Non-porous Fibers Research Articles

Evaluation of the Highly Ordered Structure, Ligature, and Enzymatic Degradation of Poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] Elastic Porous Fibers.

We prepared biocompatible elastic fibers with high porosity and high tensile strength from poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate], which is a microbial polyester that can be produced from renewable carbon resources by isothermal crystallization. It was possible to control the pore size by adjusting the isothermal crystallization time. Most of the pores were approximately less than 10 μm in diameter, did not penetrate, and were distributed discontinuously throughout the fibers. The elasticity of the fibers was apparently attributable to the generation of tie molecules with planar zigzag conformations between lamellar crystals and to the deformation of the pores. The ligature area occupied by the porous fibers in surgical knots was reduced by 75% compared with that of nonporous fibers. This is expected to make the ligature more difficult to untie and reduce the feeling of foreign matter. X-ray tomography revealed that the porous fibers had a relatively small fiber diameter owing to the collapse of the porous area. The rate of enzymatic degradation of the porous fibers was more than four times that of nonporous fibers. These results suggest that this elastic porous fiber will have many applications, including in the medical and marine material fields.

Creation and Study of a Model Cobalt Catalyst for High-Performance Fischer–Tropsch Synthesis Using Nonporous Carbon Fiber as a Support

Creation and Study of a Model Cobalt Catalyst for High-Performance Fischer–Tropsch Synthesis Using Nonporous Carbon Fiber as a Support

Highly Porous Curcumin-Loaded Polymer Mats for Rapid Detection of Volatile Amines

Here, the development of highly porous colorimetric indicators that are able to rapidly sense the presence of amine vapors is presented. Specifically, porous, curcumin-loaded polycaprolactone fibers are formed by electrospinning through non-solvent-induced phase separation. In comparison to the non-porous fibers, the developed system shows significantly higher sensitivity and responsivity to the presence of dimethylamine vapors, with a distinct color change at very low vapor concentrations (2.33 ppm compared to 9.26 ppm) within the first 5 s of exposure. Indeed, CIELAB analysis proves that the induced color changes can be easily perceived visually, as the differences between the initial and the final color of the indicator after its interaction with the modified environment are well above the limit for visual perception, even by inexperienced users. Furthermore, the color changes are reversible, enabling the use of the same indicator several times, making it, thus, a sustainable colorimetric indicator system that can be used in applications where the rapid detection of low concentration of alkaline vapors is necessary.

Comparative analysis of sound and thermal insulation properties of porous and non-porous polystyrene submicron fiber membranes

Interior and surface porous materials have widespread use in a wide variety of applications, especially for thermal and sound insulation due to their porous structure. Both sound and thermal insulation have great importance in a wide range of technical textile application areas including clothing and transportation such as train, car, aerospace and so on. In this study, for the first time, porous and non-porous polystyrene submicron fibers membranes have been compared for both sound absorption insulation and thermal insulation properties at the same time. Porous polystyrene electrospun fibers were produced at two different ratios of DMF:THF (4:1 and 7:3 ratio of DMF:THF) under conrolled humidity environment (60% RH). The results show that higher sound absorption insulation (SAC values) were obtained for non-porous fiber membrane (PS-ref) produced under ambient condition (30% RH) than porous fiber membrane (PS/7:3/RH and PS/4:1/RH) produced under controlled humidity condition (60% RH) by use of DMF:THF in 7:3 ratio and 4:1 ratio. Similar tendency was observed for thermal conductivity coefficient. Thus, all these results show that thinner fiber leading higher surface area has more dominant effect on both thermal insulation and sound absorption insulation than the formation of porous structures on the surface or internal structure of the fiber.

Permeable Weldable Elastic Fiber Conductors for Wearable Electronics.

Elastic fiber conductors are advantageous for applications in wearable electronics due to their small size, light weight, and excellent integration ability. Here, we report the fabrication of elastic fiber conductors with a three-dimensional (3D) porous structure using electrospun thermoplastic elastomer (TPE) microfibers and silver nanoparticles (AgNPs) as the building blocks. With the 3D porous structure, such a fiber is highly permeable to gases and liquids. As such, the performance of the fiber in many applications of wearable electronics (especially wearable sensors and detectors) can be improved significantly. Benefitting from the excellent processability of TPE and dispersibility of AgNPs, the fiber is highly compatible with thermal and solvent welding. In addition, the fiber also possesses super stretchability, high conductivity, and robust endurance to deformation. As a proof-of-concept application, we demonstrate that a rope-shaped capacitor made by plying one pair of such fibers can detect the volume change of artificial sweat with 17-times higher sensitivity than the capacitor using nonporous fibers as electrodes. We further demonstrate that, by integrating two groups of perpendicularly arranged fibers into a monolithic porous mat, sensitive matrix-addressed monitoring of artificial sweat can be realized.

Fabricating porous poly(lactic acid) fibres via electrospinning

In this paper, amorphous poly(lactic acid) (PLA), a biodegradable polymer with excellent bio-compatibility, is successfully electrospun into micron-sized fibres with controlled surface and internal morphologies. By careful solvent selection, either surface porosity or internal porosity can be achieved through different mechanisms. Use of chloroform as the solvent gives rise to circular pores of 100 nm diameter confined to the surface. These are obtained in humid conditions by the so-called ‘Breath Figure’ mechanism. It is found that combining chloroform with a water-miscible non-solvent yields either surface porosity (wrinkled effect) using a low boiling point liquid, e.g. ethanol, or internal porosity using a high boiling point liquid, e.g. dimethyl sulphoxide (DMSO). Both these microstructures are obtained through a non-solvent induced phase separation (NIPS) mechanism. Finally, it is found possible to produce both surface and internal porosity using DMSO by a vapour induced phase separation (VIPS) mechanism. The porous electrospun PLA mats were shown to exhibit significantly increased oil absorption capacity compared with the non-porous fibre mats.

Electrospun Iron-Based Fibers for Use in MEMS Sensors

This letter reports on the characterization of iron containing nanofibers using a polyvinyl alcohol (PVA)-based solution in a batch electrospinning processing method. Variation of iron content within the pre-fiber solution, and characterization of fiber size and porosity are important for the use of these nanomaterials in sensing. Simulated non-porous fibers are compared with nanofibers obtained utilizing this method. Pre-calcination (thermal) fibers had diameters of 243 nm on average with a standard deviation of ±43 nm and a standard error of ±4.53 nm. Fabrication of mesoporous iron-based nanofibers was achieved after the calcination of the iron/PVA fibers. With the calcination process, we produced fibers with 32-nm diameters, and a standard deviation of ±12 nm and a standard error of ±1.41 nm. The error between model and experimental results is 37.5% for producing Fe3O4 fibers. This error percentage and oversized dimensions suggest near total conversion to Fe3O4 occurring due to calcination as well as creating mesoporous fibers. [2017-0014]

Porous composite membranes based on cellulose acetate and cellulose nanocrystals via electrospinning and electrospraying

Porous and non-porous cellulose acetate (CA) – cellulose nanocrystal (CNC) electrospun nanocomposite fibers and electrosprayed-electrospun composite membranes were fabricated using two different binary solvent systems. To evaluate the expression of CNC as the active entity in the membrane, dye adsorption studies were carried out using Victoria Blue. To overcome the low surface area of thick porous fibers, a porous electrosprayed-electrospun composite has developed which exhibited 98% dye removal compared to non-porous counterparts (67.9%). The porous membrane with CNC showed an increase of 38mV in surface zeta potential compared to 9mV increases in the case of the nonporous membrane and after the dye adsorption, it maintained the negative charge, indicating that further adsorption is feasible. Moreover, the mechanical properties of porous fibers were found to be ten-fold better than that of nonporous fibers. Creating porous CA-CNC composites is demonstrated as a tool for ensuring better exposure of active materials during the adsorption reaction.

Sol–gel synthesis of porous titania fibers by electro-spinning for water purification

ABSTRACTIn this study, porous ceramic fibers were prepared by the sol–gel-assisted electro-spinning process using colloidal dispersion of complex fluids for the application of phtotocatalysts. First, polystyrene nanospheres were synthesized by dispersion polymerization as sacrificial templates for porous fibers. Then, the mixture of polyvinylpyrrolidone and the ceramic precursor with the polymeric nanospheres was prepared as the spinning solution and self-organized by electro-spinning, followed by calcination of the electrospun composite fibers. The morphologies of the porous fibers could be controlled according to the size of the templates and the amount of the ceramic precursor. The nano-structure of the pores in the fibrous materials could also be adjusted as open or closed cavities with various potential applications. As a demonstrative application, the macroporous titania fibers could be utilized as photocatalysts for the removal of organic dyes dissolved in water. A better photocatalytic activity of the macroporous fibers with 700-nm pore diameter was observed compared to the result of nonporous titania fibers due to the increased porosity. Collectively, the macroporous ceramic fibers were found to be efficient functional materials to prepare the unique nano-structured materials other than simple nonporous fibers.

Assessing the Increase in Specific Surface Area for Electrospun Fibrous Network due to Pore Induction.

The effect of pore induction on increasing electrospun fibrous network specific surface area was investigated in this study. Theoretical models based on the available surface area of the fibrous network and exclusion of the surface area lost due to fiber-to-fiber contacts were developed. The models for calculation of the excluded area are based on Hertzian, Derjaguin-Muller-Toporov (DMT), and Johnson-Kendall-Roberts (JKR) contact models. Overall, the theoretical models correlated the network specific surface area to the material properties including density, surface tension, Young's modulus, Poisson's ratio, as well as network physical properties, such as density and geometrical characteristics including fiber radius, fiber aspect ratio and network thickness. Pore induction proved to increase the network specific surface area up to 52%, compared to the maximum surface area that could be achieved by nonporous fiber network with the same physical properties and geometrical characteristics. The model based on Johnson-Kendall-Roberts contact model describes accurately the fiber-to-fiber contact area under the experimental conditions used for pore generation. The experimental results and the theoretical model based on Johnson-Kendall-Roberts contact model show that the increase in network surface area due to pore induction can reach to up to 58%.

Preparation of a cellulose acetate/organic montmorillonite composite porous ultrafine fiber membrane for enzyme immobilization

ABSTRACTFour types of fibrous membranes based on cellulose acetate (CA)—CA membranes with nonporous fibers, CA/organic montmorillonite (O‐MMT) membranes with nonporous fibers, CA membranes with porous fibers, and CA/O‐MMT membranes with porous fibers—were prepared by electrospinning, and then, they were used for enzyme immobilization. The surface morphologies of the composite fibrous membranes were investigated with scanning electron microscopy and transmission electron microscopy. The optimum pH was 3.5 for all of the immobilized enzymes, and the optimum temperature was 50 °C. Compared with the free enzyme, the immobilized enzyme showed better stability for pH and temperature changes. Moreover, the addition of O‐MMT and the pores on the fibers improved the storage stability and the operational stability. Among the four kinds of fibrous membranes, the CA/O‐MMT membranes with porous fibers showed the best stability for the immobilized enzymes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43818.

Electrospun preparation of polylactic acid nanoporous fiber membranes via thermal-nonsolvent induced phase separation

A novel polylactic acid (PLLA) fiber membrane with nanoporous structures has been successfully developed via thermal-nonsolvent induced a phase separation technique by electrospinning a single solvent system of PLLA/dichloromethane. A water bath receiver was necessary for preparing the nanoporous fiber membranes in this paper. The results showed that the nanoporous fiber membranes could be obtained within a wide range of humidity. Compared with non-porous PLLA fiber membranes, the nanoporous fiber membranes displayed significantly improved specific surface area (improved about 20%) and rejection ratio (about 3 times) toward methylene blue. Besides, the PLLA nanoporous fiber membranes showed a water flux up to 4836.6 L m−2 h−1, increased by 25% than that of the non-porous fiber membranes. In addition, the oil adsorption capacity of the PLLA nanoporous fiber membranes could reach 26.8 g g−1. The new developed PLLA nanoporous fiber membranes via thermal-nonsolvent induced phase separation technique would demonstrate an impressive prospect for oil adsorption and organic dye filtration.

Fabrication of aligned, porous and conductive fibers and their effects on cell adhesion and guidance

The potential applications of aligned, conductive electrospun fibers have been widely studied in anisotropic tissue regeneration. In this study, aligned porous poly L-lactic acid fibers were obtained with electrospinning, then polypyrrole nanoparticles (PPy NPs) were coated onto the porous fibers with oxidation polymerization to prepare electrically conductive fibers with about 1.24μm of diameter, and their surface conductivity was about 50mS. The results of L929 cell test showed that more than 55% of cells grew along the aligned porous fiber axis, confirming that the cell guidance of aligned porous fibers was better than that of non-porous fibers. The results of differentiated PC12 cells on porous fibers showed that the alignment degree of neurite outgrowth and average neurite length of the cells were 84% and 111μm, respectively, which were larger than those on the non-porous fibers. A primary mechanism was proposed to explain effect of these pores on cell/neurite adhesion and orientation along the aligned porous fibers.

Facile one-pot formation of ceramic fibres from preceramic polymers by pressurised gyration

This paper reports for the very first time a facile and simple method, consisting of simultaneous centrifugal spinning and solution blowing, to mass produce ceramic fibres from preceramic polymers. Solutions of two different commercially available silicone resins and a mixture of a silicone resin and graphene were used, and a polymer (polyvynilpyrolidone) was added to aid the fibre generation process. The fibre diameter and the morphology of the spun and the pyrolysed fibres were shown to be influenced by rotating speed, working pressure and the polymer concentration. Non-porous fibres were obtained using a low volatility binary solvent system and, after pyrolysis at high temperature, dense SiOC ceramic fibre bundles were produced. This fabrication method based on pressurised gyration shows great promise in the mass production of ceramic fibre bundles.

Novel bioresorbable stent coating for drug release in congenital heart disease applications.

A novel double opposed helical poly-l-lactic acid (PLLA) bioresorbable stent has been designed for use in pediatrics. The aim was to test the PLLA stent biocompatibility. The PLLA stent was immersed into whole pig's blood in a closed loop circuit then fibrin and platelet association was assessed via enzyme-linked immunosorbent assay. D-Dimer was valued at 0.2 ± 0.002 ng/mL and P-selectin 0.43 ± 00.01 ng/mL indicating limited association of fibrin and platelets on the stent. To improve biocompatibility by targeting inflammatory cells, dexamethasone was incorporated on PLLA fibers with two coating methods. Both coatings were poly(l-lactide-co-glycolide) acid (PLGA) but one was made porous with sucrose while the other remained nonporous. There was no change in mechanical properties of the fiber with either coating of PLGA polymer. The total amount of dexamethasone released was then determined for each coating. The cumulative drug release for the porous fiber was significantly higher (∼100%) over 8 weeks than the nonporous fiber (40%). Surface examination of the fiber with scanning electron microscopy showed more surface microfracturing in coatings that contain pores. The biocompatibility of this novel stent was demonstrated. Mechanical properties of the fiber were not altered by coating with PLGA polymer. Anti-inflammatory drug release was optimized using a porous PLGA polymer.

Study of capillary rise in biodegradable porous poly (l-lactic acid) electrospun nano/micro fiber yarns

Specific surface and surface porosity are governing factors in the penetration rate and the amount of liquid rise into the yarn. In this work, porous and non-porous fiber yarns of poly (l-lactic acid) (PLLA) were fabricated via electrospinning and twist insertion. The surface of PLLA electrospun fibers became porous after evaporation of highly volatile solvent in controlled humidity and temperature and changing the concentration of PLLA solution, resulted in the fibers with different surface porosity. Smooth PLLA nanofibers were obtained using non-volatile solvent. Consequently, capillary rise was investigated in both the porous fiber yarns and smooth nanofiber yarn. Experimental evidences revealed that two morphological characteristics of fibers, i.e. surface porosity and fineness of fibers in the electrospun yarn have a governing effect on the capillary rise phenomenon. Liquid penetration in electrospun yarn was increased by increasing the fiber fineness and/or decreasing the surface porosity. The results of this work suggest that finer fiber and smooth surface would be more beneficial for wicking.

Cellulose nanocrystals and self-assembled nanostructures from cotton, rice straw and grape skin: a source perspective

Cellulose nanocrystals (CNCs) have been derived by sulfuric acid hydrolysis (64–65 wt% H2SO4, 10 mL/g cellulose, 45 °C) of pure cellulose isolated from cotton, rice straw and grape skin, producing relatively consistent products in 60, 45 and 30 min, respectively, and generally reflecting the extent of crystallinity and crystallite sizes of these cellulose sources. CNCs in nanorod forms are observed from all three cellulose sources and, in the case of cotton and grape skin, in the presence of more dominant forms of nanoparticles. Cotton CNCs are <10-nm-wide nanorods at up to 40 aspect ratios, whereas rice straw CNCs are flat ribbon cross-sectional shaped in 10:2:1–44:5:1 length/width/thickness ratios, and those from grape skin are abundant nanoparticles but fewer nanorods, all of very different nanoscale dimensions. Freezing (−196 °C) and freeze-drying (−50 °C) of dilute CNC suspensions induce self-assembling of these CNC populations into yet further distinctly different morphologies. Self-assembled cotton CNCs are loosely organized nanorods and nanospheres, whereas grape skin CNCs are mainly nanospheres of 5-nm-sized nanoparticles clusters around nanorod cores. Uniquely, rice straw CNCs assembled anisotropically into ultra-thin non-porous fibers. These source-linked unique CNC geometries and the ability of CNCs to self-assemble into different morphologies present wide ranging dimensions of these renewable cellulose nanomaterial building blocks from by-products of the world largest fiber, cereal and fruit crops.

Porous core/sheath composite nanofibers fabricated by coaxial electrospinning as a potential mat for drug release system

This study focused on fabrication and characterization of porous core/sheath structured composite nanofibers with a core of blended salicylic acid (SA) and poly(ethylene glycol) (PEG) and a sheath of poly(lactic acid) (PLA) using a dual-capillary electrospinning system. Results of water contact angle measurements, field-emission scanning electron microscopy, and transmission electron microscopy indicated that feed rates of the core and sheath strongly affect the stability of the core/sheath structure and porous density of the composite nanofibers obtained, significantly influencing their SA release characteristics. At a lower ratio of feed rates of the core and the sheath, better stable core/sheath structures of nanofibers with higher porous density on the surface were formed resulting in a sustained release of SA over 5 days. Non-porous fibers showed a lower amount of drug release because the drug was embedded inside the core layer of the non-porous sheath layer. SA release from porous core/sheath nanofibers was described based on a one-dimensional Fickian diffusion mechanism, indicating that drug diffusion is a predominant factor in drug release. A cytotoxicity test suggested that the porous core/sheath nanofibers are non-toxic and support cell attachment. Therefore, this fiber mat may find application in the design of wound-healing patches with long-term activity.

Fabrication of superhydrophobic fiber coatings by DC‐biased AC‐electrospinning

AbstractMesh‐like fiber mats of polystyrene (PS) were deposited using DC‐biased AC‐electrospinning. Superhydrophobic surfaces with water contact angles greater than 150° and gas fraction values of up to 97% were obtained. Rheological study was conducted on these fiber surfaces and showed a decrease in shear stress when compared with a noncoated surface (no slip), making them excellent candidates for applications requiring the reduction of skin‐friction drag in submerged surfaces. We have also shown that addition of a second, low‐surface energy polymer to a solution of PS can be used to control the fiber internal porosity depending on the concentration of the second polymer. Contact‐angle measurements on mats consisting of porous and nonporous fibers have been used to evaluate the role of the larger spaces between the fibers and the pores on individual fibers on superhydrophobicity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Spectral characterization of porous dielectric subwavelength THz fibers fabricated using a microstructured molding technique

We report two novel fabrication techniques, as well as THz spectral transmission and propagation loss measurements of subwavelength plastic wires with highly porous (up to 86%) and non-porous transverse geometries. The two fabrication techniques we describe are based on the microstructured molding approach. In one technique the mold is made completely from silica by stacking and fusing silica capillaries to the bottom of a silica ampoule. The melted material is then poured into the silica mold to cast the microstructured preform. Another approach uses a microstructured mold made of a sacrificial plastic which is co-drawn with a cast preform. Material from the sacrificial mold is then dissolved after fi ber drawing. We also describe a novel THz-TDS setup with an easily adjustable optical path length, designed to perform cutback measurements using THz fibers of up to 50 cm in length. We fi nd that while both porous and non-porous subwavelength fibers of the same outside diameter have low propagation losses (alpha <or= 0.02 cm(-1)), the porous fi bers exhibit a much wider spectral transmission window and enable transmission at higher frequencies compared to the non-porous fibers. We then show that the typical bell-shaped transmission spectra of the subwavelengths fibers can be very well explained by the onset of material absorption loss at higher frequencies, due to strong confinement of the modal fields in the material region of the fi ber, as well as strong coupling loss at lower frequencies, due to mismatch between the modal field diameter and the size of the gaussian-like beam of a THz source.