Ultrafine Fibers Research Articles

Quantitation of Iron(III) Ions Complexed by Tetraphenylporphyrin and Its Effect on the Structure of Ultrafine Poly(3-Hydroxybutyrate) Fibers

We demonstrate a methodical approach to quantitation of iron ions on the surface and in bulk of ultrafine fibrous materials of poly(3-hydroxybutyrate) (P3HB), taking the tetraphenylporphyrin iron(III) chloride (FeClTPP) complex as an example. Ultrafine fibers based on the P3HB biopolymer and containing 1–5 wt % of FeClTPP are fabricated by electrospinning. As analytical techniques, UV spectroscopy and electron paramagnetic resonance (EPR) are successfully used for quantitation of iron(III) species. We identify the effect of the complex on the crystalline phase and segmental mobility of P3HB molecules in amorphous domains of the ultrafine fibers. Adding small amounts of FeClTPP (up to 5%) leads to a marked increase in the crystallite size and the degree of P3HB crystallinity and to densification of the amorphous regions. Our findings suggest that UV spectroscopy and EPR are promising analytical techniques for quantitation of iron ions in nonwoven fibrous sorbents designed for removal of oil products and heavy metals from waste waters.

A model for predicting the tensile strength of ultrafine glass fiber felts with mathematics and artificial neural network

In this article, a model for predicting the tensile strength of ultrafine glass fiber felts is presented with theoretical formula. On the basis of this model, the tensile strength depends on the mean diameter of fibers, resin content and bulk density, but the exact value of strength cannot be calculated directly. The artificial neural network (ANN) is introduced to work out the problem, where the mean diameter of fibers, resin content and bulk density are selected as input parameters, and the tensile strength of longitudinal direction and transverse direction are selected as output parameters. After compared with measured data, the predicted results by the optimized ANN model have been confirmed to have a high accuracy. The mean relative errors of the strength values of longitudinal and transversal direction predicted by the ANN model are 0.0193 and 0.0288, respectively. Three-dimensional planes for the predicted tensile strength as a function of each parameters are established to exhibit the relationship intuitively.

Diversity of Electrospinning Approach for Vascular Implants: Multilayered Tubular Scaffolds

The biomimetics of biological structures found in nature remains one of the most promising approaches to engineer functional tissues from natural or synthetic biocompatible materials for the replacement of damaged or injured parts of the human body. Recently, medical therapeutic regimes have advanced into a new era, overcoming the known mechanical and biological variances that occur when using autologous or synthetic grafts. Basically, the core concept of tissue biofabrication, commonly referred to as tissue engineering, is to find out the favorable cellular microenvironments to grow a living tissue prior to clinical uses. In fact, the ability of stem cells to regenerate is controlled via signaling pathways (growth factors) and supporting materials (scaffolds) that guide the cellular activities. After the first successful experiments to fabricate polymer fibers from their solutions, Cooley proposed the use of an electric field a century ago (Cooley (US 692:631,1902 ). The electrospinning technique has been continually developed as a fruitful polymer processing technique to draw ultrafine nonwoven fibers. Electrospun polymer fibers have been used for a wide range of technical and biotechnical applications such as filtration, organic solar cells, tissue engineering, and drug releasing implants. In this regard, this review begins with an overview about the various spinning approaches for the fabrication of polymer fibers as well as the basic principles of electrospinning process. In addition, this review will highlight vascular bypass surgery and, in particular, the needs for vascular tissue engineering. Finally, the review includes some of the latest attempts to improve the mechanical and biological properties of electrospun polymeric fibers and summarizes the challenges and prospects for the future. However, vascular defects are treated successfully via bypass surgical bypass grafting using autologous or synthetic vessels. The small-diameter vessels (less than 6) are often associated with high failure rate. This review reports some of the recent features that should be highlighted to fabricate an ideal graft for small-diameter vascular grafts. The review introduces multilayered conduits as an alternative approach to overcome the known mechanical and biological mismatches of single layered vascular grafts of electrospun polymers.

Solar evaporation and electricity generation of porous carbonaceous membrane prepared by electrospinning and carbonization

Efficient solar evaporation requires photothermal conversion materials with broad band absorption in solar spectrum, high specific area for water evaporation, and sufficient water transport paths. In the current work, porous carbonaceous membrane consists of continuous ultrafine carbon fibers was prepared by electrospinning followed by carbonation and oxidation. The carbonaceous membrane can absorb more than 95% of incident solar energy in the range from 250 to 2500 nm. The carbonaceous membrane has hydrophilic characteristics and continuous channels for sufficient water transport. The ultrafine carbon fibers on the surface of the membrane provide tremendous interfaces for water evaporation. With localized heating design, the carbonaceous membrane delivers a water evaporation rate of 1.33 kg m−2 h−1 and a solar evaporation efficiency of 81.71%. It is also demonstrated that the carbonaceous membrane can recover fresh water from seawater, acid solutions and alkali solutions. Furthermore, the carbonaceous membrane shows the potential of electricity generation driven by solar evaporation.

Fabrication of novel dual thermo- and pH-sensitive poly (N-isopropylacrylamide-N-methylolacrylamide-acrylic acid) electrospun ultrafine fibres for controlled drug release.

Dual temperature- and pH-sensitive materials used as drug carriers have attracted a particularly high level of interest. However, it is limited by low sensitivity to changes in conditions because of large size and low specific surface area. In this work, novel dual temperature- and pH-sensitive poly(N-isopropylacrylamide-N-methylolacrylamide acrylic acid) (PNIPAm-NMA-AAc) ultrafine fibres were successfully prepared by radical copolymerisation, electrospinning and thermal chemical treatment. The PNIPAm-NMA-AAc ultrafine fibres were characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), spectroscopy UV-visible spectroscopy, scanning electron microscopy (SEM) and cell counting kit-8 (CCK-8) assay. The uniformity and small size of PNIPAm-NMA-AAc ultrafine fibres with LCST range from 31 °C to 43 °C were used to drug carrier because of good thermal stability, no cytotoxic. Curcumin as a model drug was well distributed in PNIPAm-NMA-AAc ultrafine fibres. In addition, analysis of curcumin release at different pH values and temperatures confirmed that the PNIPAm-NMA-AAc ultrafine fibres are responsive to both temperature and pH. The maximum amount of curcumin released was 98.47% ± 1.87%. In addition, the release mechanism of curcumin-based PNIPAm-NMA-AAc ultrafine fibres was shown to conform to Fickian diffusion (r2 ≥ 0.95). These results indicated that dual-responsive PNIPAm-NMA-AAc ultrafine fibres are promising as drug carriers.

An Exploration of Electrospun Fibers Containing Drug-Cyclodextrin Inclusion Complexes

A series of new core-shell fibers were developed containing anticancer drugs (5-fluorouracil or ferulic acid) and their cyclodextrin inclusion complexes, with a gadolinium-based magnetic resonance imaging (MRI) contrast agent. These were prepared by electrospinning, a simple method for producing ultra-fine fibers through the application of a strong electrostatic force on a polymer solution. The shell of the fibers was formed from Eudragit S100, and the drugs were loaded in the core. Scanning electron microscopy images showed the formation of smooth ribbon-like fibers, with diameters ranging from 1.4 to 5.1 μm, and transmission electron microscopy reveals a transparent interface between the core and shell compartments. X-ray diffraction and differential scanning calorimetry data confirmed the encapsulation of the drug into the cyclodextrin cavity and the formation of amorphous solid dispersions in the fibers. Drug release from the systems at pH 1 and 7 showed that all the drug loading was released within one hour at pH 1. Based on these results, it is proposed that the relatively low molecular weight drugs were able to diffuse out of the system into the release medium at acidic pH, despite the insolubility of the shell polymer under these conditions. These findings have important implications for the design of electrospun drug delivery systems.

Numerical simulation analysis of the influence of ultra-fine glass fiber production process on product homogeneity

Glass fiber felt is produced by flame blowing process, in which primary glass filament splits into glass fiber through the gas jet into the diffusion duct. In the diffusion duct, the velocity difference at axial direction creates a fiber recirculating zone at some position downstream in the duct while affecting the homogeneity of the product. In order to understand the impact of diffusion duct design to the felt forming, numerical simulations with experiment-based boundary conditions were performed to investigate the movement of fiber suspension flow. In the numerical analysis, the fiber slender-body theory is introduced. A visualization method is developed to characterize the uniformity of glass fiber, through charge coupled device camera imaging demonstrating the intensity of glass fiber in the surface of the product. The proposed methodology enabled new design of the diffusion duct, which eliminated the recirculating zone in the duct, resulting in more uniform products.

Scalable fabrication of rechargeable photoactive cellulose nanofibrous membranes for efficient degradation of dyes

Construction of photoactive nanofibrous membranes for effective treatment of dyeing effluents is critical to meet the great demands of environmental protection in textile industry, yet still remains a big challenge. In this work, we report a cost-effective strategy to create rechargeable photoactive cellulose nanofibrous membranes (BPTCD-CeNM) under mild conditions that can effectively and repeatedly produce hydroxyl radicals for dye degradation. The principle of this design is that BPTCD-CeNM could store photoactivity under UV light irradiation and release hydroxyl radicals under dark conditions. The membranes possess an ultra-fine fiber diameter (275 nm), large surface area (3.06 m2 g−1) and excellent degradation performance for reactive red 195, reactive yellow 4 and acid blue 7 (> 99.99% within 60 min). The successful fabrication of such materials may open up new avenues for designing and constructing highly efficient photoactive membrane materials for environmental applications.

Advances in Electrospinning of Natural Biomaterials for Wound Dressing

Electrospinning has been recognized as an efficient technique for the fabrication of polymer nanofibers. Various polymers have been successfully electrospun into ultrafine fibers in recent years. These electrospun biopolymer nanofibers have potential applications for wound dressing based upon their unique properties. In this paper, a comprehensive review is presented on the researches and developments related to electrospun biopolymer nanofibers including processing, structure and property, characterization, and applications. Information of those polymers together with their processing condition for electrospinning of ultrafine fibers has been summarized in the paper. The application of electrospun natural biopolymer fibers in wound dressings was specifically discussed. Other issues regarding the technology limitations, research challenges, and future trends are also discussed.

Bacterial cellulose coated ST-cut quartz surface acoustic wave humidity sensor with high sensitivity, fast response and recovery

A Love mode surface acoustic wave (SAW) humidity sensor based on bacterial cellulose (BC) coated ST-cut quartz was developed in this study. The BC film is composed of ultrafine interwoven fibers to form a highly porous network, and its surface contains a large amount of hydroxyl groups, which significantly improve the adsorption capability of SAW sensing layer for water molecules. This results in significant mass loading effects and enhanced responsivity of the SAW sensor. The resonant frequency of the sensor changes linearly with RH at lower relative humidity (RH) values (e.g. RH < 30%), but when RH > 80%, an exponential increase in frequency shift as a function of RH is obtained due to the enhanced mass loading effect. A frequency shift of 89.8 kHz was measured using a sensor with a BC film with a thickness of 148 nm thick when the RH was increased from 30% to 93%. The frequency of the sensor can be fully shifted back to the original reading when the RH was returned back to 30%, with the response and recovery times of 12 s and 5 s, respectively. The SAW sensor also exhibits good short-term repeatability and long-term stability for humidity sensing.

Effect of poly(ethylene oxide) on the electrospinning behavior and characteristics of ethyl cellulose composite fibers

Ethylcellulose (EC) is a nontoxic polymer widely used in food, pharmaceutical, and biomedical applications. Previous studies showed that the electrospinning of EC is challenging due to the formation of beads rather than continuous fibers. To overcome this limitation, this study evaluated poly(ethylene oxide) (PEO) as a process aid to enhance the electrospinning of EC solutions. Fibers were electrospun using free surface electrospinning technique which is more conducive for scale up production than the typical spinneret approach. The effects of PEO content, PEO molecular weight, and aqueous ethanol concentration on EC solutions parameters, spinnability, and fiber morphology were studied. Among the spin dope solutions, neat EC solution had the highest conductivity (38.28 ± 0.47 µS/cm) , but lowest surface tension (42.3 ± 0.1 mN/m) and viscosity (0.331 ± 0.006 Pa.s) values. These properties led to the formation of irregular particulates interweaved with ultrafine fibers of an average diameter of 0.075 ± 0.003 µm. The incorporation of 1% (w/w) PEO (Mw = 100 kDa) in EC solution enhanced its spinnability, where stable polymer jets were observed during the electrospinning process, producing fibers of significantly (p < 0.05) larger average diameter (0.297 ± 0.007 µm). Interactions between EC and PEO in the electrospun were elucidated using Fourier transformed infrared spectroscopy. This study contributed to the understanding of the effect of PEO on the electrospinnability of EC solutions, which can be useful during the development of EC-PEO nonwovens for specific end use applications.

Preparation and Performance of Ultra-Fine Polypropylene Antibacterial Fibers via Melt Electrospinning.

Polypropylene (PP) fibers are employed commonly as the raw material of technical textiles (nonwovens), and the research focuses on fine-denier fibers and their functionalities. In this work, antibacterial PP masterbatches with different dosage (1–5 wt.%) of nano-ZnO particles as the antibacterial agent were prepared via a twin-screw extruder. The as-prepared PP masterbatches were electrospun on a home-made electrospinning device to afford ultra-fine PP fibers. The morphologies of as-spun ultrathin PP fibers with 16 μm of average diameter were observed by SEM. The structure and element distribution were characterized by means of energy-dispersive spectroscopy (EDS) and Fourier-transfer infrared spectroscopy (FTIR), respectively. There was some zinc obviously distributed on the surface when a dosage of ZnO more than 1 wt.% was used, which contributed to the antibacterial activity. The crystallinity of PP fibers was not affected strongly by the dosage of ZnO based on the differential scanning calorimetry (DSC) heating curves, while thermal decomposition improved with the increase in ZnO content, and the mechanical strength decreased predictably with the increase in inorganic ZnO content.

Influence of Polymer Concentration and Nozzle Material on Centrifugal Fiber Spinning.

Centrifugal fiber spinning has recently emerged as a highly promising alternative technique for the production of nonwoven, ultrafine fiber mats. Due to its high production rate, it could provide a more technologically relevant fiber spinning technique than electrospinning. In this contribution, we examine the influence of polymer concentration and nozzle material on the centrifugal spinning process and the fiber morphology. We find that increasing the polymer concentration transforms the process from a beaded-fiber regime to a continuous-fiber regime. Furthermore, we find that not only fiber diameter is strongly concentration-dependent, but also the nozzle material plays a significant role, especially in the continuous-fiber regime. This was evaluated by the use of a polytetrafluoroethylene (PTFE) and an aluminum nozzle. We discuss the influence of polymer concentration on fiber morphology and show that the choice of nozzle material has a significant influence on the fiber diameter.

Ultra-fine electrospun nanofibrous membranes for multicomponent wastewater treatment: Filtration and adsorption

Electrospun sulfonated polyethersulfone (SPES) nanofibrous membranes with ultra-fine mean fiber diameter, e.g., 62 ± 16 nm, were fabricated by a two-nozzle electrospinning approach and employed as a multi-functional membrane for removal of nanoparticles, dyes, and heavy metal ions from multicomponent wastewater through filtration and adsorption, simultaneously. The pore size and pore size distribution of the membrane could be varied and adjusted by controlling the fiber diameter, which affects the filtration retention of nanoparticles while the sulfonic groups located on the surface of the nanofibers work as active sites for the adsorption of dyes and heavy metal ions by electrostatic interaction. Increase in the degree of sulfonation and decrease in the concentration of solution led to the reduction of fiber diameter of the electrospun nanofibrous membranes, as evidenced by SEM and TEM measurements, in addition to the increase in the molecular weight of SPES. The adsorption kinetics and thermodynamics of the nanofibrous membrane for cationic dye and heavy metal ions were investigated, separately, in addition to the filtration performance of nanoparticle suspensions. The ultra-fine nanofibrous SPES membrane was finally tested, with simulated multicomponent wastewater containing 0.2 μm-particles, methylene blue (MB), and Pb (II) ions. The membrane exhibited high permeation flux of 320 L/m2h, high retention of >99.0% against nanoparticles, MB and Pb (II), as well as high treated capacity in the filtration performance. The nanofibrous SPES membranes after adsorption of MB and Pb (II) were able to be recovered which indicated the sustainable nature of the membrane for real wastewater treatment.

Preparation of underwater superoleophobic membranes via TiO2 electrostatic self-assembly for separation of stratified oil/water mixtures and emulsions

Huge discharge of oily wastewater has seriously threatened the ecosystem and human's health. Superhydrophilic/underwater superoleophobic porous materials have engaged considerable attentions in the application for separation of oil/water mixtures. However, there still exist several challenges in the existing material designs for oil/water separation that need to be addressed, such as terrible stability, high production cost and complex fabrication procedure. Herein, a series of all-inorganic superhydrophilic and underwater superoleophobic filtration materials were designed and fabricated by coating TiO2 via a facile and universal technique of self-assembly, as well as successfully applied for the separation of both stratified oil/water mixtures and emulsions. The as-prepared TiO2 nanoparticle coating is extremely dense, ultrathin and widely applicable for various two-dimensional (2D) and three-dimensional (3D) substrates such as stainless-steel mesh (SSM), metal felt and glass fibrous (GF) membrane. The coating can even be coated on the ultrafine fibers with diameter reaching to hundreds of nanometers. The TiO2 coated SSM with large pores (~35 μm diameter) could efficiently separate the stratified oil/water mixtures with the flux up to 54000 L⋅m−2⋅h−1. Moreover, the TiO2 coated GF membrane with small pores (~5 μm diameter) can separate diverse surfactant-free and surfactant-stabilized emulsions with separation efficiency higher than 98%. More importantly, excellent filtration flux up to ~4000 L⋅m−2⋅h−1 was realized under solely gravity, which is one to two orders of magnitude larger than the flux of traditional filtration membranes, as well as more superior than most of the reported superwettable membranes. Furthermore, the as-prepared GF membrane displays outstanding high-temperature resistance and reusability for long-term application of oil/water separation.

Micro/nanofabrication of brittle hydrogels using 3D printed soft ultrafine fiber molds for damage-free demolding

Hydrogels are very popular in biomedical areas for their extraordinary biocompatibility. However, most bio-hydrogels are too brittle to perform micro/nanofabrication. An effective method is cast molding; yet during this process, many defects occur as the excessive demolding stress damages the brittle hydrogels. Here, we propose a brand-new damage-free demolding method and a soft ultrafine fiber mold (SUFM) to replace the traditional mold. Both mechanical and finite element analysis (FEA) reveal that SUFMs have obvious advantages especially when the contact area between hydrogel and mold gets larger. By means of a high-resolution 3D printing called electrohydrodynamic (EHD) printing, SUFMs with various topological structures can be achieved with the fiber diameter ranging from 500 nm to 100 μm, at a low cost. Microfluidics and cell patterns are implemented as the demonstration for potential applications. Owing to the tiny scale of microstructures and the hydrophilicity of hydrogels, significant capillary effect occurs which can be utilized to deliver liquid and cells autonomously and to seed cells into those ultrafine channels evenly. The results open up a new avenue for a wider use of hydrogels in biomedical devices, tissue engineering, hydrogel-based microfluidics and wearable electronics; the proposed fabrication method also has the potential to become a universal technique for micro/nanofabrication of brittle materials.

Preparation and characterization of green carboxymethylchitosan (CMCS) – Polyvinyl alcohol (PVA) electrospun nanofibers containing gold nanoparticles (AuNPs) and its potential use as biomaterials

Green chemistry was used in nanostructures preparation to impart it amazing innovating application in the medical field. Herein we prepared novel, cost effective and ultra-safe antibacterial nanocomposite. This nanocomposite contains carboxymethylchitosan (CMCS) as safe reducing agent for gold nanoparticles (AuNPs) and polyvinyl alcohol (PVA) as nanofiber aiding material formation. The AuNPs has spherical shapes, its diameter ranged from 15 to 25 nm and uniform distributed within CMCS nanofibers. The optimum conditions for electrospinning were 10 wt% total solution contains 2 wt% CMCS and 8 wt% PVA. UV–vis, TEM and XRD were used to characterize AuNPs whereas FTIR and SEM were used to characterize nanofibers. Results showed that ultra-fine fibers were generated after addition of PVA to CMCS solution. Also, CMCS nanofibers containing AuNPs has excellent antibacterial activity towards tested bacteria. Finally, the cytotoxicity of CMCS has been evaluated through Cell viability assay, which confirm that the nanofiber composite is non-toxic and tissue compatible.

Large-scale fabrication of robust textile triboelectric nanogenerators

Smart energy textiles based on triboelectric nanogenerators (TENGs) are promising power supply and sensor arrays for wearable electronics and artificial intelligence. However, the challenges of the smart textile in large-scale industrialized production, facile and universal fabrication process, and enough robustness still remains. In this study, a textile-based triboelectric nanogenerator (t-TENG) is proposed through a facile and universal fabrication process. Liquid-metal/polymer core/shell fibers (LCFs) structure as the basic unit of TENG textiles, can be extensively achieved by pumping liquid metal into uniform ultrafine polymer hollow fibers, which contribute to the large-scale industrialized production of TENG textiles. In addition to gaining a high output, the t-TENG demonstrates excellent acid and alkali resistance, and high friction durability. Furthermore, profiting from the universal fabrication process, the polymer hollow fibers can be replaced by any type of fibers with various functions or colors according to practical applications (e.g., the silicone rubber could be an excellent choice for highly stretchable devices). Moreover, the fabricated t-TENGs demonstrate great capability in self-powered sensors for smart home controlling. All these advantages of the t-TENG exhibit its great potential for further application in wearable electronics and artificial intelligence and it will speed up the development of IoTs in the near future.

Metal-free N-doped ultrafine carbon fibers from electrospun Polymers of Intrinsic Microporosity (PIM-1) based fibers for oxygen reduction reaction

Synthesis of nitrogen-doped carbon fibers (CF) has been proved to be one of the most promising oxygen reduction reaction (ORR) catalysts which can replace the state-of-art Pt catalyst for non-noble metal-free light-weight devices. Polymers of Intrinsic Microporosity (PIM-1) is soluble in common organic solvents and can be tailored by functionalization owing to nitrile groups in the backbone. PIM-1 was functionalized to amide (hydrolyzed PIM-1), amine and amidoxime groups. The modified PIM-1s were electrospun into ultrafine fibers and pyrolyzed to obtain CF. The present article investigates the influence of different functional groups on the properties of PIM-1 based CF and their nitrogen-doping. Particularly, their ORR performance has been evaluated. Interestingly, CF from hydrolyzed PIM-1 have the highest pore volume with small pore size among the CF based on PIM-1, amine and amidoxime PIM-1. The amount of nitrogen-doping in these CF shows the trend according to the functional groups as PIM-1 > amine > amidoxime > amide. Among all these PIM-1 based CF; CF from hydrolyzed PIM-1 has the highest percentage of pyridinic and graphitic nitrogen, furthermore, electrocatalysis revealed that ORR processed through four-electron with the onset potential 985 mV vs. reversible hydrogen electrode (RHE) which is comparable with the standard Pt/C catalysts.

Deep learning-based automated morphology classification of electrospun ultrafine fibers from M44 element image of muller matrix

Electrospun ultrafine fibers with microporous morphology have been wildly used in the fields of drug release, filtering material, and tissue engineering, and it is more difficult to obtain the information of their microporous morphology. In this paper, electrospun ultrafine fibers with different morphologies: smooth surface, microporous, and beaded microspheres were prepared. Then, the polarized information of various fibers was obtained with polarized light microscope and calculate the Muller matrix. Subsequently, the method of transfer learning was introduced, to train the discriminant model with only a small amount of data based on M44 image element of the Mueller matrix, and to realize the automatic classification of the microporous morphology of electrospun ultrafine fibers. These results show that this classification method with a high accuracy in the test set could provide a fast, simple, reliable and real-time analysis for researchers to screen fiber samples with different morphologies.