Comparative Analysis of the Effect of Needle‐Based Spinneret/Collector Combinations on Morphological Properties of PVA Electrospun Mats

Modeling effects of fiber rigidity on thickness and porosity of virtual electrospun mats

A physicochemical parameter, represented by the symbol Σs*, based on molar solubility in water and molar attraction constants of Small, has been developed to express quantitatively the relative hydrophobicity, or nonpolar character, of the hydrocarbon molecule. The value of Σs* can be calculated for a hydrocarbon from its chemical structure. The scale of Σs* is consistent within each group of aromatic, cyclic, and noncyclic hydrocarbons. Reverse osmosis data have been obtained at 250 psig for single‐solute aqueous feed solution systems involving low concentrations of 39 different hydrocarbons (including 13 aromatics, 10 cyclic, and 16 noncyclic compounds) and several samples of cellulose acetate membranes of different surface porosities. The effect of operating pressure on membrane performance has also been studied for two aromatic hydrocarbon solutes. The values of Σs* for the solutes used were in the range of 425 to 924 for aromatic hydrocarbons, 521 to 931 for cyclic hydrocarbons, and 369 to 960 for noncyclic hydrocarbons. The reverse osmosis data have been correlated with Σs* for each group of hydrocarbons studied. In all cases, positive solute separations were obtained, and the ratio [PR]/[PWP] was less than 1. With respect to each film, solute separation increased with increase in Σs*, and decreased with increase in operating pressure. Also, solute separation decreased in the order aromatic hydrocarbon > cyclic hydrocarbon > noncyclic hydrocarbon at any given value of Σs*. At a given operating pressure, for low values of Σs* (∼500 or less) solute separation increased with progressive decrease in average pore size on the membrane surface. For high values of Σs* (∼800 or more), solute separation initially increased with decrease in average pore size, then passed through a maximum and minimum with further decrease in average pore size, and again increased with still further decrease in average pore size. The results are discussed on the basis of preferential sorption of solute at the membrane–solution interface under the experimental conditions studied.

Electrospun mats from nano/micro-fibers with control porosity and pore shape may be ideal candidate for tissue engineering scaffolds. In this study three type of poly(vinyl alcohol) (PVA) mats of 48-65 µm thickness with different nano/micro-fibers diameters mostly of 100-200 nm were deposited by electrospinning process. Controlled density porosity in the electrospun mats was introduced by Yb:KGW femtosecond laser micromachining system. The influence of electrospun mat micro structure, the distance between the adjacent laser ablation points, the number of femtosecond laser pulses on quality and structure of laser irradiated holes were investigated. It was demonstrated that the quality of irradiated holes depend on structure of electrospun mats (diameter of nano/micro-fibers, thickness of mats) and femtosecond laser processing parameters. Varying the distance between points and number of applied femtosecond laser pulses it is possible to fabricate electrospun mats with pores of 22-36 μm diameter.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.10249

Electrospinning is a versatile technique to produce micron or nano sized fibers using synthetic or bio polymers. The unique structural characteristic of the electrospun mats (ESM) which mimics extracellular matrix (ECM) found influential in regenerative tissue engineering application. ESM with different morphologies or ESM functionalizing with specific growth factors creates a favorable microenvironment for the stem cell attachment, proliferation and differentiation. Fiber size, alignment and mechanical properties affect also the cell adhesion and gene expression. Hence, the effect of ESM physical properties on stem cell differentiation for neural, bone, cartilage, ocular and heart tissue regeneration will be reviewed and summarized. Electrospun fibers having high surface area to volume ratio present several advantages for drug/biomolecule delivery. Indeed, controlling the release of drugs/biomolecules is essential for sustained delivery application. Various possibilities to control the release of hydrophilic or hydrophobic drug from the ESM and different electrospinning methods such as emulsion electrospinning and coaxial electrospinning for drug/biomolecule loading are summarized in this review.

Nano/micro electro-spun polyethylene terephthalate fibrous mat preparation and characterization

The development of functionalized polymers that can elicit specific biological responses is of great interest in the biomedical community, as well as the development of methods to fabricate these biologically functionalized polymers. For example, the generation of fibrous matrices with biological properties and fiber diameters commensurate with those of the natural extracellular matrix (ECM) may permit the development of novel materials for use in wound healing or tissue engineering. The goal of this work is, therefore, to create a biologically active functionalized electrospun matrix to permit immobilization and long-term delivery of growth factors. In this work, poly(ethylene glycol) functionalized with low molecular weight heparin (PEG-LMWH) was fabricated into fibers for possible use in drug delivery, tissue engineering, or wound repair applications. Electrospinning was chosen to process the LMWH into fiber form due to the small fiber diameters and high degree of porosity that can be obtained relatively quickly and using small amounts of starting material. Both free LMWH and PEG-LMWH were investigated for their ability to be incorporated into electrospun fibers. Each of the samples were mixed with a carrier polymer consisting of either a 10 wt % poly(ethylene oxide) (PEO) or 45 wt % poly(lactide-co-glycolide) (PLGA). Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray analysis (EDX), UV-vis spectroscopy, and multiphoton microscopy were used to characterize the electrospun matrices. The incorporation of heparin into the electrospun PEO and PLGA fibers did not affect the surface morphology or fiber diameters. The fibers produced had diameters ranging from approximately 100 to 400 nm. Toluidine blue assays of heparin suggest that it can be incorporated into an electrospun matrix at concentrations ranging from 3.5 to 85 mug per milligram of electrospun fibers. Multiphoton microscopy confirmed that incorporation of PEG-LMWH into the matrix permits retention of the heparin for at least 14 days. Improvements in the binding of basic fibroblast growth factor to the electrospun fibers were also observed for fibers functionalized with PEG-LMWH over those functionalized with LMWH alone. The combination of these results suggests the utility for producing electrospun fibers that are appropriately functionalized for use in biomaterials applications.

It has been well-known that process, solution and environmental parameters have significant effects on characteristics of electrospun mats. Electrospinning is a promising technique for manufacturing of functional, lightweight and novel surfaces due to producibility of fibrous mats from polymer solutions loaded with various additives. In this study, Bi2O3 was incorporated into binary polymer solutions prepared with polymers having high and moderate shielding efficiency (PS and PVC, respectively) and their appropriate solvents. The characterization of electrospun mats showed that electrospinnability of prepared solution was possible with wet electrospinning at identical process, solution and environmental conditions. It was noticed that the average fiber diameter was 979.18 nm, thicker nanofibrous mats were fabricated and a few bead formation was observed in wet electrospun mats. But bead-dominant structure was obtained in dry electrospun mats despite of finer average fiber diameter (271.22 nm). Similar crystalline structure and no distinct bond occurence was observed in wet and dry electrospun nanocomposite mats. The average mat thickness of wet electrospun mats was approximately 65 times higher than dry electrospun mat. In wet electrospinning, use of liquid in collector promoted surface unevenness, decreased beading formation, facilitated fiber-to-fiber interaction and influenced pore distribution positively due to high surface tension of distilled water.

New comparative tests on different types of solar collectors are presented in this paper. Tests have been performed at the solar energy conversion laboratory of the University of Padova. Two standard glazed flat plate collectors and one evacuated tube collector are installed in parallel; the evacuated collector is a direct flow through type with external CPC (compound parabolic concentrator) reflectors. The present test rig allows to make measurements on the flat plate, on the evacuated collector or on both simultaneously, by simply acting on the valves to modify the circuit. In this paper measurements of the performance of the evacuated tube collector and flat plate collectors working at the same conditions are reported. Efficiency in stationary conditions is measured following the standard EN 12975-2 [1] and it is compared with the input/output curves measured for an entire day. The main purpose of the present work is to characterize and to compare the daily energy performance of the two types of collectors. An effective mean for describing and analyzing the daily performance is the so called input/output diagram, in which the collected solar energy is plotted against the daily incident solar radiation. Test runs have been performed in several conditions to reproduce different conventional uses (hot water, space heating, solar cooling).

Wetting of electrospun mats plays a huge role in tissue engineering and filtration applications. However, it is challenging to trace the interrelation between the wetting of individual nano-sized fibers and the macroscopic electrospun mat. Here we measured the wetting of different nylon-11 samples – solution-cast films, electrospun fibers deposited onto a substrate, and free-standing mats. With electrospun nylon-11 on aluminium foil, we traced the dependence of the wetting contact angle on the fibers' surface density (substrate coverage). When the coverage was low, the contact angle increased almost linearly with it. At ∼17–20% coverage, the contact angle achieved its maximum of 124 ± 7°, which matched the contact angle of a non-woven electrospun mat, 126 ± 2°. Our results highlight the importance of the outermost layer of fibers for the wetting of electrospun mats.

Electrostatic dust purifiers are widely used in many industries such as thermal power plants, cement plants, waste incineration and glass production. Optimization of the electrode and collector is important for higher efficiency (to achieve high efficiency) in electrostatic dust filtration. This study examines the electrostatic properties of four types of collector plates: flat, curved, spike, and spike with groove. The electric field strength, the charge density, the velocity of movement, and the collection efficiency are analysed for each type of collector. The inflow of air is perpendicular to the collector plate instead of parallel in traditional models, which improves the efficiency. The velocity of dust towards the collector plate depends on the electrostatic force and the velocity field around the collector. The Deutsch model is used to determine the performance among receiver plate types. The results show that the spike plate achieves the best collection efficiency because of the optimal static electric field and velocity field around it.

This research focuses on the design of biocompatible materials/scaffold suitable for use for tissue engineering. Porous fiber mats were produced through electrospinning of polythiophene phenylene (PThP) conducting polymers blended with poly(lactide- co-glycolic acid) (PLGA). A peptide containing an arginylglycylaspartic acid (RGD) fragment was synthesized using solid phase peptide synthesis and subsequently grafted onto a PThP polymer using azide-alkyne "click" chemistry. The obtained RGD functionalized PThP was also electrospun into a fiber mat. The electrospun mats' morphology, roughness and stiffness were studied by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM) and their electroactivity by cyclic voltammetry. The fibers show excellent cytocompatibility in culture assays with human dermal fibroblasts-adult (HDFa) and human epidermal melanocytes-adult (HEMa) cells. The electrospun fibers' roughness and stiffness changed after exposing the fiber mats to the cell culture medium (measured in dry state), but these changes did not affect the cell proliferation. The cytocompatibility of our porous scaffolds was established for their applicability as cell culture scaffolds by means of investigating mitochondrial activity of HDFa and HEMa cells on the scaffolds. The results revealed that the RGD moieties containing PThP scaffolds hold a promise in biomedical applications, including skin tissue engineering.

Thickness is an important characteristic parameter of electrospun submicron of fiber mats and membranes. The thickness of the mats directly influences performance properties such as permeability and is necessary when determining volumetric parameters such as porosity. Typical electrospun mats are very thin (less than 1 mm) and highly compressive due to the small diameter fibers, both of which make accurate measurements difficult when using conventional methods. An accurate measure of the thickness is desired for characterizing and comparing membrane performances. In this work, a thickness measurement instrument using laser interferometry has been designed to measure electrospun fiber mat thickness. A small disk is used to apply a small (reproducible) force applied across a reasonably small area of the fiber mat. A traversing pin moves to contact the disk and completes an electrical circuit to stop movement and determine the location of the disk relative to a reference plane. The fiber mat thickness is determined by measuring the difference in locations of the disk with and without the fiber mat between the disk and the reference plane. The prototype is simple to operate and user-friendly. Precision and accuracy of the prototype are discussed.

Silk microfibrous mats with long-lasting antimicrobial function

Functionalized electrospun mats from styrene–maleic anhydride copolymers for immobilization of acetylcholinesterase

High-temperature dynamic failure behavior and compressive mechanical properties of alumina porous ceramic with various pore sizes