Double‐nozzle air‐jet electrospinning for nanofiber fabrication

A novel double‐nozzle air‐jet electrospinning apparatus was developed to fabricate nanofibers on a large scale. The distribution of the electric field at different nozzle distances was simulated to analyze the jet path, productivity, and deposition area of nanofiber webs and the nanofiber morphology. Our experiments showed that the bubbles usually ruptured intermittently on the top surface of the two nozzles and the jets traveled in a straight path with a high initial velocity. A continuous and even thickness of the nanofiber webs were obtained when the nozzle distances was less than 55 mm. At nozzle distances of 55 mm, the received fibers were thin with the lowest standard deviation. Experimental parameters involving the applied voltage, collecting distance, and air flow rate were also investigated to analyze the nanofiber morphology at a nozzle distance of 55 mm. The results show that the nanofibers presented a finer and thinner diameter at an applied voltage of 36 kV, a collecting distance of 18 cm, and an air flow rate of 800 mL/min. The nanofiber production of this setup increased to nearly 70 times that with a single‐needle electrospinning setup. On the basis of the principle of this air‐jet electrospinning setup, various arrangements of multinozzle electrospinning setups could be designed for higher throughput of nanofibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40040.     

Electrospinning and crosslinking of zein nanofiber mats

Electrospinning processing can be applied to fabricate fibrous polymer mats composed of fibers whose diameters range from several microns down to 100 nm or less. In this article, we describe how electrospinning was used to produce zein nanofiber mats and combined with crosslinking to improve the mechanical properties of the as‐spun mats. Aqueous ethanol solutions of zein were electrospun, and nanoparticles, nanofiber mats, or ribbonlike nanofiber mats were obtained. The effects of the electrospinning solvent and zein concentration on the morphology of the as‐spun nanofiber mats were investigated by scanning electron microscopy. The results showed that the morphologies of the electrospun products exhibited a zein‐dependent concentration. Optimizing conditions for zein produced nanofibers with a diameter of about 500 nm with fewer beads or ribbonlike nanofibers with a diameter of approximately 1–6 μm. Zein nanofiber mats were crosslinked by hexamethylene diisocyanate (HDI). The tensile strength of the crosslinked electrospun zein nanofiber mats was increased significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:380–385, 2007     

对称共轭电纺法制备连续纳米纤维

利用一对带有异种电荷的对称共轭喷丝头,通过静电纺丝法制备了几种聚合物的连续排列有序的微/纳米纤维,并与常规静电纺丝方法制备的纳米纤维进行了比较。结果发现:利用对称共轭电纺法制备的纤维的直径比常规电纺法制备的要大2～3倍,而且纤维具有良好的排列有序性;而用常规方法制备的纳米纤维则是无规排列的。扫描电子显微镜(SEM)被用来表征制备的微/纳米纤维和纳米纤维膜。     

Polymeric nanofibers containing solid nanoparticles prepared by electrospinning and their applications

Generally, polymer solution or sol–gel is used to produce electrospun nanofibers via the electrospinning technique. In the utilized sol–gel, the metallic precursor should be soluble in a proper solvent since it has to hydrolyze and polycondensate in the final solution; this strategy straitens the applications of the electrospinning process and limits the category of the electrospinnable materials. In this study, we are discussing electrospinning of a colloidal solution process as an alternative strategy. We have utilized many solid nanopowders and different polymers as well. All the examined colloids have been successfully electrospun. According to the SEM and FE SEM analyses for the obtained nanofiber mats, the polymeric nanofibers could imprison the small nanoparticles; however, the big size ones were observed attaching the nanofiber mats. Successfully, the proposed strategy could be exploited to prepare polymeric nanofibers incorporating metal nanoparticles which might have interesting properties compared with the pristine. For instance, PCL/Ti nanofiber mats exhibited good bioactivity compared with pristine PCL. The proposed strategy can be considered as an innovated methodology to prepare a new class of the electrospun nanofiber mats which cannot be obtained by the conventional electrospinning technique.     

Alginate‐nanofibers fabricated by an electrohydrodynamic process

Alginate, a natural polymer, is potentially useful in biomedical applications, because it is very similar to macromolecular substances, unlike synthetic polymers that may cause problems due to toxicity and lack of recognition by cells. Alginate's processability characteristics, however, are a potential drawback to its use as a biomedical nanofiber scaffold. To improve electrospinnability, alginate has been processed with various synthetic polymers and surfactants. Although this has enhanced the processability of the polymer, a new approach is required to obtain a sufficient production rate over a short period of time. We used a multiple‐nozzle electrospinning system complemented with auxiliary cylindrical electrodes. The nanofibers of alginate/poly(ethylene oxide) supplemented with lecithin as a surfactant were electrospun using a multiple nozzle system. We measured the production rate and size uniformity of the spun fibers with and without auxiliary electrodes. We observed that a multiple nozzle system with auxiliary electrodes provided much better and more stable processability, as well as higher mass productivity of alginate nanofibers compared with a normal multiple nozzle system. The resulting nanofiber mat showed potential for use as a biomedical scaffold based on our tests with cell‐cultured human dermal fibroblasts. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Ion-assisted collection of Nylon-4,6 electrospun nanofibers

In electrospinning, electrostatic interaction between charged fibers and the collection substrate can result in poor and non-uniform coverage, particularly when electrically insulating substrates are used, because they are prone to surface charge accumulation. Charged electrospun Nylon-4,6 nanofiber coatings were deposited onto substrates of varying size, conductivity and morphology. The density and uniformity of the nanofiber coatings were significantly enhanced, both on insulating and on conducting substrates, by a new method based on rapid sequential deposition of charged nanofibers and oppositely charged ions onto substrates that were mounted onto a rotating collecting electrode (mandrel) located between an electrospinning source and a focused ion source. Sequential fiber/ion deposition presumably led to surface charge neutralization or reversed charging, and minimization of electrostatic fiber/substrate interactions. An electrostatics model was developed to interpret the experimental results. It was also theoretically argued that any degree of ion charging will induce continuous fiber accumulation.     

Effect of air blowing on the morphology and nanofiber properties of blowing‐assisted electrospun polycarbonates

Polycarbonate (PC) nanofibers are prepared using the air blowing‐assisted electrospinning process. The effects of air blowing pressure and PC solution concentration on the physical properties of fibers and the filtration performance of the nanofiber web are investigated. The air blowing‐assisted electrospinning process produces fewer beads and smaller nanofiber diameters compared with those obtained without air blowing. Uniform PC nanofibers with an average fiber diameter of about 0.170 μm are obtained using an applied voltage of 40 kV, an air blowing pressure of 0.3 MPa, a PC solution concentration of 16%, and a tip‐to‐collection‐screen distance (TCD) of 25 cm. The filtration efficiency improvement of the air blowing‐assisted electrospun web can be attributed to the narrow distribution of fiber diameter and small mean flow pore size of the electrospun web. Performance results show that the air blowing‐assisted electrospinning process can be applied to produce PC nanofiber mats with high‐quality filtration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The thermal effects on electrospinning of polylactic acid melts

We demonstrate that melt electrospinning can be a feasible way to produce sub-micron scale polylactic acid (PLA) fibers in this paper. This solvent-free approach to produce sub-micron scale fibers is more environmentally benign than common solution electrospinning processes, and has a potential to increase the production rate significantly. Our experimental results show that temperatures at the spinneret and in the spinning region are critical to produce sub-micron sized fibers: a high-speed photographic investigation reveals that when spinning temperature is below glass transition temperature, whipping of the jet is suppressed by fast solidification in the spinning region, leading to a larger jet diameter. Both thermal and mechanical degradations of PLA in melt electrospinning can be significant but no change in chemical composition is found. Due to rapid solidification, melt electrospun PLA fibers are mostly amorphous, and the small presence of β crystals is noted in the sub-micron scale PLA fibers by XRD studies. The highly oriented structure of PLA fibers gives rise to cold crystallization at around 95 °C, and the degree of crystallinity of fibers increases with increasing the degree of annealing. Finally, PLA nanofibers have directly been electrospun onto cellulose filter media, and a drastic enhancement in collection efficiency of sub-micron sized dust particles is presented. Melt electrospun PLA nanofiber mats with no residual solvent may serve as better filter media and tissue scaffolds than those obtained from solution electrospinning processes.     

An applicable electrospinning process for fabricating a mechanically improved nanofiber mat

Engineered polymer scaffolds play an important role in tissue engineering. An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area and high porosity, nanofibers have good potential as biomimetic scaffolds. However, the main shortcomings of scaffolds consisting of nanofibers are their mechanical inability to sustain a stress environment for neotissues and shape‐ability to form a variety of shapes and sizes. In this study, we produced design‐based poly (ε‐carprolactone) (PCL) nanofiber mats using an electrospinning method with various auxiliary electrodes and an x‐y moving system. To achieve stable initial solution at a nozzle tip of the electrospinning, various types of auxiliary electrodes were introduced. To characterize the effect of the electrodes in the electric‐field distribution near the nozzle tip, we calculated the electric field concentration factor and compared it with the experimental results. The nanofiber mat produced using the moving x‐y target system demonstrated orthotropic mechanical properties due to the fiber orientation, and human dermal fibroblasts seeded on the structure tended to grow according to nanofiber orientation. POLYM. ENG. SCI., 47:707–712, 2007. © 2007 Society of Plastics Engineers.     

Electrospinning of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibrous tissue engineering scaffolds in two different electric fields

Poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) was electrospun into ultrafine fibrous nonwoven mats. Different from the conventional electrospinning process, which involves a positively charged conductive needle and a grounded fiber collector (i.e., positive voltage (PV) electrospinning), pseudo‐negative voltage (NV) electrospinning, which adopted a setup such that the needle was grounded and the fiber collector was positively charged, was investigated for making ultrafine PHBV fibers. For pseudo‐NV electrospinning, the effects of various electrospinning parameters on fiber morphology and diameter were assessed systematically. The average diameters of PHBV fibers electrospun via pseudo‐NVs were compared with those of PHBV fibers electrospun via PVs. With either PV electrospinning or pseudo‐NV electrospinning, the average diameters of electrospun fibers ranged between 500 nm and 4 μm, and they could be controlled by varying the electrospinning parameters. The scientific significance and technological implication of fiber formation by PV electrospinning and pseudo‐NV electrospinning in the field of tissue engineering were discussed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effect of organic solvent on morphology and mechanical properties of electrospun syndiotactic polypropylene nanofibers

We study the stress–strain behaviors of the electrospun sPP single nanofibers as well as nonwoven mats, which were electrospun from sPP solutions using two different solvents (decalin and cyclohexane) by electrospinning. The effects of organic solvents were explored on the morphologies and the mechanical properties of the corresponding electrospun sPP single nanofibers and nonwoven mats. It was found that the nature of organic solvents dramatically affected the surface morphologies, the circular and looping deposition of the electrospun sPP fibers, and the mechanical properties. The tensile strength of both electrospun sPP single nanofibers and nonwoven mats prepared from decalin-base solution was stronger than that of cyclohexane-base solution.     

Empirical model to simulate morphology of electrospun polycaprolactone mats

This work is the first to report a study aimed at generating 3D virtual geometries that represent the microstructure of an electrospun fibrous mat comprised curly fibers. Polycaprolactone (PCL) mats are considered in our study as an example of such fibrous structures. We started with simulating the formation of PCL filaments and observed good agreement between the predicted and measured fiber diameters. In the absence of quantitative information about the shape of a curly PCL fiber, we treated these fibers as arrays of beads arranged on epitrochoid profiles. We then used the fiber deposition diameter and velocity in a mass-spring-damper (MSD) model to generate 3D fibrous geometries comprised hundreds of such curly fibers. The damping and spring constants in the MSD model were obtained through calibration with experimental data reported for single electrospun PCL nanofibers. The size of the epitrochoid-like fibers was obtained empirically through matching the average thickness of the resulting mats with those measured experimentally. With the calibrated code, we studied the effects of electrospinning conditions on the porosity of PCL nanofiber mats. It was found that increasing the voltage or decreasing the needle-to-collector distance results in PCL mats with thicker fibers, and consequently, lower porosities. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48242.     

Improvement in nanofiber filtration by multiple thin layers of nanofiber mats

Nanofiber filtration is drawing great interest nowadays because of its large surface collection area as well as low air resistance. In this study, electrospun nanofiber mats of different thicknesses were evaluated for their filter quality factors. Shorter-term electrospun fiber mats exhibited a better quality factor than those longer-term electrospun ones. Multiple thin layers of nanofiber mats to improve the filter quality of the nanofiber filters were then evaluated. Filtration test results showed that the filter made up of multiple thin layers of nanofiber mats had a filter quality factor much higher than the single thick layer nanofiber mat. Better thickness uniformity in the multi-layer structure due to stacking compensation and smaller fiber diameters in nanofibers of short-term deposition time are two possible reasons for the improvement of the filter quality.     

Preparation of the chitosan containing nanofibers by electrospinning chitosan–gelatin complexes

Electrospinning is an interesting technique, which provides a facile and an effective mean in producing nonwoven fibrous materials; however, for producing nanofibers, investigation of the electrospinning conditions is very important. In this study, chitosan, gelatin, and their polyelectrolyte complexes (PECs) were electrospun to prepare nonwoven nanofibrous mats. The concentrations of chitosan and gelatin solutions and electric field (kV/cm) were optimized. The solutions were then blended in different ratios (0–100%) to get electrospun nanofibrous mats. Solution concentration and electric field showed pronounced effect on the electrospinnability and fiber diameter of these systems. Mostly large beads coexisted with the fibers were observed for chitosan at 1 wt% solution concentration, which then showed good electrospinnability at 2 wt% (nanofiber diameter was 145 and 122 nm at 15 and 20 kV/10 cm, respectively), whereas gelatin showed no electrospinnability below 15 wt% solution concentration and a homogenous fibers network at 15 wt% (149 nm at 20 kV/10 cm). The morphology and diameter of chitosan–gelatin PEC nanofibers varied with the chitosan/gelatin ratio. The crystallinity of chitosan was also observed to reduce with electrospinning and addition of gelatin. POLYM. ENG. SCI. 50:1887–1893, 2010. © 2010 Society of Plastics Engineers     

Polyamide 6 nanofibrous nonwovens via electrospinning

Electrospinning of Polyamide 6 (PA 6) in 2,2,2‐trifluoroethanol (TFE) was investigated for the fabrication of nanofibrous nonwoven membranes useful for separation systems. The effects of solution characteristics such as concentration and conductivity as well as the effects of processing conditions such as relative humidity and applied potential on the resultant nonwoven fibers were studied. By changing the relative humidity of the electrospinning chamber and the conductivity of the solvent, it is possible to modulate the fiber's size and consequently the porosity of the mats. The morphology of the electrospun PA 6 nanofibers was observed by scanning electron microscopy. The mechanical properties of the nanofibers were also studied. The results showed that PA 6 nanofibers having a diameter ranging from 100 to 600 nm, has been successfully prepared. The electrospun PA 6 nanofiber mats show good mechanical properties, such as a high‐tensile strength (12 ± 0.2 MPa) and elongation (300% ± 50%). The strength of the web was high enough to use as filter without the need of any supporting matrix and could be applicable in the field of self‐supporting membranes. The X‐ray and DSC analyses of the PA 6 electrospun fibers show the presence of the γ‐form of PA 6 crystallite that is usually obtained in the condition where a high stress of the fibers is applied. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and antibacterial activity of PET/chitosan nanofibrous mats using an electrospinning technique

The nanofiber deposition method, by electrospinning, was employed to introduce antibacterial activity and biocompatibility to the surface of poly (ethylene terephthalate) (PET) textiles. The polymer blends of PET and chitosan were electrospun on to the PET micro‐nonwoven mats for biomedical applications. The PET/chitosan nanofibers were evenly deposited on to the surface, and the diameter of the nanofibers was in the range between 500 and 800 nm. The surface of the nanofibers was characterized using SEM, ESCA, AFM, and ATR‐FTIR. The wettability of the PET nanofibers was significantly enhanced by the incorporation of chitosan. The antibacterial activity of the samples was evaluated utilizing the colony counting method against Staphylococcus aureus and Klebsiella pneumoniae. The results indicated that the PET/chitosan nanofiber mats showed a significantly higher growth inhibition rate compared with the PET nanofiber control. In addition, the fibroblast cells adhered better to the PET/chitosan nanofibers than to the PET nanofibers mats, suggesting better tissue compatibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Shear-aided high-throughput electrospinning: A needleless method with enhanced jet formation

In this article, we introduce a novel high productivity electrospinning setup for scaling up the classical method. We propose a new spinneret concept, which allows the shearing of the polymer solution prior to electrospinning. Most of the solutions used in electrospinning are shear-thinning, that is, as they are sheared, they show smaller resistance against the deformations caused by the electrostatic field. Therefore, enhanced Taylor-cone formation can be achieved, and it also gives a hand in controlling the nanofiber morphology easily, even during operation. In this study, we investigated the influence of shearing on the electrospinning process and the fiber morphology. When shearing was applied by rotation, the operation became more stable and the fiber morphology improved. Multiple jets were observed along the circular edges of the spinneret, also became thinner as an effect of the shearing rotation. The average diameter of the electrospun nanofibers was decreased by 18% with rotation speed applied, compared to those of the nonrotating condition (0 rpm). Besides that, we found that the electrospun nanofiber diameter distribution was significantly different for the various rotation speeds for which we found an applicable explanation with the aid of high-speed camera recordings.     

Effects of Fe2+ ions on morphologies,microstructures and mechanical properties of electrospun nylon‐6 nanofibers

In this study, nylon‐6 nanofiber mats containing Fe²⁺ ions were fabricated via electrospinning. The resultant electrospun nylon‐6/FeCl₂ nanofiber mats were characterized by SEM, TEM, Fourier transform IR spectroscopy, wide angle XRD and DSC. Unique morphological features, such as spider's‐web‐like morphologies, were observed and became evident with increasing additive Fe²⁺ ions. The metastable γ form was predominant in the as‐spun nylon‐6 nanofibers. The relative intensity of such γ form gradually decreased with increasing additive Fe²⁺ ions, indicative of transformation of the crystalline structure in the electrospun nylon‐6/FeCl₂ nanofibers due to strong molecular interactions between the nylon‐6 backbone and the additive Fe²⁺ ions. The effects of additive Fe²⁺ ions on the mechanical properties of both nonwoven nanofiber mats and single nanofibers were investigated. In particular, Young's modulus of nylon‐6/FeCl₂ single nanofibers gradually increased from 1.46 to 5.26 GPa with increasing additive Fe²⁺ ions. © 2013 Society of Chemical Industry     

Apparatus for preparing electrospun nanofibers: designing an electrospinning process for nanofiber fabrication

Nanofibers are widely used in a range of material applications, such as filter media, biosensors, military protective coatings, three‐dimensional tissue scaffolds, composites, drug delivery, wound dressings and electronic devices. To fabricate nanofibers with desired physical and chemical functions, a variety of electrospinning processes have been introduced using specially designed collectors, microelectromechanical system (MEMS) nozzle tips and auxiliary electrodes to stabilize the spin jets. However, the development of new electrospinning processes continues in the search for ‘tailor‐made’ nanofibers, in which parameters such as the fiber orientation and three‐dimensional structure are ultimately controllable. This paper discusses recently suggested electrospinning methods that are designed to impart specific functionality. It also details the correlations between applied processing parameters and the obtained physical properties of electrospun fibers. Finally, future design directions are suggested for developing an electrospinning apparatus capable of producing optimally structured nanofibers. Copyright © 2007 Society of Chemical Industry     

Determination of twisting angle of electrospun nanofiber bundle for continuous electrospinning system

Electrospinning continuously produced twisted nanofibers with a convergence coil and a rotating ring collector. The positively charged nozzle was used in the electrospinning process to deposit electrospun fibers of polyacrylonitrile onto a rotating ring collector. By withdrawing the electrospun fibers from the rotating ring collector, it was possible to spin the electrospun fibers yarn. In this study, theoretical approaches and numerical simulations were used to determine the twisting angle of the yarn. Using the equations developed in this study, we performed numerical simulations and compared the experimental results with the numerical simulation results. Mechanical properties of the fiber bundle were analyzed for twisting angle. It was confirmed the relationship among the winding drum, the ring collector, and flux of the fibers mass per time during electrospinning in the developed system. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45528.