Electrospun Nanofibrous Membranes: A Versatile Medium for Waterproof and Breathable Application.

Waterproof and breathable membranes that prevent liquid water penetration, while allowing air and moisture transmission, have attracted significant attention for various applications. Electrospun nanofiber materials with adjustable pore structures, easily tunable wettability, and good pore connectivity, have shown significant potential for constructing waterproof and breathable membranes. Herein, a systematic overview of the recent progress in the design, fabrication, and application of waterproof and breathable nanofibrous membranes is provided. The various strategies for fabricating the membranes mainly including one-step electrospinning and post-treatment of nanofibers are given as a starting point for the discussion. The different design concepts and structural characteristics of each type of waterproof and breathable membrane are comprehensively analyzed. Then, some representative applications of the membranes are highlighted, involving personal protection, desalination, medical dressing, and electronics. Finally, the challenges and future perspectives associated with waterproof and breathable nanofibrous membranes are presented.

Superstable and Intrinsically Self-Healing Fibrous Membrane with Bionic Confined Protective Structure for Breathable Electronic Skin.

Considerable effort has been devoted to the fabrication of electronic skin that can imitate the self-healing and sensing function of biological skin. Almost all self-healing electronic skins are composed of airtight elastomers or hydrogels, which will cause skin inflammation. Fibrous membranes are ideal materials for preparing highly sensitive breathable electronic skins. However, the development of intrinsically self-healing fibrous membranes with high stability is still a challenge. Here, a novel interface protective strategy is reported to develop intrinsically self-healing fibrous membranes with a bionic confined structure for the first time, which were further assembled into an all-fiber structured electronic skin through interfacial hydrogen bonding. The electronic skin is multifunctional with self-powering, self-healing, breathability, stretchability, and thermochromism functionalities, which is highly promising for application in intelligent wearable sensing systems.

Visible-Light-Driven and Self-Hydrogen-Donated Nanofibers Enable Rapid-Deployable Antimicrobial Bioprotection.

The novel coronavirus SARS-CoV-2 has prompted a worldwide pandemic and poses a great threat to public safety and global economies. Most present personal protective equipment (PPE) used to intercept pathogenic microorganisms is deficient in biocidal properties. Herein, we present green nanofibers with effective antibacterial and antiviral activities that can provide sustainable bioprotection by continuously producing reactive oxygen species (ROS). The superiority of the design is that the nanofibers can absorb and store visible light energy and maintain the activity under light or dark environment. Moreover, the nanofibers can uninterruptedly release ROS in the absence of an external hydrogen donor, acting as a biocide under all weather conditions. A facile spraying method is proposed to rapidly deploy the functional nanofibers to existing PPE, such as protective suits and masks. The modified PPE exhibit stable ROS production, excellent capacity for storing activity potential, long-term durability, and high bactericidal (>99.9%) and viricidal (>99.999%) efficacies.

Smart, Elastic, and Nanofiber-Based 3D Scaffolds with Self-Deploying Capability for Osteoporotic Bone Regeneration.

It has been a major challenge to treat osteoporotic bone defects with irregular shapes. Although bioactive glass offers an attractive material for bone regeneration, its inherent brittleness has greatly limited its scope of application. Herein, we report the fabrication of bioactive glass (SiO2-CaO) nanofibers with excellent flexibility to even allow for 180° bending. The bioactive glass nanofibers could be further assembled into 3D fibrous scaffolds with chitosan serving as the linkers. The scaffolds constructed from an assembly of 85SiO2-15CaO nanofibers and chitosan (85SiO2-15CaO NF/CS) possessed significantly better mechanical properties when benchmarked against both 75SiO2-25CaO nanofiber- and chitosan-based scaffolds. Moreover, the 85SiO2-15CaO NF/CS scaffolds exhibited an elastic behavior, with full recovery from 80% compression and good fatigue resistance over 1000 cycles of compression under water. Upon implantation, the elastic fibrous scaffolds were able to deform and fit irregularly shaped bone defects, followed by a self-deploying behavior to achieve a perfect match with the cavities. When applied to the repair of an osteoporotic calvarial defect in a rat model, the 85SiO2-15CaO NF/CS scaffolds showed substantial promotion of bone regrowth and vascularization. This new class of 3D fibrous scaffold provides a promising advancement in engineering smart materials for complex bone repair.

Waterproof and Breathable Electrospun Nanofibrous Membranes.

Waterproof and breathable (W&B) membranes combine fascinating properties of resistance to liquid water penetration and transmitting of water vapor, playing a key role in addressing problems related to health, resources, and energy. Electrospinning is an efficient and advanced way to construct nanofibrous materials with easily tailored wettability and adjustable pore structure, therefore providing an ideal strategy for constructing W&B membranes. In this review, recent progress on electrospun W&B membranes is summarized, involving materials design and fabrication, basic properties of electrospun W&B membranes associated with waterproofness and breathability, as well as their applications. In addition, challenges and future trends of electrospun W&B membranes are discussed.

Continuous, Spontaneous, and Directional Water Transport in the Trilayered Fibrous Membranes for Functional Moisture Wicking Textiles.

Directional water transport is a predominant part of functional textiles used for continuous sweat release in daily life. However, it has remained a great challenge to design such textiles which ensure continuous directional water transport and superior prevention of water penetration in the reverse direction. Here, a scalable strategy is reported to create trilayered fibrous membranes with progressive wettability by introducing a transfer layer, which can guide the directional water transport continuously and spontaneously, thus preventing the skin from being rewetted. The resulting trilayered fibrous membranes exhibit a high one-way transport index R (1021%) and a desired breakthrough pressure (16.1 cm H2 O) in the reverse direction, indicating an ultrahigh directional water transport capacity. Moreover, on the basis of water transport behavior, a plausible mechanism is proposed to provide insight into the integrative and cooperative driving forces at the interfaces of trilayered hydrophobic/transfer/superhydrophilic fibrous membranes. The successful synthesis of such fascinating materials would be valuable for the design of functional textiles with directional water transport properties for personal drying applications.

Nanofiber-Based Hydrogels: Controllable Synthesis and Multifunctional Applications.

Nanofiber-based hydrogels (NFHGs) prepared by the combination of traditional hydrogels and novel nanofibers have demonstrated great potential in various application fields, owing to their integrated advantages of superhydrophilicity, high water-holding capacity, good biocompatibility, enhanced mechanical strength, and excellent structural tenability. In this review, a comprehensive overview of the structure design and synthetic strategy of NFHGs derived from electrospinning technique, weaving, freeze-drying, 3D printing, and molecular self-assembling method is provided. The widely researched multifunctional applications, primarily involving tissue engineering, drug delivery, sensing, intelligent actuator, and oil/water separation are also presented. Furthermore, some unsolved scientific issues and possible directions for future development of this field are also intensively discussed.

Janus Nanofibrous Patch with In Situ Grown Superlubricated Skin for Soft Tissue Repair with Inhibited Postoperative Adhesion.

The patch with a superlubricated surface shows great potential for the prevention of postoperative adhesion during soft tissue repair. However, the existing patches suffer from the destruction of topography during superlubrication coating and lack of pro-healing capability. Herein, we demonstrate a facile and versatile strategy to develop a Janus nanofibrous patch (J-NFP) with antiadhesion and reactive oxygen species (ROS) scavenging functions. Specifically, sequential electrospinning is performed with initiators and CeO2 nanoparticles (CeNPs) embedded on the different sides, followed by subsurface-initiated atom transfer radical polymerization for grafting zwitterionic polymer brushes, introducing superlubricated skin on the surface of single nanofibers. The poly(sulfobetaine methacrylate) brush-grafted patch retains fibrous topography and shows a coefficient of friction of around 0.12, which is reduced by 77% compared with the pristine fibrous patch. Additionally, a significant reduction in protein, platelet, bacteria, and cell adhesion is observed. More importantly, the CeNPs-embedded patch enables ROS scavenging as well as inhibits pro-inflammatory cytokine secretion and promotes anti-inflammatory cytokine levels. Furthermore, the J-NFP can inhibit tissue adhesion and promote repair of both rat skin wounds and intrauterine injuries. The present strategy for developing the Janus patch exhibits enormous prospects for facilitating soft tissue repair.

A feasible strategy to balance the performance of stereo-complexed polylactide by incorporating poly(butylene adipate-co-terephthalate).

The raw material of polylactide (PLA) is lactic acid obtained by biological fermentation. PLA is the most promising degradable polymer to replace traditional plastics to address the pollution problems caused by their non-degradability. However, the application of PLA is hindered by its low softening temperature, easy hydrolysis, and poor toughness. Herein, the ternary composites with PLLA, PDLA and Poly (butylene adipate-co-terephthalate) (PBAT) were prepared by melt blending to balance its thermal stability, hydrolysis, and toughness. The effects of PBAT content (3 %, 6 %, 9 % and 12 %) and isothermal crystallization temperature on composite properties were fully investigated. The results show that the composite of stereo-complexed PLA (sc-PLA) with 6 % PBAT crystallized at 110 °C exhibits good comprehensive properties. Its vicat softening temperature (VST), mass loss rate under alkaline (pH = 12) and breaking elongation are 166 °C, 21.6 % and 4.40 %, respectively. Compared with the pure PLLA sample crystallized at same condition, the VST, mass loss rate and breaking elongation are 159 °C, 24.7 % and 3.76 % respectively, which increased by nearly 5 %, 13 % and 20 %. This indicates that this strategy is feasible to balance the heat resistance, hydrolysis resistance and toughness of PLA, while it sacrifices the tensile strength a little. This work provides a new way to modify and improve the PLA properties. Nonetheless, it is also necessary to coordinate the compatibility of PLA and PBAT.

In situ forming double-crosslinked hydrogels with highly dispersed short fibers for the treatment of irregular wounds.

In situ forming injectable hydrogels hold great potential for the treatment of irregular wounds. However, their practical applications were hindered by long gelation time, poor mechanical performance, and a lack of a natural extracellular matrix structure. Herein, amino-modified electrospun poly(lactic-co-glycolic acid) (APLGA) short fibers with uniform distribution were introduced into gelatin methacrylate/oxidized dextran (GM/ODex) hydrogels. In comparison with the fiber aggregation structure in the PLGA fiber-incorporated hydrogels, the hydrogels with APLGA fibers possessed a uniform porous structure. The highly dispersed APLGA short fibers accelerated the sol-gel phase transition of the hydrogel due to the formation of dynamic Schiff-base bonds between the fibers and hydrogels. Furthermore, in combination with UV-assisted crosslinking, a rapid gelation time of 90 s was achieved for the double-crosslinked hydrogels. The addition of APLGA short fibers as fillers and the formation of the double-crosslinking network enhanced the mechanical performance of the hydrogels. Furthermore, the fiber-hydrogel composites exhibited favorable injectability, excellent biocompatibility, and improved cell infiltration. In vivo assessment indicated that the GM/ODex-APLGA hydrogels successfully filled the full-thickness defects and improved wound healing. This work demonstrates a promising solution for the treatment of irregular wounds.

Nanofibrous hemostatic materials: Structural design, fabrication methods, and hemostatic mechanisms.

Development of rapid and effective hemostatic materials has always been the focus of research in the healthcare field. Nanofibrous materials which recapitulate the delicate nano-topography feature of fibrin fibers produced during natural hemostatic process, offer large length-to-diameter ratio and surface area, tunable porous structure, and precise control in architecture, showing great potential for staunching bleeding. Here we present a comprehensive review of advances in nanofibrous hemostatic materials, focusing on the following three important parts: structural design, fabrication methods, and hemostatic mechanisms. This review begins with an introduction to the physiological hemostatic mechanism and current commercial hemostatic agents. Then, it focuses on recent progress in electrospun nanofibrous hemostatic materials in terms of composition and structure control, surface modification, and in-situ deposition. The article emphasizes the development of three-dimensional (3D) electrospun nanofibrous materials and their emerging evolution for improving hemostatic function. Next, it discusses the fabrication of self-assembling peptide or protein-mimetic peptide nanofibers, co-assembling supramolecular nanofibers, as well as other nanofibrous hemostatic agents. Further, the article highlights the external and intracavitary hemostatic management based on various nanofiber aggregates. In the end, this review concludes with the current challenges and future perspectives of nanofibrous hemostatic materials. STATEMENT OF SIGNIFICANCE: This article reviews recent advances in nanofibrous hemostatic materials including fabrication methods, composition and structural control, performance improvement, and hemostatic mechanisms. A variety of methods including electrospinning, self-assembly, grinding and refining, template synthesis, and chemical vapor deposition, have been developed to prepare nanofibrous materials. These methods provide robustness in control of the nanofiber architecture in the forms of hydrogels, two-dimensional (2D) membranes, 3D sponges, or composites, showing promising potential in the external and intracavitary hemostasis and wound healing applications. This review will be of great interest to the broad readers in the field of hemostatic materials and multifunctional biomaterials.

Superelastic, Breathable, and High-Barrier Nanofibrous Membranes with Biomimetic ECM Structure for Toxic Chemical Protection.

As the last line of protection for humans, chemical protective suits provided safe and effective protection where chemical warfare agents (CWAs) or chemical reagents leaked; however, the existing chemical protective clothing had poor wearing pressure comfort due to the limitation of inherent materials. Herein, we reported a scalable strategy to fabricate chemical protective fabric (CPF) with a biomimetic extracellular matrix (ECM) barrier layer composed of an elastic fiber framework based on the cross-linked nanofiber membrane and the styrene-butadiene-styrene block copolymer (SBS)/acticarbon matrix. The construction of the reliable and strategical biomimetic ECM structure succeeded in fulfilling hazardous chemical barrier properties, recoverable deformation, and thermal comfort improvement. The resulting CPF exhibited waterproofness with exceeding 200 kPa hydrostatic pressure and exceptional WVT of 550.96 g m-2 d-1, rapid elastic recovery from a strain of 80%, high-cycle fatigue resistance, superior barrier performance against toxic chemicals, and keeping CEES resistance after 100 tensile loading cycles. The successful preparation of the fascinating biomimetic nanofibrous membrane may provide a particular research foundation for developing chemical protective clothing in the future.

Copper hydroxide nanosheets-assembled nanofibrous membranes for anti-biofouling water disinfection.

Copper hydroxide (Cu(OH)2) has been elected as a newly-emerging green disinfectant to deal with membrane biofouling in the treatment of bacteria-contaminated water; however, the decoration strategy of it with the granular form on membrane substrates limits the practical application. Here a novel surface-confined methodology was proposed for preparing freestanding Cu(OH)2 nanosheet-assembled nanofibrous membranes (CNNMs) with the anti-biofouling property via the in-suit coprecipitation and heat-induced growth method. The vertically aligned Cu(OH)2 nanosheets were in-suit rooted on the surface of the nanofiber scaffold with high binding fastness. The acquired CNNMs possess comprehensive performances of high porosity, prominent mechanical strength, fatigue resistance, and superior bactericidal efficiency of 99.999%, which endowed the CNNMs ultrahigh filtration fluxes (24000 L m-2 h-1) and durability to disinfect bacteria-containing water effectively. This facile strategy may throw light on manufacturing novel inorganic nanosheet-rooted nanofibrous membranes for water disinfection and public health.

Fabrication of eco-friendly and efficient flame retardant modified cellulose with antibacterial property.

Flame retardant and antibacterial investigation of cellulose has attracted more and more attention. In order to improve the modification efficiency, inspired by multiple hydrogen bonding in spider silk, flame retardant and antibacterial dual function modified cellulose was achieved by multi structure hydrogen bonding in this research. A novel nano SiO2 based Schiff base flame retardant (SiAPH) and dodecyl quaternary ammonium salt (HDAC) were synthesized. Tannin (TA) was introduced as medium to provide synergistic flame retardant and antibacterial with SiAPH and HDAC. The flame retardancy assessment demonstrated that the limiting oxygen index (LOI) of modified cotton fabrics increased from 18% to 26.1%, and the peak of heat release rate (pHRR) decreased by 41.0%, UL-94 vertical combustion proved the modified cotton fabrics had capability of self-extinguishing. The antibacterial of modified fabrics were confirmed against Staphylococcus aureus and Escherichia coli, and the inhibition rate reached to 99.1%. In addition, it worth noting that the biocompatibility and antibacterial activity of modified fabrics were evaluated via MTS assay and establishment of animal wound model. Low toxicity of the fabrics was verified by the L929 fibroblast cells. The anti-infection experiment model showed that the modified fabrics had a positive effect on prevention of infection, and the wound healing rate reached to 86.8% after 14 days' treatment. The flame retardancy, antibacterial and biocompatibility of the functional cotton fabrics indicated that they were ideal candidate for applications of vehicle interior, soft decoration in public and medical scene.

Exploring the dark side of MTT viability assay of cells cultured onto electrospun PLGA-based composite nanofibrous scaffolding materials.

One major method used to evaluate the biocompatibility of porous tissue engineering scaffolding materials is MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The MTT cell viability assay is based on the absorbance of the dissolved MTT formazan crystals formed in living cells, which is proportional to the number of viable cells. Due to the strong dye sorption capability of porous scaffolding materials, we propose that the cell viability determined from the MTT assay is likely to give a false negative result. In this study, we aim to explore the effect of the adsorption of MTT formazan on the accuracy of the viability assay of cells cultured onto porous electrospun poly(lactic-co-glycolic acid) (PLGA) nanofibers, HNTs (halloysite nanotubes)/PLGA, and CNTs (multiwalled carbon nanotubes)/PLGA composite nanofibrous mats. The morphology of electrospun nanofibers and L929 mouse fibroblasts cultured onto the nanofibrous scaffolds were observed using scanning electron microscopy. The viability of cells proliferated for 3 days was evaluated through the MTT assay. In the meantime, the adsorption of MTT formazan onto the same electrospun nanofibers was evaluated and the standard concentration-absorbance curve was obtained in order to quantify the contribution of the adsorbed MTT formazan during the MTT cell viability assay. We show that the PLGA, and the HNTs- or CNTs-doped PLGA nanofibers display appreciable MTT formazan dye sorption, corresponding to 35.6-50.2% deviation from the real cell viability assay data. The better dye sorption capability of the nanofibers leads to further deviation from the real cell viability. Our study gives a general insight into accurate MTT cytotoxicity assessment of various porous tissue engineering scaffolding materials, and may be applicable to other colorimetric assays for analyzing the biological properties of porous scaffolding materials.

One-step electro-spinning/netting technique for controllably preparing polyurethane nano-fiber/net.

Electro-spinning/netting (ESN) as a cutting-edge technique evokes much interest because of its ability in the one-step preparation of versatile nano-fiber/net (NFN) membranes. Here, a controllable fabrication of polyurethane (PU) NFN membranes with attractive structures, consisting of common electrospun nanofibers and two-dimensional (2D) soap bubble-like structured nano-nets via an ESN process is reported. The unique nanoscaled NFN architecture can be finely controlled by regulating the solution properties and several ESN process parameters. The versatile PU nano-nets comprising interlinked nanowires with ultrathin diameters (5-40 nm) mean that the NFN structured membranes possess several excellent characteristics, such as an extremely large specific surface area, high porosity and large stacking density, which would be particularly useful for applications in ultrafiltration, special protective clothing, ultrasensitive sensors, catalyst support and so on.

Asymmetric Wettable, Waterproof, and Breathable Nanofibrous Membranes for Wound Dressings.

Despite the progression in wound treatment, the development of wound dressings with considerable skin regeneration capability and improved patient comfort still faces huge challenges. In this study, a type of asymmetric wettable gradient nanofibrous membrane, which is composed of a hydrophobic polyvinyl butyral (PVB)-polydimethylsiloxane (PDMS) upper layer, a PVB-PDMS/gelatin middle layer, and a hydrophilic gelatin lower layer, has been fabricated. The PVB-PDMS upper layer gave dramatically elevated water contact angles from 71.27° to 125.45° as compared with the gelatin membrane, indicating an asymmetric wettability. The composite membrane exhibited outstanding waterproof capability with a hydrostatic pressure of 58.21 kPa, excellent breathability with a water vapor transmission rate of 8.80 kg m-2 d-1, improved stretchability and tear resistance, and dramatic improvement in mesenchymal stem cell recruitment with the immobilization of stromal-cell-derived factor-1α for accelerating skin regeneration. The development of asymmetric wettable nanofibrous membranes offers insight into wound-dressing design.

Waterborne electrospinning of fluorine-free stretchable nanofiber membranes with waterproof and breathable capabilities for protective textiles.

HYPOTHESIS: Smart membranes with robust liquid water resistance and water vapor transmission capabilities have attracted growing attentions in personal protective equipment and environmental protection. However, current fluorine-free waterproof and breathable nanofibrous membranes are usually prepared through toxic solvent-based electrospinning, which raises great concerns about their environmental impacts. EXPERIMENTS: We develop environmentally friendly fluorine-free polyurethane nanofibrous membranes with robust waterproof and breathable performances via waterborne electrospinning without post-coating treatment. The incorporation of the low surface energy long-chain alkyls and polycarbodiimide crosslinker imparts the interconnective porous channels with high hydrophobicity to waterborne fluorine-free polyurethane nanofibrous membranes. FINDINGS: The waterborne fluorine-free nanofibrous membranes show high water contact angle of 137.1°, robust hydrostatic pressure of 35.9 kPa, desirable water vapor transmission rate of 4885 g m-2 d-1, excellent air permeability of 19.9 mm s-1, good tensile elongation of 372.4%, and remarkable elasticity of 56.9%, thus offering strong potential for protective textiles and leaving no toxic solvent residues. This work could also serve as a guide for the design of green and high-performance fibrous materials used for medical hygiene, wearable electronics, water desalination, and oil/water separation.

Water-stable zirconium-based metal-organic frameworks armed polyvinyl alcohol nanofibrous membrane with enhanced antibacterial therapy for wound healing.

Inadequate water-stability and antibacterial activity limit the biomedical application of polyvinyl alcohol (PVA)-based membranes in moist environments. In this work, we propose a strategy to improve the water-stability of PVA membranes via metal complexation and heat treatment. We report a simple routine where the zirconium-based UiO-66-NH2 metal-organic frameworks (MOFs) are nucleated as a layer on the surface of PVA nanofibrous membranes (UiO-66-NH2@PVA NFMs). We find that the chemical modification of membranes increases their hydrophilicity and adds on mechanical support for the brittle UiO-66-NH2 MOFs. Additionally, we demonstrate the application of UiO-66-NH2 MOFs as drug carriers for antibacterial drug, levofloxacin (LV). The active drug component is preloaded during the one-step nucleation process. The obtained LV loaded UiO-66-NH2@PVA NFMs (LV@UiO-66-NH2@PVA) are shown to be bactericidal with the efficiency > 99.9% at 100 µg/mL against two bacterial species, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Compared with the commercially available gauzes, the UiO-66-NH2@PVA and LV@UiO-66-NH2@PVA treatments will significantly improve the wound healing process. Animal studies show that the LV@UiO-66-NH2@PVA will effectively offer a safe alternative solution for the patients to protect against bacterial infections, demonstrating the potential application of MOF-based NFMs as wound dressing agents.

In-situ electrospinning of thymol-loaded polyurethane fibrous membranes for waterproof, breathable, and antibacterial wound dressing application.

Skin-like flexible membrane with excellent water resistance and moisture permeability is an urgent need in the wound dressing field to provide comfort and protection for the wound site. Despite efforts that have been made in the development of waterproof and breathable (W&B) membranes, the in-situ electrospinning of W&B membranes suitable for irregular wound surfaces as wound dressings still faces huge challenges. In the current work, a portable electrospinning device with multi-functions, including adjustable perfusion speed for a large range from 0.05 mL/h to 10 mL/h and high voltage up to 11 kV, was designed. The thymol-loaded ethanol-soluble polyurethane (EPU) skin-like W&B nanofibrous membranes with antibacterial activity were fabricated via the custom-designed device. Ultimately, the resultant nanofibrous membranes composed of EPU, fluorinated polyurethane (FPU), and thymol presented uniform structure, robust waterproofness with the hydrostatic pressure of 17.6 cm H2O, excellent breathability of 3.56 kg m-2 d-1, the high tensile stress of 1.83 MPa and tensile strain of 453%, as well as high antibacterial activity. These results demonstrate that the new-type device has potential as a portable electrospinning apparatus for the fabrication of antibacterial membranes directly on the wound surface and puts a new way for the development of portable electrospinning devices.