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.     

Needleless electrospinning of nanofibers with a conical wire coil

In this article, we have demonstrated a novel needleless electrospinning of PVA nanofibers by using a conical metal wire‐coil as spinneret. Multiple polymer jets were observed to generate on the coil surface. Up to 70 kV electric voltage can be applied to this needleless electrospinning nozzle without causing “corona discharge.” Compared with conventional needle electrospinning, this needleless electrospinning system produced finer nanofibers on a much larger scale, and the fiber processing ability showed a much greater dependence on the applied voltage. Finite element calculation indicates that the electric field intensity profiles for the two systems are also quite different. This novel concept of using wire coil as the electrospinning nozzle will contribute to the further development of new large‐scale needleless electrospinning system for nanofiber production. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Electrospinning of heated gelatin‐sodium alginate‐water solutions

Most polymers that are electrospun are dissolved in a solvent and are spun at ambient temperature. Gelatin, a natural polymer, has excellent potential in medical applications as a biodegradable polymer, especially when combined with sodium alginate. Unfortunately, gelatin/water or gelatin/sodium alginate/water solutions cannot be electrospun at ambient temperature without the incorporation of substances that are considered potentially toxic to the human body, such as acetic acid. In this study, gelatin/water solutions with and without sodium alginate were successfully electrospun without the use of additional solvents by using heated water solutions. The effect of electrospinning parameters such as solution concentration and applied voltage on the nanofiber morphology of these solutions was studied. These nanofibers from heated gelatin/water solutions exhibited good morphology with an average size of 291 ± 67 nm at 18% concentration to 414 ± 52 nm at 20% concentration. Similar sizes were observed when sodium alginate was incorporated into the gelatin/water solutions, although the relationship was dependent upon the amount of sodium alginate in the solution as well as the total concentration. Typically, these nanofibers containing sodium alginate were produced at a lower gelatin concentration compared with the gelatin/water nanofibers because of the increase of viscosity and conductivity of the solutions due to the addition of the highly viscous and conductivity sodium alginate. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Fabrication of nanofibers by a modified air-jet electrospinning method

A modified air-jet electrospinning (MAE) setup was demonstrated for contributing to the large-scale nanofibers production. With this single nozzle air-jet electrospinning device, the productivity of nanofibers can be increased more than forty times as compared with using the single-needle electrospinning (SNE) setup. When compared with other needle-less electrospinning setups, the benefits of this setup include ability to keep stable concentration of electrospun solution and to produce more uniform and thinner fibers, controlling of the jets formed speed and position, higher throughput, lower critical voltage, easier assembling, simpler operation, and so on. Four different parts of the fiber generator were, respectively, charged as electrospun electrodes to produce fibers. The distributions of the electric field with different electrodes were simulated and investigated for explaining the experimental results including the fibers productivity, the deposition area of nanofiber mats, as well as the surface morphology of the fibers. When the whole nozzle was charged, as compared with charging other electrodes, the MAE system produced thinner fibers with larger standard deviation on a much larger scale. By reduction of charged area, the received fibers presented lower productivity and thicker diameter with lower standard deviation. Especially, when a half of the nozzle was charged, the deposition area of nanofiber mats was larger than charging other electrodes. Besides, when a half of the nozzle was charged, the influences of electrospinning parameters such as applied voltage, collecting distance and the flow rate of air on nanofibers morphology were also investigated. Furthermore, based on this spinning unit, multi-nozzle air-jet electrospinning setup can be designed for larger production of nanofibers.     

Effect of experimental parameters on needleless electrospinning from a conical wire coil

In this study, a conical wire coil was used as spinneret to launch a novel needleless electrospinning. Multiple polymer jets were observed on the surface of the coil in the electrospinning process. Productivity of the nanofibers can be enhanced to >2.5 g/h by using this novel nozzle. The fiber productivity and diameter together with diameter distribution were dependent on the concentration of the polymer solution, applied voltage, and collecting distance. This novel concept of using wire coil as the electrospinning nozzle depicts a model of large‐scale needleless electrospinning system for nanofiber production. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Production of Synthetic,Para‐Aramid and Biopolymer Nanofibers by Immersion Rotary Jet‐Spinning

Nanofiber production platforms commonly rely on volatile carrier solvents or high voltages. Production of nanofibers comprised of charged polymers or polymers requiring nonvolatile solvents thus typically requires customization of spinning setup and polymer dope. In severe cases, these challenges can hinder fiber formation entirely. Here, a versatile system is presented which addresses these challenges by employing centrifugal force to extrude polymer dope jet through an air gap, into a flowing precipitation bath. This voltage‐free approach ensures that nanofiber solidification occurs in liquid, minimizing surface tension instability that results in jet breakup and fiber defects. In addition, nanofibers of controlled size and morphology can be fabricated by tuning spinning parameters including air gap length, spinning speed, polymer concentration, and bath composition. To demonstrate the versatility of our platform, para‐aramid (e.g., Kevlar) and biopolymer (e.g., DNA, alginate) nanofibers are produced that cannot be readily produced using standard nanofiber production methods.

     

A study on nanofiber‐reinforced thermoplastic composites (II): Investigation of the mixing rheology and conduction properties

This article is portion of a comprehensive study on the development of nanofiber‐reinforced polymer composites for electrostatic discharge materials and structural composites. Vapor‐grown carbon fibers with an average diameter of 100 nm were used as a precursor and model fiber system for carbon nanotubes. These nanofibers were purified and functionalized to provide for an open network of high‐purity nanofibers. Banbury‐type mixing was used to disperse the nanofibers in the polymer matrix. Rheological and microscopic analysis showed that the high shear processing of the polymer/nanofiber mixture led to a homogeneous dispersion of nanofibers with no agglomerates present and no shortening of the nanofibers. The shear thinning behavior of polymeric materials helps in the mixing of the nanofibers to form the composites. A percolation threshold for electrical conduction of 9–18 wt % was observed for the highly dispersed nanofiber networks. The electrical behavior of these materials was not affected by changes in humidity. Microscopic analysis showed highly dispersed nanofibers with no indications of porosity. These conducting polymers are well suited for electrostatic discharge applications, and might well become multifunctional materials for strength/electrical applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1162–1172, 2001     

Bicomponent nanofibers from core–shell nozzle in gas jet spinning process

This work evaluates the use of a core–shell nozzle assembly in conjunction with gas jet spinning technique for production of bicomponent nanofibers from an immiscible polymer pair of polyvinylpyrrolidone (PVP) and poly(vinyl acetate) (PVAc) with three morphological forms—interpenetrating network (IPN), core–shell, and bilobal structurers—by varying the sets of miscible solvents offering different affinity for the polymers. Such fiber structures have strong potential in drug delivery and wound dressing applications. Solutions of PVP and PVAc in respective single solvents metered through a core–shell nozzle assembly meet at the exit of the nozzle and a liquid jet is initiated upon contact with a turbulent gas jet. The gas jet stretches the liquid jet into nanofibers. The results indicate that miscible solvent pairs with low affinity for one of the polymer component yield core–shell morphology with distinct polymer interfaces, while the miscible solvent pairs with high affinity for both polymers produce IPN morphology. Also, interchanging core and shell solutions does not alter the IPN morphology. Finally, bilobal nanofiber structures result from spinning of polymer solutions in miscible solvents with low affinity for the second polymer using a nonconcentric core–shell nozzle assembly. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48901.     

Solution blow spinning: A new method to produce micro‐ and nanofibers from polymer solutions

A solution blow spinning technique was developed using elements of both electrospinning and melt blowing technologies as an alternative method for making non‐woven webs of micro‐ and nanofibers with diameters comparable with those made by the electrospinning process with the advantage of having a fiber production rate (measured by the polymer injection rate) several times higher. The diameters of fibers produced ranged from 40 nm for poly(lactic acid) to several micrometers for poly(methyl methacrylate). This solution blow spinning method uses a syringe pump to deliver a polymer solution to an apparatus consisting of concentric nozzles whereby the polymer solution is pumped through the inner nozzle while a constant, high velocity gas flow is sustained through the outer nozzle. Analysis of the process showed that pressure difference and shearing at the gas/solution interface jettisoned multiple strands of polymer solution towards a collector. During flight, the solvent component of the strands rapidly evaporates forming a web of micro and nanofibers. The effect of injection rate, gas flow pressure, polymer concentration, working distance, and protrusion distance of the inner nozzle was investigated. Polymer type and concentration had a greater effect on fiber diameter than the other parameters tested. Injection rate, gas flow pressure, and working distance affected fiber production rate and/or fiber morphology. Fibers were easily formed into yarns of micro‐ and nanofibers or non‐woven films that could be applied directly onto biological tissue or collected in sheets on a rotating drum. Indeed, virtually any type of target could be used for fiber collection. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nanofiber technology: current status and emerging developments

Nanofibers have emerged as exciting one-dimensional nanomaterials for a broad spectrum of research and commercial applications owing to their unique physicochemical properties and characteristics. As a class of nanomaterials with cross-sectional diameters ranging from tens to hundreds of nanometers, nanofibers possess extremely high specific surface area and surface area-to-volume ratio. They are capable of forming networks of highly porous mesh with remarkable interconnectivity between their pores, making them an attractive choice for a host of advanced applications. In fact, the significant impact of nanofiber technology can be traced from the wide range of fundamental materials that can be used for the synthesis of nanofibers. These include natural polymers, synthetic polymers, carbon-based materials, semiconducting materials, and composite materials. Correspondingly, the emerging proof-of-concept applications of nanofibers spanning several important areas have been rapidly reported. This Review explores the current status and up-and-coming development of nanofiber technology, with an emphasis on its syntheses and applications. First, we highlight the current and emerging strategies used in synthesizing nanofibers. We briefly introduce the various established nanofiber synthesis techniques, especially the electrospinning method. We then focus on the emerging nanofiber synthesis strategies, such as solution blow spinning, centrifugal jet spinning, and electrohydrodynamic direct writing. Next, we discuss the emerging applications of nanofiber technology in various fields, specifically in three important areas of energy generation and storage, water treatment and environmental remediation, and healthcare and biomedical engineering. Despite all these advancements, there are still challenges to be addressed and overcome for nanofiber technology to move towards maturation. Nevertheless, we envision that with further progress in the development of nanofiber synthesis strategies and identification of “killer” applications of nanofibers, nanofiber technology will mature and move beyond its current state towards commercial realization and applications.     

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.     

One‐dimensional polymer nanofiber arrays with high aspect ratio obtained by thermal nanoimprint method

Polymer surface modification that mimicks natural behaviors has been a subject of great interest. Fabrication of polymer nanofiber arrays with various applications has been studied intensively. Avoidance of chemical solvents, reduction of processing time, improvement of the nanofiber size distribution and aspect ratios, and improvement of reproducibility have been sought for industrial value creation. This study examines an alternative fabrication methods for polymer nanofiber arrays using a combination of anodic aluminum oxide (AAO) nanoporous template and thermal nanoimprinting lithography for simple, precise processing. Based on those results, nanofiber arrays were fabricated with 40‐µm‐thick film and 50–100 nm fiber diameter polystyrene (PS) and polypropylene (PP). For this study, 50‐nm diameter PS nanofibers with 50 µm maximum length and a maximum aspect ratio of 1,000 were produced in addition to PP nanofibers having 130 µm maximum length and an aspect ratio of 2,600. The nanofiber lengths were affected considerably by molten polymer flow related to imprint processing conditions, polymer properties, AAO properties, and surface wettability between AAO and molten polymers. Moreover, AAO nanoconfinement demonstrated molecular orientation alignment of polymers that affect thermal properties, crystallinity, and mechanical properties of the obtained polymer nanofiber arrays. POLYM. ENG. SCI., 57:214–223, 2017. © 2016 Society of Plastics Engineers     

Study of electrospinning of sodium alginate,blended solutions of sodium alginate/poly(vinyl alcohol) and sodium alginate/poly(ethylene oxide)

Alginate is an interesting natural biopolymer for many of its merits and good biological properties. This paper investigates the electrospinning of sodium alginate (NaAlg), NaAlg/PVA‐ and NaAlg/PEO‐ blended systems. It was found in this research that although NaAlg can easily be dissolved in water, the aqueous NaAlg solution could not be electrospun into ultrafine nanofibers. To overcome the poor electrospinnability of NaAlg solution, synthetic polymers such as PEO and PVA solutions were blended with NaAlg solution to improve its spinnability. The SEM images of electrospun nanofibers showed that the alginate (2%, w/v)–PVA (8%, w/v) blended system in the volume ratio of 70 : 30 and the alginate (2%, w/v)–PEO (8% w/v) blended system in the volume ratio of 50 : 50 could be electrospun into finest and uniform nanofibers with average diameters of 118.3 nm (diameter distribution, 75.8–204 nm) and 99.1 nm (diameter distribution, 71–122 nm), respectively. Rheological studies showed a strong dependence of spinnability and fiber morphology on solution viscosity and thus on the alginate‐to‐synthetic polymer (PVA or PEO) blend ratios. FTIR studies indicate that there are the hydrogen bonding interactions due to the ether oxygen of PEO (or the hydroxyl groups of PVA) and the hydroxyl groups of NaAlg. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Three-dimensional coating of nanofibers on surfaces of poorly conductive objects

Rectangular-shaped, poorly conductive synthetic polymer scaffolds composed of a mixture of polycaprolactone and poly-L-lactic acid (PCL/PLLA, 75:25) were coated directly with nanofibers composed of PLLA using an electrospinning technique having a modified design for the electrically grounded collector. The design modification consisted of mounting each scaffold onto a fine-point needle which was attached directly to the ground electrode of the electrospinning unit. Nanofibers were collected on all six surfaces of each scaffold. The coated scaffolds were then dried at ambient temperature overnight before sterilization by immersion in 100% ethanol to assess and ensure adherence between the scaffold and nanofibers. Photomicrographs from scanning electron microscopy illustrate nanofiber coverage over all six surfaces of the polymer scaffold. The design in this manner for three-dimensional coating of poorly conductive objects advances electrospinning capability for numerous new applications.     

Design and Fabrication of Fibrous Nanomaterials Using Pull Spinning

The assembly of natural and synthetic polymers into fibrous nanomaterials has applications ranging from textiles, tissue engineering, photonics, and catalysis. However, rapid manufacturing of these materials is challenging, as the state of the art in nanofiber assembly remains limited by factors such as solution polarity, production rate, applied electric fields, or temperature. Here, the design and development of a rapid nanofiber manufacturing system termed pull spinning is described. Pull spinning is compact and portable, consisting of a high‐speed rotating bristle that dips into a polymer or protein reservoir and pulls a droplet from solution into a nanofiber. When multiple layers of nanofibers are collected, they form a nonwoven network whose composition, orientation, and function can be adapted to multiple applications. The capability of pull spinning to function as a rapid, point‐of‐use fiber manufacturing platform is demonstrated for both muscle tissue engineering and textile design.

     

Controlling the Diameter of Electrospun Yttria‐Stabilized Zirconia Nanofibers

This work reports the precise diameter control of electrospun yttria‐stabilized zirconia (YSZ) nanofibers from 200 to 900 nm after calcination. Fabricated YSZ nanofibers showed porous nanocrystalline structures with high aspect ratios of more than 500:1 and high surface‐to‐volume ratios with a specific surface area of 43.32 m²/g. The diameter of the YSZ nanofibers increased with the viscosity of the precursor solution, which was controlled by the concentrations of either polymers (polyacrylonitrile) or ceramic precursors (YSZ). We present a modified correlation between the diameter of a nanofiber and the synthetic conditions, as the observed behavior for calcined ceramic nanofibers deviated from the expected behavior. Our results demonstrate a modified but simple approach to fabricate ceramic nanofibers with desired diameters, providing a new design guideline for many electrochemical applications.     

静电纺丝纳米纤维在特殊领域的研究现状和应用

综合阐述了静电纺丝制备纳米纤维的工艺变量以及静电纺丝纳米纤维在特殊领域的研究和应用现状。研究表明:静电纺丝是在静电场作用下将聚合物溶液(或熔体)从喷头喷射出制备纳米纤维的工艺过程,纤维直径从几微米到<100nm,具有独特功能的纳米结构,可广泛应用于导电纤维、生物医用高分子材料等特殊领域。     

Scalable production of polymer nanofiber‐based ropes,cables, and coatings

This article presents a single, scalable manufacturing process for the continuous production of nanofiber‐based ropes, cables, microscale wire coatings, and multimaterial mats. The ropes, cables, and wire coatings were manufactured with a cascading electrospinning setup that was used in conjunction with a rotating ring collector and a take‐up reel. The fibrous mats were realized by replacing the ring collector with a directed nozzle. Both configurations allowed for nanofiber architectures with multiple layers and material combinations. The tensile failure patterns of the cables revealed distinct effects of the multimaterial sheaths. The adhesion strength and load–displacement profiles for the nanofiber coating interfaces were observed to be polymer‐specific. For multimaterial mats, the cospinning of the polymers resulted in a blended mechanical behavior for the composite mats, in contrast to the sequential ply failure observed in laminated mats. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43747.     

Conjugate electrospinning of continuous nanofiber yarn of poly(L‐lactide)/nanotricalcium phosphate nanocomposite

The continuous nanofiber yarns of poly(L ‐lactide) (PLLA)/nano‐β‐tricalcium phosphate (n‐TCP) composite are prepared from oppositely charged electrospun nanofibers by conjugate electrospinning with coupled spinnerets. The morphology and mechanical properties of PLLA/n‐TCP nanofiber yarns are characterized by scanning electron microscope, transmission electron microscope, and electronic fiber strength tester. The results show that PLLA/n‐TCP nanofibers are aligned well along the longitudinal axis of the yarn, and the concentration of PLLA plays a significant role on the diameter of the nanofibers. The thicker yarn of PLLA/n‐TCP composite with the weight ratio of 10/1 has been produced by multiple conjugate electrospinning using three pairs of spinnerets, and the yarn has tensile strength of 0.31cN/dtex. A preliminary study of cell biocompatibility suggests that PLLA/n‐TCP nanofiber yarns may be useable scaffold materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

静电纺丝制备纳米纤维的进展及应用

简述了静电纺丝的制备原理和影响静电纺丝纤维成形的主要工艺因素;介绍了静电纺丝法制备高分子聚合物、生物大分子、无机物纳米纤维的最新进展,以及这些纳米纤维在过滤、传感器、超疏水性材料、生物医用功能材料、纳米模板等领域的应用;指出静电纺丝制备纳米连续长丝技术亟待发展。