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

Tough and Multifunctional Composite Film Actuators Based on Cellulose Nanofibers toward Smart Wearables

Although humidity-responsive actuators serve as a promising candidate in smart wearables, artificial muscles, and biomimetic devices, most of them derived from synthetic polymers could not simultaneously achieve multifunctional properties. In this work, a cellulose nanofiber (CNF)-based film actuator with high mechanical properties, excellent Joule heating, and antibacterial capability is successfully constructed by integrating with Ti₃C₂T_x (MXene) and tannic acid (TA) via a vacuum-assisted filtration approach. Owing to the unique nacrelike structure and strong hydrogen bonds, the tensile strength and toughness of the composite film could reach 275.4 MPa and 10.2 MJ·m^-3, respectively. Importantly, the hydrophilic nature of CNFs and alterable interlayer spacing of MXene nanosheets endow the composite film with sensitive humidity response and extraordinary stability (1000 cycles). With the assistance of MXene nanosheets and TA, the composite film could not only present outstanding Joule heating but also possess remarkable antibacterial properties against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Benefiting from the above merits, the proof-of-concept smart garment is assembled by the as-prepared film and is capable of regulating humidity and temperature.

Biosafe, self-adhesive, recyclable, tough, and conductive hydrogels for multifunctional sensors

As a bioelectronic material used in personalized medicine, it is necessary to integrate excellent adhesion and stretchability in hydrogels for ensuring biosafety. Herein, a high-performance multifunctional hydrogel of polyvinyl alcohol-sodium alginate-g-dopamine-silver nanowire-borax (PSAB) is reported. It can not only easily adhere to the surface of various substrates, but also exhibit excellent mechanical properties. Its tensile strength, elongation at break and toughness are 0.286 MPa, 500% and 55.15 MJ m^-3, respectively. The excellent mechanical properties and high conductivity guarantee that the PSAB hydrogel can successfully serve as a multifunctional sensor for detecting small activities and large-scale movements of the human body through strain and pressure changes. Meanwhile, the long-lasting potent and broad-spectrum antibacterial activity, combined with good in vitro biocompatibility, guarantees the biological safety and non-toxicity of the PSAB hydrogel. These compelling features, such as high flexibility and elasticity, high adhesion, multi-functional sensing and recyclability, as well as biological safety, pave the way for the application of PSAB hydrogel e-skin in biomedicine.

High performance, environmentally friendly and sustainable nanofiber membrane filter for removal of particulate matter 1.0

Particulate matter (PM) air pollution is becoming more and more serious and dangerous to public health, especially in developing countries where industrialization is accelerating. The use of electrospun membrane-based materials for air filtration is a widespread and effective way to help individuals avoid air pollution. However, most electrospun membrane preparation processes require the use of organic solvents, resulting in secondary environmental pollution. In this study, an environmentally friendly polyvinyl alcohol (PVA) - tannic acid (TA) composite nanofiber membrane filter was prepared by the green electrospinning and the physical cross-linking method. The filtration efficiency of the membrane filter for PM_1.0 reached 99.5%, and the pressure drop was only 35 Pa. In addition, due to the existence of intermolecular hydrogen bond between PVA and TA, the mechanical properties of the nanofiber membrane were improved to meet the requirements of practical application of the filter. Therefore, the PVA-TA composite nanofiber membrane is expected to provide a solution for the development of efficient and environmentally friendly air filter.

Aramid nanofibers reinforced polyvinyl alcohol/tannic acid hydrogel with improved mechanical and antibacterial properties for potential application as wound dressing

The poor mechanical properties and the lack of antibacterial ability of hydrogels limit their applications as wound dressing. In this work, a novel and high strength polyvinyl alcohol (PVA)/tannic acid (TA) hydrogel with aramid nanofibers (ANFs) as the reinforcement was successfully fabricated. The surface composition and microstructure of the hydrogel were characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The mechanical properties, water content and swelling behaviors, as well as the antibacterial abilities and biocompatibility of the prepared hydrogel were systematically analyzed as well. The results indicated that the prepared hydrogel showed excellent mechanical properties. The tensile strength and elongation of the prepared hydrogel can respectively reach 2.06 MPa and 950% owing to the formation of the multiple H bonds among PVA, ANFs and TA. What's more, PVA/ANFs/TA (PAT) hydrogel possessed shape memory and broad-spectrum antibacterial properties against S. aureus, E. coli and P. aeruginosa (100% antibacterial rate) at the concentration of 12 mg/mL. PAT hydrogels also had low cytotoxicity, affirming its potential application as wound dressing.

Ultrarobust, tough and highly stretchable self-healing materials based on cartilage-inspired noncovalent assembly nanostructure

Self-healing materials integrated with excellent mechanical strength and simultaneously high healing efficiency would be of great use in many fields, however their fabrication has been proven extremely challenging. Here, inspired by biological cartilage, we present an ultrarobust self-healing material by incorporating high density noncovalent bonds at the interfaces between the dentritic tannic acid-modified tungsten disulfide nanosheets and polyurethane matrix to collectively produce a strong interfacial interaction. The resultant nanocomposite material with interwoven network shows excellent tensile strength (52.3 MPa), high toughness (282.7 MJ m^‒3, which is 1.6 times higher than spider silk and 9.4 times higher than metallic aluminum), high stretchability (1020.8%) and excellent healing efficiency (80-100%), which overturns the previous understanding of traditional noncovalent bonding self-healing materials where high mechanical robustness and healing ability are mutually exclusive. Moreover, the interfacical supramolecular crosslinking structure enables the functional-healing ability of the resultant flexible smart actuation devices. This work opens an avenue toward the development of ultrarobust self-healing materials for various flexible functional devices.

Tough double-network elastomers with slip-rings

In order to surmount the inherent trade-off between toughness and stiffness for most elastomers, we developed a strategy which let two polymer networks form an interpenetrated structure through introducing slip-rings by a very simple one-step synthesis method.

Fabrication of an injectable hydrogel with inherent photothermal effects from tannic acid for synergistic photothermal-chemotherapy

Developing injectable hydrogels with near-infrared (NIR)-responsive photothermal effects has increasingly become a promising strategy for local cancer treatment via combinational photothermal-chemotherapy. Herein, a biocompatible hydrogel with a remarkable shear-thinning and recovery capability for injection application was fabricated from 4-arm-PEG-SH and tannic acid through chemical crosslinking and multiple physical interactions. Benefiting from the formation of dynamic TA/Fe3+ complexes within gel networks, the obtained hydrogel exhibited an intrinsic NIR absorption property for photothermal ablation of tumor cells, and enhanced cellular uptake of chemotherapeutic drugs. Both in vitro and in vivo experiments revealed that the injectable hydrogel exhibited an excellent biocompatibility and a synergistic therapeutic effect on tumor growth via combinational photothermal-chemotherapy. Therefore, this work provides a promising attempt to develop an injectable and NIR-responsive hydrogel from TA/Fe3+ complexes, which could work as a localized drug delivery platform for synergistic photothermal-chemotherapy.

Tannic Acid-Silver Dual Catalysis Induced Rapid Polymerization of Conductive Hydrogel Sensors with Excellent Stretchability, Self-Adhesion, and Strain-Sensitivity Properties

The application of conductive hydrogels in intelligent biomimetic electronics is a hot topic in recent years, but it is still a great challenge to develop the conductive hydrogels through a rapid fabrication process at ambient temperature. In this work, a versatile poly(acrylamide) @cellulose nanocrystal/tannic acid-silver nanocomposite (NC) hydrogel integrated with excellent stretchability, repeatable self-adhesion, high strain sensitivity, and antibacterial property, was synthesized via radical polymerization within 30 s at ambient temperature. Notably, this rapid polymerization was realized through a tannic acid-silver (TA-Ag) mediated dynamic catalysis system that was capable of activating ammonium persulfate and then initiated the free-radical polymerization of the acrylamide monomer. Benefiting from the incorporation of TA-Ag metal ion nanocomplexes and cellulose nanocrystals, which acted as dynamic connecting bridges by hydrogen bonds to efficiently dissipate energy, the obtained NC hydrogels exhibited prominent tensile strain (up to 4000%), flexibility, self-recovery, and antifatigue properties. In addition, the hydrogels showed repeatable adhesiveness to different substrates (e.g., glass, wood, bone, metal, and skin) and significant antibacterial properties, which were merits for the hydrogels to be assembled into a flexible epidermal sensor for long-term human-machine interfacial contact without concerns about the use of external adhesive tapes and bacterial breeding. Moreover, the remarkable conductivity (σ ∼ 5.6 ms cm^-1) and strain sensitivity (gauge factor = 1.02) allowed the flexible epidermal sensors to monitor various human motions in real time, including huge movement of deformations (e.g., wrist, elbow, neck, shoulder) and subtle motions. It is envisioned that this work would provide a promising strategy for the rapid preparation of conductive hydrogels in the application of flexible electronic skin, biomedical devices, and soft robotics.

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

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