Micro- and Nanostructured Surface Morphology on Electrospun Polymer Fibers

Effect of relative humidity on the morphology of electrospun polymer fibers

The effect of relative humidity on the morphology of electrospun fibers of poly(vinyl alcohol), poly(methyl methacrylate), poly(vinyl chloride), polystyrene, and poly(lactic acid) dissolved in solvents such as toluene, N,N-dimethylformamide, 2,2,2-trifluoroethanol, and deionized water was studied by scanning electron microscopy to investigate the factors that may contribute to pore formation. Results showed that the presence of pores depends on factors such as the type of polymers used, the polymer–solvent combination, molecular weight, and the size of the electrospun structure. The final morphology developed implies a competition between the dynamics of phase separation and the rate of solvent evaporation. In addition, continuous solvent evaporation and constant stretching owing to the electric potential difference give rise to the final shape of porous electrospun fibers.Key words: electrospinning, relative humidity, porous fibers, polymers.

Optical and electrical properties of indium tin oxide nanofibers prepared by electrospinning

Indium tin oxide (ITO) nanofibers were successfully prepared via an electrospinning method, followed by annealing at 400 °C. Mixed solutions of ITO nanoparticle sol and polyethylene oxide (PEO) were used as precursors of the nanofibers. The PEO decomposed during annealing to yield ITO fibers. The fibers were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), thermo-gravimetric/differential thermal analysis (TG/DTA), UV-vis spectrophotometry and four-probe resistivity measurements. The diameter of the prepared fibers was controlled by adjusting the flow rate and the applied electric current. In(2)O(3) crystallized in the ITO nanofibers with a crystallite size of 27 nm. The optical transmittance in the visible region approached 90% in films deposited for 5 min, confirming that the nanofiber film is still transparent in the optical region. The sheet resistance of the nanofiber film was linearly dependent on the inverse of the deposition time and on the PEO/ITO ratio.

Electrospun linear polyethyleneimine scaffolds for cell growth

Unique biocompatible scaffolds were produced by electrospinning cross-linked linear polyethyleneimine (PEI) with succinic anhydride and 1,4-butanediol diglycidyl ether. Nonwoven mats of PEI fibers in the range of 1600-687nm were evaluated as interaction scaffolds for normal human fibroblast (NHF) cells. The electrospun scaffolds were characterized by Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. The growth of the NHF cells was followed by scanning electron microscopy as well as optical and fluorescence microscopies. Cell viability was evaluated by staining with propidium iodide for dead cells and fluorescein diacetate for live cells. Immunofluorescence with fixed cells on the scaffolds was examined by staining the endoplasmic reticulum with rabbit anti-GRP 78/Alexa 488 goat anti-rabbit and staining the nuclei with 4'-6'-diamidino-2-phenylindole. Fluorescence studies confirmed that NHF cells attached and spread throughout the cross-linked linear polyethyleneimine scaffold. The attachment and spreading of cells suggests that electrospun linear polyethyleneimine scaffolds support growth of normal human fibroblasts cells. Thus, these biomaterial scaffolds may be useful in tissue engineering.

Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers

Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.

Electrospun aliphatic polycarbonates as tailored tissue scaffold materials

Two different aliphatic polycarbonates were synthesised from CO(2) and the respective epoxides. Poly(propyl carbonate) (PPC) was prepared by heterogeneous catalysis with zinc glutarate. Poly(cyclohexyl carbonate) (PCHC) was prepared via living copolymerisation homogeneously catalysed by a 3-amino-2-cyanoimidoacrylate zinc acetate complex and subjected to electrospinning. The obtained nanofibres had a well-defined morphology free of beads along the fibres and with slightly porous structures on their surface. Subsequently, low-power deep UV irradiations, previously applied for photochemical surface modifications of two-dimensional and three-dimensional scaffolds from biostable polymers, were performed. Here, an effect on surface and bulk properties of PPC nanofibres was observed. Surface modifications of both polymers affected plasma protein adsorption. Photochemical bulk modifications observed for the first time on PPC nanofibres are indicating the possibility of spatial control of biodegradation rates, hence allow for control of the progression of host/implant interactions in vivo. In particular PPC was used for cell culture of L929 fibroblasts and primary rat hepatocytes. Even delicate primary cells showed good adhesion to the scaffolds and high viability.

Electric field induced orientation of polymer chains in macroscopically aligned electrospun polymer nanofibers

The results presented in this work show for the first time that an electric field used to macroscopically align polymer nanofibers can also align polymer chains parallel to the fiber axis. This important result indicates that anisotropic structural properties (mechanical, electrical, etc.) can be induced in polymer nanofibers during the electrospinning process. Such uniaxially oriented nanofibers exhibit a variety of potential applications in biomedicine, microelectronics, and optics. A simple technique of vertical electrospinning with an electric field induced, stationary collection was employed to obtain the molecular orientation in polymer nanofibers. This manuscript describes the orientation process via electrospinning and verifies this molecular orientation in the polymer nanofibers using three independent methods: polarized Fourier transform infrared spectroscopy, polarized Raman scattering, and X-ray diffraction.

Controllable porous polymer particles generated by electrospraying

In this paper, an electrospraying technique was applied to prepare polycaprolactone (PCL) polymer particles with a different microstructure. The PCL particles can be controlled to have a porous microstructure by tailoring the evaporation of solvents during the electrospraying process. The effect of various concentrations on the morphology and microstructure of PCL particles was investigated. The experiment has demonstrated the versatile capability of the electrohydrodynamic atomization process for preparing polymer PCL porous particles and fibers. The thermally induced and evaporation-induced phase separations are proposed as the main mechanisms for the porous microstructure formation. The results demonstrate that the electrospraying method is a simple, innovative and cost-effective method for preparing polymer particles with controllable microstructures.

Interaction of cells and nanofiber scaffolds in tissue engineering

Nanofibers and nanomaterials are potentially recent additions to materials in relation to tissue engineering (TE). TE is the regeneration of biological tissues through the use of cells, with the aid of supporting structures and biomolecules. Mimicking architecture of extracellular matrix is one of the challenges for TE. Biodegradable biopolymer nanofibers with controlled surface and internal molecular structures can be electrospun into mats with specific fiber arrangement and structural integrity for drug delivery and TE applications. The polymeric materials are widely accepted because of their ease of processability and amenability to provide a large variety of cost-effective materials, which help to enhance the comfort and quality of life in modern biomedical and industrial society. Today, nanotechnology and nanoscience approaches to scaffold design and functionalization are beginning to expand the market for drug delivery and TE is forming the basis for highly profitable niche within the industry. This review describes recent advances for fabrication of nanofiber scaffolds and interaction of cells in TE.

Electrospun polymer nanofibers with internal periodic structure obtained by microphase separation of cylindrically confined block copolymers

Continuous fibers are described having concentric layer or aligned sphere microphase-separated, styrene-isoprene block copolymer morphologies. The fibers are obtained by a two-fluid coaxial electrospinning technique in which the desired block copolymer is encapsulated as the core component within a polymer shell having a high glass transition temperature (Tg). The fibers range in diameter from 300 to 800 nm, and the block copolymer core ranges from 50 to 500 nm. Subsequent annealing of the fibers above the upper Tg of the block copolymer but below the Tg of the shell polymer results in microphase separation of the block copolymer under cylindrical confinement. The resulting fibers exhibit improved long-range order. This two-step strategy creates the opportunity to fabricate continuous nanofibers with periodic internal structure.

Nanoporous structured submicrometer carbon fibers prepared via solution electrospinning of polymer blends

A facile means for obtaining submicrometer carbon fibers with a nanoporous structure is presented. A mixture of polyacrylonitrile (PAN) and a copolymer of acrylonitrile and methyl methacrylate (poly(AN-co-MMA)) in dimethylformamide was electrospun into submicrometer fibers with a microphase-separated structure. During the followed oxidation process, the copolymer domains were pyrolyzed, resulting in a nanoporous structure that was preserved after carbonization. The microphase-separated structure of the PAN/poly(AN-co-MMA) electrospun fibers, the morphology, and porous structure of both the oxidized and the carbonized fibers were observed with scanning electron microscopy and transmission electron microscopy. The carbon fibers have diameters ranging from several hundred nanometers to about 1 microm. The nanopores or nanoslits throughout the fiber surface and interior with diameters of several tens of nanometers are interconnected and oriented along the longitudinal axis of the fibers. This unique nanoporous morphology similar to the microphase-separated structure in the PAN/poly(AN-co-MMA) fibers is attributed to the rapid phase separation, solidification, as well as the stretching of the fibers during electrospinning. The pore volume and pore size distribution of the carbonized fibers were investigated by nitrogen adsorption and desorption.

Electrospun Micro- and Nanofibers for Sustained Delivery of Paclitaxel to Treat C6 Glioma in Vitro

PURPOSE

The present study aims to develop electrospun PLGA-based micro- and nanofibers as implants for the sustained delivery of anticancer drug to treat C6 glioma in vitro.

METHODS

PLGA and an anticancer drug--paclitaxel-loaded PLGA micro- and nanofibers were fabricated by electrospinning and the key processing parameters were investigated. The physical and chemical properties of the micro- and nanofibers were characterized by various state-of-the-art techniques, such as scanning electron microscope and field emission scanning electron microscope for morphology, X-ray photoelectron spectroscopy for surface chemistry, gel permeation chromatogram for molecular weight measurements and differential scanning calorimeter for drug physical status. The encapsulation efficiency and in vitro release profile were measured by high performance liquid chromatography. In addition, the cytotoxicity of paclitaxel-loaded PLGA nanofibers was evaluated using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide MTT) assay on C6 glioma cell lines.

RESULTS

PLGA fibers with diameters of around several tens nanometers to 10 microm were successfully obtained by electrospinning. Ultrafine fibers of around 30 nm were achieved after addition of organic salts to dilute polymer solution. The encapsulation efficiency for paclitaxel-loaded PLGA micro- and nanofibers was more than 90%. DSC results suggest that the drug was in the solid solution state in the polymeric micro- and nanofibers. In vitro release profiles suggest that paclitaxel sustained release was achieved for more than 60 days. Cytotoxicity test results suggest that IC50 value of paclitaxel-loaded PLGA nanofibers (36 microg/ml, calculated based on the amount of paclitaxel) is comparable to the commercial paclitaxel formulation-Taxol.

CONCLUSIONS

Electrospun paclitaxel-loaded biodegradable micro- and nanofibers may be promising for the treatment of brain tumour as alternative drug delivery devices.

Relationships between phase morphology and deformation mechanisms in polymer nanocomposite nanofibres prepared by an electrospinning process

Relationships between phase morphology and mechanical deformation processes in various electrospun polymer nanocomposite nanofibres (PNCNFs) containing different types of one-, two- and three-dimensional nanofiller have been investigated by transmission electron microscopy using in situ tensile techniques. From the study of the phase structure of electrospun PNCNFs, two morphological standard types are classified for the analysis of deformation mechanisms: the binary system (polymer matrix and nanofillers), and the ternary system (polymer matrix, nanofillers and nanopores on the fibres surface). According to these categories, deformation processes have been characterized, and different schematic models for these processes are proposed. The finding of importance in the present work is a brittle-to-ductile transition in polymer nanocomposite fibres during in situ tensile deformation processes. This unique feature in the deformation behaviour of electrospun PNCNFs provides an optimal balance of stiffness, strength and toughness for use as reinforcing elements in a polymer based composite of a new kind.

Highly Porous Fibers by Electrospinning into a Cryogenic Liquid

Highly porous fibers of various polymers were created by electrospinning with a modified collector. A bath of liquid nitrogen was used to freeze the fibers, inducing a phase separation between the polymer and the solvent. When the solvent was removed in vacuo, highly porous fibers were obtained. Poly(styrene), poly(acrylonitrile), poly(vinylidene fluoride), and poly(epsilon-caprolactone) were all electrospun into porous fibers using this simple method. These porous fibers have a range of potential applications in encapsulation, controlled release, superhydrophobic coating, and lightweight reinforcement.

Structure and nanomechanical characterization of electrospun PS/clay nanocomposite fibers

Electrospinning has been emerging as one of the most efficient methods to fabricate polymer nanofibers. In this paper, PS/clay nanocomposite fibers with varying diameters were electrospun onto solid substrates. The fiber diameters were adjusted from 4 microm to 150 nm by changing the solution concentration. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to characterize the fiber morphology. Shear modulation force microscopy (SMFM) was utilized to investigate the surface nanomechanical properties of electrospun fibers as a function of the fiber diameter and temperature. In the absence of clay, no change in T(g) was observed, even though a large increase of shear modulus below the glass transition temperature was found. This effect was postulated to result from the molecular chain alignment during electrospinning. The addition of functionalized clays to the spinning solution produced fibers with a highly aligned montmorillonite layer structure at a clay concentration of 4 wt %. Clay agglomerates were observed at higher concentrations. The existence of clay further enhanced the shear modulus of fibers and increased the glass transition temperature by nearly 20 degrees C.

Phospholipid Nonwoven Electrospun Membranes

Nonwoven fibrous membranes were formed from electrospinning lecithin solutions in a single processing step. As the concentration of lecithin increased, the micellar morphology evolved from spherical to cylindrical, and at higher concentrations the cylindrical micelles overlapped and entangled in a fashion similar to polymers in semi-dilute or concentrated solutions. At concentrations above the onset of entanglements of the wormlike micelles, electrospun fibers were fabricated with diameters on the order of 1 to 5 micrometers. The electrospun phospholipid fibers offer the potential for direct fabrication of biologically based, high-surface-area membranes without the use of multiple synthetic steps, complicated electrospinning designs, or postprocessing surface treatments.

Challenges in biocatalysis for enzyme-based biofuel cells

Enzyme-based biofuel cells are attracting attention rapidly partially due to the promising advances reported recently. However, there are issues to be addressed before biofuel cells become competitive in practical applications. Two critical issues are short lifetime and poor power density, both of which are related to enzyme stability, electron transfer rate, and enzyme loading. Recent progress in nanobiocatalysis opens the possibility to improve in these aspects. Many nano-structured materials, such as mesoporous media, nanoparticles, nanofibers, and nanotubes, have been demonstrated as efficient hosts of enzyme immobilization. It is evident that, when nanostructure of conductive materials are used, the large surface area of these nanomaterials can increase the enzyme loading and facilitate reaction kinetics, and thus improving the power density of biofuel cells. In addition, research efforts have also been made to improve the activity and stability of immobilized enzymes by using nanostructures. It appears to be reasonable to us to expect that progress in nanostuctured biocatalysts will play a critical role in overcoming the major obstacles in the development of powerful biofuel cells.