Submicron-sized Fibers Research Articles

Washable PEDOT:PSS Coated Polyester with Submicron Sized Fibers for Wearable Technologies.

The use of non-metallic conductive yarns in wearable technologies like smart textiles requires compliant washable fibers that can withstand domestic washing without losing their conductive properties. A one-pot coating with PEDOT:PSS conductive polymers was applied to polyester submicron fibers, increasing the water resistance and washability under various domestic washing conditions. Plasma treatment of the untreated samples improved the anchoring of the coating to the fibers, producing smooth and homogeneous coatings. The primary doping of PEDOT:PSS with ethylene glycol (EG), dimethyl sulfoxide (DMSO), and a non-ionic surfactant as well as the secondary doping of the composite fibers improved the sheet resistance at room temperature. The as-obtained composite materials showed similar mechanical properties as the parent fibers, indicating that the coating and post-treatment do not affect the overall mechanical property of the composite. The performance of the composites under different temperature and humidity conditions and washability using the standardized ISO 6330:2012 procedure for domestic washing and drying showed that the obtained composites are good candidates for reliable washable wearable technologies, such as all-organic washable Joule heaters in functional textiles.

Catechin loaded PLGA submicron-sized fibers reduce levels of reactive oxygen species induced by MWCNT in vitro

Reactive oxygen species (ROS) are common products of normal aerobic cellular metabolism, but high levels of ROS lead to oxidative stress and cellular damage. Therefore, effective antioxidant therapies are needed to prevent ROS overproduction. This study reports the development of poly(l-lactide-co-glycolide) (PLGA) bicomponent fibers loaded with selected amounts of the natural polyphenolic antioxidant catechin. Thereby a novel route based on emulsion electrospinning is investigated to obtain tailored and sustained release rates for chatechin. The activity of the released catechin was assessed for its influence on multi-walled carbon nanotube (MWCNT) induced formation of reactive oxygen species (ROS) in the human alveolar epithelial the cell line A549.Homogenous fiber morphologies were obtained at specified ranges of PLGA concentrations within the emulsions including the formation of a core – sheath structure localizing the drug within the fiber core. In vitro measurements of the delivery showed moderate burst release kinetics in a first phase followed by a linear and smooth release at long term. In combination with polymer degradation studies a mostly diffusion controlled release mechanism was revealed exhibiting only marginal degradation of the polymer during the time span of the drug delivery. As a proof of concept, the activity of released catechin in A549 cells stimulated with MWCNTs was determined and revealed a high reduction of ROS production in a dose dependent manner. This effect diminishes over time indicating a depletion of catechin.

Surface modification of endovascular stents with rosuvastatin and heparin-loaded biodegradable nanofibers by electrospinning.

This study describes the development of drug-loaded nanofibrous scaffolds as a nanocoating for endovascular stents for the local and sustained delivery of rosuvastatin (Ros) and heparin (Hep) to injured artery walls after endovascular procedures via the electrospinning process.PurposeThe proposed hybrid covered stents can promote re-endothelialization; improve endothelial function; reduce inflammatory reaction; inhibit neointimal hyperplasia of the injured artery wall, due to well-known pleiotropic actions of Ros; and prevent adverse events such as in-stent restenosis (ISR) and stent thrombosis (ST), through the antithrombotic action of Hep.MethodsBiodegradable nanofibers were prepared by dissolving cellulose acetate (AC) and Ros in N,N-dimethylacetamide (DMAc) and acetone-based solvents. The polymeric solution was electrospun (e-spun) into drug-loaded AC nanofibers onto three different commercially available stents (Co–Cr stent, Ni–Ti stent, and stainless steel stent), resulting in nonwoven matrices of submicron-sized fibers. Accordingly, Hep solution was further used for fibrous coating onto the engineered Ros-loaded stent. The functional encapsulation of Ros and Hep drugs into polymeric scaffolds further underwent physicochemical analysis. Morphological characterization took place via scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses, while scaffolds’ wettability properties were obtained by contact angle (CA) measurements.ResultsThe morphology of the drug-loaded AC nanofibers was smooth, with an average diameter of 200–800 nm, and after CA measurement, we concluded to the superhydrophobic nature of the engineered scaffolds. In vitro release rates of the pharmaceutical drugs were determined using a high-performance liquid chromatography assay, which showed that after the initial burst, drug release was controlled slowly by the degradation of the polymeric materials.ConclusionThese results imply that AC nanofibers encapsulated with Ros and Hep drugs have great potential in the development of endovascular grafts with anti-thrombogenic properties that can accelerate the re-endothelialization, reduce the neointimal hyperplasia and inflammatory reaction, and improve the endothelial function.

Solvent-induced crystallization of electrospun syndiotactic polystyrene nanofibers and its reversible desorption/sorption of volatile organic vapors

Electrospun fiber mats are promising media for chemical separation because of their porous interior and high surface area, which enhance penetrant permeation and provide a large number of active sites. The application of this technology was fulfilled in the present study, wherein syndiotactic polystyrene (sPS) fibers were prepared by high-temperature solution electrospinning to absorb volatile organic compounds. The as-spun sPS fibers had an average radius of ~360 nm and were amorphous as revealed by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction. When the electrospun fibers were exposed to different solvent vapors, solvent-induced crystallization occurred in these submicron-sized fibers to form δ- or γ-form sPS crystals, depending on the solvent used. To trace the microstructure transformation of sPS chains induced by the solvent vapors, in situ FTIR spectral measurements were performed. The absorbance of crystallization-sensitive IR bands was plotted against time, from which the crystallization kinetics were analyzed based on the Avrami equation. Results showed that the rate of solvent-induced crystallization was higher for solvents with a higher saturated vapor pressure. Subsequent solvent desorption from the crystallized sPS fibers was also studied under ambient conditions by monitoring the absorbance variation of the solvent-sensitive IR band. Two-stage solvent desorption was observed in the δ-form sPS fibers; this process consisted of initial rapid desorption from the amorphous region, followed by slow desorption from the crystalline region. Notably, all the solvent molecules in the treated fibers can be completely removed in this manner, thereby leading to the formation of δ e-form crystals for repetitive sorption/desorption applications.

Vertical rod method for electrospinning polymer fibers

Electrospinning is often used to produce sub-micron size fibers. Most electrospinning applications employ charged needles or nozzles but have low production rates. For higher production rates several needleless systems have been developed. This work reports on a simple unique needleless method that employs charged vertically oriented threaded rods for holding multiple drops to launch many simultaneous jets. Experiments were conducted with a single rod or multiple rods arranged in a linear array. The direction of the launched jets was controlled using a secondary electrode to direct the jets towards the grounded collector. Results show a single rod of about 50 cm in length can produce PVP fibers at a rate of 4.5 g/hr and 200–400 nm size range.

Engineering cell matrix interactions in assembled polyelectrolyte fiber hydrogels for mesenchymal stem cell chondrogenesis

Cell–cell and cell–matrix interactions are important events in directing stem cell chondrogenesis, which can be promoted in matrix microenvironments presenting appropriate ligands. In this study, interfacial polyelectrolyte complexation (IPC) based hydrogels were employed, wherein the unique formation of submicron size fibers facilitated spatial orientation of ligands within such hydrogels. The influence of aligned, collagen type I (Col I) presentation in IPC hydrogel on chondrogenic differentiation of human mesenchymal stem cells (MSC) was investigated. Early morphological dynamics, onset of N-cadherin/β-catenin mediated chondrogenic induction and differentiation were compared between MSCs encapsulated in IPC-Col I and IPC-control (without Col I) hydrogels, and a conventional Col I hydrogel. MSCs in IPC-Col I hydrogel aligned and packed uniformly, resulting in enhanced cell–cell interactions and cellular condensation, facilitating superior chondrogenesis and the generation of mature hyaline neocartilage, with notable downregulation of fibrocartilaginous marker. Inhibition study using function blocking β1-integrin antibodies reversed the aforementioned outcomes, indicating the importance of coupling integrin mediated cell–matrix interactions and N-cadherin/β-catenin mediated downstream signaling events. This study demonstrated the significance of oriented ligand presentation for MSC chondrogenesis, and the importance of facilitating an orderly sequence of differentiation events, initiated by proximal interactions between MSCs and the extracellular matrix for robust neocartilage formation.

Modified electric fields to control the direction of electrospinning jets

Electrospinning is a well known process for fabricating sub-micron size fibers. A high voltage potential is used in electrospinning to launch a polymer jet from a droplet of polymer solution towards a grounded collector. Most of the electrospun fibers collect on the grounded collector, but depending on the design of the electrospinning apparatus and the environment, some of the fibers drift away from the collector and are captured on other objects.In this work we apply the hypothesis that the electrospinning jet follows the path of the electric field's current density lines. By controlling the direction of the current density lines one can control the path of the electrospinning jet and hence can control the location of where the fibers are collected.The current density lines are determined by the gradient of the static electric potential field. The electric field is modified in this work by positioning charged electrodes that change the potential field and hence change the potential gradient and the path of the current density lines. In this way, the jet, following the current density lines, can be directed towards desired locations and away from undesired locations. The static electric field was modeled by numerically solving Laplace's equation for the potential field. Electrospinning experiments were conducted with the same geometric arrangement of electrodes for comparison. The results show the center of mass of the electrospinning jets generally followed the current density lines. This work shows it is possible to direct the electrospinning jets away from undesired objects by use of secondary electrodes.

Glioma Cell Migration on Three-dimensional Nanofiber Scaffolds Is Regulated by Substrate Topography and Abolished by Inhibition of STAT3 Signaling

A hallmark of malignant gliomas is their ability to disperse through neural tissue, leading to long-term failure of all known therapies. Identifying new antimigratory targets could reduce glioma recurrence and improve therapeutic efficacy, but screens based on conventional migration assays are hampered by the limited ability of these assays to reproduce native cell motility. Here, we have analyzed the motility, gene expression, and sensitivity to migration inhibitors of glioma cells cultured on scaffolds formed by submicron-sized fibers (nanofibers) mimicking the neural topography. Glioma cells cultured on aligned nanofiber scaffolds reproduced the elongated morphology of cells migrating in white matter tissue and were highly sensitive to myosin II inhibition but only moderately affected by stress fiber disruption. In contrast, the same cells displayed a flat morphology and opposite sensitivity to myosin II and actin inhibition when cultured on conventional tissue culture polystyrene. Gene expression analysis indicated a correlation between migration on aligned nanofibers and increased STAT3 signaling, a known driver of glioma progression. Accordingly, cell migration out of glioblastoma-derived neurospheres and tumor explants was reduced by STAT3 inhibitors at subtoxic concentrations. Remarkably, these inhibitors were ineffective when tested at the same concentrations in a conventional two-dimensional migration assay. We conclude that migration of glioma cells is regulated by topographical cues that affect cell adhesion and gene expression. Cell migration analysis using nanofiber scaffolds could be used to reproduce native mechanisms of migration and to identify antimigratory strategies not disclosed by other in vitro models.

Surface Chemistry of Electrospun Cellulose Nitrate Nanofiber Membranes

Electrospinning is a rapidly developing technology that provides a unique way to produce novel polymer nanofibers with controllable diameters. Cellulose nitrate non-woven mats of submicron-sized fibers with diameters of 100-1200 nm were prepared. The effects of processing equipment collector design void gap, and steel drum coated with polyvinylidene dichloride (PVDC) were investigated. The PVDC layer applied to the rotating drum aided in fiber harvesting. Electron microscopy (FESEM and ESEM) studies of as-spun fibers revealed that the morphology of cellulose nitrate fibers depended on the collector type and solution viscosity. When a rotating steel drum was employed a random morphology was observed, while the void gap collector produced aligned fiber mats. Increases in viscosity lead to larger diameter fibers. The fibers collected were free from all residual solvents and could undergo oxygen plasma treatment to increase the hydropholicity.

Electrospun-fiber induced transcrystallization of isotactic polypropylene matrix

To reveal the influences of fiber diameter and characteristics on the surface-induced matrix crystallization, four different fibers, i.e. syndiotactic polystyrene (sPS), Nylon 6, and polyhydroxyamide (PHA) and poly(p-phenylene benzobisoxazole) (PBO) fibers, were used to study their nucleating abilities towards isotactic polypropylene (iPP) matrix. Among them, micron-sized PBO fibers were obtained from the supplier, whereas submicron-sized fibers of sPS, Nylon 6 and PHA were prepared by the solution electrospinning process developed in this laboratory. To resolve the observation difficulty due to the fast nucleation rate and crystal growth at high supercooling degrees (>60 °C), a high speed camera was mounted on the polarized optical microscope equipped with a hot stage to successfully snapshot the corresponding processes at various crystallization temperatures ( T c) in the range of 96–120 °C. For all the active fibers, only α-form iPP transcrystallites were observed at the fiber/matrix interface. Two crucial parameters were proposed for characterizing the fiber nucleating ability, i.e. the interfacial free energy difference (Δ σ) based on the heterogeneous nucleation from a thermodynamic point of view, and the maximum temperature for transcrystalline layer observed ( T max) based on a kinetic consideration. Values of Δ σ for different fibers were derived on the basis of the tertiary nucleation taking place in the selective “grooves” at the fiber surface. It was found that the nucleating rate of sPS fibers was scaled with the fiber diameter, and Δ σ showed a negligible diameter dependence, but T max slightly increased with increasing fiber diameter. For all the fibers investigated, an intimate relation between the Δ σ and T max was derived and used to compare their nucleating abilities.

Electrospun Cellulose Nitrate Nanofibers

Cellulose nitrate nonwoven mats of submicron-sized fibers (100-1200 nm in diameter) were obtained by electrospinning cellulose nitrate solutions. Two solvent systems were evaluated. A 70:30 (wt) ratio of ethanol to acetone and a 60:40 (wt) ratio of tetrahydrofuran (THF) to N,N-dimethylformamide (DMF) were studied. The effects of the two solvent systems, and type two different collectors; void gap, and steel drum coated with polyvinylidene dichloride (PVDC), were investigated. The PVDC layer applied to the rotating drum aided in fiber harvesting. Electron microscopy (FESEM and ESEM) studies of as-spun fibers revealed that the morphology of cellulose nitrate fibers depended on the collector type and solution viscosity. When a rotating steel drum was employed a random morphology was observed, while the void gap collector produced aligned fiber mats. Increases in viscosity lead to larger diameter fibers.

Magnetic-field-assisted electrospinning of aligned straight and wavy polymeric nanofibers.

Electrospinning has emerged as a very attractive approach to the fabrication of nanometer (nm)- and submicron-sized fibers.[1–6] Nanofibers generated using the electrospinning technique have been explored for a wide range of applications such as tissue engineering and bioassay,[5, 7–13] sensing,[14, 15] textile,[16] filtration,[17] electrode,[18] and catalyst supports.[19] In many of these cases, the ability to control the alignment and arrangement of fibers is critical to achieve the designed functions, particularly for tissue engineering that requires the release of proteins and growth factors in a guided fashion.[20–22] Improvements in fiber quality has been achieved in recent year through the optimization of electrospinning conditions and oriented fiber arrays can be produced using either rotating collectors or patterned electrodes.[1, 23–26] Furthermore, when magnetic nanoparticles are mixed with polymers, aligned fibers can also be fabricated.[27]

Electrospun nickel oxide/polymer fibrous electrodes for electrochemical capacitors and effect of heat treatment process on their performance

Abstract Electrospinning is a versatile method for preparation of submicron-size fibers under ambient temperature. We demonstrate a new approach based on this method for preparing an electrode which consists of the fibers coated with nickel oxide (NiO) and acetylene black (AB) on their surfaces. The NiO/polymer fibrous electrodes show the electrochemical responses based on the electrochemical reaction of Ni(OH) 2 which is produced from NiO in alkaline aqueous solution. The capacitance of the test half cell with the as-prepared NiO/polymer fibrous electrode in 1 mol l −1 KOH aqueous solution is 5.8 F g −1 (per gram of NiO). Heat treatment (at 150 °C for 1 h in the air) of the NiO/polymer fibrous electrode increases the capacitance of the NiO/polymer fibrous electrode. The capacitance of the cell with the heat treated (HT) NiO/polymer fibrous electrode is 163 F g −1 (per gram of NiO). SEM observation of the heat treated electrode suggests that partial melt of the fibers on the current collector forms the conducting passes and networks between the NiO particles and the collector and increases the specific capacity of the fibrous electrode.

Electrospun Porous Mats for High Efficiency Filtration

Submicron size fibers (so-called nanofibers) are easily produced with an electrospinning apparatus from polymer solutions of poly(ethylene oxide), poly(vinyl alcohol), and polyamide-6. Electrospinning seems the most powerful tool for fabricating polymer nanofibers. Fibers were directly deposited in the form of random fiber webs with high area-to-volume ratio and small porous size on ordinary nonwoven filters of PET microfibers. Morphology and diameter distribution of the electrospun filaments were characterized by SEM investigations. The flow resistance of the produced composite filters are evaluated by means of air permeability measurements. The electrospun fibers have diameters ranging from about 70—500 nm and are interconnected each other to form thin webs that have very small pore size. After the electrospinning treatment, the air permeability of the filter media decreases 6—17 times showing a significant change of flow resistance that can be controlled by the thickness of nanofibers layer and the pore size. High efficiency nano-microfibers composite filters could be used in a wide range of applications, ranging from air cleaning for automotive to environment conditioning or liquid filtration.

Electrospun nanofibrous polysulfone membranes as pre-filters: Particulate removal

This paper explores the viability of developing high surface area pre-filters through electrospinning. Pre-filters are regularly used in removing particulate contaminants that can have a deleterious effect on downstream membrane elements such as ultrafiltration and nanofiltration. They should possess high internal surface area and thus sub-micron size fibers are ideal. In this study, polysulfone nanofibers were electrospun into membranes and their ability to remove micro-particles from solution was investigated. The nanofibrous membranes possess high porosity together with high surface area to produce high flux pre-filters with high loading capacity. The membrane had a bubble-point of 4.6 μm and was able to remove above 99% of 10, 8 and 7 μm particles without any permanent fouling. However, the membrane was observed to foul irreversibly by 2 and 1 μm particles with a ‘cake-layer’ forming on the membrane surface. Below 1 μm, the membrane behaved as a depth filter with 0.5 and 0.1 μm particles being attracted onto the nanofiber surface. This study highlights that nanofibers do have potential as pre-filters for particulate removal. Such nanofibrous pre-filters can be used in various applications such as removal of micro-particles from waste-water, prior to ultrafiltration or nanofiltration membranes, to prolong the life of these membranes.

Transport properties of porous membranes based on electrospun nanofibers

Electrospinning is a process by which high voltages are used to produce an interconnected membrane-like web of small fibers (10–500 nm in diameter). This novel fiber spinning technique provides the capacity to lace together a variety of types of polymers, fibers, and particles to produce ultrathin layers. Of particular interest are electrospun membranes composed of elastomeric fibers, which are under development for several protective clothing applications. The various factors influencing electrospun nonwoven fibrous membrane structure and transport properties are discussed. Performance measurements on experimental electrospun fiber mats compare favorably with transport properties of textiles and membranes currently used in protective clothing systems. Electrospun layers present minimal impedance to moisture vapor diffusion required for evaporative cooling. There may be special considerations in the application of elastomeric membranes for protective clothing. Effects of membrane distortion upon transport behavior of the structure might be significant. Preliminary measurements have found that changes in elastomeric membrane structure under different states of biaxial strain were reflected in measurements of air flow through the membrane. Changes in membrane structure are also evident in environmental scanning electron microscope (SEM) images of the pore/fiber rearrangement as the membrane is stretched. Experimental measurements and theoretical calculations show electrospun fiber mats to be extremely efficient at trapping airborne particles. The high filtration efficiency is a direct result of the submicron-size fibers generated by the electrospinning process. Electrospun nanofiber coatings were applied directly to an open cell polyurethane foam. The air flow resistance and aerosol filtration properties correlate with the electrospun coating add-on weight. Particle penetration through the foam layer, which is normally very high, was eliminated by extremely thin layers of electrospun nanofibers sprayed on to the surface of the foam. Electrospun fiber coatings produce an exceptionally lightweight multifunctional membrane for protective clothing applications, which exhibits high breathability, elasticity, and filtration efficiency.

Improving the performance of porous radiant burners through use of sub-micron size fibers

An analysis has been carried out to determine the performance of porous radiant burners (PRB) as a function of fiber size. PRB made with silica or alumina fibers are considered. The radiative properties of the fibers are determined using the electromagnetic wave scattering theory for two different characteristics temperatures— 1000 and 1500°C. The properties are used in a combined-mode heat transfer model to calculate the amount of energy radiated by the PRB. It is found that fibers smaller than the order of 1 μm in diameter produce significantly higher radiant output. For a characteristic temperature of 1000°C, in some cases, the increase in output is as high as 63 and 109% for silica and alumina fibers, respectively. For a characteristic temperature of 1500°C, the corresponding increases are 72 and 150%, respectively.