Polymer Sheath Research Articles

Core-Liquid-Induced Transition from Coaxial Electrospray to Electrospinning of Low-Viscosity Poly(lactide-co-glycolide) Sheath Solution

Co-electrospinning has demonstrated that polymer solutions below the entanglement concentration can be made into fibers as an encapsulated core in an electrospinnable sheath solution containing a carrier/template polymer. The carrier polymer may require removal at a later stage. This work shows for the first time that without increasing the polymer concentration/molecular weight or needing a template polymer, simply infusing a liquid in the core nozzle can cause the sheath polymer solution (viscosity <20 mPa s) to electrospin instead of electrospray in a coaxial electrified jet. Different from coelectrospinning, the core liquid can be a common solvent such as water and does not require a readily electrospinnable carrier polymer. The process was not limited to one core liquid system; infusing solvents and nonsolvents with different properties in the core generated either beaded fibers or continuous fibers from the sheath solution. The process of fiber formation instead of particle breakup was attributed to the relaxation time of the elastic polymer sheath solution becoming longer than the growth rate of the Rayleigh instability in the compound jet upon the infusion of a second solvent in the core. Key parameters of the process included high surface tension of the core liquid (e.g., water and glycerol), high interfacial tension between the core and the sheath liquids, and electrohydrodynamic operating parameters such as flow rate and applied voltage. Given that charge was transferred from the sheath solution to the core liquid, differences in the dielectric constant and electrical conductivity of the core liquids showed little influence on the process. Fibers also formed irrespective of the miscibility and solubility of the solvent, though in the case of a nonsolvent, a lower miscibility was desirable to minimize polymer precipitation at the core–sheath interface. The process was investigated using poly(lactide-co-glycolide) as a model system, with polycaprolactone and polymethylsilsesquioxane systems presented as two additional examples. This work documents new roles of solvents in coaxial electrohydrodynamic processes and presents a useful method to obtain micro- and nanofibers from low-viscosity solutions without using a template polymer.

Vertically aligned ZnO nanorod core-polypyrrole conducting polymer sheath and nanotube arrays for electrochemical supercapacitor energy storage.

Nanocomposite electrodes having three-dimensional (3-D) nanoscale architecture comprising of vertically aligned ZnO nanorod array core-polypyrrole (PPy) conducting polymer sheath and the vertical PPy nanotube arrays have been investigated for supercapacitor energy storage. The electrodes in the ZnO nanorod core-PPy sheath structure are formed by preferential nucleation and deposition of PPy layer over hydrothermally synthesized vertical ZnO nanorod array by controlled pulsed current electropolymerization of pyrrole monomer under surfactant action. The vertical PPy nanotube arrays of different tube diameter are created by selective etching of the ZnO nanorod core in ammonia solution for different periods. Cyclic voltammetry studies show high areal-specific capacitance approximately 240 mF.cm-2 for open pore and approximately 180 mF.cm-2 for narrow 30-to-36-nm diameter PPy nanotube arrays attributed to intensive faradic processes arising from enhanced access of electrolyte ions through nanotube interior and exterior. Impedance spectroscopy studies show that capacitive response extends over larger frequency domain in electrodes with PPy nanotube structure. Simulation of Nyquist plots by electrical equivalent circuit modeling establishes that 3-D nanostructure is better represented by constant phase element which accounts for the inhomogeneous electrochemical redox processes. Charge-discharge studies at different current densities establish that kinetics of the redox process in PPy nanotube electrode is due to the limitation on electron transport rather than the diffusive process of electrolyte ions. The PPy nanotube electrodes show deep discharge capability with high coulomb efficiency and long-term charge-discharge cyclic studies show nondegrading performance of the specific areal capacitance tested for 5,000 cycles.

Hyperspectral imaging of exciton photoluminescence in individual carbon nanotubes controlled by high magnetic fields.

Semiconducting carbon nanotubes (CNTs) provide an exceptional platform for studying one-dimensional excitons (bound electron-hole pairs), but the role of defects and quenching centers in controlling emission remains controversial. Here we show that, by wrapping the CNT in a polymer sheath and cooling to 4.2 K, ultranarrow photoluminescence (PL) emission line widths below 80 μeV can be seen from individual solution processed CNTs. Hyperspectral imaging of the tubes identifies local emission sites and shows that some previously dark quenching segments can be brightened by the application of high magnetic fields, and their effect on exciton transport and dynamics can be studied. Using focused high intensity laser irradiation, we introduce a single defect into an individual nanotube which reduces its quantum efficiency by the creation of a shallow bound exciton state with enhanced electron-hole exchange interaction. The emission intensity of the nanotube is then reactivated by the application of the high magnetic field.

An improved free surface electrospinning for high throughput manufacturing of core–shell nanofibers

A novel coaxial electrospinning process modified from free surface electrospinning has been successfully developed to massive production of core–shell nanofibers in the present paper. A two-layer polymer system, with the lower layer consisting a core polymer solution and the upper layer consisting a sheath polymer solution, is subjected to a sufficient electrical field. As a result, multiple coaxial jets spontaneously form on the edges of the stepped pyramid-shaped spinneret. Compared with the conventional concentric spinneret based coaxial electrospinning, the possibility of clogging was avoided and an enhancement of more than 100 times over the traditionally obtained core–shell nanofibers productivity was obtained. This novel design has potential for high throughput of electrospun core–shell nanofibers.

Crosslinked polymer sheaths for dispersing individual single-walled carbon nanotubes in nonaqueous solvents

Single-walled carbon nanotubes have been suspended individually in water by encasing them in a thin, uniform layer of the crosslinkable polymer poly (N-vinylpyrrolidone-co-allylamine). When this polymer is crosslinked under dilute conditions, the polymer sheath, formerly stabilized by the hydrophobic effect, becomes stable to changes in the solvent system.

Fast Equilibrium Micro-Extraction from Biological Fluids with Biocompatible Core–Sheath Electrospun Nanofibers

Sample preparation methods with high temporal resolution and matrix resistance will benefit fast direct analysis of analytes in a complex matrix, such as drug monitoring in biofluids. In this work, the core-sheath biocompatible electrospun nanofiber was fabricated as a micro-solid phase extraction material. With the poly(N-isopropylacrylamide) (PNIPAAm) as sheath polymer and polystyrene (PS) as core polymer, the fiber membrane was highly hydrophilic and exhibited good antifouling ability to proteins and cells. Its complete expansion in aqueous solution and its nanoscale fiber (100-200 nm) structure offered high mass transfer rate of analytes between liquid and solid phases. The equilibration time of microextraction with this membrane was all shorter than 2 min for eight drugs tested, and the linear ranges covered more than 3 orders of magnitude for most of them. This membrane could be applied to monitor free drugs in plasma and their protein binding kinetics by equilibrium-microextraction with a 2 min temporal resolution. The results showed that the core-sheath electrospun nanofiber membrane would be a better alternative of solid phase material for microextraction with good matrix-resistance ability and high temporal resolution.

Morphology and Core Continuity of Liquid‐Crystal‐Functionalized, Coaxially Electrospun Fiber Mats Tuned via the Polymer Sheath Solution

AbstractBy electrospinning liquid crystals coaxially inside a polymer sheath, responsive fibers with application potential, e.g., in wearable sensors can be produced. We conduct a combined scanning electron/polarizing microscopy study of such fibers, concluding that a match between the properties of the sheath solution and that of the core fluid is vital for achieving well‐formed and well‐filled fibers. Problems that may otherwise arise are fibers that are continuously filled, but partially collapsed; or fibers in which the core breaks up into droplets due to a mismatch in elongational viscosity between inner and outer fluids. magnified image

Electrospun biphasic drug release polyvinylpyrrolidone/ethyl cellulose core/sheath nanofibers

The capability of core/sheath nanofibers prepared using coaxial electrospinning to provide adjustable biphasic drug release was investigated. Using ketoprofen (KET) as the model drug, polyvinylpyrrolidone as the sheath polymer, and ethyl cellulose as the core matrix, the coaxial process could be conducted smoothly and continuously without spinneret clogging. Scanning electron microscopy and transmission electron microscopy revealed linear nanofibers with homogeneous and clear core/sheath structures. Differential scanning calorimetry and X-ray diffraction verified that the core/sheath nanofibers were nanocomposites, with the drug present in the polymer matrix in an amorphous state. Attenuated total reflectance–Fourier transform infrared spectra demonstrated that the sheath polymer and core matrix were compatible with KET owing to hydrogen bonding. In vitro dissolution tests showed that the core/sheath nanofibers could provide typical biphasic drug release profiles consisting of an immediate and sustained release. The amount of drug released in the first phase was tailored by adjusting the sheath flow rate, and the remaining drug released in the second phase was controlled by a typical diffusion mechanism. The present study shows a simple and useful approach for the systematic design and fabrication of novel biomaterials with structural characteristics for providing complicated and programmed drug release profiles using coaxial electrospinning.

A novel over-the-scope deployment method for enteral stent placement

Over the last two decades, self-expanding enteral stents have gained popularity and shown therapeutic potential for strictures, obstructions, fistulae, and perforations of the gastrointestinal (GI) tract. Currently available stent delivery systems make deployment in many locations in the GI tract difficult due to the inability to traverse curves or impossible due to the size requirements of the deployment systems. A 67-year-old male presented to our hospital with severe gallstone pancreatitis, requiring a prolonged intensive care unit course. Two days after discharge to a rehabilitation facility he developed acute abdominal pain and pneumoperitoneum. Operative exploration failed to identify a perforation. Subsequently, a left-upper-quadrant abscess developed that was drained percutaneously, yielding coliform bacteria. The drain produced several hundred milliliters of stool a day. A barium enema demonstrated a perforation in the descending colon from an old colo-colic anastomosis site. We proposed a novel over-the-scope (OTS) stent deployment method. Utilizing a heat-activated polymer sheath, the stent was affixed to the endoscope. A modified speed-banding attachment was created to permit release of the polymer sheath once endoscopic and fluoroscopic confirmation of the correct position was obtained. Utilizing this method of OTS stent deployment, a fully covered 23 × 155 mm self-expanding metal stent (WallFlex, Boston Scientific, Natick, MA) was placed in the colon. Endoscopic and fluoroscopic evaluation following stent placement confirmed stent coverage of the perforation with no ongoing evidence of leak. The patient was discharged to his home state 2 weeks after stent placement in stable condition. We have developed a novel method of OTS stent placement that permits deployment of a variety of enteral stents on any available endoscope. This method permits placement of fully covered stents in locations in the GI tract not reachable with currently available delivery systems.

Electrospun drug-loaded core–sheath PVP/zein nanofibers for biphasic drug release

Core-sheath nanofibers prepared using coaxial electrospinning were investigated for providing biphasic drug release profiles. With ketoprofen (KET) as the model drug, polyvinylpyrrolidone and zein as the sheath polymer and core matrix, respectively, the coaxial process could be carried out smoothly and continuously without any clogging of the spinneret. Scanning electron microscopy and transmission electron microscopy observations demonstrated that the nanofibers were linear with homogeneous structure and had a clear core-sheath structure with an average diameter of 730 ± 190 nm, in which the sheath had a thickness of ca. 90 nm. Differential scanning calorimetric and X-ray diffraction analyses verified that all the components in the core-sheath nanofibers were present in an amorphous state. Attenuated total reflectance Fourier transform infrared spectra demonstrated both the sheath and core matrix had good compatibility with KET owing to hydrogen bonding. In vitro dissolution tests showed that the nanofibers could provide an immediate release of 42.3% of the contained KET, followed by a sustained release over 10h of the remaining drug. The present study exhibited a simple and useful approach to systematically design and fabricate nanostructures using coaxial electrospinning for providing biphasic drug release profiles.

Synthesis and characterization of Ag@polycarbazole coaxial nanocables and their enhanced dispersion behavior

Ag@polycarbazole coaxial nanocables (CNCs) have been successfully fabricated by the oxidative polymerization of carbazole over Ag nanowires (NWs) in acetonitrile. The morphology of Ag NWs and CNCs was studied by employing a transmission electron microscope (TEM) and a scanning electron microscope (SEM), which showed them to be a monodisperse material. The thickness of the polymer sheath was found to be 5 nm to 8 nm by observation under a high-resolution transmission electron microscope (HR-TEM). Energy dispersive X-ray spectroscopy (EDS), FT-IR and Raman measurements were used to characterize the polymer sheath, which demonstrated it to be a carbon material in polycarbazole form. X-ray photoelectron spectroscopy (XPS) was used for an interfacial study, which revealed that Ag surface atoms remained intact during polymer growth. In the end, zeta potential showed that the dispersion stability of Ag NWs increased due to polymer encapsulation, which is significant to obtain a particular alignment for anisotropic measurement of electrical conductivity.

SU‐E‐T‐373: Treatment Plan Validation of the XPS (Interstitial) Applicator for Use with the Xoft Axxent 50kVp X‐Ray Source

Purpose: To determine the dosimetric properties of a new interstitial applicator designed for the Xoft 50 kVp X‐ray Electronic Brachytherapy (eBx) system. Methods: A 0.64 cm diameter polymer sheath applicator interfaces with the Xoft 50kVp x‐ray source to provide radiation treatment to interstitial and other small target areas using eBx. Measurements of the dose profiles in a plane parallel to the applicator axis were determined. The absolute dose delivered to a prescription point at 90° off the central axis 1 cm from the source center, was determined using GafChromic EBT‐2 radiochromic film. The dose distribution measured in this parallel plane is compared to the distribution determined by the treatment planning software (Varian Brachyvision V8). Three x‐ray sources were paired with three interstitial applicators for the tests. Results: Using a single position treatment plan, the absolute dose at the defined prescription point was determined from calibrated film images. The measured dose agreed with the dose predicted by the treatment plan to within ±5%, with the actual range from −4.6% to +3.1% for the three samples. The measured isodose contours, including the 1 cm prescription point contour, agreed with the contours predicted by the treatment plan to within 5% (1 sigma) and the applicator does not perturb the water‐based dose distribution. The absolute dose determined from each of these contours agreed with the predicted dose to within +1/−6%. Conclusions: The XPS applicator can be used to treat small cavities using eBx with the Xoft X‐ray source. The applicator delivers dose profiles in good agreement with those predicted from the treatment planning software. It can be used for treatment in lightly shielded rooms due to the low energies employed. There are also intriguing possibilities for this applicator to be used intra‐operatively.Research supported by Xoft, Inc. — an iCAD Company

Magnetic nanofibers with core (Fe3O4 nanoparticle suspension)/sheath (poly ethylene terephthalate) structure fabricated by coaxial electrospinning

One-dimensional magnetic nanostructures have recently attracted much attention because of their intriguing properties that are not realized by their bulk or particle form. These nanostructures are potentially useful for the application to ultrahigh-density data storages, sensors and bulletproof vest. The magnetic particles in magnetic nanofibers of blend types cannot fully align along the external magnetic field because magnetic particles are arrested in solid polymer matrix. To improve the mobility of magnetic particles, we used magneto-rheological fluid (MRF), which has the good mobility and dispersibility. Superparamagnetic core/sheath composite nanofibers were obtained with MRF and poly (ethylene terephthalate) (PET) solution via a coaxial electrospinning technique. Coaxial electrospinning is suited for fabricating core/sheath nanofibers encapsulating MRF materials within a polymer sheath. The magnetic nanoparticles in MRF were dispersed within core part of the nanofibers. The core/sheath magnetic composite nanofibers exhibited superparamagnetic behavior at room temperature and the magnetic nanoparticles in MRF well responded to an applied magnetic field. Also, the mechanical properties of the nanofiber were improved in the magnetic field. This study aimed to fabricate core/sheath magnetic composite nanofibers using coaxial electrospinning and characterize the magnetic as well as mechanical properties of composite nanofibers.

Web fabrication and characterization of unique winged shaped, area-enhanced fibers via a bicomponent spunbond process

High surface area fibers are sought after for a variety of applications such as liquid and air filtrations, medical and biopharmaceutical applications. Typically, higher specific surface area is achieved by resorting to using smaller fibers. This paper focuses on the development of a new shaped bicomponent spunbond structure for achieving high surface area. The fibers used in the spunbond process comprise a sacrificial sheath polymer and the shaped core polymer. Nonwovens were directly produced by using these fibers in a spunbond process. The spunbond webs were mechanically bonded by high energy water-jets and subsequently, the sheath polymer was removed in a 6 wt% NaOH solution at 90 °C. The final fibers showed a unique cross-sectional shape having 32 flaps or wings held together with a reasonable backbone. We report the results for a variety of polymer combinations including PP, PET, PBT, and PLA as the core and PLA and EastONETM as the sheath. The fiber morphologies were observed by SEM and showed 7–12 micron of the minor and 12–21 microns of the major with various core polymers used. The surface area of these fibers was compared to those of other shaped fibers.

The synthesis of Ag/polypyrrole coaxial nanocables via ion adsorption method using different oxidants

Ag/polypyrrole (PPy) coaxial nanocables (NCs) were synthesized by an ion adsorption method. In this method, the pre-made Ag nanowires (NWs) were dispersed in the aqueous solution of copper acetate (Cu(Ac)2), and the Cu2+ ions adsorbed onto the surface of Ag NWs can oxidize pyrrole monomers to polymerize into uniform PPy sheath outside Ag NWs after the Cu(Ac)2-treated Ag NWs were re-dispersed in the aqueous solution of pyrrole. The morphology of NCs was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM). The relationship between the thickness of polymer sheath and the concentration of Cu(Ac)2 was established. As Cu(Ac)2 which served as the oxidant can also be replaced by AgNO3 in this synthesis, the differences on the structure of polymer sheath caused by different oxidants were studied by surface-enhanced Raman scattering (SERS), high-resolution transmission electron microscope (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Comparing with the characterization results of Ag/PPy NCs synthesized using AgNO3 as the oxidant which indicates the random arrangement of PPy chains at the interface between polymer sheath and Ag NWs, PPy chain oxidized by Cu2+ tends to show a relatively ordered conformation at the interface with the pyrrole rings identically taking the plane vertical to the surface of Ag NWs. In addition, although the main part of the polymer sheath was composed of PPy whatever kind of oxidant was used, the sheath of the NCs oxidized by Cu2+ is typical for the existence of Cu(I)–pyrrole coordinate structures with strong Cu(I)–N bond signal shown in XPS characterization.

Coaxially Electrospun PVDF−Teflon AF and Teflon AF−PVDF Core−Sheath Nanofiber Mats with Superhydrophobic Properties

This work reports the coaxial electrospinning of poly(vinylidene fluoride) (PVDF)-Teflon amorphous fluoropolymer (AF) and Teflon AF-PVDF core-sheath nanofiber mats yielding superhydrophobic properties. The coaxial electrospinning configuration allows for the electrospinning of Teflon AF, a nonelectrospinnable polymer, with the help of an electrospinnable PVDF polymer. PVDF-Teflon AF and Teflon AF-PVDF core-sheath fibers have been found to a have mean fiber diameter ranging from 400 nm to less than 100 nm. TEM micrographs exhibit a typical core-sheath fiber structure for these fibers, where the sheath fiber coats the core fiber almost thoroughly. Water contact angle measurements by sessile drop method on these core-sheath nanofiber mats exhibited superhydrophobic characteristics with contact angles close to or higher than 150 degrees. Surprisingly, PVDF-Teflon AF and Teflon AF-PVDF nanofiber mat surface properties were dominated by the fiber dimensions and less influenced by the type of sheath polymer. This suggests that highly fluorinated polymer Teflon AF does not advance the hydrophobicity beyond what surface physics and slightly fluorinated polymer PVDF can achieve. It is concluded that PVDF-Teflon AF and Teflon AF-PVDF core-sheath electrospun nanofiber mats may be used in lithium (Li)-air batteries.

Formation mechanism of silver nanoparticle 1D microstructures and their hierarchical assembly into 3D superstructures

Flower-like silver nanoparticle superstructures are prepared by the reaction of silver nitrate and ascorbic acid in an acidic aqueous solution of a polynaphthalene system. The three-dimensional flower-like structure has a purely hierarchic arrangement, wherein each petal is composed of bundles of silver particle chains, each enclosed in a polymer sheath. The ordering arises from strong adsorption of silver ions onto the polymer and by the interplay of the redox properties of nitric and ascorbic acid. As a result, linear silver cyanide, formed on the polymer, probably due to intrinsic electric dipole fields, organizes the silver particle chains in dumbbell-like structures, resembling buds and flower-like structures. By dilution and heating of the mother liquors, it is also possible to obtain single petals, i.e. micrometer sized bundles of linearly aggregated silver nanoparticle chains, each enclosed in a polymer sheath.The comprehension of the hierarchic assembly of silver nanoparticles, paves the way to a facile general method to prepare polymer-metal nanoparticle chains and flower-like superstructures.The results of this study improve both the understanding of the formation mechanism of hierarchic structures at mild temperatures and our ability to tailor them to sizes and shapes appropriate for technological purposes.

Regulated non-viral gene delivery from coaxial electrospun fiber mesh scaffolds

In an effort to add to the versatility of three-dimensional scaffolds for tissue engineering applications, recent experimental designs are incorporating biological molecules such as plasmids and proteins within the scaffold structure. Such scaffolds act as reservoirs for the biological molecules of interest while regulating their release over various durations of time. Here, we describe the use of coaxial electrospinning as a means for the fabrication of fiber mesh scaffolds and the encapsulation and subsequent release of a non-viral gene delivery vector over a period of up to 60 days. Various fiber mesh scaffolds containing plasmid DNA (pDNA) within the core and the non-viral gene delivery vector poly(ethylenimine)-hyaluronic acid (PEI-HA) within the sheath of coaxial fibers were fabricated based on a fractional factorial design that investigated the effects of four processing parameters at two levels. Poly(ε-caprolactone) sheath polymer concentration, poly(ethylene glycol) core polymer molecular weight and concentration, and the concentration of pDNA were investigated for their effects on average fiber diameter, release kinetics of PEI-HA, and transfection efficiency. It was determined that increasing the values of each of the investigated parameters caused an increase in the average diameter of the fibers. The release kinetics of PEI-HA from the fibers were affected by the loading concentration of pDNA (with PEI-HA concentration adjusted accordingly to maintain a constant nitrogen to phosphorous (N:P) ratio within the complexes). Two-dimensional cell culture experiments with model fibroblast-like cells demonstrated that complexes of pDNA with PEI-HA released from fiber mesh scaffolds could successfully transfect cells and induce expression of enhanced green fluorescent protein (EGFP). Peak EGFP expression varied with the investigated processing parameters, and the average transfection observed was a function of poly(ethylene glycol) (core) molecular weight and concentration. Furthermore, fibroblast-like cells seeded directly onto coaxial fiber mesh scaffolds containing PEI-HA and pDNA showed EGFP expression over 60 days, which was significantly greater than the EGFP expression observed with scaffolds containing pDNA alone. Hence, variable transfection activity can be achieved over extended periods of time upon release of pDNA and non-viral gene delivery vectors from electrospun coaxial fiber mesh scaffolds, with release and subsequent transfection controlled by tunable coaxial fiber mesh fabrication parameters.

Fabrication of Nonwoven Coaxial Fiber Meshes by Electrospinning

There is a great need for biodegradable polymer scaffolds that can regulate the delivery of bioactive factors such as drugs, plasmids, and proteins. Coaxial electrospinning is a novel technique that is currently being explored to create such polymer scaffolds by embedding within them aqueous-based biological molecules. In this study, we evaluated the influence of various processing parameters such as sheath polymer concentration, core polymer concentration and molecular weight, and salt ions within the core polymer on coaxial fiber morphology. The sheath polymer used in this study was poly(e-caprolactone) (PCL), and the core polymer was poly(ethylene glycol) (PEG). We examined the effects of the various processing parameters on core diameters, total fiber diameters, and sheath thicknesses of coaxial microfibers using a 2(4) full factorial statistical model. The maximum increase in total fiber diameter was observed with increase in sheath polymer (PCL) concentration from 9 to 11 wt% (0.49+/-0.03 microm) and salt concentration within the core from 0 to 500 mM (0.38+/-0.03 microm). The core fiber diameter was most influenced by the sheath and core polymer (PCL and PEG, respectively) concentrations, the latter of which increased from 200 to 400 mg/mL (0.40+/-0.01 microm and 0.36+/-0.01 microm, respectively). The core polymer (PEG) concentration had a maximal negative effect on sheath thickness (0.40+/-0.03 microm), while salt concentration had the maximal positive effect (0.28+/-0.03 microm). Molecular weight increases in core polymer (PEG) from 1.0 to 4.6 kDa caused moderate increases in total and sheath fiber diameters and sheath thicknesses. These experiments provide important information that lays the foundation required for the synthesis of coaxial fibers with tunable dimensions.

Fabrication and morphology control of poly(methyl methacrylate) hollow structures via coaxial electrospinning

AbstractA modified electrospinning method known as coaxial electrospinning was used to fabricate poly(methyl methacrylate) (PMMA) hollow structures. In this study to understand morphology control, the effect of processing parameters such as concentration of polymer sheath solution, size of core/sheath capillaries, feed rate, and applied voltage had been evaluated. Morphological observations via scanning electron microscope (SEM) revealed that via the control of polymer concentration within the sheath solution, morphologies such as hollow particles and fibers could be obtained. With the use of fine core/sheath capillaries, micron hollow fibers with walls of less than 20 nm were obtained. This study has demonstrated how the investigated processing parameters have a direct influence on the structures and how these parameters have supported the notion that effective encapsulation process is the key to the dual layer bicomponent structures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009