Electrospinning Instabilities in the Drop Formation and Multi-Jet Ejection Part II: Various Nozzle Diameters for PVA (Polyvinyl Alcohol) Polymer Solution

Electrospinning is recognized as a simple and easy method to produce fibers with nanoscale diameters. However, the methods for controlling the shape, structure, and uniformity of electrospun fibers have not yet been fully investigated. In this research, the electrospinning jet behavior, corresponding nanofiber deposition, and average fiber diameter are examined for various nozzle diameters. Fluctuations in the sequence of drop growing, electrospinning, and/or termination of electrospinning are analyzed. We propose two different fluctuations according to nozzle diameter. The multi-jet ejections, that are closely related to the amount of nanoweb deposition and the deposition pattern, are explored.     

Electrospinning of Poly(Hydroxybutyrate-co-hydroxyvalerate) Fibrous Scaffolds for Tissue Engineering Applications: Effects of Electrospinning Parameters and Solution Properties

Electrospinning, a technology capable of fabricating ultrafine fibers (microfibers and nanofibers), has been investigated by various research groups for the production of fibrous biopolymer membranes for potential medical applications. In this study, poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), a natural, biocompatible, and biodegradable polymer, was successfully electrospun to form nonwoven fibrous mats. The effects of different electrospinning parameters (solution feeding rate, applied voltage, working distance and needle size) and polymer solution properties (concentration, viscosity and conductivity) on fiber diameter and morphology were systematically studied and causes for these effects are discussed. The formation of beaded fibers was investigated and the mechanism presented. It was shown that by varying electrospinning parameters within the processing window that was determined in this study, the diameter of electrospun PHBV fibers could be adjusted from a few hundred nanometers to a few microns, which are in the desirable range for constructing “biomimicking” fibrous scaffolds for tissue engineering applications.     

Electrospun cross linked rosin fibers

In this study, we describe the first reported preparation of rosin in fiber form through use of an electrospinning technique utilizing various solvent systems. The polymer concentration of the formed fiber was studied by using various solvents such as chloroform, ethanol, N-N dimethylformamide (DMF), tetrahydrofuran (THF), acetone, and methylene chloride (MC). An electrospray of the solution resulted in the beaded form of the rosin. By varying the polymer concentration with MC, we were then able to obtain uniform fibers. However, the fibers exhibited large diameter. We believe that it is possible to reduce the diameter of the rosin fibers through appropriate selection of electrospinning parameters. In addition, the morphological transitions from beads, to beaded fiber, to fiber were studied at different polymer concentrations. We propose a possible physical cross linking mechanism for the formation of rosin fibers during the electrospinning process. Our results demonstrate the feasibility of producing fiber nanostructures of rosin by using an electrospinning technique.     

Mechanism of Electrospinning for Poly(amic acid)/Polyacrylonitrile Fiber Fabrication

A poly(amic acid) (PAA) solution in xylene was prepared for electrospinning in order to fabricate fibers. However, jet breaking occurred at the point of the occurrence of whipping instability, resulting in forming micro-particles. This was an exceptional jet behavior compared with the general electro-spraying process that occurs directly from the surface of the polymer droplet. It is important to understand the mechanism of electrospinning and the instability of PAA in order to form fibers for mat deposition. Thus, the behavior of the jet breaking was clearly observed by a high-speed camera and the dynamic behavior of the jet was explored by an image analysis technique. Furthermore, polyacrylonitrile (PAN) was added to the PAA/xylene solution with various concentrations to change the elongation viscosity. Uniform diameter fibers were obtained by increasing the content of PAN to the level that the drag force between the polymer chains increased enough to overcome the drawing force. As a result the optimum content ratio of the PAA/PAN mixed solution to obtain the desired fiber spinning and deposition was determined as being 5:5.     

Electrospinning Mechanism for Producing Nanoscale Polymer Fibers

Electrospinning provides a straightforward method to produce polymer fibers with nanoscale diameters. Although the setup for electrospinning is simple and convenient, the spinning mechanism itself is quite complicated. A complete understanding of this mechanism remains to be elucidated and the factors that govern fiber formation are not well understood. In this study, we investigate the electrospinning instabilities by observing the electrospinning jet behaviors with various photographic exposure times ranging from 1/100 to 1/10,000 of a second and the corresponding fiber depositions. We propose an electrospinning mechanism responsible for producing nanoscale fibers and their deposition patterns.     

Manufacture and Characterization of Poly (butylene terephthalate) Nanofibers by Electrospinning

Poly (butylene terephthalate) (PBT) nanofiber mats were prepared by electrospinning, being directly deposited in the form of a random fibers web. The effect of changing processing parameters such as solution concentration and electrospinning voltage on the morphology of the electrospun PBT nanofibers was investigated with scanning electron microscopy (SEM). The electrospun fibers diameter increased with rising concentration and decreased by increasing the electrospinning voltage, thermal and mechanical properties of electrospun fibers were characterized by DSC and tensile testing, respectively.     

Electrospinning of polyacrylonitrile fibers from ionic liquid solution

We developed a temperature-controlled electrospinning apparatus specially for the polymers/IL system with high viscosity and surface tension and investigated the electrospinning of polyacrylonitrile (PAN)/1-butyl-3-methyl-imidazolium bromide ([BMIM][Br]) solutions. The rheological behaviors, surface tensions and conductivities of PAN/[BMIM]/[Br] solutions at different temperatures indicated that appropriately increasing the temperature is beneficial to their spinnability. It is also shown that PAN/[BMIM]/[Br] with a concentration of 3 wt%, 4 wt% and 5 wt% can be electrospun to fibers by increasing their temperatures to 70°C, 75°C or 85°C, respectively. A rotating drum composed of a dacron mesh was used as a collector in order to avoid the contraction of the wet fibers. This present study provides an alternative method for electrospinning polymer fibers.     

Electrospinning method for the preparation of silver chloride nanoparticles in PVP nanofiber

It has been successfully developed by the electrospinning technology that AgCl nanoparticles were incorporated into polymer fiber. In this paper, we chose poly(vinyl pyrrolidone) (PVP) because it was not only a good material for electrospinning but also it was excellent capping reagent of various metal nanoparticles. The silver ions interacted with the carbonyl groups in the PVP molecules. The formation of AgCl nanoparticles inside the PVP were carried out via the reaction of silver ions and HCl. TEM proved that most of the AgCl nanoparticles were uniformly dispersed in the PVP fibers.     

The impact of 1-butyl-3-methylimidazolium chloride on electrospinning process of SAN polymer solutions and electrospun fiber morphology

The aim of this research was to investigate how addition of IL [Bmim]Cl¹ into SAN² solution in 1,2-DCE³ will influence electrospinning variables, stability of process and morphology of obtained nanofibers and find out the appropriate way of utilizing [Bmim]Cl in the electrospinning process. The solutions of pure SAN in 1,2-DCE of different concentrations (10–20%) and solutions with different concentrations (0.5–20%) of IL were spun at different variables (10–20 cm and 10–20 kV). All results were investigated by optical and SEM microscopy. Also solution parameters like electrical conductivity, surface tension and viscosity were measured and their effect on the obtained fibers morphology estimated.     

Electrospun precursor carbon nanofibers optimization by using response surface methodology

Ultrafine fibers were electrospun from Polyacrylonitrile and N,N-dimethylformamide solution to be used as a precursor for carbon nanofibers. An electrospinning set-up was used to collect fibers with diameter ranging from 104 nm to 434 nm. Morphology of fibers and its distribution were investigated by varying Berry's number, charge density, spinning angle, spinneret diameter and collector area. A more systematic understanding of process parameters was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by using response surface methodology. It was concluded that; Berry's number, charge density and spinneret diameters played an important role to the diameter of nanofibers and its standard deviation. Spinning angle and collector area had no significant impact. Based on response surface methodology the optimum Polyacrylonitrile average fiber diameter of 280 nm and 28 nm standard deviation, were collected at 1.6 kV/cm charge density, 8 Berry's number and 0.9 mm spinneret diameter.     

Poly(m‐Phenylene Isophthalamide) Ultrafine Fibers from an Ionic Liquid Solution by Dry‐Jet‐Wet‐Electrospinning

Ultrafine poly(m‐phenylene isophthalamide) (PMIA) fibers from PMIA solution in an ionic liquid via dry‐jet‐wet electrospinning technology are described. The morphology of the fibers with and without treatment in a coagulation water bath in the dry‐jet‐wet‐electrosinning process was observed by scanning electrical microscopy (SEM) and a high resolution optical microscope. The crystal structure of the fibers was analyzed by wide angle X‐ray diffraction (WAXD). The differences of morphologies and properties between the ultrafine fibers obtained by the electrospinning process and fibers from conventional wet‐spinning technology are discussed. The thermal properties of the ultrafine PMIA fibers were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

Poly (Vinyl Alcohol)/Chitosan/Akermanite Nanofibrous Scaffolds Prepared by Electrospinning

Abstract

Electrospinning, as an effective method for preparation of scaffolds for cell growth templates, has attracted great attention. In this study electrospinning was used to prepare poly (vinyl alcohol) (PVA)/chitosan scaffolds for bone tissue engineering. In order to improve the bioactivity and mechanical properties of the fibrous scaffolds, 0.5, 1 and 2?wt% akermanite, a calcium silicate based bioceramic, was added to the electrospinning solution. The morphology of the electrospun scaffolds was observed by using field emission-scanning electron microscopy and their mechanical strengths were analyzed by tension tests. The results showed that the formed scaffolds consisted of fibers with less than 100?nm diameter. In the case of the composite containing 1?wt% akermanite, the fibers were more homogeneous and no beads were formed during electrospinning, while in the composite containing 2?wt% akermanite a considerable number of beads were formed which we attribute to an improper viscosity of the electrospinning solution. Among the different compositions, the composite containing 1?wt% akermanite showed higher ultimate tensile strength (10.6?MPa) and fracture strain (9%). These values were increased by crosslinking the scaffold by reaction with glutaraldehyde, up to 13?MPa and 9.4%, respectively.     

Controlled assembly of poly(vinyl pyrrolidone) fibers through an electric-field-assisted electrospinning method

In this paper, we develop an effective electric-field-assisted electrospinning method for the controlled deposition of poly(vinyl pyrrolidone) fibers. The electric field distribution becomes uniform and convergent due to the introduction of a metal plate and a focusing aid into the conventional electrospinning setup. As a result, the bending instability is suppressed and the jet is restricted to moving to the collector along a straight line. Helical structure of fibers with lateral width of about 10 μm is formed and aligned on a rotating substrate. The morphology of helical fibers can also be effectively adjusted by varying the collecting velocity.     

Elaboration and characterization of magnetic nanocomposite fibers by electrospinning

We describe a simple method based on the electrospinning process to prepare heterogeneous hybrid submicronic fibers with magnetic behavior, consisting of Co nanoparticles embedded in a polyacrylonitrile (PAN) polymer. Quantity and anisotropy of magnetic nanoparticles are key parameters to improve the specific magnetic properties of fibers. We notably show that for higher Co nanoparticles concentration, their lower dispersity into the resulting fibers lead to dipolar interactions that become demagnetizing. The structural and morphological properties of Co nanodisks and of the resulting nanocomposite fibers are investigated by SEM, TEM, and EDX. The magnetic properties of the hybrid electrospun fibers have been evaluated with a SQUID magnetometer.     

Drug Release Behavior of a Drug-Loaded Polylactide Nanofiber Web Prepared via Laser-Electrospinning

In recent years drug-loaded nanofibers prepared using solution electrospinning methods have been actively studied. However, there are a number of problems connected to their solution electrospinning with respect to medical applications because of the hazards associated with the residual solvents. To avoid the use of solvents in this study we prepared and evaluated drug-loaded polylactide (PLA) fiber webs using a laser-electrospinning (LES) type of a melt electrospinning process. The structures and properties of the obtained drug-loaded PLA fiber webs were evaluated by scanning electron microscopy, fluorescence microscopy, wide-angle X-ray diffraction and UV–vis spectrometry. As shown by the various characterization techniques, we employed LES to prepare PLA nanofiber webs with average fiber diameters of 4.21 and 0.67?μm. Additionally, the webs were loaded with argatroban, a thrombin inhibitor, resulting in amorphous structures for both the argatroban and the PLA matrix. An in-vitro investigation of the drug release behavior of the webs revealed that higher release rates occurred for the fiber samples with the small fiber diameters, particularly in comparison with melt spun fibers with an average diameter of 150?μm. Overall, we expect that the herein described drug-loaded PLA nanofiber webs can be applied as medical materials with drug delivery system functions.     

Electrospinning of non-woven poly(styrene-co-acrylonitrile) nanofibrous webs for corrosive chemical filtration: Process evaluation and optimization by Taguchi and multiple regression analyses

Nano-fibrous ultra-filtration membranes of poly(styrene-co-acrylonitrile) were produced from n-butanone solution by electrospinning. Effects of governing parameters on morphology and variation in diameter of the electrospun fibers were experimentally investigated by orthogonal experimental design. The process parameters were selected by Taguchi's method. Multiple regression analysis was used to obtain a quantitative relationship between selected electrospinning parameters and average fiber diameter and ANOVA was used to identify the statistically significant parameters and set the optimal level for each parameter. Confirmation experiment revealed a good agreement between the predicted values of the response obtained from optimum level parameters and the observed experimental values.     

Interference between the Charged Jets in Electrospinning of Polyvinyl Alcohol

It is well known that the production rate of electrospinning is remarkably lower than that of the general process of fiber spinning. Currently, the solution of this problem has been investigated with various methods including a multi-nozzle system instead of a single nozzle. In this study, the effect of using various nozzles on nanoweb formation by electrospinning has been investigated. Three nozzles consisting of single, dual, and triple needles were used to study the interaction between needles. In addition, the effect of changing the diameter of the spinning needle, a factor that has an effect on the polymer solution flow rate and nanoweb formation on the collector, was examined.     

Predicting Polymorphism of Electrospun Polyvinylidene Fluoride Membranes by Their Morphologies

Although electrospinning of polyvinylidene fluoride (PVDF) has been studied for more than 10 years, the crystalline phase differentiation of the electrospun mats is still normally through the combination of different characterization techniques, and the relationship between polymorphism and morphology of the fibers in electrospun PVDF membranes has never been reported. Here, we show their close relationships by conducting room-temperature electrospinning experiments on various polymer/solvent systems. The electrospun membranes full of bead-free fibers have a very high fraction of β-phase, F(β), over 90%, and high orientation, whereas the membranes comprising beads and/or a large number of beaded fibers most often result in a low fraction of β-phase (F(β) normally below 50%) and low orientation. On the other hand, electrospun membranes consisting of both bead-free fibers and a very limited number of beaded fibers showed a medium high fraction of β-phase, F(β) more than 70% but less than 90%. These findings suggest the feasibility of intuitively predicting the crystalline phase of electrospun PVDF membranes directly by their morphologies, which is obviously simple, inexpensive and convenient for future investigations.     

Controlling the fiber diameter during electrospinning

We present a simple analytical model for the forces that determine jet diameter during electrospinning as a function of surface tension, flow rate, and electric current in the jet. The model predicts the existence of a terminal jet diameter, beyond which further thinning of the jet due to growth of the whipping instability does not occur. Experimental data for various electrospun fibers attest to the accuracy of the model.     

Production of nanofibers by electrospinning under pressurized CO2

Electrospinning is one of the simple technical methods for the production of polymer nanoparticles and nanofibers. Various polymers have been successfully electrospun into ultrafine particles and fibers in recent years mostly in solvent solution and some in melt form. In this work, near- and supercritical CO₂ were used as media for this process. At these conditions, the solubility can be tuned by controlling the temperature and pressure. Therefore, it is possible to form particles and fibers within a thermodynamic window where the biopolymer has been softened, but not dissolved. The experiments were conducted by using electrospinning under pressurized CO₂ system at pressures of ～ 8.0 MPa and temperature of 313 K to produce several polymers fibers. Polyvinylpyrrolidone was used as the starting material. During the electrospinning process, the applied voltage was 10–17 kV and the distance of nozzle and collector was 8 cm. The concentration of polymer solution was 4 wt%. The morphology- and structure-produced fibers were observed by scanning electron microscopy. The results showed that temperature and pressure affected the morphology of fibers produced by electrospinning in pressurized CO₂. This suggests that the thermal behavior of the polymer can be optimized by adjusting the polymer through the adjustment of pressure and temperature by using CO₂ as a solvent.