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At least 19 recordsLinked to original sources
PubMed2006

From monomeric nanofibers to PbS nanoparticles/polymer composite nanofibers through the combined use of gamma-irradiation and gas/solid reaction.

Organic metal-salt (lead dimethacrylate (Pb(MA)2)) nanofibers are prepared, and these Pb(MA)2 monomeric nanofibers are successfully converted into PbS nanoparticles/polymer composite nanofibers through the combined use of gamma-irradiated polymerization and gas/solid reaction. The resulting composite nanofibers have excellent thermal and chemical stability, and the PbS nanoparticles (with diameters of about 4 nm) are well dispersed in the polymer-fiber matrices. This approach could also be extended to methacrylates containing other metal ions. We anticipate that this method would provide a platform for the fabrication of diverse and multifunctional polymer nanocomposite fibers, which would have potential applications in fabricating devices with optical, electric, and magnetic properties.

Journal Article↗
PubMed2004

Synthesis of polyaniline nanofibers by "nanofiber seeding".

Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers (usually <1%) dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nanofibers. The nanoscale morphology of the original seed template is transcribed almost quantitatively to the bulk precipitate. These findings could have immediate impact in the design and development of high-surface area electronic materials.

Aniline Compounds↗
PubMed2004

Hydrogen titanate nanofibers covered with anatase nanocrystals: a delicate structure achieved by the wet chemistry reaction of the titanate nanofibers.

Hydrogen titanate nanofibers synthesized by a hydrothermal reaction, are chemically reactive, readily reacting with dilute acid. This reaction is a topochemical process in which in situ phase transition from H-titanate to anatase takes place and the product retains the fibril morphology. The extent of this reaction can be precisely controlled, allowing us to achieve a delicate composite structure at nanoscale: long titanate fibers of 40-100 nm thick and up to 30 mum long covered with anatase nanocrystals of 10-30 nm. The structure has desired photocatalytic properties and can be separated readily after use. This study demonstrates new opportunities to create delicate inorganic nanostructures with advanced functions by wet chemical reactions.

Journal Article↗
PubMed2005

Strict preparation and evaluation of water-soluble hat-stacked carbon nanofibers for biomedical application and their high biocompatibility: influence of nanofiber-surface functional groups on cytotoxicity.

Water-soluble H-CNFs modified with a carboxyl group possessed the ability to induce TNF-alpha, whereas CHAPS-treated H-CNFs possessed significantly greater activity and were also found to activate NF-kappaB reporter activity, to a significantly greater level than H-CNFs; furthermore the functional group modified or coated on the surface of H-CNFs was a significant cytotoxic factor that affected cell activation.

Carbon↗
PubMed2006

New renewable resource amphiphilic molecular design for size-controlled and highly ordered polyaniline nanofibers.

We demonstrate here, for the first time, a unique strategy for conducting polyaniline nanofibers based on renewable resources. Naturally available cardanol, which is an industrial waste and main pollutant from the cashew nut industry, is utilized for producing well-defined polyaniline nanofibers. A new amphiphilic molecule is designed and developed from cardanol, which forms a stable emulsion with aniline for a wide composition range in water (1:1 to 1:100 dopant/aniline mole ratio) to produce polyaniline nanofibers. The scanning electron microscopy and transmission electron microscopy analysis of the nanofibers reveals that the dopant/aniline ratio plays a major role in determining the shape and size of polyaniline nanofibers. The nanofiber length increases with the increase in the dopant/aniline ratio, and perfectly linear, well-defined nanofibers of lengths as long as 7-8 muM were produced. The amphiphilic dopant has a built-in head-to-tail geometry and effectively penetrates into the polyaniline chains to form highly organized nanofibers. Wide-angle X-ray diffraction (WXRD) spectra of the nanofibers showed a new peak at 2theta = 6.3 (d spacing = 13.9 A) corresponding to the three-dimensional solid-state ordering of polyaniline-dopant chains, and this peak intensity increases with increase in the nanofiber length. The comparison of morphology and WXRD reveals that high ordering in polyaniline chains results in the formation of long, well-defined nanofibers, and this direct correlation for the polyaniline nanofibers with solid-state ordering has been established. The conductivity of the polyaniline nanofibers also increases with increase in the solid-state ordering rather than increasing with the extent of doping. The polyaniline nanofibers are freely soluble in water and possess high environmental and thermal stability up to 300 degrees C for various applications.

Journal Article↗
PubMed2004

Bioresorbable nanofiber-based systems for wound healing and drug delivery: optimization of fabrication parameters.

Wound healing is a complex process that often requires treatment with antibiotics. This article reports the initial development of a biodegradable polymeric nanofiber-based antibiotic delivery system. The functions of such a system would be (a) to serve as a biodegradable gauze, and (b) to serve as an antibiotic delivery system. The polymer used in this study was poly(lactide-co-glycolide) (PLAGA), and nanofibers of PLAGA were fabricated with the use of the electrospinning process. The objective of this study was to determine the effect of fabrication parameters: orifice diameter (needle gauge), polymer solution concentration, and voltage per unit length, on the morphology and diameter of electrospun nanofibers. The needle gauges studied were 16 (1.19 mm), 18 (0.84 mm), and 20 (0.58 mm), and the range of polymer solution concentration studied was from 0.10 g/mL to 0.30 g/mL. The effect of voltage was determined by varying the voltage per unit electrospinning distance, and the range studied was from 0.375 kV/cm to 1.5 kV/cm. In addition, the mass per unit area of the electrospun nanofibers as a function of time was determined and the feasibility of antibiotic (cefazolin) loading into the nanofibers was also studied. The results indicate that the diameter of nanofibers decreased with an increase in needle gauge (decrease in orifice diameter), and increased with an increase in the concentration of the polymer solution. The voltage study demonstrated that the average diameter of the nanofibers decreased with an increase in voltage. However, the effect of voltage on fiber diameter was less pronounced as compared to polymer solution concentration. The results of the areal density study indicated that the mass per unit area of the electrospun nanofibers increased linearly with time. Feasibility of drug incorporation into the nanofibers was demonstrated with the use of cefazolin, a broad-spectrum antibiotic. Overall, these studies demonstrated that PLAGA nanofibers can be tailored to desired diameters through modifications in processing parameters, and that antibiotics such as cefazolin can be incorporated into these nanofibers. Therefore, PLAGA nanofibers show potential as antibiotic delivery systems for the treatment of wounds.

Anti-Bacterial Agents↗
PubMedDate not supplied

Recent advances in polymer nanofibers.

Polymer nanofibers, with diameters in the nanometer range, possess larger surface areas per unit mass and permit easier addition of surface functionalities compared with polymer microfibers. Hence, polymer nanofiber mats are being considered for use as filters, scaffolds for tissue engineering, protective clothing, reinforcement in composite materials and sensors. Although some of these applications are in the development stage, a few have been commercially exploited. Research on polymer nanofibers, nanofiber mats, and their applications has seen a remarkable growth over the last few years. However, a review of the various issues related to these nanofibers has not been published. This article presents a review of the recent trends in the processing methods and characterization techniques for polymer nanofibers. Research challenges and future trends in the processing and characterization of polymer nanofibers are discussed in the article. Five processing methods have been examined in this review, namely drawing, template synthesis, phase separation, self-assembly, and electrospinning. Among these methods, electrospinning has been used to convert a large variety of polymers into nanofibers and may be the only process that has the potential for mass production. The structure, morphology, and geometry of nanofibers and the porosity and tensile properties of nanofiber mats can be investigated through conventional techniques and instruments. But new techniques are needed for the mechanical testing of single nanofibers. Although measurement of mechanical properties such as tensile modulus, strength, and elongation is difficult because of the small diameters of the fibers, these properties are crucial for the proper use of nanofiber mats.

Biocompatible Materials↗
PubMed2006

Continuing differentiation of human mesenchymal stem cells and induced chondrogenic and osteogenic lineages in electrospun PLGA nanofiber scaffold.

Nanofibers have recently gained substantial interest for potential applications in tissue engineering. The objective of this study was to determine whether electrospun nanofibers accommodate the viability, growth, and differentiation of human mesenchymal stem cells (hMSCs) as well as their osteogenic (hMSC-Ob) and chondrogenic (hMSC-Ch) derivatives. Poly(d,l-lactide-co-glycolide) (PLGA) beads with a PLA:PGA ratio of 85:15 were electrospun into non-woven fibers with an average diameter of 760+/-210 nm. The average Young's modulus of electrospun PLGA nanofibers was 42+/-26 kPa, per nanoindentation with atomic force microscopy (AFM). Human MSCs were seeded 1-4 weeks at a density of 2 x 10(6)cells/mL in PLGA nanofiber sheets. After 2 week culture on PLGA nanofiber scaffold, hMSCs remained as precursors upon immunoblotting with hKL12 antibody. SEM taken up to 7 days after cell seeding revealed that hMSCs, hMSC-Ob and hMSC-Ch apparently attached to PLGA nanofibers. The overwhelming majority of hMSCs was viable and proliferating in PLGA nanofiber scaffolds up to the tested 14 days, as assayed live/dead tests, DNA assay and BrdU. In a separate experiment, hMSCs seeded in PLGA nanofiber scaffolds were differentiated into chodrogenic and osteogenic cells. Histological assays revealed that hMSCs continuously differentiated into chondrogenic cells and osteogenic cells after 2 week incubation in PLGA nanofibers. Taken together, these data represent an original investigation of continuous differentiation of hMSCs into chondrogenic and osteogenic cells in PLGA nanofiber scaffold. Consistent with previous work, these findings also suggest that nanofibers may serve as accommodative milieu for not only hMSCs, but also as a 3D carrier vehicle for lineage specific cells.

Biocompatible Materials↗
PubMedDate not supplied

Electrospinning of silk fibroin nanofibers and its effect on the adhesion and spreading of normal human keratinocytes and fibroblasts in vitro.

An electrospinning method was used to fabricate silk fibroin (SF) nanofiber nonwovens for cell culture of normal human keratinocytes and fibroblasts. The electrospinning of regenerated SF was performed with formic acid as a spinning solvent. For insolubilization, as-spun SF nanofiber nonwovens were chemically treated with an aqueous methanol solution of 50%. Morphology and microstructure of as-spun and chemically treated SF nanofibers were investigated by scanning electron microscopy and mercury porosimetry. As-spun SF nanofibers exhibited a circular cross-section with a smooth surface. From the image analysis, they had an average diameter of 80 nm and their diameters ranged from 30 to 120 nm. During the chemical treatment for 60 min, porosity of nonwovens composed of SF nanofibers decreased from 76.1% up to 68.1%. To assay the cytocompatibility and cell behavior onto the electrospun SF nanofibers, cell attachment and spreading of normal human keratinocytes and fibroblasts seeded on the SF nanofibers and interaction between cells and SF nanofibers were studied. Cell morphology on SF nanofibers was examined by scanning electron microscopy. Our results indicate that the SF nanofibers may be a good candidate for the biomedical applications, such as wound dressing and scaffolds for tissue engineering.

Adolescent↗
PubMed2004

Assembly of well-aligned multiwalled carbon nanotubes in confined polyacrylonitrile environments: electrospun composite nanofiber sheets.

Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.

Journal Article↗
PubMed2006

Fabrication and characterization of polycrystalline WO3 nanofibers and their application for ammonia sensing.

We describe the fabrication and characterization of tungsten oxide nanofibers using the electrospinning technique and sol-gel chemistry. Tungsten isopropoxide sol-gel precursor was incorporated into poly(vinyl acetate)(PVAc)/DMF solutions and electrospun to form composite nanofibers. The as-spun composite nanofibers were subsequently calcinated to obtain pure tungsten oxide nanofibers with controllable diameters of around 100 nm. SEM and TEM were utilized to investigate the structure and morphology of tungsten oxide nanofibers before and after calcination. The relationship between solution concentration and ceramic nanofiber morphology has been studied. A synchrotron-based in situ XRD method was employed to study the dynamic structure evolution of the tungsten oxide nanofibers during the calcination process. It has been shown that the as-prepared tungsten oxide ceramic nanofibers have a quick response to ammonia with various concentrations, suggesting potential applications of the electrospun tungsten oxide nanofibers as a sensor material for gas detection.

Journal Article↗
PubMedDate not supplied

Fabrication and endothelialization of collagen-blended biodegradable polymer nanofibers: potential vascular graft for blood vessel tissue engineering.

Electrospun collagen-blended poly(L-lactic acid)-co-poly(epsilon-caprolactone) [P(LLA-CL), 70:30] nanofiber may have great potential application in tissue engineering because it mimicks the extracellular matrix (ECM) both morphologically and chemically. Blended nanofibers with various weight ratios of polymer to collagen were fabricated by electrospinning. The appearance of the blended nanofibers was investigated by scanning electron microscopy and transmission electron microscopy. The nanofibers exhibited a smooth surface and a narrow diameter distribution, with 60% of the nanofibers having diameters between 100 and 200 nm. Attenuated total reflectance-Fourier transform infrared spectra and X-ray photoelectron spectroscopy verified the existence of collagen molecules on the surface of nanofibers. Human coronary artery endothelial cells (HCAECs) were seeded onto the blended nanofibers for viability, morphogenesis, attachment, and phenotypic studies. Five characteristic endothelial cell (EC) markers, including four types of cell adhesion molecule and one EC-preferential gene (von Willebrand factor), were studied by reverse transcription-polymerase chain reaction. Results showed that the collagen-blended polymer nanofibers could enhance the viability, spreading, and attachment of HCAECs and, moreover, preserve the EC phenotype. The blending electrospinning technique shows potential in refining the composition of polymer nanofibers by adding various ingredients (e.g., growth factors) according to cell types to fabricate tissue-engineering scaffold, particularly blood vessel-engineering scaffold.

Biocompatible Materials↗
PubMed2005

Biological evaluation of chitosan nanofiber membrane for guided bone regeneration.

BACKGROUND: Chitosan is known as a biodegradable and non-toxic natural polymer that enhances wound healing and bone formation. The aims of this study are to evaluate the biocompatibility of chitosan nanofiber membranes and to examine the effect of the chitosan nanofiber membranes on bone regeneration in rabbit calvarial defects. METHODS: In vitro cell proliferation tests using human osteosarcoma cell line MG63 and reverse transcription-polymerase chain reaction (RT-PCR) to evaluate the expression of alkaline phosphatase (ALP), collagen, osteocalcin (OCN), and GAPDH were done on chitosan nanofiber membranes. Chitosan nanofiber membranes were implanted in subcutaneous connective tissue and observed for 2, 4, and 6 weeks in rats. Ten-millimeter diameter round cranial defects were made in rabbits and covered by chitosan nanofiber membranes for 4 weeks. Specimens were decalcified and observed by a light microscope. RESULTS: MG63 cells proliferated for 28 days on the chitosan nanofiber membranes and expressed ALP, collagen, OCN, and GAPDH at 2 weeks. Chitosan nanofiber membranes that were grafted into rat subcutaneous tissue maintained their shape and space for bone regeneration for as long as 6 weeks. No inflammation could be seen on the membrane surface or in the surrounding tissues. In the rabbit calvarial defects, new bone filled the defects and fused to the original old bone in 4 weeks. CONCLUSIONS: The biocompatibility of the chitosan nanofiber membrane was confirmed, with enhanced bone regeneration and no evidence of an inflammatory reaction. This experiment shows that the novel biodegradable chitosan nanofiber membrane may be useful as a tool for guided bone regeneration.

Analysis of Variance↗
PubMed2006

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.

Antineoplastic Agents, Phytogenic↗
PubMed2005

Increased osteoblast functions on theta + delta nanofiber alumina.

Nanophase materials, or materials with grain sizes less than 100 nm in at least one direction, are promising materials for various implant applications since our tissues are composed of nanometer components (i.e., proteins and/or inorganics). Specifically, bone is comprised of nanostructured hydroxyapatite and collagen fibers which continuously provide an extracellular matrix surface to bone-forming cells (osteoblasts) with a high degree of nanometer roughness. Despite this fact, materials currently utilized for orthopedic implants, whether metallic or ceramic, have constituent grain sizes in the non-biologically inspired micron regime. For this reason, the objective of the present in vitro study was to determine osteoblast functions on one classification of nanomaterials for orthopedic applications: nanofiber alumina. Various crystalline forms of nanofiber alumina were tested in this study. To obtained different crystalline structured nanofiber alumina, boehmite nanofiber alumina was sintered at either 400 degrees C, 600 degrees C, 800 degrees C, 1000 degrees C, or 1200 degrees C for 2 h in air. X-ray diffraction results provided evidence that boehmite nanofiber alumina remained boehmite when sintered at 400 degrees C but changed crystalline phases to gamma, gamma + delta, theta + delta, and alpha when sintered at 600 degrees C, 800 degrees C, 1000 degrees C, and 1200 degrees C, respectively. Moreover, compared to any other alumina formulation tested in this study, osteoblast functions (as measured by alkaline phosphatase activity and calcium deposition) were the greatest on theta + delta crystalline phase nanofiber alumina after 14 days of culture. Boehmite had the next greatest amount of calcium deposition by osteoblasts followed by gamma + delta. Gamma crystalline phase then followed and was greater than alpha crystalline phase nanofiber alumina which promoted osteoblast functions the least of all the compacts with the exception of borosilicate glass (reference substrate). For this reason, this study suggests that theta+delta nanofiber alumina should be further investigated in orthopedic applications.

Aluminum Oxide↗
PubMed2006

Sonochemical synthesis of polyaniline nanofibers.

Conventionally, micro-sized irregular polyaniline (PANI) particles were synthesized by dropwise addition of the ammonium persulfate (APS) solution into the aniline (ANI) solution with mechanical stirring. By replacing the mechanical stirring with an ultrasonic irradiation, PANI nanofibers in diameters of approximately 50 nm and lengths of 200 nm to several micrometers were prepared. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that at the early stage of polymerization, the polymers formed in both the mechanical stirred and ultrasonicated systems are in the form of nanofiber. However, with continuing of the reaction, these primary nanofibers grow and agglomerate into irregular shaped PANI particles in the mechanical stirred system, while in the case of the ultrasonic irradiation, the growth and agglomeration are effectively prevented, preserving thus the PANI nanofibers in the final product. By increasing the APS/ANI molar ratio from 0.5 to 2.5, the aspect ratios of the PANI nanofibers decreased. The PANI nanofibers exhibit higher solubility than the irregular shaped PANI particles. Although the yield, as well as the conductivity of the ultrasonic synthesized PANI nanofibers, was slightly lower than the irregular shaped PANI particles, the ultrasonic synthesis approach is one of the facile and scalable approaches in synthesizing PANI nanofibers in comparison with other ones without use of templates (e.g., the interfacial polymerization and rapid mixing polymerization). UV-Vis and Fourier transformed infrared (FTIR) spectra indicated ultrasound had no significant effect on the chemical structure of the PANI.

Aniline Compounds↗
PubMed2006

Growth of mesenchymal stem cells on electrospun type I collagen nanofibers.

We reconstituted type I collagen nanofibers prepared by electrospin technology and examined the morphology, growth, adhesion, cell motility, and osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (MSCs) on three nano-sized diameters (50-200, 200-500, and 500-1,000 nm). Results from scanning electron microscopy showed that cells on the nanofibers had a more polygonal and flattened cell morphology. MTS (3-[4,5-dimethythiazol-2-yl]-5-[3-carboxy-methoxyphenyl]-2-[4-sul-fophenyl]-2H-tetrazolium compound) assay demonstrated that the MSCs grown on 500-1,000-nm nanofibers had significantly higher cell viability than the tissue culture polystyrene control. A decreased amount of focal adhesion formation was apparent in which quantifiable staining area of the cytoplasmic protein vinculin for the 200-500-nm nanofibers was 39% less compared with control, whereas the area of quantifiable vinculin staining was 45% less for both the 200-500-nm and 500-1,000-nm nanofibers. The distances of cell migration were quantified on green fluorescent protein-nucleofected cells and was 56.7%, 37.3%, and 46.3% for 50-200, 200-500, and 500-1,000 nm, respectively, compared with those on the control. Alkaline phosphatase activity demonstrated no differences after 12 days of osteogenic differentiation, and reverse transcription-polymerase chain reaction (RT-PCR) analysis showed comparable osteogenic gene expression of osteocalcin, osteonectin, and ostepontin between cells differentiated on polystyrene and nanofiber surfaces. Moreover, single-cell RT-PCR of type I collagen gene expression demonstrated higher expression on cells seeded on the nanofibers. Therefore, type I collagen nanofibers support the growth of MSCs without compromising their osteogenic differentiation capability and can be used as a scaffold for bone tissue engineering to facilitate intramembranous bone formation. Further efforts are necessary to enhance their biomimetic properties.

Alkaline Phosphatase↗