The use of an electrostatic lens to enhance the efficiency of the electrospinning process

Electrospun scaffolds manufactured using conventional electrospinning configurations have an intrinsic thickness limitation, due to a charge build-up at the collector. To overcome this limitation, an electrostatic lens has been developed that, at the same relative rate of deposition, focuses the polymer jet onto a smaller area of the collector, resulting in the fabrication of thick scaffolds within a shorter period of time. We also observed that a longer deposition time (up to 13 h, without the intervention of the operator) could be achieved when the electrostatic lens was utilised, compared to 9–10 h with a conventional processing set-up and also showed that fibre fusion was less likely to occur in the modified method. This had a significant impact on the mechanical properties, as the scaffolds obtained with the conventional process had a higher elastic modulus and ultimate stress and strain at short times. However, as the thickness of the scaffolds produced by the conventional electrospinning process increased, a 3-fold decrease in the mechanical properties was observed. This was in contrast to the modified method, which showed a continual increase in mechanical properties, with the properties of the scaffold finally having similar mechanical properties to the scaffolds obtained via the conventional process at longer times. This “focusing” device thus enabled the fabrication of thicker 3-dimensional electrospun scaffolds (of thicknesses up to 3.5 mm), representing an important step towards the production of scaffolds for tissue engineering large defect sites in a multitude of tissues.

Preparation and Luminescence Properties of YVO4:Ln and Y(V, P)O-4:Ln (Ln = Eu3+, Sm3+, Dy3+) Nanofibers and Microbelts by Sol-Gel/Electrospinning Process

One-dimensional YVO4:Ln and Y(V, P)O-4:Ln nanofibers and quasi-one-dimensional YVO4:Ln microbelts (Ln = Eu3+, Sm3+, Dy3+) have been prepared by a combination method of sol-gel process and electrospinning. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), and time-resolved emission spectra as well as kinetic decays were used to characterize the resulting samples.

Fabrication and Luminescence Properties of One-Dimensional CaMoO4: Ln(3+) (Ln = Eu, Tb, Dy) Nanofibers via Electrospinning Process

One-dimensional CaMoo(4):Ln(3+) (Ln = Eu, Tb, Dy) nanofibers have been prepared by a combination method of sol-gel and electrospinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and low voltage cathodoluminescence (CL) as well as kinetic decays were used to characterize the resulting samples. SEM and TEM analyses indicate that the obtained precursor fibers have a uniform size, and the as-formed CaMoO4:Ln(3+) nanofibers consist of nanoparticles. Under ultraviolet excitation, the CaMoO4 samples exhibit a blue-green emission band with a maximum at 500 nm originating from the MoO42- groups. Due to an efficient energy transfer from molybdate groups to dopants, CaMoO4:Ln(3+) phosphors show their strong characteristic emission under ultraviolet excitation and low-voltage electron beam excitation.

Preparation and luminescence properties of Mn2+-doped ZnGa2O4 nanofibers via electrospinning process

One-dimensional Mn2+-doped ZnGa2O4 nanofibers were prepared by a simple and cost-effective electrospinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. SEM results indicated that the as-formed precursor fibers and those annealed at 700 degrees C are uniform with length of several tens to hundred micrometers, and the diameters of the fibers decrease greatly after being heated at 700 degrees C. Under ultraviolet excitation (246 nm) and low-voltage electron beams (1-3 kV) excitation, the ZnGa2O4:Mn2+ nanofibers presents the blue emission band of the ZnGa2O4 host lattice and the strong green emission with a peak at 505 nm corresponding to the T-4(1)-(6)A(1) transition of Mn2+ ion.

Nanostructured barbed wire architecturing of organic conducting material blends by electrospinning

In this study, fibers of barbed wire structure were obtained by electrospinning blend of organic conducting crystalline material and polyethylene oxide. Thermal and structural characterization of the blend fibers has been carried out to study the fiber characteristics. An increase in crystallinity in the electrospun fibers was observed and was attributed to both electrospinning process as well as addition of organic conducting crystalline material. A mechanism for the formation of this barbed wire structure has also been proposed. (C) 2012 American Institute of Physics. [doi:10.1063/1.3673620]

One-Dimensional Ce3+- and/or Tb3+-Doped X-1-Y2SiO5 Nanofibers and Microbelts: Electrospinning Preparation and Luminescent Properties

One-dimensional X-1-Y2SiO5:Ce3+ and -Tb3+ nanofibers and quasi-one-dimensional X-1-Y2SiO5:Ce3+ and -Tb3+ microbelts have been prepared by a simple and cost-effective electrospinning process. X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry, transmission electron microscopy, high-resolution transmission electron microscopy, photoluminescence (PL), and cathodoluminescence spectra were used to characterize the samples. SEM results indicate that the as-prepared fibers and belts are smooth and uniform with a length of several tens to hundreds of micrometers, whose diameters decrease after being annealed at 1000 degrees C for 3 h. Under ultraviolet excitation and low-voltage electron beam excitation, the doped rare earth ions show their characteristic emission, that is, Ce3+ 5d-4f and Tb3+ D-5(4)-F-7(J) (J = 6, 5 4, 3) transitions, respectively.

Electrospinning Synthesis and Luminescence Properties of One-Dimensional Zn2SiO4:Mn2+ Microtibers and Microbelts

One-dimensional Mn2+-doped Zn2SiO4 rnicrobelts and microfibers were prepared by a simple and cost-effective electrospinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The XRD and DTA results show that the Zn2SiO4 phase begins to crystallize at 800 degrees C and crystallizes completely around 1000 degrees C. SEM results indicate that the as-prepared microbelts/fibers are smooth, whose diameters decrease with increasing the annealing temperature. The average diameter of the Zn2SiO4:Mn2+ microfibers annealed at 1000 degrees C is 0.32 mu m, and their lengths reach up to several millimeters. The average width and thickness of the Zn2SiO4:Mn2+ microbelts fired at 1000 degrees C are around 0.48 and 0.24 mu m, respectively.

Electrospinning of multicomponent ultrathin fibrous nonwovens for semi-occlusive wound dressings

This work describes the design and assembly of multifunctional and cost-efficient composite fiber nonwovens as semi-occlusive wound dressings using a simple electrospinning process to incorporate a variety Of functional components into an Ultrathin fiber. These components include non-hydrophilic poly(L-lactide) (PLLA) as fibrous backbone, hydrophilic poly(vinyl pyrrolidone)iodine (PVP-I), TiO2 nanoparticles, zinc chloride as antimicrobial, odor-controlling, and antiphlogistic agents, respectively. The process of synthesis starts with a multicomponent solution Of PLLA, PVP, TiO2 nanoparticles plus zinc chloride, in which TiO2 nanoparticles are synthesized by in situ hydrolysis of TiO2 precursors in a PVP Solution for the sake of obtaining the particle-uniformly dispersive solution. Subsequent electrospinning generates the corresponding composite fibers. A further iodine vapor treatment to the composite fibers combines iodine with PVP to produce the PVP-I complexes. Experiments indicate that the assembled composite fibers (300-400 nm) possess the ointment-releasing characteristic and the phase-separate, core-sheath structures in which PVP-I residing in fiber Surface layer becomes the sheath, and PLLA distributing inside the fiber acts as the core.

Syndiotactic 1,2-polybutadiene fibers produced by electrospinning

Syndiotactic 1,2-polybutadiene (s-PB) is a typical thermoplastic elastomer with various applications because of its high reactivity. In the past, it is difficult to form s-PB fibers with a diameter below 10 mu m because of the limitation of the conventional method such as melt spinning. Here, we report for the first time on the production of s-PB nanofibers by using a simple electrospinning method. Ultrafine s-PB fibers without beads were electrospun from s-PB solutions in dichloromethane and characterized by environmental scanning electron microscope (ESEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). At 4 wt.% concentration of s-PB, the average diameter of s-PB was about 130 nm. We found that dichloromethane was a unique suitable solvent for the electrospinning of s-PB fibers, and the structure of syndiotactic was changed through the electrospinning process.

Electrospun pH-sensitive core–shell polymer nanocomposites fabricated using a tri-axial process

A modified tri-axial electrospinning process was developed for the generation of a new type of pH-sensitive polymer/lipid nanocomposite. The systems produced are able to promote both dissolution and permeation of a model poorly water-soluble drug. First, we show that it is possible to run a tri-axial process with only one of the three fluids being electrospinnable. Using an electrospinnable middle fluid of Eudragit S100 (ES100) with pure ethanol as the outer solvent and an unspinnable lecithin-diclofenac sodium (PL–DS) core solution, nanofibers with linear morphology and clear core/shell structures can be fabricated continuously and smoothly. X-ray diffraction proved that these nanofibers are structural nanocomposites with the drug present in an amorphous state. In vitro dissolution tests demonstrated that the formulations could preclude release in acidic conditions, and that the drug was released from the fibers in two successive steps at neutral pH. The first step is the dissolution of the shell ES100 and the conversion of the core PL–DS into sub-micron sized particles. This frees some DS into solution, and later the remaining DS is gradually released from the PL–DS particles through diffusion. Ex vivo permeation results showed that the composite nanofibers give a more than twofold uplift in the amount of DS passing through the colonic membrane as compared to pure DS; 74% of the transmitted drug was in the form of PL–DS particles. The new tri-axial electrospinning process developed in this work provides a platform to fabricate structural nanomaterials, and the core–shell polymer-PL nanocomposites we have produced have significant potential applications for oral colon-targeted drug delivery.

Using an additive to control the electrospinning of fibres of poly(epsilon-caprolactone)

Electrospinning is a route to polymer fibres with diameters considerably smaller than available from most fibre-producing techniques. We explore the use of a low molecular weight compound as an effective control additive during the electrospinning of poly(epsilon-caprolactone). This approach extends the control variables for the electrospinning of nanoscale fibres from the more usual ones such as the polymer molecular weight, solvent and concentration. We show that through the use of dual solvent systems, we can alter the impact of the additive on the electrospinning process so that finer as well as thicker fibres can be prepared under otherwise identical conditions. As well as the size of the fibres and the number of beads, the use of the additive allows us to alter the level of crystallinity as well as the level of preferred orientation of the poly(epsilon-caprolactone) crystals. This approach, involving the use of a dual solvent and a low molar mass compound, offers considerable potential for application to other polymer systems. (C) 2010 Society of Chemical Industry

Chapter 16: Electrospinning of polymer solutions

Electrospinning is a technique that involves the production of nanoscale to microscale sized polymer fibres through the application of an electric field to a droplet of polymer solution passed through a spinneret tip. This chapter considers the optimisisation of the electrospinning process and in particular the variation with solution concentration. We show the strong connection between overlapping chains and the successful spinning of fibres. We use small-angle neutron scattering to evaluate the molecular conformations in the solutions and in the fibres.

Charge generation, charge transport, and residual charge in the electrospinning of polymers: A review of issues and complications

Electrospinning has become a widely implemented technique for the generation of nonwoven mats that are useful in tissue engineering and filter applications. The overriding factor that has contributed to the popularity of this method is the ease with which fibers with submicron diameters can be produced. Fibers on that size scale are comparable to protein filaments that are observed in the extracellular matrix. The apparatus and procedures for conducting electrospinning experiments are ostensibly simple. While it is rarely reported in the literature on this topic, any experience with this method of fiber spinning reveals substantial ambiguities in how the process can be controlled to generate reproducible results. The simplicity of the procedure belies the complexity of the physical processes that determine the electrospinning process dynamics. In this article, three process domains and the physical domain of charge interaction are identified as important in electrospinning: (a) creation of charge carriers, (b) charge transport, (c) residual charge. The initial event that enables electrospinning is the generation of region of excess charge in the fluid that is to be electrospun. The electrostatic forces that develop on this region of charged fluid in the presence of a high potential result in the ejection of a fluid jet that solidifies into the resulting fiber. The transport of charge from the charge solution to the grounded collection device produces some of the current which is observed. That transport can occur by the fluid jet and through the atmosphere surrounding the electrospinning apparatus. Charges that are created in the fluid that are not dissipated remain in the solidified fiber as residual charges. The physics of each of these domains in the electrospinning process is summarized in terms of the current understanding, and possible sources of ambiguity in the implementation of this technique are indicated. Directions for future research to further articulate the behavior of the electrospinning process are suggested. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3682464]

Preparation of porous nanofibers from electrospun polyacrylonitrile/calcium carbonate composite nanofibers using porogen leaching technique

Production of nanofibrous polyacrylonitrile/calcium carbonate (PAN/CaCO3) nanocomposite web was carried out through solution electrospinning process. Pore generating nanoparticles were leached from the PAN matrices in hydrochloric acid bath with the purpose of producing an ultimate nanoporous structure. The possible interaction between CaCO3 nanoparticles and PAN functional groups was investigated. Atomic absorption method was used to measure the amount of extracted CaCO3 nanoparticles. Morphological observation showed nanofibers of 270–720 nm in diameter containing nanopores of 50–130 nm. Monitoring the governing parameters statistically, it was found that the amount of extraction (ε) of CaCO3was increased when the web surface area (a) was broadened according to a simple scaling law (ε = 3.18 a0.4). The leaching process was maximized in the presence of 5% v/v of acid in the extraction bath and 5 wt % of CaCO3 in the polymer solution. Collateral effects of the extraction time and temperature showed exponential growth within a favorable extremum at 50°C for 72 h. Concentration of dimethylformamide as the solvent had no significant impact on the extraction level.

Structure-tunable Janus fibers fabricated using spinnerets with varying port angles

The preparation of Janus fibers using a new side-by-side electrospinning process is reported. By manipulating the angle between the two ports of the spinneret emitting the working fluids, Janus nanofibers with tunable structures in terms of width, interfacial area and also volume of each side can be easily fabricated.