Porous Nanofibrous Structure Research Articles

Aerogel microspheres based on cellulose nanofibrils as potential cell culture scaffolds

Crosslinked poly(vinyl alcohol) (PVA)/cellulose nanofibril (CNF) hybrid aerogel micro-spheres with two different particle sizes were fabricated via a combination of the water-in-oil (W/O) emulsification process and the freeze-drying process. The aerogel micro-spheres were highly porous with a bulk density as low as 0.0047 g/cm3 for the large microspheres. The pore size of the microspheres ranged from nano- to micro-meters. Preliminary biocompatibility assays of the aerogel microspheres were investigated with NIH 3T3 cells to explore their potential application as cell culture scaffolds. The highly crosslinked aerogel microspheres were robust and were able to maintain their shape during the cell culture process. The live/dead assay showed that the cells could be seeded, attached, and proliferated on the surface of PVA/CNF aerogel microspheres. The fluorescence images showed that some of the cells migrated into the inner pores of the microspheres. Moreover, the large microspheres with larger average pore sizes had a higher cell count than that of the small microspheres. This study confirms that the PVA/CNF aerogel microspheres fabricated in this work are nontoxic and biocompatible. Furthermore, the interconnected, highly porous nanofibrous structure of the microspheres can successfully facilitate cell attachment, differentiation, and proliferation.

Morphology and cell responses of three-dimensional porous silica nanofibrous scaffold prepared by sacrificial template method

Three-dimensional (3D) nanofibrous scaffolds morphologically mimicking natural extracellular matrix show great potential in the application of tissue repair. Herein, we report a novel 3D nanofibrous silica (SiO2) scaffold fabricated via a sacrificial template method. The sacrificed template used was 3D bacterial cellulose and the resultant silica nanofiber has a ultrasmall diameter of 21nm. SEM, TEM, and AFM evidence the 3D porous nanofibrous structure and pore structure measurement confirms the existence of macro- and meso-pores in the as-prepared silica scaffold. Cell studies using osteoblast cells demonstrate excellent biocompatibility and high ALP activity. These results suggest that the 3D silica nanofibrous scaffold is a promising candidate for hard tissue engineering.

Antioxidant activity and photostability of α-tocopherol/β-cyclodextrin inclusion complex encapsulated electrospun polycaprolactone nanofibers

Cyclodextrin inclusion complexes (CD-ICs) can be encapsulated into electrospun nanofibers in order to achieve delivery systems having high surface area and highly porous nanofibrous structures. In this study, a well-known antioxidant molecule, α-tocopherol (α-TC) (vitamin E) was chosen as an active agent for inclusion complexation with β-cyclodextrin. Polycaprolactone (PCL) nanofibers encapsulating α-tocopherol/β-cyclodextrin inclusion complex (α-TC/β-CD-IC) which has high antioxidant activity and photostability was produced via electrospinning (PCL/α-TC/β-CD-IC-NF). The formation of α-TC/β-CD-IC was confirmed by XRD. Phase solubility studies showed An-type complex formation between α-TC and β-CD. SEM revealed that bead-free nanofibers were successfully produced from PCL/α-TC/β-CD-IC system. PCL nanofibers encapsulating α-TC without CD-IC was also produced for comparison (PCL/α-TC-NF). Antioxidant test results showed that PCL/α-TC/β-CD-IC-NF had higher antioxidant activity as compared to PCL/α-TC-NF in methanol:water (1:1) system due to the stabilization and solubility increment of α-TC in the cavity of β-CD. PCL/α-TC/β-CD-IC-NF was more stable against UV-light when compared to PCL/α-TC-NF due to the presence of inclusion complexation. In brief, PCL/α-TC/β-CD-IC-NF with the advantages of having nanofibrous structure and encapsulating CD-ICs, may serve as a novel route for administration of α-TC due to its higher antioxidant activity and better UV-light stability.

Sensitive naked-eye detection of gaseous ammonia based on dye-impregnated nanoporous polyacrylonitrile mats

Herein, highly sensitive colorimetric detection of gaseous ammonia is reported based on bromocresol green–impregnated polyacrylonitrile (BCG–PAN) nanofibers. The sensing layer with a porous nanofibrous structure was prepared simply by drop-casting a BCG solution containing polyethylene glycol (PEG) and oxalic acid on an electrospun PAN mat. The nanofiber mat exhibited durable structural stability under various conditions of acid, base, acetone and hot water. A smooth nanoporous structure of the sensor provided better color uniformity with a brighter reflectance than the porous paper, thus providing an ideal medium for high-quality colorimetric detection. Upon exposure to 25ppm ammonia, the yellow BCG–PAN mat quickly changed and became saturated to blue within 1min. The sensor was confirmed to have a detection limit of less than 1ppm in the detection by the naked eyes, good selectivity to common volatile organic solvents and reversible color change behavior at ambient conditions. These results straightforwardly demonstrate that sensitive and reversible NH3 detection is possible simply by observing the sensor color without the help of any detecting instruments. The addition of water-soluble PEG into a BCG solution was found to enhance sensor response probably due to its strong hydrophilicity, while the oxalic acid prevented BCG dye from deprotonating by the ambient humidity. Based on the change in reflection spectrum and a great response to amine compounds, the colorimetric detection mechanism was proposed to be the transform of BCG acid form to the base counterpart through the acid-base reaction with basic analytes dissolved into the water-containing nanofiber matrix.

Synthesis of mesoporous NiCo2O4 fibers and their electrocatalytic activity on direct oxidation of ethanol in alkaline media

Well-dispersed mesoporous NiCo2O4 fibers as anode catalysts for the electrooxidation of ethanol were synthesized by an easy-controlled template-free method. Their structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption/desorption analysis. The electrochemical oxidation of ethanol on mesoporous NiCo2O4 fibers modified glassy carbon electrode (NiCo2O4/GCE) in alkaline solutions was systematically evaluated by cyclic voltammetry (CV), double-step chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The NiCo2O4 materials showed typical intertwined porous nanofibrous structures with specific surface area of 54.469m2g−1 and average pore size of 13.5nm. The NiCo2O4/GCE exhibited significantly high electrocatalytic activity with higher current density and lower onset potential compared to those of Co3O4 and NiO in CV measurement. The linear relationship between the ethanol concentration and the square root of scan rate indicated that diffusion of ethanol is a rate-determining step in its oxidation on mesoporous NiCO2O4 fibers. The electrochemical mechanism of ethanol oxidation on NiCo2O4/GCE was also proposed.

Electrospinning of gelatin nanofiber scaffolds with mild neutral cosolvents for use in tissue engineering

Electrospun gelatin nanofibers are effective tissue engineering scaffolds with high biocompatibility and cell adhesion activity. In gelatin electrospinning, fluorinated alcohols, which are irritants, and acidic organic solvents are used as solvents to prevent gelation. This study established a technique to embed protein reagents into the nanofibers using mild solvents. From 22 mixtures of 50% organic solvent–50% H2O, less denaturing neutral dipolar aprotic solvents (specifically N,N-dimethylacetamide, N,N-dimethylformamide and N-methyl-2-pyrrolidone), were screened to assess their suitability for use in electrospinning of gelatin nanofiber scaffolds by their ability to maintain gelatin in a sol state at room temperature. By selecting the solvents and their concentrations, gelatin nanofibers were electrospun with different structures from a thick, wide, porous nanofibrous structure to a thin, fine, nanofibrous mesh structure. Swiss 3T3 fibroblasts grew well on the gelatin nanofibers. In particular, some cells showed in vivo-like spindle morphologies on the thick porous nanofibers using N,N-dimethylacetamide. Additionally, as a model protein reagent, alkaline phosphatase was embedded in the gelatin nanofibers while maintaining high activity. Considering these results, the gelatin nanofibers in this study are expected to provide effective structural and chemical cues and will be useful for tissue engineering and regenerative medicine. Gelatin nanofibers were electrospun using mild N,N-dimethylacetamide, N,N-dimethylformamide and N-methyl-2-pyrrolidone. Various gelatin nanofibers were fabricated, ranging from a thick, wide, porous nanofibrous structure to a thin, fine, nanofibrous mesh structure, depending on the solvents and their concentrations. In particular, Swiss 3T3 fibroblasts exhibited in vivo-like spindle morphologies on the thick nanofibers. A model protein, alkaline phosphatase, embedded in the gelatin nanofibers maintained high activity.

Preparation and morphology of electroconductive PEDOT/PSS/ATO nanocomposite microsphere

Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)/antimony-doped tin oxide (PEDOT/PSS/ATO) nanocomposite microspheres with the size range from 10 to 50 µm have been prepared by a solution mixing and self-assembling method in the presence of ammonium persulfate. The transparent PEDOT/PSS/ATO nanocomposites were prepared by dispersing the aqueous ATO suspension in PEDOT/PSS ethanol solution. Two types of acicular-shaped ATO (ATO-A) with average diameter of 20 and 50 nm, and two types of spherical-shaped ATO (ATO-S) with average particle sizes of 20 and 50 nm were selected. To measure the electrical resistivity of prepared nanocomposites, the transparent suspensions were coated onto polyethylene terephthalate film a dry thickness of about 50 µm. The nanocomposites containing ATO-S with diameter of 50 nm exhibited lowest electrical resistivity than other nanocomposites. The effects of the ATO loading on the morphology, porosity, and thermal stability of the prepared microspheres were also investigated. From the scanning electron microscopy, the morphology of PEDOT/PSS/ATO-S suspensions develops a cauliflower structure with many recesses in it whereas PEDOT/PSS/ATO-A shows a porous nanofibrous structure composed of PEDOT/PSS aggregates and ATO-A fibrils. POLYM. COMPOS., 36:1352–1364, 2015. © 2014 Society of Plastics Engineers

Synthesis and Characterization of Conductive Core-Shell Polyacrylonitrile-Polypyrrole Nanofibers

Nonwoven polyacrylonitrile-polypyrrole (PAN-PPy) core-shell nanofiber mats were prepared through the growth of PPy layers on electrospun PAN nanofibers via a two-step vapor-phase polymerization, i.e., the wet-coating of ferric tosylate (FeTos) oxidants on PAN nanofibers followed by exposure to pyrrole monomers in the gas phase. Under the conditions ([FeTos] = 10 wt%, reaction time = 15 min, temperature = 15 degrees C), the PPy polymerization procedure led to both a uniform coating over the PAN surface with an average thickness of 18 nm and cross-linkages among the nanofibers without a noticeable change in the highly porous nanofibrous structures. The oxidant concentration and polymerization time were found to be key parameters for achieving a good nanostructured core-shell fiber mat. FT-IR, XPS, XRD and conductivity measurements confirmed the synthesis of Tos-doped PPy with some degree of crystallinity and a high conductivity.

Polymer-metal nanofibrous composite for thermal management of microsystems

In this letter, a composite structure based on a porous electrospun polyimide structure infiltrated with indium aimed at thermal interface material applications is presented. A porous nanofibrous structure was prepared by electrospinning of polyimide. An interfacial nanocomposite layer of silver nanoparticles partially or fully embedded in the polyimide matrix was synthesized on the fiber surfaces, followed by autocatalytic deposition of a uniform silver coating (using the interfacial layer as an anchored seed layer) serving as a reactive wetting layer for the infiltrating melt. The thermal performance of the composite was evaluated and the thermal conductivity was determined to be 27W/mK, accompanied by low contact resistance of the metallurgical bond (<1Kmm2/W). Consequently, the composite exhibits promising thermal properties as a thermal interface material, indicating the potential for use in thermal management of microsystems.

Study of water vapor permeability of shape memory polyurethane nanofibrous nonwovens

In this paper, water vapor permeability (WVP) properties of shape memory polyurethane (SMPU) nanofibrous nonwovens are investigated systematically. The results indicate that, in addition to the excellent shape memory effect, the SMPU nanofibrous nonwovens show excellent liquid transfer properties and water vapor transport properties. Moreover, the WVP of a SMPU nanofibrous nonwoven is sensitive to the change of relative humidity (RH) and temperature. For example, the WVP decreases with the increase of RH above a critical RH, e.g. 50%, and increases significantly with the increase of temperature below a turnover temperature, e.g. 50°C. The diameter of the nanofiber has little influence on the WVP while the turnover temperature is higher in SMPU nanofibrous nonwovens with larger diameters. Finally, SEM images at a higher temperature suggest that the porous nanofibrous nonwoven structure is the foundation of unique WVP properties, and the collapse of the nanofiber at the higher temperature results in the abrupt decrease in WVP.

Wicking properties of various polyamide nanofibrous structures with an optimized method

AbstractIn comparison with conventional structures, nanofibrous structures have unique characteristics, such as higher surface‐to‐volume ratios, smaller pores, and higher porosity. Their hydrophilic nature is a key characteristic for many applications. However, because of their high porosity, it is difficult to measure the hydrophilicity of nanofibrous structures with contact‐angle measurements. Therefore, characterization through wicking behavior is more appropriate. The International Organization for Standardization norm on wicking needs some refining to account for the specific nature of highly porous nanofibrous structures. A refined method was used on several structures that differed in the fiber diameter and the polyamide type. The structures with the thickest nanofibers had the highest wicking rates. At equilibrium, the wicking heights of structures of different polyamide types with the same average fiber diameter followed the trend expected from their intrinsic hydrophilicity. In the initial phase, the capillary forces established the wicking behavior. Later in the process, the wicking behavior was determined by the capillary forces and the hydrophilicity. In conclusion, the hydrophilicity of nanofibrous structures can be successfully determined by an optimized wicking procedure, and the fiber diameter is the dominant parameter for the resulting wicking height at equilibrium. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Single-step fabrication of microfluidic channels filled with nanofibrous membrane using femtosecond laser irradiation

In this paper, we demonstrate a new method of fabricating silicon microfluidic channels filled with a porous nanofibrous structure utilizing a femtosecond laser. The nanofibrous structure can act as a membrane used for microfiltration. This method allows us to generate both the microfluidic channel and the fibrous nanostructure in a single step under ambient conditions. Due to laser irradiation, a large number of nanoparticles ablate from the channel surface, and then aggregate and grow into porous nanofibrous structures and fill the channels. Energy dispersive x-ray spectroscopy (EDS) analysis was conducted to examine the oxygen concentration in the membrane structure. Our results demonstrated that by controlling the laser parameters including pulse repetition, pulse width and scanning speed, different microfluidic channels with a variety of porosity could be obtained.

Liquefied petroleum gas (LPG) sensing properties of nanocrystalline CdO thin films prepared by chemical route: Effect of molarities of precursor solution

We report synthesis of cadmium oxide (CdO) thin films by a simple, inexpensive chemical bath deposition (CBD) method and their application to a liquefied petroleum gas (LPG) sensor. The dependence of LPG sensing properties on the structural and surface morphological properties has been studied. The structural and surface morphological properties of the films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The CdO films were highly oriented along (1 1 1) and (2 0 0) with the cubic crystal structure. The SEM observation reveals that porous nano-fibrous structure of CdO is grown, but the thickness increases as the molarity of the Cd2+ precursor increases and the film becomes nearly flat. The mechanism of LPG sensing by the CdO thin film is explained on the basis of adsorbed oxygen on the sensor surface. The maximum response of 23.28% to 0.2 vol.% of LPG was observed at 698 K with the CdO film deposited using a 0.15 M Cd2+ precursor solution.