Optimum Electrospinning Conditions Research Articles

Proton conductive properties of composite membranes containing uniaxially aligned ultrafine electrospun polyimide nanofiber

The nanofiber electrospun from the five-membered ring sulfonated polyimide containing the fluorinated group showed an ultrafine and uniform non-beaded structure and the optimized electrospinning conditions produced the sulfonated polyimide nanofibers with several appropriate diameters ranging from 80 to 160 nm. Novel sulfonated copolyimide membranes containing uniaxially aligned ultrafine sulfonated copolyimide nanofibers were prepared for proton exchange membrane fuel cell applications. The proton conductivity of the composite membrane in the parallel direction to the nanofibers alignment increased with the decreasing nanofiber diameter and the increasing amount of nanofibers in the composite membrane and reached 0.3 S cm−1 at 90 °C and 98% RH. In addition, the parallel proton conductivity indicated significantly higher values when compared to that determined for the composite membrane in the perpendicular direction or for the membrane without nanofibers prepared by a conventional solution-casting method. The composite membranes also showed higher chemical stabilities than those of the membrane without nanofibers. Consequently, nanofibers proved to be promising proton exchange materials and the composite membranes containing nanofibers may have potential application for use in fuel cells.

High Surface Area Lithium Titanate Electrode for Li-ion Batteries

A lithium titanate (Li4Ti5O12) anode composed of submicron fibers with nanosize grains was fabricated by electrospinning from spin dopes prepared from nanoparticles of lithium titanium oxide (Li4Ti5O12) and polyvinylpyrolidone (PVP) in a solvent. Optimal electrospinning conditions and solvent composition that could be electrospun into fibers under a variety of ambient conditions were determined. Pyrolyzing the electrospun fibers at high temperatures (700°C for 5 hours in air) and plasma-treating in oxygen (500 m Torr for 30 m) revealed a nano-size grain structure within the individual fibers. Electrochemical testing with metallic lithium as a reference electrode displayed promising capacities for three charging cycles. The C rates displayed complete charging when the charging time was at least 10 minutes. However, faster charging resulted in a loss of capacity to as low as 50% when charged in less than three minutes. This degradation appears to be triggered by trace amounts of a secondary phase introduced by standard purity precursors used for preparing lithium titanate. Evidence for this was found using x-ray fluorescence revealing the presence of iron and silicon oxides.

Drug release from electrospun fibers of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) grafted with poly(N‐vinylpyrrolidone)

AbstractPoly(N‐vinylpyrrolidone) (PVP) groups were grafted onto poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) backbone to modify the properties of PHBV and synthesize a new novel biocompatible graft copolymer. Based on these graft copolymers, electrospun fiber mats and commonly cast films were explored as drug delivery vehicles using tetracycline hydrochloride as a model drug. Toward that end, the fibers were electrospun and the films were cast from chloroform solutions containing a small amount of methanol to solubilize the drug. The Brookfield viscosities of the solution were determined to achieve the optimal electrospinning conditions. The vitro release of the tetracycline hydrochloride from these new drug delivery systems was followed by UV–vis spectroscopy. To probe into the factors affected on the release behavior of these drug delivery systems, their water absorbing abilities in phosphate buffer solution were investigated, together with their surface hydrophilicity, porosity and crystallization properties were characterized by water contact angles, capillary flow porometer, DSC, and WAXD, respectively. The morphological changes of these drug delivery vehicles before and after release were also observed with SEM. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Electrospinning of cellulose and SWNT-cellulose nano fibers for smart applications

Recently, electrospinning has attracted a great deal of attention as a means of producing non-woven membranes of nanofibers due to its simple methodology and the promise of nano applications. Despite its simplicity and relative low cost, there still remain a number of challenges associated with this process, such as low fiber production, presence of beads and repeatability issues due to the large number of experimental variables. In this paper, we investigated the use of the Design of Experiments (DOE) method and factorial testing as a means to identify the optimum electrospinning conditions and ensure repeatability of the process. We focused on two polymer solutions as the model systems, namely pure cellulose and cellulose with single wall carbon nanotubes (SWNTs). During the electrospinning experiment, we carefully monitored and adjusted the environmental conditions due to the highly sensitive nature of the solutions. We also adopted various ways of reducing surface tension to promote electrospinning, including convective heating of the solutions. As a first step, through initial screening using the DOE method, we eliminated the experimental variables that were less crucial to the electrospinning process, namely the distance from the needle to the grounded target and the needle size. Next, we demonstrated that three of the variables, i.e., flow rate, applied voltage and temperature, were essential to initiating the electrospinning process and were responsible for controlling the fiber diameter, dimension consistency, and abundance.

Electrospinning fabrication of partially crystalline bisphenol A polycarbonate nanofibers: Effects on conformation, crystallinity, and mechanical properties

The application of an electrostatic and centrifugal field (1800rpm) in a novel electrospinning process was shown to improve the degree of uniaxial alignment in polymer nanofibers and to enhance orientational order in polymer chains, producing bisphenol A polycarbonate (BPAPC) nanofibers with superior mechanical properties. High-speed videography showed that the additional centrifugal field effectively removed electrical bending instability and promoted molecular orientation during the electrospinning process. Infrared spectroscopic (IR) characterization revealed that the fraction of trans–trans conformers in BPAPC nanofibers reached 67% under optimal electrospinning conditions (25kV and 1800rpm at 25°C). Modulated differential scanning calorimetry (MDSC) and wide-angle X-ray diffraction (WXRD) assays showed that a degree of crystallinity of 6.5% could be achieved. Moreover, two crystal phases at angles of 2θ=17.3° and 21.9° were produced in BPAPC nanofibers. The elastic modulus of BPAPC nanofibers with a crystallinity of 6.5% was 7.11 and 5.13GPa, as measured via atomic force microscopy (AFM) and nanoindenter (NI) experiments, respectively. These results demonstrated that the mechanical behavior of BPAPC nanofibers could be improved by conducting the proposed electrospinning technique. Moreover, BPAPC nanofibers produced through the proposed method could be potentially applied for the reinforcement of composites.

Electrospun chitosan–gelatin nanofiberous scaffold: Fabrication and in vitro evaluation

In this study, chitosan and gelatin solutions were blended at five different ratios. Samples were fed into electrospinning apparatus to produce non-woven nanofibrous mats. Scanning electron microscopy (SEM) showed that the low-viscosity sample with 30% chitosan and 70% gelatin (sample 30/70) formed the least amount of beads and droplets and yielded fibers with the highest morphological uniformity. To examine the effect of processing parameters on fibers morphology and nanofibers diameter, flow rate, voltage and distance between needle to the collector were changed in the sample 30/70. SEM revealed that high voltages (25 kV) and flow rates (1.5 ml·h⁻¹) decrease the uniformity of fibers and lead to bead and droplet formation. It has also shown that the distance between the tip and the collector have no significant effect on fibers' structure. The values of 15 kV (voltage), 0.2 ml·h⁻¹ (flow rate) and the fixed distance of 15 cm were identified as the optimal electrospinning conditions, which produce fibers with a mean diameter of 180±20 nm. Fourier transform infrared (FTIR) experiment revealed an increase in N-H bending and decrease in C-O stretching vibration in both chitosan and gelatin at 1060 and 1148 cm⁻¹. The in vitro biocompatibility tests performed with human skin fibroblasts showed excellent cell proliferation (MTT assay) and attachment (SEM) on these scaffolds confirming its highly acceptable biological properties.

Creation of highly aligned electrospun poly-L-lactic acid fibers for nerve regeneration applications

Aligned, electrospun polymer fibers have shown considerable promise in directing regenerating axons in vitro and in vivo. However, in several studies, final electrospinning parameters are presented for producing aligned fiber scaffolds, and alignment where minimal fiber crossing occurs is not achieved. Highly aligned species are necessary for neural tissue engineering applications to ensure that axonal extension occurs through a regenerating environment efficiently. Axonal outgrowth on fibers that deviate from the natural axis of growth may delay axonal extension from one end of a scaffold to the other. Therefore, producing aligned fiber scaffolds with little fiber crossing is essential. In this study, the contributions of four electrospinning parameters (collection disk rotation speed, needle size, needle tip shape and syringe pump flow rate) were investigated thoroughly with the goal of finding parameters to obtain highly aligned electrospun fibers made from poly-L-lactic acid (PLLA). Using an 8 wt% PLLA solution in chloroform, a collection disk rotation speed of 1000 revolutions per minute (rpm), a 22 gauge, sharp-tip needle and a syringe pump rate of 2 ml h−1 produced highly aligned fiber (1.2–1.6 µm in diameter) scaffolds verified using a fast Fourier transform and a fiber alignment quantification technique. Additionally, the application of an insulating sheath around the needle tip improved the rate of fiber deposition (electrospinning efficiency). Optimized scaffolds were then evaluated in vitro using embryonic stage nine (E9) chick dorsal root ganglia (DRGs) and rat Schwann cells (SCs). To demonstrate the importance of creating highly aligned scaffolds to direct neurite outgrowth, scaffolds were created that contained crossing fibers. Neurites on these scaffolds were directed down the axis of the aligned fibers, but neurites also grew along the crossed fibers. At times, these crossed fibers even stopped further axonal extension. Highly aligned PLLA fibers generated under optimized electrospinning conditions guided neurite and SC growth along the aligned fibers. Schwann cells demonstrated the bipolar phenotype seen along the fibers. Using a novel technique to determine fiber density, an increase in fiber density correlated to an increase in the number of neurites, but average neurite length was not statistically different between the two different fiber densities. Together, this work presents methods by which to produce highly aligned fiber scaffolds efficiently and techniques for assessing neurite outgrowth on different fiber scaffolds, while suggesting that crossing fibers may be detrimental in fostering efficient, directed axonal outgrowth.

Electrospinning of uniform polystyrene fibers: The effect of solvent conductivity

By means of the electrospinning technique, micron- and nanofibers can be obtained from polymer solutions under a very high electrical field. A special challenge is to produce bead-free uniform fibers since any minor changes in the electrospinning parameters such as slight variations in the polymer solutions and/or electrospinning experimental parameters may result in significant variations in the final nanofiber morphology. Furthermore, it is often not trivial at all to obtain reproducible uniform electrospun nanofibers for the optimized electrospinning conditions. Here we report that the conductivity of the solvent is the key factor for the reproducible electrospinning of uniform polystyrene (PS) fibers from dimethylformamide (DMF) solutions. It is shown that even slight changes in the conductivity of the DMF solutions can greatly affect the morphology of the resulting electrospun PS fibers. Here, we have carried out a thorough and systematic study on the effect of solution conductivity on the electrospinning of bead-free polystyrene (PS) fibers when dimethylformamide (DMF) was used as the solvent. Interestingly, we found out that different grades of solvent as-received (DMF) from various suppliers have slightly different solution conductivities. Consequently, the polymer solutions prepared with the same PS concentration have different conductivities, which are shown to have significant changes on the morphology of the PS fibers resulting in beaded or bead-free uniform fibers when electrospun under the identical electrospinning conditions. Such as, bead-free PS fibers were obtained from PS solutions in the range of 20% (w/v) through 30% (w/v) depending on the DMF grade used. In brief, it was observed that solutions with a higher conductivity yielded bead-free fibers from lower polymer concentrations, which confirms that the solution conductivity plays a very significant role in producing bead-free uniform PS fibers.

Development of thermoplastic polyurethane vascular prostheses

AbstractIn this study, the optimum electrospinning conditions for a thermoplastic polyurethane/N,N‐dimethylformamide solution were sought. Under these conditions, polyurethane tubes for artificial blood vessels were produced via electrospinning, and various properties of the specimen were measured. The optimum electrospinning conditions were a concentration of 16 wt %, a voltage of 13.0 kV, and a tip‐to‐collector distance of 15 cm at 27°C and 80% relative humidity. The thermal behavior from a differential scanning calorimeter showed that this polyurethane web was thermally stable in the body temperature range. Enzyme hydrolysis of the web revealed that the polyurethane vascular prostheses would perform as nondegradable blood vessels in the body system. The pore size range of the electrospun polyurethane vascular prostheses was 0–3.5 μm. With a tensile stress of about 8–9 MPa and a tensile strain of about 80%, the tensile properties were expected to be superior to those of existing vascular prostheses made of polyester and expanded polytetrafluoroethylene. In the last stage, heparin and collagen were treated on the surfaces of artificial vessels to reduce the probability of thrombi forming during the initial stage of grafting, and so the treated specimens exhibited a lower possibility of thrombi forming than untreated ones in a blood coagulation test. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

New generation of super absorber nano-fibroses hybrid fabric by electro-spinning

Abstract PAM (polyacrylamide) has been used in granular like shapes as a water super absorber and soil erosion resistant agent in irrigation systems as well as in conservation systems. The idea of making fibers out of PAM seems to be very interesting since the surface area per unit mass will increase tremendously from granular to fibroses like shape structures. In this paper electro-spinning technique has been used to investigate the ability to produce ultra-fine PAM fibers. Effect of electro-spinning parameters such as Berry's number, spinning height, and spinning angle on PAM fiber diameter have been studied till successfully 290 nm average fiber diameter has been collected. To enhance the amount of collected electro-spun PAM nano-fiber and to study its absorption characteristics PAN (polyacrylonitrile) nano-fibroses membrane has been suggested as a good candidate to carry the electro-spun PAM nano-fibroses structure since PAN has been proved its ability to coagulate in water keeping all its morphological behavior. PAM/PAN hybrid nano-fibroses fabric has been produced at the optimum electro-spinning conditions. The new super absorber PAM/PAN nano-fibroses hybrid fabric has been tested and proved its ability to enhance water absorption 4.3–3.6 times more than commercial PAM granular like shape based on experimental calculations on the macroscopically and microscopically levels, respectively.

Development of photocatalytic TiO 2 nanofibers by electrospinning and its application to degradation of dye pollutants

We have developed photocatalytic TiO 2 nanofibers for the treatment of organic pollutants by using electrospinning method. We found that the optimized electrospinning conditions (electric field and flow rate) were 0.9 kV cm −1 and 50 μL min −1. After annealing at 550 °C for 30 min, we fabricated TiO 2 nanofibers (average 236 nm thick) with anatase crystalline phase. To increase photocatalytic activity and effective surface area, we coated photocatalytic TiO 2 particles on the TiO 2 nanofibers by using sol–gel method. The degradation rate ( k′ = 85.4 × 10 −4 min −1) of composite TiO 2 was significantly higher than that (15.7 × 10 −4 min −1) of TiO 2 nanofibers and that (14.3 × 10 −4 min −1) of TiO 2 nanoparticles by the sol–gel method. Therefore, we suggested that the composite TiO 2 of nanofibers and nanoparticles be suitable for the degradation of organic pollutants.