Orientation Of Nanofibers Research Articles

Oriented electrospun nanofibers on stand-alone multi-segmented cylindrical collectors

Single-segment collectors, commonly used in electrospinning, distribute nanofibers randomly over their entire length. To improve the orientation of resultant nanofibers, a multi-segmented collector has been developed having alternate conducting and nonconducting segments. The alignment principle is based upon the attraction of nanofibers towards conductive segments, while the nonconductive segments, having least attraction for nanofibers, do not pull the fibers toward themselves. This causes the nanofibers to stretch over the nonconductive segments, thanks to attractive forces from the adjacent conductive segments. The best orientation was obtained on the cylindrical collector with 12.5 mm nonconductive segment length, 20 mm conductive segment length and 11% polymer concentration. Different polymeric materials can be electrospun on these types of multi-segmented collectors with high fiber orientation for various applications.

Analysis and prediction of the diameter and orientation of AC electrospun nanofibers by response surface methodology

In this study, we analyzed the influence of process parameters on the diameter and orientation of nanofibers electrospun with alternating current (AC), using surface response methodology. The design of experiment was adopted with four main process parameters: solution concentration, collection distance, voltage and collection speed. The morphology of nanofibers was examined with a scanning electron microscope. Nanofiber orientation was characterized by the fast Fourier transform method. We used the Box-Behnken design model to predict the diameter and orientation of the nanofibers, and the results showed good agreement with the measured results. The results also indicated that solution concentration and collection speed have a similar influence on fiber diameter and orientation, as in the case of direct current electrospinning. Furthermore, in this study, we optimized the process parameters to generate thinner nanofibers with better alignment, and it also can be used as a reference to make nanofiber yarns with AC electrospinning.

Flexible energy harvester based on aligned PZT/SMPU nanofibers and shape memory effect for curved sensors

The popularity of flexible energy harvesters has grown rapidly in recent decades because of their high flexibility for application in wearable and implantable devices. Flexibility and functionality are key issues for their use in wider engineering applications. In this study, we present a multifunctional flexible energy harvester based on aligned lead zirconate titanate (PZT)/shape memory polyurethane (SMPU) nanofibers and applying its shape memory properties for use with surfaces with curved and/or complex structures. Mechanical and thermomechanical analyses and energy harvesting tests were performed on random and aligned nanofibers to investigate the influence of nanofiber orientation and its shape memory properties. Our results showed that, compared with random nanofibers, 0° aligned PZT/SMPU nanofibers (the nanofibers’ direction is parallel to the tensile direction) demonstrated higher mechanical, shape memory and energy harvesting properties. In particular, the energy harvesting properties (output voltages) were increased by 5.4 times. In addition, taking advantage of the shape memory effect, the PZT/SMPU energy harvester can be deformed into various curved shapes to match complex structures while maintaining its original piezoelectric characteristics, which resulted in enhanced energy harvesting from curved surfaces. The developed energy harvester realized better piezoelectricity as a result of its nanofiber arrangement, and offers a flexible ability to match various surfaces with complex structures to achieve more effective energy harvesting.

Biocompatible polymeric electrospun matrices: Micro–nanotopography effect on cell behavior

AbstractThis work reports a preliminary biological study performed on nanofibrous biocompatible polylactidecopolycaprolactone (PLA‐PCL) scaffolds intended for tissue regeneration. The aim was to evaluate how matrix surface topography affects cell adhesion and proliferation. Scaffolds prepared by electrospinning either equipped with plane or rotating mandrel collectors, were characterized for their surface topography and nanofiber size. Cell culture studies were carried out using mouse embryonic fibroblast cells lines (NIH‐3T3), as model for skin, murine neuroblastoma neuro‐2α cell line, as model for neuronal tissue, and mouse mesenchymal stem cells (MSCs), because of their differentiation ability. Imaging analysis by scanning electron microscope and laser scanning confocal microscopy together with cell viability (MTT, L 3‐(4,5‐dymethiltiazol‐2‐y)‐2,5 diphenyltetrazolium bromide) test, were performed on cell cultures at fixed time laps. The results showed that electrospun nanofibers supported growth and proliferation of the tested cell lines, but electrospun matrices obtained with rotating mandrel showed significantly higher cell viability that follows the orientation of electrospun nanofibers.

A Comparison of Mechanical Properties of Different Hydroxyapatite (HAp) Based Nanocomposites: The Influence of Morphology and Preferential Orientation.

Three different types of hydroxyapatite (HAp) based porous ceramic materials were obtained through the modified gel casting method; one of them was made of commercial HAp particles and used as a reference in the mechanical characterization. Other type of ceramic was elaborated using HAp nanofibers, which were synthesized through the microwave assisted hydrothermal method and they possess a high crystallinity, purity and a preferential crystalline orientation in the [300], such were grown along the [001]. The third type of porous ceramic was elaborated using a combination of HAp nanofibers and particles. The HAp nanofibers and particles were previously analyzed by using X-ray diffraction to study their crystal structure, the topology and morphology of those HAp aggregates were observed with scanning electron microscopy (SEM); high-resolution transmission electron microscopy was useful to carry out a detailed crystallographic analysis. Afterwards, an organic phase made of gelatin was added to the porous ceramics in order to obtain nanocomposite materials. Two different concentrations of gelatin were used separately, and the combination of three types of porous ceramics and two concentrations of gelatin produced six different nanocomposite materials. All of these composite materials were observed through the SEM to see their topology and porosity and after that, they were probed under compression tests and their corresponding mechanical behavior was analyzed. All the composites showed mechanical properties similar to those observed in cellular materials. The Young modulus and ultimate strength were compared, finally, it was determined the contribution to the mechanical properties of the morphology, crystalline quality and preferential crystalline orientation in the HAp nanofibers. According to such properties, the composite material made of HAp nanofibers has bone tissue implant potential applications.

Modified cylindrical collectors for improved orientation of electrospun nanofibers

In many biomedical applications of nanofibers, such as vascular grafts, longitudinal orientation of the fibers is required in order to enable the grafts to withstand high blood pressures. This study is aimed at developing novel cylindrical collectors and orientation processes for electrospun nanowebs with better and controlled fiber orientation. Effect of the length of conductive and non-conductive collector segments was investigated, along with the effect of polymer concentration, feed rate, electrospinning voltage, distance and groove depth of the non-conductive segment on the mean fiber diameter and orientation of polyacrylonitrile nanofibers. Results of the study show that polymer concentration has major effect on the fiber diameter followed by length of the conductive segment and groove depth. Fiber orientation was mainly affected by length of the non-conductive segments of the collector and the polymer concentration.

Orientation of Electrospun Magnetic Nanofibers Near Conductive Areas.

Electrospinning can be used to create nanofibers from diverse polymers in which also other materials can be embedded. Inclusion of magnetic nanoparticles, for example, results in preparation of magnetic nanofibers which are usually isotropically distributed on the substrate. One method to create a preferred direction is using a spinning cylinder as the substrate, which is not always possible, especially in commercial electrospinning machines. Here, another simple technique to partly align magnetic nanofibers is investigated. Since electrospinning works in a strong electric field and the fibers thus carry charges when landing on the substrate, using partly conductive substrates leads to a current flow through the conductive parts of the substrate which, according to Ampère’s right-hand grip rule, creates a magnetic field around it. We observed that this magnetic field, on the other hand, can partly align magnetic nanofibers perpendicular to the borders of the current flow conductor. We report on the first observations of electrospinning magnetic nanofibers on partly conductive substrates with some of the conductive areas additionally being grounded, resulting in partly oriented magnetic nanofibers.

Design of an Ultrasensitive Flexible Bend Sensor Using a Silver-Doped Oriented Poly(vinylidene fluoride) Nanofiber Web for Respiratory Monitoring.

We propose a design strategy to fabricate a flexible bend sensor (BS) with ultrasensitivity toward airflow using all-poly(vinylidene fluoride) (PVDF) nanofiber web-based sensing elements and electrodes to monitor human respiration. The unique electrospinning (rotational speed of collector of 2000 rpm and tip-to-collector distance of 4 cm) with silver nanoparticle interfacing was introduced to prepare a Ag-doped oriented PVDF nanofiber web with high β-phase content as a sensing element (AgOriPVDF, β-phase crystallinity ∼44.5%). After that, a portion of the prepared AgOriPVDF was processed into a flexible and electrically conductive electrode through an electroless silver plating technique (SP-AgOriPVDF). Interestingly, the encapsulated AgOriPVDF BS with the SP-AgOriPVDF electrode exhibited superior piezoelectric bending response (open-circuit peak-to-peak output voltage, Vp-p ≈ 4.6 V) to injected airflow, which is more than 200 times higher than that of the unpackaged randomly aligned PVDF nanofiber web BS with a conductive tape electrode (Vp-p ≈ 0.02 V). In addition, the factors influencing the bend sensitivity of the BS such as the β-phase content, nanofiber orientation, flexibility of the electrode, and so forth were thoroughly analyzed and then discussed. We also demonstrated that the AgOriPVDF BS has sufficient capability to detect and identify various respiratory signals, presenting a great potential for wearable applications, for example, smart respiratory protective equipment.

Molecular Orientation in Individual Electrospun Nanofibers Studied by Polarized AFM–IR

Molecular orientation is critical to the properties of fibers, yet analysis of electrospun nanofibers of small diameters is challenging due to limited spatial resolution of the characterization tec...

Biomimetic dual-oriented/bilayered electrospun scaffold for vascular tissue engineering

Natural blood vessels have a multi-layered, cell-specific oriented spatial structure, mimicking of this structure is a promising way for blood vessel regeneration. In this study, a newly developed dual-oriented/bilayered small-diameter tubular scaffold was electrospun using a mixture of poly (ε-caprolactone) (PCL), poly (D, L-lactide-co-glycolide) (PLGA) and gelatin. The nanofiber orientations of the bilayers were spatially perpendicular to each other, aiming at guiding cell-specific orientation of smooth muscle cells (SMCs) and endothelial cells (ECs) in vitro respectively. The results showed that the hydrophilicity of scaffold was greatly improved by gelatin, and the mechanical property of this scaffold was the best among all. The in vitro degradation demonstrated that by mixing of three biodegradable polymers, a relatively fast degradation rate was achieved. After SMCs and ECs were seeded on scaffolds, cell viability, cellular morphology, and cytoskeleton behavior were investigated. The results revealed that as-electrospun scaffolds could promote both SMCs and ECs proliferation. Moreover, topographic cues offered by oriented nanofibers could guide the growth and orientation of SMCs and ECs. Therefore, the dual-oriented/bilayered electrospun scaffold is a superior structural and functional analogue to natural blood vessel and a potential candidate for vascular tissue engineering.

Modelling the Strength of Cellulose Nanofiber-Filled Rigid Low-Density PU Foams

Rigid low-density closed-cell polyurethane (PU) foams are used primarily as a thermal insulation material. The foams have to possess a sufficient strength and stiffness in order to ensure their mechanical integrity and dimensional stability in service. The mechanical characteristics of foams are enhanced by adding cellulose nanofibers to the polyol system, which both modify the foaming process and act as a reinforcement of cell struts and walls. A model of composite foam strength is developed based on a regular unit cell and assuming the onset of strut failure as the foam fracture criterion. The load-bearing capacity of foam struts is estimated by the modified Fukuda and Chou model considering the orientation of nanofibers along the strut axis. The model developed is shown to provide a reasonably accurate prediction for the nanofiber loading effect on the strength of composite foams.

Fabrication, mechanical properties and failure mechanism of random and aligned nanofiber membrane with different parameters

AbstractPolyacrylonitrile (PAN) nanofiber membranes with different concentrations, rotary speeds and four kinds of aligned with fiber orientation of 0∘, 0∘/90∘, 0∘/90∘/+45∘and 0∘/90∘/+45∘/−45∘were prepared via electrospinning technique. The nanofiber membranes were morphologically characterized and mechanically tested. The results showed that nanofibers have uniform structure without any beads when the concentration increased 12wt%. The tensile strength and modulus of PAN nanofiber membranes increase with increasing the concentration. The orientation of nanofibers increases significantly with increasing rotary speed and fabricated nanofibers membrane has best orientation and tensile properties at 2500rpm. Moreover, the tensile properties can be affected greatly by the fiber structure and these decrease significantly with increasing the fiber orientation angle. The results also show that the nanofiber membranes exhibit obvious ductile fracture characteristics. Moreover, shear characteristics become more evident with increasing the concentration, and the failure mode changes from shear feature to flush fracture with increasing the rotary speed. In addition, the failure patterns vary with fiber structure and the main damage is in the form of interlayer delaminating, interface debonding, fibers tearing and breakage of the nanofibers.

Improvement of interlaminar fracture toughness of phenolic laminates interleaved with electrospun polyvinyl butyral nanofibers

Among different types of composites, laminated composites are those may be delaminated under applied loads. Phenolic resin/Glass fiber composite is one of the most widely used composites, however, it is susceptible to delamination very likely that it will delaminate. In this research, polyvinyl butyral (PVB) electrospun nanowebs have been used as the interlayer to toughen phenolic resin/glass fiber composites. In order to evaluate the effect of main factors on the fracture toughness of the laminates, interlayer dimensional parameters such as interlayer thickness (30, 90 and 150 µm), nanofiber diameter (200 and 500 nm) and nanofiber orientation (random and aligned) were investigated in Mode I and Mode II fractures. The surface response method (RSM) was used to find the optimal diameter of PVB electrospun nanofibers. The results showed that the thickness of the interlayer is the most effective factor in improving the composite toughness in Mode I and Mode II. The thickness of 30 μm showed the best result in Mode I and Mode II and increased GIc and GIIc values by 70% and 38%, respectively. Also, with decreasing the nanofibers diameter and increasing the collision level, the amount of energy absorbed from the crack increases and results in to improvement of the fracture toughness. Nanofiber alignment showed less effect on the composite fracture compared to other factors.

Strain engineered biocompatible h-WO3 nanofibers based highly selective and sensitive chemiresistive platform for detection of Catechol in blood sample

In this work, we demonstrate a simple, low-cost biocompatible 1D-WO3 electrospun nanofibers based strain-induced high-performance chemiresistive catechol sensor. WO3 nanofibers were synthesized using e-spinning, annealed and drop-casted on to flexible PET substrate. X-Ray Diffraction (XRD) studies confirm the formation of Hexagonal phase-WO3 and Raman spectroscopy proved the presence of O-W-O bending modes. Field emission scanning electron microscopy (FESEM) images displayed the random orientation of dense WO3 nanofibers on PET substrate. Hall measurements confirmed the formation of n-type WO3 nanofibers with carrier density of 1019 cm-3. The sensor responded to a broad dynamic range of catechol concentrations from 1 μM to 100 μM with sensitivity of 51.29 μM-1 cm-2 and limit of detection of 0.52 μM which are better than previously reported catechol sensors. Interestingly, upon application of compressive strain to the flexible sensor, a remarkable increase in sensitivity to 88.34 μM-1 cm-2 was observed with further reduction of the limit of detection to 42 nM. Upon subjecting the sensor to strain ranging from 3.14% to 47.6%, an increase in sensitivity to catechol was observed due to the increase in the exposed surface area of interconnected WO3 nanofibers which enhances the active sites for catechol oxidation by enhancing the tunneling current. The sensor could detect catechol in simulated blood samples with excellent selectivity against AA, UA, Na+, Ca+, hydroquinone and glucose.

Molecular Orientation and Organization of Technical Lignin-Based Composite Nanofibers and Films.

Natural materials are highly anisotropic, maximizing performance of the polymeric structures while conserving mass and enhancing function. In synthetic materials, nanoscale fibers produced by electrospinning often contain molecular alignment of polymers along the fiber axis achieving some similarity to natural fibers. In this study, isolated softwood kraft lignin (SKL) was electrospun into aligned fibers utilizing a special collector. The molecular organization of lignin within the aligned nanofibers was investigated by polarized light optical microscopy. Furthermore, the functional groups that had preferred alignment along the fiber axis were identified with polarized Fourier transform infrared (FTIR) spectroscopy based on dichroism measurements. In addition, nanocrystalline cellulose (NCC) was added to the lignin solutions in order to create composite nanofibers. Both the orientation of NCC within the nanoscale fibers and the impact this component had on the degree of orientation of SKL within the aligned nanofibers were revealed by utilizing polarized FTIR. Finally, solvent cast lignin films were analyzed for their anisotropic polarizability, demonstrating birefringence with and without nanocrystalline cellulose. The work provided unique insight into both preferred orientation (fibers) and assembly (films) for technical lignin due to processing.

Enhanced dielectric properties of poly(vinylidene fluoride-co-hexafluoropropylene) nanocomposites using oriented nickel nanowires

Abstract The alignment of fillers in polymer matrix plays an important role in the dielectric properties of composite materials, but there are currently limited ways to effectively control the orientation of the fillers. In this paper, nickel nanowires (Ni NWs) with natural ferromagnetism were aligned under the external magnetic field during the fabrication process of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) based nanocomposite. Subsequently, orientation effects of Ni NWs, including the in-plane, through-plane and random patterns along the electric field orientation, on the dielectric performance of P(VDF-HFP) nanocomposites were investigated. The results showed that the dielectric properties of Ni NWs-P(VDF-HFP) nanocomposites were related to the anisotropy of Ni NWs. The highest dielectric constant of polymer nanocomposites with the 1.3 vol% Ni NWs reached to 41 at 1 kHz when the orientation of nanofiber was parallel to electric field, which is 274% higher than that of unaligned one and is 513% higher than the neat polymer. In addition, the nanocomposites kept the low dielectric loss. The results can be explained by combining the percolation theory, micro capacitor model and interfacial polarization theory. The finding provides a new method to prepare the nanocomposite dielectric materials with fillers arrangement. On the other hand, it is meaningful to in-depth understand the effect of fillers arrangement on the dielectric properties of composite materials.

Carbonized Copolymers Nonwoven Nanofibers Composite: Surface Morphology and Fibers Orientation

Carbonized nonwoven nanofibers composite were fabricated using the electrospinning method of a polymeric solution composite followed by heat treatment including stabilization and calcination steps. The spun polymeric solution was a binary polymer mixture/organic solvent. In this study, two types of polymers (Polymethylmethacrylate (PMMA) and Polyethylene glycol (PEG)) were used separately as a copolymer with the base polymer (Polyacrylonitrile (PAN)) to prepare a binary polymer mixture in a mixing ratio of 50:50. The prepared precursor solutions were used to prepare the precursor nanofibers composite (PAN: PMMA) and (PAN: PEG). The fabricated precursors nonwoven fibers composite were stabilized and carbonized to produce carbon nonwoven nanofibers composite. The effect of the combined polymer type on the fiber size, fiber size distribution, and surface morphology of the prepared nonwoven nanofibers was studied. The nonwoven fibers orientation and surface morphology were characterized using field emission scanning electron microscope (FESEM). In addition, ImageJ software has been used to calculate the fiber size and fiber size distribution. Here, the obvious effect of the copolymer type on the surface morphology, fiber size, and fiber orientation has been demonstrated. Using a copolymer with PAN polymer led to increasing the fiber size. The carbonized nanofibers composite prepared using PEG polymer as a copolymer was more ordered fibers in comparison with the fiber orientation of carbon nanofibers based on pure PAN. In contrast of that, using PMMA as a copolymer resulted curly carbonized nonwoven nanofiber composite.

Effect of nanofiber diameter and arrangement on fracture toughness of out of autoclave glass/phenolic composites - Experimental and numerical study

In this study, the effect of (Polyvinyl butyral) PVB-nanofiber diameter and orientation on the mode II fracture toughness of laminated phenolic composite was investigated by means of experimental and numerical methods. The motivation was to explore the potential of nanofiber veils as an inter-laminar toughener of laminated composites in consideration of the importance of improving the inter-laminar fracture toughness of phenolic-based composites. As regards the experimental investigation, the fracture behavior of glass/phenolic composites was determined by end notched flexure (ENF) test taking into account four different nanofiber diameters (100, 165, 314 and 500 nm) and two fiber orientations: random and aligned. In addition, a finite element model including cohesive elements was applied to investigate numerically the fracture behavior of composites during mode II loading. The results indicate that there is an optimal value of nanofiber diameter that maximizes the initial fracture toughness (GIIC). The outcome also shows that aligned nanofibers are not able to improve the fracture toughness under mode II loading. The GIIC value of optimal sample (fiber diameter 165 nm and random orientation) is 26% higher than the reference laminates. On the other hand, it is proven that the bi-linear traction-separation law is a suitable method to model PVB-modified laminates under mode II loading. The effect of nanofiber diameter and orientation on cohesive parameters (K0, GIIC, σmax) was also studied.

Analyzing the effect of nanofiber orientation on membrane filtration properties with the progressive increase in its thickness: a numerical and experimental approach

One of the merits of modeling is that the computer-generated data is used in optimizing equipment and experimental designs, eliminating the costs associated with scaling up by experimentation. In this work, the filtration performance of nanofibers aligned diversely within virtual webs was numerically analyzed using Star CCM + and Ansys Fluent software. This knowledge was then used to fabricate two distinctly oriented nanofiber membranes via free surface electrospinning. Their filtration performance was studied by capillary flow porometry technology using POROLUX™ 100. The results of this were in agreement with the simulation work.

Nanoscale properties and deformation of human enamel and dentin

This research uses quasi-static nanoindentation and nanoscratching to quantify human tooth deformation as a function of enamel rod and dentin tubule orientations at the nanoscale. Nanoindentation tests were performed on enamel and dentin to determine elastic modulus, hardness, and observe fracture. Additionally, nanoscratch tests were performed to determine pileup geometry and parameters such as recovery, scratch hardness, and scratch roughness. In enamel, it was found that nanofiber orientation gives rise to unique microcrack propagation and nanofiber behavior that affect these properties. For dentin, densification and organic content affect these properties.