Electro-spinning/netting: A strategy for the fabrication of three-dimensional polymer nano-fiber/nets

A Sulfur Copolymers (SDIB)/Polybenzoxazines (PBz) Polymer Blend for Electrospinning of Nanofibers

This study demonstrated the processability of sulfur copolymers (SDIB) into polymer blend with polybenzoxazines (PBz) and their compatibility with the electrospinning process. Synthesis of SDIB was conducted via inverse vulcanization using elemental sulfur (S8). Polymer blends produced by simply mixing with varying concentration of SDIB (5 and 10 wt%) and fixed concentration of PBz (10 wt%) exhibited homogeneity and a single-phase structure capable of forming nanofibers. Nanofiber mats were characterized to determine the blending effect on the microstructure and final properties. Fiber diameter increased and exhibited non-uniform, broader fiber diameter distribution with increased SDIB. Microstructures of mats based on SEM images showed the occurrence of partial aggregation and conglutination with each fiber. Incorporation of SDIB were confirmed from EDX which was in agreement with the amount of SDIB relative to the sulfur peak in the spectra. Spectroscopy further confirmed that SDIB did not affect the chemistry of PBz but the presence of special interaction benefited miscibility. Two distinct glass transition temperatures of 97 °C and 280 °C indicated that new material was produced from the blend while the water contact angle of the fibers was reduced from 130° to 82° which became quite hydrophilic. Blending of SDIB with component polymer proved that its processability can be further explored for optimal spinnability of nanofibers for desired applications.

Ultralight and Resilient Electrospun Fiber Sponge with a Lamellar Corrugated Microstructure for Effective Low-Frequency Sound Absorption

Low-density 3D ultrafine fiber assemblies obtained from direct electrospinning enable promising applications in sound absorption fields but are often hindered by their poor structure stability. Here, we demonstrate an electrospun ultrafine fiber sponge with a microstructure-derived reversible elasticity and high sound absorption property, which is achieved by designing a hierarchical lamellar corrugated architecture that functioned as elastic units. The obtained electrospun fiber sponge can quickly recover to the original height even under the distortion from burdens 8900 times its weight. Particularly, the material can maintain its structural stability after 100 cycles at 60% strain. Moreover, the initial hierarchical structure and hydrophobicity of the prepared materials endow them with an ultralight property (density of 6.63 mg cm^-3), superior low-frequency sound absorption, and excellent performance maintenance. The successful synthesis of these fascinating materials may provide new insights into the design of lightweight and efficient sound absorption materials.

Electrospun Jets Number and Nanofiber Morphology Effected by Voltage Value: Numerical Simulation and Experimental Verification

Electrical voltage has a crucial effect on the nanofiber morphology as well as the jet number in the electrospinning process, while few literatures were found to explain the deep mechanism. Herein, the electrical field distribution around the spinning electrode was studied by the numerical simulation firstly. The results show that the electrical field concentrates on the tip of a protruding droplet under relatively low voltage, while subsequently turns to the edge of needle tip when the protruding droplet disappears under high voltage. The experimental results are well consistent with the numerically simulated results, that is, only one jet forms at low voltage (below 20 kV for PVDF-HFP and PVA nanofiber), but more than one jet forms under high voltage (two jets for PVDF-HFP nanofiber, four jets for PVA nanofiber). These more jets lead to (1) higher fiber diameter resulting from actually weaker electrical field for each jet and (2) wide distribution of fiber diameters due to unstable spinning process (changeable jet number/site/height) under high voltage. The results will benefit the nanofiber preparation and application in traditional single-needle electrospinning and other electrospinning methods.

Dye Adsorption and Electrical Property of Oxide-Loaded Carbon Fiber Made by Electrospinning and Hydrothermal Treatment

Our current study deals with the dye adsorption and electrical property of a partially carbonized composite fiber containing transition metal oxides including, iron oxide, nickel oxide, and titanium oxide. The fiber was made by electrospinning, carbonization, and hydrothermal treatment. During the electrospinning, titanium oxide particles were dispersed in polyacrylonitrile (PAN) polymer-dimethylformamide (DMF) solution. Nickel chloride and iron nitrate were added into the solution to generate nickel oxide and iron oxide in the subsequent heat treatment processes. The polymer fiber was oxidized first at an elevated temperature of 250 °C to stabilize the structure of PAN. Then, we performed higher temperature heat treatment at 500 °C in a furnace with hydrogen gas protection to partially carbonize the polymer fiber. After that, the oxide-containing fiber was coated with activated carbon in a diluted sugar solution via hydrothermal carbonization at 200 °C for 8 h. The pressure reached 1.45 MPa in the reaction chamber. The obtained product was tested in view of the dye, Rhodamine B, adsorption using a Vis-UV spectrometer. Electrical property characterization was performed using an electrochemical work station. It was found that the hydrothermally treated oxide-containing fiber demonstrated obvious dye adsorption behavior. The visible light absorption intensity of the Rhodamine B dye decreased with the increase in the soaking time of the fiber in the dye solution. The impedance of the fiber was increased due to the hydrothermal carbonization treatment. We also found that charge build-up was faster at the surface of the specimen without the hydrothermally treated carbon layer. Electricity generation under visible light excitation is more intensive at the hydrothermally treated fiber than at the one without the hydrothermal treatment. This result is consistent with that obtained from the dye adsorption/decomposition test because the charge generation is more efficient at the surface of the hydrothermally treated fiber, which allows the dye to be decomposed faster by the treated fibers with activated carbon.

One-Step Synthesis of Silver Nanoparticles Embedded Polyurethane Nano-Fiber/Net Structured Membrane as an Effective Antibacterial Medium

A new and straightforward route was proposed to incorporate silver nanoparticles (Ag NPs) into the surface of polyurethane nanofibers (PU NFs). Uniform distribution of in situ formed Ag NPs on the surface of PU NFs was achieved by adding AgNO3 and tannic acid in a PU solution prior to the electrospinning process. The synthesized nanofiber mats were characterized with state-of-the-art techniques and antibacterial performances were tested against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria. The cytocompatibility and cell behavior were studied by using fibroblast cells. Following this preparation route, Ag/PU NFs can be obtained with excellent antibacterial performance, thus making them appropriate for various applications such as water filtration, wound dressings, etc.

Drug Delivery Applications of Core-Sheath Nanofibers Prepared by Coaxial Electrospinning: A Review

Electrospinning has emerged as one of the potential techniques for producing nanofibers. The use of electrospun nanofibers in drug delivery has increased rapidly over recent years due to their valuable properties, which include a large surface area, high porosity, small pore size, superior mechanical properties, and ease of surface modification. A drug loaded nanofiber membrane can be prepared via electrospinning using a model drug and polymer solution; however, the release of the drug from the nanofiber membrane in a safe and controlled way is challenging as a result of the initial burst release. Employing a core-sheath design provides a promising solution for controlling the initial burst release. Numerous studies have reported on the preparation of core-sheath nanofibers by coaxial electrospinning for drug delivery applications. This paper summarizes the physical phenomena, the effects of various parameters in coaxial electrospinning, and the usefulness of core-sheath nanofibers in drug delivery. Furthermore, this report also highlights the future challenges involved in utilizing core-sheath nanofibers for drug delivery applications.

Preparation and Characterization of Poly(Methyl Methacrylate) (PMMA) Fibers by Electrospinning

Fibers are materials with advantageous properties such as lightweight material properties, has small pore size, and has high surface area, porosity,and permeability. An easy and simple method to prepare fibers is electrospinning. Using this method poly(methyl methacrylate) (PMMA) fibers were prepared. Several parameters include polymer concentration, solution flow rate, the distance of the nozzle tip to the collector, and the applied voltage were investigated to control the morphology, structure, and diameter of PMMA fibers. The Optimal electrospinning conditions for PMMA fibers production were a PMMA concentration is 8% (w/v), a power supply voltage is 20 kV, a distance of the tip of the nozzle to the ground collector is 15 cm, and a flow rate is 0.004 mL/min. The diameter distribution and morphology of the fibers were determined and characterized by Optical Microscopy and Scanning Electron Microscope (SEM), which showed that the produced fiber had an average diameter of 1.4925 µm, the contact angle of fiber PMMA is 125.307o and the spreading time of fibers PMMA is about 360 minutes

Acrylic acid-grafted pre-plasma nanofibers for efficient removal of oil pollution from aquatic environment

Oily wastewater is a worldwide problem threatening the environment and humans. High flux and low-energy consumption separation of oil and water is urgently required but still faces great challenges. In this study, nanofibrous membranes with superhydrophilic and underwater superoleophobic surfaces were fabricated by grafting acrylic acid onto plasma-treated electrospun polystyrene/polyacrylonitrile (PS/PAN) membranes. The morphologies, chemical compositions, mechanical and surface properties of the membranes were examined in detail. The water contact angles of the PS/PAN membranes were 137.4°, 130.1°, 119.5°, 88.1° and 80.2°, respectively, which decreased to 76.5°, 47.9°, 34.4°, 0° and 0° after grafting treatment, proving that the modification improved the surface hydrophilicity of the membranes due to the introduction of hydrophilic groups. In addition, a gravity-driven filtration device was utilized to investigate the oil/water separation potential of the membranes. The results indicated that the grafted PS/PAN membranes separated the layered oil/water mixtures with permeate flux up to 57509 L m^-2 h^-1, while high fluxes of 1390-6460 L m^-2 h^-1 for the separation of different oil-in-water emulsions. Importantly, the membranes still maintained high flux and efficiency even after several cycles of separation. Therefore, the reusable membranes can be expected to be potential cost-effective materials for oil/water treatment.

Efficient nanoparticles removal and bactericidal action of electrospun nanofibers membranes for air filtration

Human exposure to air pollution and especially to nanoparticles is increasing due to the combustion of carbon-based energy vectors. Fibrous filters are among the various types of equipment potentially able to remove particles from the air. Nanofibers are highly effective in this area; however, their utilization is still a challenge due to the lack of studies taking into account both nanoparticle collection efficiency and antibacterial effect. The aim of this work is to produce and evaluate novel silver/polyacrylonitrile (Ag/PAN) electrospun fibers deposited on a nonwoven substrate to be used as air filters to remove nanoparticles from the air and also showing antibacterial activity. In order to determine the optimum manufacturing conditions, the effects of several electrospinning process parameters were analyzed such as solution concentration, collector to needle distance, flow rate, voltage, and duration. Ag/PAN nanofibers were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infra-Red spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and Scanning Electron Microscopy (SEM). In addition, filtration performances were determined by measuring the pressure drop and collection efficiency of sodium chloride (NaCl) aerosol particles (9 to 300 nm diameters) using Scanning Mobility Particle Sizers (SMPS). Filters with high filtration efficiency (≈100%) and high-quality factor (≈0.05 Pa^-1) were obtained even adding different concentrations of Ag nanoparticles (AgNPs) to PAN nanofibers. The resultant Ag/PAN nanofibers showed excellent antibacterial activity against 10⁴ CFU/mL E. coli bacteria.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Direct electronetting of high-performance membranes based on self-assembled 2D nanoarchitectured networks

There is an increasing demand worldwide on advanced two-dimensional (2D) nanofibrous networks with applications ranging from environmental protection and electrical devices to bioengineering. Design of such nanoarchitectured materials has been considered a long-standing challenge. Herein, we report a direct electronetting technology for the fabrication of self-assembled 2D nanoarchitectured networks (nano-nets) from various materials. Tailoring of the precursor solution and of the microelectric field allows charged droplets, which are ejected from a Taylor cone, to levitate, deform and phase separate before they self-assemble a 2D nanofibre network architecture. The fabricated nano-nets show mechanical robustness and benefit from nanostructural properties such as enhanced surface wettability, high transparency, separation and improved air filtration properties. Calcination of the nano-nets results in the formation of carbon nano-nets with electric conductivity and titanium dioxide nano-nets with bioprotective properties.

Test strips based on iron(iii)-impregnated alginate/polyacrylonitrile nanofibers for naked eye screening of tetracycline

Tetracycline (TC) is an inexpensive broad-spectrum antibiotic used to treat infectious diseases and to promote growth in animals. However, driven by economic interest, abuse of TC poses a serious threat to human beings, and it remains a significant challenge to create easy-to-use TC colorimetric test strips for public use. Herein, we present a strategy to prepare free-standing, nanofibrous structured test strips with tortuous porous structure and large surface area by combining polyacrylonitrile nanofibrous membranes (PAN NMs), alginate, and Fe3+. In this approach, alginate was first functionalized on the PAN NMs and then, Fe3+ was assembled into the alginate to construct a TC-sensing surface. The resultant test strips exhibited the following integrated properties: fast sensing process (10 min), low naked eye detection limit (5 μg kg-1), excellent anti-interference ability, and satisfactory reusability. Furthermore, the TC concentration-dependent color change (yellow to maroon) was quantitatively visualized by an iPhone read-out hue parameter. All the findings indicate that this intriguing approach may pave the way for versatile designing of NMs to serve as a preventive treatment for the public.

Electrospun sandwich polysulfonamide/polyacrylonitrile/polysulfonamide composite nanofibrous membranes for lithium-ion batteries

The demands for novel approaches that ensure stability in lithium-ion batteries are increasing and have led to the development of new materials and fabrication strategies. In this study, sandwich structure-like polysulfonamide (PSA)/polyacrylonitrile (PAN)/polysulfonamide (PSA) composite nanofibrous membranes were prepared via an electrospinning method and used as a separator in lithium-ion batteries. The spinning time of each polymer nanofiber layer of the composite membranes was respectively and precisely controlled to maximize the merits of each component. It was found that the PSA/PAN/PSA composite nanofibrous membranes exhibited superior thermal stability and excellent porosity, liquid electrolyte uptake and ionic conductivity, showing obvious enhancement as compared to those of the commercial microporous polyolefin separator (Celgard 2400), pure PSA and pure PAN membranes. In addition, they were evaluated in the assembled Li/LiFePO₄ cells with an electrolyte solution, and good cycling performance and C-rate capacity were obtained; especially for the case of the PP6P membrane, the first discharge capacity of the battery reached 152 mA h g⁻¹, and the discharge capacity retention ratio was 85.94% from 0.2C to 2C; moreover, the battery displayed highest capacity retention ratio after 70 cycles, which was found to be 96.2% of its initial discharge capacity. Therefore, the PSA/PAN/PSA composite nanofibrous membranes can be regarded as a promising candidate for application in lithium-ion batteries.

The demands for novel approaches that ensure stability in lithium-ion batteries are increasing and have led to the development of new materials and fabrication strategies.

Novel Inorganic-Based N-Halamine Nanofibrous Membranes As Highly Effective Antibacterial Agent for Water Disinfection

Novel superhydrophilic inorganic-based N-halamine nanofibrous membranes with high active chlorine contents, outstanding rechargeability, favorable water swelling resistance, and superior mechanical performance were prepared through the combination of electrospinning and sol-gel processing, which could be applied to the dynamic disinfection of bacteria-contaminated water with high disinfection efficiency, large processing flux, and long-term durability. The successful preparation of such silica nanofiber membranous N-halamine antimicrobial with intriguing properties would provide the reference for developing novel antimicrobial nanofibers for multifunctional applications.

Anionic Surfactant-Triggered Steiner Geometrical Poly(vinylidene fluoride) Nanofiber/Nanonet Air Filter for Efficient Particulate Matter Removal

The emergence of Steiner minimal tree is of fundamental importance, and designing such geometric structure and developing its application have practical effect in material engineering and biomedicine. We used a cutting-edge nanotechnology, electrospinning/netting, to generate a Steiner geometrical poly(vinylidene fluoride) (PVDF) nanofiber/nanonet filter for removing airborne particulate matter (PM). Manipulation of surface morphologies by precise control of charged situation enabled the creation of two-dimensional nanonets with Steiner geometry. A significant crystalline phase transition of PVDF from α-phase to β-phase was triggered by the dipole orientation and the intermolecular interactions derived from the electrostatic potential analysis. Particularly, the synergy of electrical interaction (ion-dipole and dipole-dipole) and hydrophobic interaction facilitated the formation of Steiner geometric structure during the evolution process of nanonets. The resultant PVDF nanofiber/nanonet air filter exhibited high filtration efficiency of 99.985% and low pressure drop of 66.7 Pa under the airflow velocity of 32 L/min for PM_0.26 removal by the safest physical sieving mechanism. Furthermore, such filter possessed robust structure integrity for reusability, comparable optical transmittance, superior thermal stability, and prominent purification capacity for smoke PM_2.5. The successful construction of such fascinating Steiner geometrical PVDF nanonets will provide new insights into the design and exploitation of novel filter media for air cleaning and haze treatment.

Enhanced Flexibility and Microwave Absorption Properties of HfC/SiC Nanofiber Mats

Hafnium carbide (HfC) phase, with a high melting point, excellent strength, and high electrical conductivity, could be a suitable addition to enhance the microwave absorption properties of one-dimensional silicon carbide (SiC) nanomaterials without sacrificing its high-temperature thermal stability. In the present work, HfC/SiC hybrid nanofiber mats with different HfC loading contents are fabricated by electrospinning and high-temperature pyrolysis. HfC hybrids with sizes of 5-10 nm are embedded in the SiC nanofibers. As the HfC content increases from 0 to 6.3 wt %, the average diameter of the fibers drops from 2.62 μm to 260 nm. Meanwhile, the electrical conductivity rises from 7.9 × 10^-8 to 4.2 × 10^-5 S/cm. Moreover, the flexibility of the nanofiber mats is also greatly improved, according to a 200-times 180° bending test. Furthermore, compared with pure SiC fiber mats, the HfC/SiC nanofiber mats possess much larger dielectric loss because of higher electrical conductivity. At the optimal HfC content of 2.5 wt %, the HfC/SiC nanofibers/silicon resin composite (10 wt %) exhibits a minimal reflection loss (RL) of -33.9 dB at 12.8 GHz and a 3 mm thickness with a broad effective absorption bandwidth (RL < -10 dB) of 7.4 GHz. The above results prove that introducing HfC into SiC nanofiber mats is an effective way to enhance their flexibility, dielectric properties, and microwave absorption performance.

Microsphere-Fiber Interpenetrated Superhydrophobic PVDF Microporous Membranes with Improved Waterproof and Breathable Performance

Superhydrophobic membranes with extreme liquid water repellency property are good candidates for waterproof and breathable application. Different from the mostly used strategies through either mixing or postmodifying base membranes with perfluorinated compounds, we report in this work a facile methodology to fabricate superhydrophobic microporous membranes made up of pure poly(vinylidene fluoride) (PVDF) via a high-humidity induced electrospinning process. The superhydrophobic property of the PVDF microporous membrane is contributed by its special microsphere-fiber interpenetrated rough structure. The effective pore size and porosity of the PVDF membranes could be well tuned by simply adjusting the PVDF concentrations in polymer solutions. The membrane with optimized superhydrophobicity and porous structure exhibits improved waterproof and breathable performance with hydrostatic pressure up to 62 kPa, water vapor transmission rate (WVT rate) of 10.6 kg m^-2 d^-1, and simultaneously outstanding windproof performance with air permeability up to 1.3 mm s^-1. Our work represents a rather simple and perfluorinated-free strategy for fabricating superhydrophobic microporous membranes, which matches well with the environmentally friendly requirement from the viewpoint of practical application.

A Novel In Situ Self-Assembling Fabrication Method for Bacterial Cellulose-Electrospun Nanofiber Hybrid Structures

Self-assembling fabrication methodology has recently attracted attention for the production of bio-degradable polymer nanocomposites. In this research work, bacterial cellulose/electrospun nanofiber hybrid mats (BC/CA-ENM) were formed by incorporating cellulose acetate electrospun nanofiber membranes (CA-ENMs) in the fermentation media, followed by in situ self-assembly of bacterial cellulose (BC) nanofibers. ENMs exhibit excessive hydrophobicity, attributed to their high crystallinity and reorientation of hydrophobic groups at the air/solid interfaces. We aimed to improve the hydrophilic and other functional properties of ENMs. As-prepared nanohybrid structures were characterized using SEM and FTIR. SEM results revealed that in situ self-assembling of BC nanofibers onto the electrospun membrane's surface and penetration into pores gradually increased with extended fermentation periods. The surface hydrophilicity and water absorption capacity of as-prepared hybrid mats was also tested and analyzed. Hybrid mats were observably more hydrophilic than an electrospun membrane and more hydrophobic compared to BC films. In addition, the incorporation of CA electrospun membranes in the culture media as a foundation for BC nanofiber growth resulted in improved tensile strength of the hybrid nanocomposites compared to ENMs. Overall, the results indicated the successful fabrication of nanocomposites through a novel approach, with samples demonstrating improved functional properties.

Pore engineering towards highly efficient electrospun nanofibrous membranes for aerosol particle removal

Electrospun nanofibrous membranes were engineered for aerosol particle removal by controlling the fiber density and alignment across electrospun mats. Electrospun nanofiber membranes were deposited on both, rotatory drum and stationary collectors, to investigate the effect of fiber alignment on filtration performance. Poly(acrylonitrile)/dimethyl formamide (PAN/DMF) solutions were used to produce membranes for applications in air purification. The air filtration performance of as-produced and hot-compacted membranes were systematically evaluated with regard to penetration, pressure drop, and quality factor when subjected to potassium chloride (KCl) aerosol particles in the size-range of 300nm to 12μm. The membranes offered air filtration efficiencies in the range of 77.7% to 99.616% and quality factors between 0.0026 and 0.0204 (1/Pa). The samples were benchmarked against commercial filters and were found to exhibit similar quality factors but higher air filtration efficiencies. These results were correlated to differences in pore morphologies and fiber orientation distributions generated from the different processing techniques, which revealed that the alteration of the fiber density is an effective method for enhancing air filtration performance.

Nitrogen doped hierarchically structured porous carbon fibers with an ultrahigh specific surface area for removal of organic dyes

Recently, tremendous efforts have been devoted to creating inexpensive porous carbon materials with a high specific surface area (SSA) as adsorbents or catalysts for the efficient removal of organic pollutants. Here, activated porous carbon fibers with hierarchical structures were designed and constructed by an electrospinning technique, in situ polymerization, and activation and carbonization processes. Benefiting from the precursor fiber design and subsequent activation techniques, the activated porous carbon fibers (APCFs) derived from a benzoxazine/polyacrylonitrile (BA-a/PAN) precursor exhibited an ultrahigh SSA of 2337.16 m2 g-1 and a pore volume of 1.24 cm3 g-1, showing excellent adsorption capacity toward methylene blue (MeB, 2020 mg g-1). Interestingly, the APCFs after pre-adsorption of MeB also display robust activation of peroxymonosulfate (PMS) with singlet oxygen for the ultrafast removal of MeB. Meanwhile, the synergistic effect of adsorption and a catalytic oxidation reaction using APCFs can realize outstanding total organic carbon (TOC) removal in a comparatively short time. Moreover, a synergistic adsorption-oxidation mechanism for promoting the removal of MeB using APCFs was proposed. This study is useful for the design and development of novel metal-free carbon adsorbents, catalysts or catalyst carriers with an ultrahigh SSA for various applications.

Ultralight and fire-resistant ceramic nanofibrous aerogels with temperature-invariant superelasticity

Ultralight aerogels that are both highly resilient and compressible have been fabricated from various materials including polymer, carbon, and metal. However, it has remained a great challenge to realize high elasticity in aerogels solely based on ceramic components. We report a scalable strategy to create superelastic lamellar-structured ceramic nanofibrous aerogels (CNFAs) by combining SiO2 nanofibers with aluminoborosilicate matrices. This approach causes the random-deposited SiO2 nanofibers to assemble into elastic ceramic aerogels with tunable densities and desired shapes on a large scale. The resulting CNFAs exhibit the integrated properties of flyweight densities of >0.15 mg cm-3, rapid recovery from 80% strain, zero Poisson's ratio, and temperature-invariant superelasticity to 1100°C. The integral ceramic nature also provided the CNFAs with robust fire resistance and thermal insulation performance. The successful synthesis of these fascinating materials may provide new insights into the development of ceramics in a lightweight, resilient, and structurally adaptive form.

Tunable Physical Properties of Ethylcellulose/Gelatin Composite Nanofibers by Electrospinning

In this work, the ethylcellulose/gelatin blends at various weight ratios in water/ethanol/acetic acid solution were electrospun to fabricate nanofibers with tunable physical properties. The solution compatibility was predicted based on Hansen solubility parameters and evaluated by rheological measurements. The physical properties were characterized by scanning electron microscopy, porosity, differential scanning calorimetry, thermogravimetry, Fourier transform infrared spectroscopy, and water contact angle. Results showed that the entangled structures among ethylcellulose and gelatin chains through hydrogen bonds gave rise to a fine morphology of the composite fibers with improved thermal stability. The fibers with higher gelatin ratio (75%), possessed hydrophilic surface (water contact angle of 53.5°), and adequate water uptake ability (1234.14%), while the fibers with higher ethylcellulose proportion (75%) tended to be highly water stable with a hydrophobic surface (water contact angle of 129.7°). This work suggested that the composite ethylcellulose/gelatin nanofibers with tunable physical properties have potentials as materials for bioactive encapsulation, food packaging, and filtration applications.

Micro and nanotechnologies for bone regeneration: Recent advances and emerging designs

Treatment of critical-size bone defects is a major medical challenge since neither the bone tissue can regenerate nor current regenerative approaches are effective. Emerging progresses in the field of nanotechnology have resulted in the development of new materials, scaffolds and drug delivery strategies to improve or restore the damaged tissues. The current article reviews promising nanomaterials and emerging micro/nano fabrication techniques for targeted delivery of biomolecules for bone tissue regeneration. In addition, recent advances in fabrication of bone graft substitutes with similar properties to normal tissue along with a brief summary of current commercialized bone grafts have been discussed.

Flexible Fe3Si/SiC ultrathin hybrid fiber mats with designable microwave absorption performance

Flexible Fe₃Si/SiC ultrathin fiber mats have been fabricated by electrospinning and high temperature treatment (1400 °C) using polycarbosilane (PCS) and ferric acetylacetonate (Fe(acac)₃) as precursors.

Graphene, electrospun membranes and granular activated carbon for eliminating heavy metals, pesticides and bacteria in water and wastewater treatment processes

The availability of safe water has a significant impact on all parts of society, its growth and sustainability, both politically and socioeconomically.

SiC Nanofiber Mat: A Broad-Band Microwave Absorber, and the Alignment Effect

Fiber alignment is a key factor that determines the physical properties of nanofiber mats. In this work, SiC nanofiber mats with or without fiber alignment are fabricated via electrospinning and the microwave electromagnetic properties of their silicone resin composites (5 wt %) are investigated in 2-18 GHz. By comparing with the composite containing SiC whisker, it is found that the nanofiber mats show superior dielectric loss and a minimal reflection loss (RL) of around -49 dB at 8.6 GHz and 4.3 mm thickness, associated with a broad effective absorption (<-10 dB) bandwidth (EAB) of about 7.2 GHz at 2.8 mm thickness. Moreover, the performance can be further enhanced (RL = -53 dB at 17.6 GHz and 2.3 mm thickness) by aligning the nanofiber in the plane of mat, accompanied by the shift of absorption peak to higher-frequency direction and broader EAB up to 8.6 GHz at 3 mm. In addition, the stacking ways of aligned SiC nanofiber mats (either parallel or perpendicular) are proved to have a negligible effect on their microwave properties. Compared with parallel stacking of the aligned mats, cross-stacking (perpendicular) only leads to a slight drop of the attenuation ability. It confirms that alignment of nanofiber in the mats offers a more effective approach to improve the microwave absorption properties than changing the ways of stacking. Furthermore, it is worth mentioning that the low loading fraction (5 wt %) is a great advantage to reduce the weight as well as the cost for large-scale production. All of these facts indicate that the aligned SiC nanofiber mats can serve as a great lightweight and broad-band microwave absorber.

Free-Standing Polyurethane Nanofiber/Nets Air Filters for Effective PM Capture

The filtration performance and light transmittance of nanofiber air filters are restricted by their thick fiber diameter, large pore size, and substrate dependence, which can be solved by constructing substrate-free fibrous membranes with true nanoscale diameters and ultrathin thicknesses, however, it has proven to be extremely challenging. Herein, a roust approach is presented to create free-standing polyurethane (PU) nanofiber/nets air filters composed of bonded nanofibers and 2D nanonets for particular matter (PM) capture via combining electrospinning/netting technique and facile peel off process from designed substrates. This strategy causes widely distributed Steiner-tree structured nanonets with diameters of ≈20 nm and bonded scaffold nanofibers to assemble into ultrathin membranes with small pore size, high porosity, and robust mechanical strength on a large scale based on ionic liquid inspiration and surface structure optimization of receiver substrates. As a consequence, the resulting free-standing PU nanofiber/nets filters exhibit high PM_1-0.5 removal efficiency of >99.00% and PM_2.5-1 removal efficiency of >99.73%, maintaining high light transmittance of ≈70% and low pressure drop of 28 Pa; even achieve >99.97% removal efficiency with ≈40% transmittance for PM_0.3 filtration, and robust purification capacity for real smoke PM_2.5 , making them promising high-efficiency and transparent filtration materials for various filtration and separation applications.

The Antibacterial Polyamide 6-ZnO Hierarchical Nanofibers Fabricated by Atomic Layer Deposition and Hydrothermal Growth

In this paper, we report the combination of atomic layer deposition (ALD) with hydrothermal techniques to deposit ZnO on electrospun polyamide 6 (PA 6) nanofiber (NF) surface in the purpose of antibacterial application. The micro- and nanostructures of the hierarchical fibers are characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy (STEM). We find that NFs can grow into "water lily"- and "caterpillar"-like shapes, which depend on the number of ALD cycles and the hydrothermal reaction period. It is believed that the thickness of ZnO seed layer by ALD process and the period in hydrothermal reaction have the same importance in crystalline growth and hierarchical fiber formation. The tests of antibacterial activity demonstrate that the ZnO/PA 6 core-shell composite fabricated by the combination of ALD with hydrothermal are markedly efficient in suppressing bacteria survivorship.