MO nanoparticle characterization. The sequence of inhibitors' release from the nano-hybrid and their effect on the electrochemical behavior of the steel sample was explored by the OCP, polarization, and, EIS analyses in the aquatic saline media. EIS analyses revealed inhibition efficiency of 88% for the sample immersed in the GO/PDA/MO-contained solution after 48 h immersion. The polarization results showed a 91% corrosion mitigation index for the sample submerged in the GO/PDA/MO extract-containing solution after 48 h immersion. An increase of the scratched coating Nyquist diameter, the lower corrosion product, and coating blister formation after exposure to the salt spray chamber, as well as the lower adhesion loss in the pull-off test (26%), revealed that the epoxy coating reinforced with GO/PDA/MO nano-hybrids could mitigate the mild steel corrosion by improving the barrier performance and active corrosion protection (self-healing mechanism) behavior.

Dual-functional anti-corrosion coatings with surface hydrophobicity and internal smart-releasing Ce3+ loaded in bentonite on carbon steel

Water-based coatings are gradually replacing traditional oil-based coatings for environmentally friendly applications, which creates a new paradigm in corrosion control of metallic components. In this work, water-based ZrO2–SiO2 sol-gel coatings were prepared for corrosion protection of carbon steel. The effects of the sol-gel ZrO2 to SiO2 ratio, coating thickness, corrosion inhibitor content and surface hydrophobicity on the coating physicochemical and anti-corrosion properties were investigated. The results showed that, compared to the pure silica coating, coating with 1/9 wt% ZrO2 in SiO2 matrix and coating thickness of 25 μm provided about 7 times higher corrosion resistance (impedance modulus 1.38 × 108 Ω cm2). A smart-releasing corrosion inhibitor containing Ce3+ ions (0.91 wt%) loaded into the layered structure of bentonite showed ability to delay the corrosion of substrate by 9 orders of magnitude by trapping Cl− ions from the environment and releasing Ce3+ ions at the cracked substrate surface. By applying a hydrophobic top layer, the water contact angle increased from 89° to 115°, which further increased the impedance modulus of the coating from 2.42 × 109 to 3.60 × 109 Ω cm2. The optimized coating passed salt spray standard corrosion test for 720 h (on scribed coating) due to the cathodic protection by corrosion inhibitor and shielding effects of a top hydrophobic layer. This work provides an enhanced strategy of dual-functional anti-corrosion coatings with surface water repellency and internal smart-releasing corrosion inhibitor for steel against environmental corrosion and damages with efficient self-healing functionality.

Fabrication of Intrinsic, Elastic, Self-healing, and Luminescent CsPbBr3 Quantum Dot-Polymer Composites via Thiol–Ene Cross-Linking

Here, we offer a straightforward approach for making elastic, self-healing, and light-conversion material, in which CsPbBr3 quantum dots (QDs) form a strong bond with a designed copolymer including elastic behavior based on the mechanical characteristics of polyisoprene and reversible bonding moieties for self-healing function. This designed composite film has highly luminescent and typically elastic properties, including good ultimate strength (∼0.14 N/mm2) and high stretchability (∼486%). The copolymer matrix exhibited excellent compatibility with CsPbBr3 QDs, in which they maintained their uniform distribution within the network after a serial stretching process due to the strong bond between copolymers and CsPbBr3 QDs. Furthermore, the composite film dynamic network is capable of 90% self-healing efficiency at room temperature without the need of any healing stimulus, heat, plasticizer, or solvent. This simple method suggested a relatively easy approach to a stable, elastic, and luminescent CsPbBr3 QD-based composite film that opens up the potential of fully stretchable light conversion material for light-emitting diodes.

Self-healable, strengthened, shape memory elastomers enabled by dual cross-linked networks

We propose a strategy of combining covalent and noncovalent cross-links into carboxyl nitrile rubber (XNBR) networks to fabricate multifunctional elastomers with self-healing and shape memory ability. Specially, commercially available XNBR was cross-linked by diethylenetriamine (DETA) and trimethylolpropane tris(3-mercaptopropionate) (TMPT) through hydrogen bond interaction and thiol-ene “click” reaction, generating reversible hydrogen bonds and robust covalent bonds cross-links, respectively. The modulus of the resulted polymers is consistently enhanced with the increase of TMPT loading, indicating the cross-linking networks are gradually constrained. In addition, the samples demonstrate self-healing and shape memory functions due to the reversible hydrogen bonds and robust covalent cross-links. When the content of TMPT is 0, the sample shows the high elongation at break and appropriate tensile strength. It can achieve almost complete healing due to the material contains noncovalent bonds only. When the content of TMPT is 2 phr, the sample exhibits both pretty self-healing and moderate shape memory ability. This strategy might provide an alternative way to construct intelligent multifunctional polymers with versatile functions.

Cross-Linked Gel Electrolytes with Self-Healing Functionalities for Smart Lithium Batteries.

Next-generation Li-ion batteries must guarantee improved durability, quality, reliability, and safety to satisfy the stringent technical requirements of crucial sectors such as e-mobility. One breakthrough strategy to overcome the degradation phenomena affecting the battery performance is the development of advanced materials integrating smart functionalities, such as self-healing units. Herein, we propose a gel electrolyte based on a uniform and highly cross-linked network, hosting a high amount of liquid electrolyte, with multiple advantages: (i) autonomous, fast self-healing, and a promising PF5-scavenging role; (ii) solid-like mechanical stability despite the large fraction of entrapped liquid; and (iii) good Li+ transport. It is shown that such a gel electrolyte has very good conductivity (>1.0 mS cm-1 at 40 °C) with low activation energy (0.25 eV) for the ion transport. The transport properties are easily restored in the case of physical damages, thanks to the outstanding capability of the polymer to intrinsically repair severe cracks or fractures. The good elastic modulus of the cross-linked network, combined with the high fraction of anions immobilized within the polymer backbone, guarantees stable Li electrodeposition, disfavoring the formation of mossy dendrites with the Li metal anode. We demonstrate the electrolyte performance in a full-cell configuration with a LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode, obtaining good cycling performance and stability.

Ultraelastic and High-Conductivity Multiphase Conductor with Universally Autonomous Self-Healing.

Next-generation, truly soft, and stretchable electronic circuits with material level self-healing functionality require high-performance solution-processable organic conductors capable of autonomously self-healing without external intervention. A persistent challenge is to achieve required performance level as electrical, mechanical, and self-healing properties optimized in tandem are difficult to attain. Here heterogenous multiphase conductor with cocontinuous morphology and macroscale phase separation for ultrafast universally autonomous self-healing with full recovery of pristine tensile and electrical properties in less than 120 and 900 s, respectively, is reported. The multiphase conductor is insensitive to flaws under stretching and achieves a synergistic combination of conductivity up to ≈1.5 S cm-1 , stress at break ≈4MPa, toughness up to >81MJ m-3 , and elastic recovery exceeding 2000% strain. Such properties are difficult to achieve simultaneously with any other type of material so far. The solution-processable multiphase conductor offers a paradigm shift for damage tolerant and environmentally resistant soft electronic components and circuits with material level self-healing.