Comparison of two electrospinning processes in obtaining finer polymer nanofibers

Two different electrospinning processes (traditional single fluid one and a modified coaxial electrospinning with organic solvent as sheath fluid) are investigated in relation to their capability of producing thinner nanofibers. Both the modified coaxial electrospinning and single fluid electrospinning can produce thinner nanofibers with polyvinylpyrrolidone (PVP) as a polymer model and using a poor volatile solvent N, N-dimethylacetamide (DMAc) in different ways. However the traditional single fluid process was less effective compared to the modified coaxial process, as it suffered more from the limitation of polymer chain entanglement threshold for maintaining structural uniformity of nanofibers. Using DMAc as sheath fluid in the modified process facilitated formation of thinner nanofibers without sacrificing their quality. The mechanism should be that an appropriate DMAc surrounding to the core polymer jet helps to retain it in a fluid state to experience a longer time electrical drawing, with little adverse influence on the polymer chain entanglements. Nanofiber diameters could also be tailored in a linear manner using the modified coaxial process simply through manipulating the sheath solvent flow rates. The modified coaxial process described here extends the capability of electrospinning process and opens a new way to obtain thinner nanofibers with fine structural uniformity.     

Manufacturing and Optimization the Nanofibres Tissue of Poly(N-vinyl-2-pyrrolidone) - Poly(e-caprolactone) Shell/Poly(N-vinyl-2-pyrrolidone)-Amphotericin B Core for Controlled Drug Release System

Controlled release of drugs is important to reduce the amount of medication in treatment of any diseases and improves life quality. Poly(e-caprolactone) (PCL) has a low biodegradation rate that is a disadvantage in the biomedical and pharmaceutical fields. Poly(N-vinyl-2-pyrrolidone) (PVP) is a water-soluble polymer that to overcome of PCL low biodegradation rate, electrospinning of PCL blended with PVP was used for shell of nanofibers with controllable degradation rates and drug release rates. Oral and vaginal mucosal infections mainly caused by candida albicans. It is usually a harmless commensal organism; however it is known as an opportunistic pathogen for almost immunologically week and immune compromised people. Amphotericin-B (AmB) is a strong polyene antifungal antibiotic that has a significantly efficacy on candida albicans. This study is manufactured and optimized the PVP-PCL shell/PVP-AmB core nanofiberous tissue by working distance and feed flow rate for controlled drug release. AmB with PVP was successfully inserted into the core. PVPPCL shell (50/50)/PVP-AmB core nanofiberous were electrospinning with two optimum distances working and two flow rates. The mechanical properties of coaxial nanofibers were analyzed by instron machine. Scanning electron microscopy and transmission electron microscopy was used for analysis morphology. Further, drug release test were done for coaxial nanofibers with AmB different morphologies. The effect of flow rate and working distance on morphology and mechanical properties were evaluated by statistical two-way analysis of the variance (ANOVA). The diameter averages of nanofibers were decreased significantly by increasing working distance. Moreover, the stress and strain were increased by increasing working distance. Coaxial nanofibers biodegradability rate and drug release of nanofibers were increased also by increasing working distance and flow rate of core. Nanofibers drug release mechanism was indicated by Korsmeyer-Peppas which they followed fick′s lows and Higuchi model significantly. Also, results presented that biodegradability and drug release rate accelerate with increasing the working distance and increasing the amount of PVP in core.     

The morphology of Taylor cone influenced by different coaxial composite nozzle structures

Coaxial electrospinning is an effective method to produce core-shell nanofibers, which is associated closely with the morphological stability of Taylor cone. However, the nozzle structure mainly influences the formation of Taylor cone during the coaxial electrospinning procedure. In the present work, since the numerical simulation is a novel and convenience method in the theoretical research of the coaxial electrospinning, the influence of different coaxial composite nozzle structures on Taylor cone shape was studied by ANSYS finite element simulation method. Different coaxial composite nozzle structures — concave type, flush type and convex type, were designed in this work. 2D electric field model of the nozzle structures was simulated by utilizing ANSYS finite element analysis software. The simulation results indicated that electric field intensity distribution of concave type nozzle structure was more uniform than those of the other two types. Therefore, a more stable coaxial Taylor cone was formed in the tip of concave type nozzle structure. To verify the accuracy of the simulation results, core-shell nanofibers were spun by using different coaxial composite nozzle structures. In each experiment, PAN and PVP were employed to be the shell and core solution respectively. Besides that high-speed camera was employed to monitor the coaxial electrospinning procedure. The cross-section morphology of electrospun nanofibers was characterized by scanning electron microscope (SEM). The experimental results showed that when the concave type nozzle was used in the coaxial electrospinning process, Taylor Cone morphology was more stable than other type coaxial composite nozzle structures. The cross-section morphology of electrospun fibers observed by SEM revealed that the high stability in core-shell structure also occurred in coaxial electrospinning by using concave nozzle structure. Furthermore, the simulation and experimental results verified the concave type nozzle is the better nozzle structure for coaxial electrospinning to form stable coaxial Taylor cone.     

Encapsulation of Phytoncide in Nanofibers by Emulsion Electrospinning and their Antimicrobial Assessment

Phytoncides are volatile organic compounds released from trees and plants and are well known for their natural antibacterial activity. In this study, emulsion electrospinning was used to encapsulate phytoncide in the core of nanofibers, with the aim of developing environmentally friendly, functional nanofibers with a sustained release of the encapsulated component. Core/sheath structured phytoncide/poly(vinyl alcohol) nanofibers were successfully prepared by emulsion electrospinning using an ordinary single-nozzle electrospinning setup. An oil-in-water emulsion of an aqueous solution of poly(vinyl alcohol) (as the aqueous phase) and phytoncide (as the oil phase) was used to prepare the core/sheath structured nanofibers. Nanocomposite fibers were electrospun under various spinning conditions and emulsion formulations to find the suitable processing conditions for fabricating nanofibers with core/sheath structures. The resulting nanofibers exhibited a well-aligned core/sheath structure with fiber diameters of 250-350 nm. The release profile of phytoncide from the core of nanofibers over a 21 day period showed that phytoncide was released in a sustained manner over 14 days. The core/sheath structured phytoncide/poly(vinyl alcohol) nanofibers exhibited 99.9 % bacterial reduction against both Staphylococcus aureus and Escherichia coli, indicating that the encapsulated phytoncide in the fiber provided strong antimicrobial effects.     

Studies of electrospinning process of zirconia nanofibers

Eletriospinning process was used to fabricate Zirconia nanofibers and polyvinyl pyrrolidone (PVP) was employed in this procedure. SEM, TGA, FT-IR and XRD were used to investigate the electrospinning process. Pure PVP was electrospun at the same conditions as comparisons. The results indicated that the fibers had an average diameter about 80 nm with smooth surface. FT-IR spectrum and TGA curve proved that PVP was removed from the fibers after a thermal treatment. It was found that the crystal structure of Zirconia changed at different calcination temperature. The use of PVP, bicomponent solvent of water and ethanol and inorganic salt had positive effects on the morphology of the fibers.     

The role of Na-montmorillonite on thermal characteristics and morphology of electrospun PAN nanofibers

Polymer organic-inorganic hybrid nanofibers constitute a new class of materials in which the polymeric nanofibers are reinforced by uniformly dispersed inorganic particles having at least one dimension in nanometer-scale. In the present study, polyacrylonitrile (PAN) and PAN/Na-montmorillonite (PAN/Na-MMT) nanofibers were conducted via electrospinning process. Electrospun PAN and PAN/Na-MMT fibers with the respective mean fiber diameter of about 220 and 160 nm were prepared. The influence of the clay-montmorillonite on the morphology and diameter of nanofibers was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The microscopic techniques propose that the PAN/Na-MMT composite nanofibers show lower mean fiber diameter than the neat PAN nanofibers. Besides, the difference in nanoclay-content has a slight effect on the distribution of fibers diameter. Thermogravimetric analysis (TGA) results suggest that introduction of clay-nanomaterials improves the thermal characteristics of fibers.     

Dyeing behavior of polyacrylonitrile nanofibers: Physicochemical parameters of dyeing with basic dye in comparison with regular polyacrylonitrile fibers

Polyacrylonitrile nanofibers were produced using the electrospinning method and dyed with a basic dye alongside regular polyacrylonitrile fibers. In order to investigate the effect of high surface area to volume ratio of nanofibers on their adsorption behavior in comparison with regular fibers, the dyeing conditions for both types of fibers were kept just the same. Physiochemical parameters of dyeing such as adsorption isotherm, standard affinity, enthalpy change, rate of dyeing constant, diffusion coefficient, and activation energy of diffusion were investigated for both types of fibers. The results showed that the adsorption process can be well described with the Langmuir adsorption isotherm for both types of fibers whereas the standard affinity of dye to nanofibers was higher than regular fibers and the higher negative values of enthalpy changes were obtained for regular fibers. The nanofibers rate of dyeing was faster than regular fibers with higher amounts of diffusion coefficients and lower amounts of activation energy of diffusion. This study also revealed that in spite of the approximately same amount of dye exhaustion for both types of fibers, the color strength of regular fibers was noticeably higher than nanofibers.     

Electrical properties of ultrafine nylon-6 nanofibers prepared via electrospinning

We report on the preparation and electrical characterization of nylon-6 nanofibers via electrospinning technique. During electrospinning, the polymer solution became highly ionized and emerging out of the micro-tip syringe by forming mesh-like ultrafine nanofibers structure in between the main fibers. The resultant nylon-6 nanofibers were well-oriented with uniform structure. The diameter of the ultrafine nanofibers (7 to 40 nm) is one order less than those of main fibers (100 to 200 nm). The current-voltage (I-V) measurements revealed a linear curve with an occurrence of negative differential resistance (NDR) behavior. The existence of NDR region in the nylon-6 nanofibers can be attributed to the tunneling current through the ultrafine structures. The fabrication of nanofibers, in the form of ultrafine mesh-like form, is relatively fast and inexpensive, and it paves the way to build up of new dimension for nano device applications.     

An Investigation into Scalability Production of Ultra-Fine Nanofiber Using Electrospinning Systems

An integrated experimental and modeling approach was utilized to study scalable production of nanofibers via electrospinning. Two concepts have been investigated to study the fabrication of PAN nanofibers, which are needle-based and orifice-guided electrospinning to utilize the optimum setup. Moreover, it was observed that the natural flow rate of electrospinning does not scale linearly with number of needles (unlike polymer processing methods such as dry spinning), which was explained based on the partial pressure of the solvent vapor, peculiar to multi-needle setup, and the stress relaxation in the solution. In addition, it was demonstrated that the minimum voltage required to continuously electrospun fibers increases as the distance between needles is reduced, which was explained by the shielding effect of neighboring needles and elucidated by the Finite Element Analysis (FEA) models. Nano-fibers with diameters less than 100 nm were produced in this investigation.     

Fabrication and characterization of electrospun nanofibers of high DP natural cotton lines cellulose

Nanofibers of natural cotton lines cellulose, with a degree of polymerization above 10000, were prepared by electrospinning. The effects of cellulose concentration, flow rate and electric field strength on the morphologies of the fibers were systematically investigated. Furthermore, two effective improvements on the electrospinning apparatus were made: heating the pathway between the tip of the needle and the collector instead of the needle or the collector, and covering the drum with activated cellulose flake. High quality cellulose nanofibers were obtained under the optimized spinning conditions combined with the apparatus improvements. Moreover, oriented cotton nanofibers were acquired by elevating the rotation speed of the drum collector. The wettability of the nonwoven was greatly improved compared with the original activated cellulose. The obtained nonwoven or nanofibers of the natural cotton cellulose could be potentially applied in tissue scaffolds, protective clothing and high efficient water absorbing materials etc.     

Fabrication of poly(vinyl alcohol) nanofibers by wire electrode-incorporated electrospinning

Wire electrodes for needleless electrospinning consist of stainless steel wires in place of cylinder electrodes. The effects of different numbers of constituent stainless steel wires on the morphology and diameter of polyvinyl alcohol (PVA) fibers are examined. With 1, 2, 3, or 4 stainless steel wires being twisted as wire electrodes, an 8, 10, or 12 wt.% polyvinyl alcohol (PVA) solution is electrospun into PVA nanofibers by using a needleless electrospinning machine. The morphology and diameter of PVA nanofibers is observed by scanning electron microscopy. The combination of the number of stainless steel wires (two), PVA solution (10 wt.%), and the collecting distance (10 cm) results in the finest diameter and an evenly formed fiber morphology. In addition, the nanofibers exhibit a wide range of diameters when electrospun with an electrode consisting of more than two stainless steel wires. Compared with the cylinder electrode, the use of a wire electrode can form nanofibers, which results in a more even morphology.     

Preparation of luminescing nanocrystal and its application to electrospinning

In this study, quantum dots (QDs) having the photophysical properties of brightness, photostability and narrow emission were synthesized. The electrospinning has been introduced to be a simple technique for generating ultrathin fibers. Herein, we have synthesized QDs and electrospun polyvinylacetate (PVAc) nanofibers having these strongly luminescing QDs particles. The size and morphology of QDs were recorded with transmission electron microscopy (TEM). The structural nanofiber webs have been discussed by scanning electron microscopy (SEM). And fluorescence properties of strongly luminescing QDs nanofibers were also discussed.     

Large scaled fabrication of microfibers by air-suction assisted needleless melt electrospinning

A cone-shape spinneret with air-suction assisted was used for the production of ultrafine fibers by melt electrospinning. The influence of the applied voltages on the number of jets and the effects of the different types of air flow (air blowing and air suction) on the fiber bundle were studied. It was demonstrated that the breadth of the diameter distribution of the fibers decreases markedly and the production rate was also improved when air suction and higher applied voltages were applied. Therefore this new melt electrostatic spinning equipment can meet the need of some special applications and industrial mass production of nanofibers.     

Surface modified ployacrylonitrile nanofibers and application for metal ions chelation

Ployacrylonitrile (PAN) nanofibers were formed by electrospinning. Amidoxime ployacrylonitrile (AOPAN) nanofibers were prepared by reaction with hydroxylamine hydrochloride, which were used as the matrix for metal ions chelation. FTIR spectra of the PAN nanofibers and AOPAN nanofibers were recorded for analysis of the surface chemical structures. The AOPAN conventional fibers were also prepared for comparison, and surface morphologies of the modified PAN conventional fibers and PAN nanofibers were observed by FESEM. Metal ions concentrations were calculated by AAS. The chelated isothermal process and kinetics parameters of the modified PAN nanofibers and PAN conventional fibers were studied in this work. Results indicated that the saturated coordinate capacity of AOPAN nanofibers to Cu²⁺, Cd²⁺ was 3.4482 and 4.5408 mmol/g (dry fiber) respectively, nearly two times higher than that of AOPAN conventional fibers. Besides, the desorption rate of Cu²⁺ and Cd²⁺ from metal chelated AOPAN nanofibers was 87 and 92 % respectively in 1 mol/l nitric acid solution for 60 min. The isothermal processes were found to be in conformity with Langmuir model.     

Shape memory properties of electrospun nafion nanofibers

Nanoscaled non-woven fibers with shape memory effect are successfully fabricated via electrospinning method from Nafion solutions consisting of a little poly(ethylene oxide) (PEO). Scanning electron microscopy (SEM) investigation shows the electrospun nanofibers with average diameters in the range 170–410 nm. The electrospun nanofibers exhibit excellent shape memory properties. When deformed Nafion nanofibers are stimulated upon heat, the temporary shape responds rapidly, and then recovers to the permanent shape in less than one minute. The shape recovery ratios and shape fixity ratios of Nafion nanofibers with 0.3 wt%, 0.5 wt% and 0.7 wt% PEO are all above 90 %. In shape memory cycle, fibrous structure is stable after the stretching recovery. Shape memory Nafion nanofibers have various potential applications in smart structures and materials in the future.     

Titanium dioxide nanofibers prepared by using electrospinning method

The synthesis of titanium dioxide nanofibers with 200–300 nm diameter was presented. The new inorganic-organic hybrid nanofibers were prepared by sol-gel processing and electrospinning technique using a viscous solution of titanium isopropoxide (TiP)/poly(vinyl acetate) (PVAc). Pure titanium dioxide nanofibers were obtained by high temperature calcination of the inorganic-organic composite fibers. SEM, FT-IR, and WAXD techniques were employed to characterize these nanofibers. The titanium dioxide nanostructured fibers have rougher surface and smaller diameter compare with PVAc/TiP composite nanofibers. The anatase to rutile phase transformation occurred when the calcination temperature was increased from 600 °C to 1000 °C.     

Core-sheath polyurethane-carbon nanotube nanofibers prepared by electrospinning

The core-sheath nanofibers consisting of polyurethane (PU) core and PU composites sheath with multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. At low MWNT concentration, MWNTs appeared highly aligned along the fiber axis with some curving in nanotubes, whereas in case of high concentration, some aggregation of MWNTs appeared due to difficulty in full dispersion of nanotubes. In comparison of the single component nanofiber webs, the core-sheath nanofiber webs showed much better mechanical properties of modulus and breaking stress, including an exceptional elongation-at-break. It indicates that the CNT-incorporated core-sheath structure is very effective for enhancing the mechanical properties of nanofiber webs. In addition, the core-sheath nanofibers demonstrated the fast shape recovery, compared with one component fibers of pure shape memory PU and PU/MWNTs, which provides the possibility of fabricating more sensitive intelligent materials.     

Electrospun poly(tetrafluoroethylene) nanofiber membranes from PTFE-PVA-BA-H<Subscript>2</Subscript>O gel-spinning solutions

As a kind of high-performance fibers, PTFE fiber has been widely used in many fields because of its unique characteristics. In this study, the poly(tetrafloroethylene) (PTFE) nanofibers manufactured by electrospinning method was reported. The gel-spinning solution of poly(tetrafluoroethylene)/poly(vinyl alcohol)/boric acid (PTFE/PVA/BA), which was prepared by the gel process of the mixture of PTFE, PVA, BA and redistilled water, was electrospun to form PTFE/PVA/BA composite nanofibers. After calcinating, the PTFE nanofibers with diameters of 200 nm to 1000 nm were obtained. The fibers before and after calcinating were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), FT-IR spectrum analysis and X-ray photoelectron spectroscopy (XPS), respectively, and the mechanical and hydrophobic properties of the fibers were also investigated. The results showed that the PTFE nanofiber membranes could be electrospun effectively used the gel-spinning solution of PTFE/PVA/BA, and may realize the applications in the fields of high-temperature filtration, catalyst supports, battery separator and so on.     

Highly conductive cellulosic nanofibers for efficient water desalination

Electrically conducting nanofibers based on cellulosic materials offer cheap and safe class of materials that can be used for water desalination. In the present work, high conducting cellulose triacetate (CTA) nanofibers containing multiwall carbon nanotubes (MWCNTs) with very low percolation threshold concentration (0.014 wt%) were produced by electrospinning. Unprecedentedly, a hydrophilic ionic liquid consists of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) was used to dissolve CTA producing a solution of 10 wt%. This CTA solution was used to engineer both bare CTA nanofibers and CTA nanofibers impregnated with MWCNT. The fabricated nanofibers were characterized by the field emission-scanning electron microscopy (FE-SEM) and the high-resolution transmission electron microscopy (HR-TEM). Both FE-SEM and HR-TEM images showed that the MWCNTs were inserted and uniformly distributed inside electrospun nanofibers. Furthermore, mechanical properties such as tensile strength of MWCNTs loaded-CTA electrospun nanofibers was significantly improved by up to 280 % and 270 % for the Young modulus, when compared with the bare CTA fibers. In addition, the surface properties as the hydrophilicity of electrospun nanofibers membrane was enhanced due to the presence of MWCNTs. Moreover, the electrical conductivity of MWCNT loaded-CTA electrospun nanofibers was greatly enhanced after the implementation of the MWCNTs inside the CTA fiber. The performance of composite nanofiber for water desalination was examined in a lab-scale classic capacitive deionization (CDI) unit, at different concentrations of salt. The obtained data revealed that the electro-adsorption of anions and cations on the surface of MWCNTs loaded-CTA electrospun nanofibers electrodes were monitored with time and their concentration were decreased progressively with time and reaches equilibrium.     

Fabrication of Biocompatible PLGA/PCL/PANI Nanofibrous Scaffolds with Electrical Excitability

Application of electrospun nanofibrous scaffolds has received immense attention in tissue engineering. Fabrication of scaffolds with appropriate electrical properties plays a key role in neural tissue engineering. Since fibers orientation in the scaffolds affects the growth and proliferation of the cells, this study aimed to prepare aligned electrospun conductive nanofibers by mixing 1 %, 10 % and 18 % (w/v) doped polyaniline (PANI) with polycaprolactone (PCL)/poly lactic-coglycolic acid (PLGA) (25/75) solution through the electrospinning process. The fibers diameter, hydrophilicity and conductivity were measured. In addition, the shape and proliferation of the nerve cells seeded on fibers were evaluated by MTT cytotoxicity assay and scanning electron microscopy. The results revealed that the conductive nanofibrous scaffolds were appropriate substrates for the attachment and proliferation of nerve cells. The electrical stimulation enhanced neurite outgrowth compared to those PLGA/PCL/PANI scaffolds that were not subjected to electrical stimulation. As polyaniline ratio increases, electric stimulation through nanofibrous PLGA/PCL/PANI scaffolds results in cell proliferation enhancement. However, a raise more than 10 % in polyaniline will result in cell toxicity. It was concluded that conductive scaffolds with appropriate ratio of PANI along with electrical stimulation have potential applications in treatment of spinal cord injuries.