The technique of electrospinning for manufacturing core-shell nanofibers

On account of their low cost coupled with acceptable efficiency, electrospinning can be considered to be both a viable and feasible method for the production of continuous nanofibers having a uniform structure. With noticeable developments in the areas spanning catalysis, fluidics, purification and even separation, nanofibers having a core-shell nanostructure have been both examined and studied with the primary purpose of achieving a uniform structure. With sustained efforts in the domain of both research and development, two electrospinning methods, namely (i) coaxial electrospinning and (ii) emulsion electrospinning, did emerge as potentially viable choices for the preparation of continuous nanofibers having a core-shell nanostructure. In this research paper, the discovery and progress made with specific reference to the techniques of coaxial electrospinning and emulsion electrospinning are examined. A prudent use of the two techniques for the preparation of hollow nanofibers is examined. Potential applications of core-shell nanofibers, prepared using the method of electrospinning, for the purpose of self-healing and drug release are examined and discussed. An outline is provided of the work that is currently being done on aspects related to both theory and experiments with the primary purpose of gaining an understanding of the two techniques.     

熔融静电纺丝技术在组织工程中的应用

介绍了熔融静电纺丝法的基本原理和特征,对其在组织工程领域上的应用进行了总结,并对其发展前景进行展望。熔融静电纺丝过程无需使用溶剂,生产过程具有环境友好性,电纺纤维无毒,生产效率高,正逐渐受到广泛关注。研究发现,由微/纳米纤维复合而成的组织工程支架可以提供更好的细胞微环境。     

Controlled continuous patterning of polymeric nanofibers on three-dimensional substrates using low-voltage near-field electrospinning

We report on a continuous method for controlled electrospinning of polymeric nanofibers on two-dimensional (2D) and three dimensional (3D) substrates using low voltage near-field electrospinning (LV NFES). The method overcomes some of the drawbacks in more conventional near-field electrospinning by using a superelastic polymer ink formulation. The viscoelastic nature of our polymer ink enables continuous electrospinning at a very low voltage of 200 V, almost an order of magnitude lower than conventional NFES, thereby reducing bending instabilities and increasing control of the resulting polymer jet. In one application, polymeric nanofibers are freely suspended between microstructures of 3D carbon on Si substrates to illustrate wiring together 3D components in any desired pattern.     

静电纺丝纳米纤维在吸附分离领域的应用进展

静电纺丝技术作为一种简单有效的制备纳米纤维的方法,制备的纳米纤维具有巨大的比表面积,而且采用该技术制备纳米纤维具有操作简单、易于控制、成本低廉等特点,已经在生物医学领域、国防领域、吸附分离领域等取得了一系列应用进展。本文首先对静电纺丝技术做了概述;其次,对其制备原理、影响因素及应用优势等做了简要的说明;然后重点综述了静电纺丝制得的纳米纤维在吸附分离领域的应用进展,总结了静电纺丝纳米纤维存在的问题并对其在吸附分离领域的应用趋势做出了展望。     

Polyacrylonitrile nanofibers prepared using coaxial electrospinning with LiCl solution as sheath fluid

A modified coaxial electrospinning process including an electrolyte solution as sheath fluid was used for preparing high quality polymer nanofibers. A series of polyacrylonitrile (PAN) nanofibers were fabricated utilizing a coaxial electrospinning containing LiCl in N, N-dimethylacetamide (DMAc) as the sheath fluid. FESEM results demonstrated that the sheath LiCl solutions have a significant influence on the quality of PAN nanofibers. Nanofibers with smaller diameters, smoother surfaces and uniform structures were successfully prepared. The diameters of nanofibers were controlled by adjusting the conductivity of the sheath fluid over a suitable range and this was determined by varying LiCl concentrations. The influence of the effect of LiCl on the formation of PAN fibers is discussed and it is concluded that coaxial electrospinning with electrolyte solutions is a convenient and facile process for achieving high quality polymer nanofibers.     

Sustained-release multiple-component cellulose acetate nanofibers fabricated using a modified coaxial electrospinning process

Two drawbacks of the traditional electrospinning process when used for producing nanofibers for drug release are that clogging of the spinneret is often experienced, and the fibers produced often exhibit a tailing-off of drug release over sustained periods. The present study investigates the preparation of ferulic acid (FA) sustained-release cellulose acetate (CA) nanofibers, in which a third component, polyvinylpyrrolidone (PVP), was included into the nanocomposites for an improved sustained drug release profile. A modified coaxial electrospinning process, in which only organic solvent N,N-dimethylacetamide was used as a sheath fluid, was exploited for a smooth and continuous fabrication of multiple-component nanofibers. Under an applied voltage of 16 kV and an optimized sheath-to-core flow rate ratio of 0.11, three types of FA/PVP/CA composite nanofibers (with varied of PVP content) were generated. These nanofibers had higher quality in terms of size and distribution of nanofiber diameter, as indicated by FESEM images. Analysis of double- and triple-component nanofibers by XRD, DSC, and ATR-FTIR confirmed the compatibility of components producing homogenous fibers in both cases, but the triple-component nanofibers exhibited better release profiles over sustained periods than the double-component nanofibers in terms of release completeness, reduced tailing-off, and adjustable release rates. The modified coaxial process and the resulting multiple-component nanocomposites should provide a new way for developing novel drug sustained materials and drug delivery systems.     

Nanofiber deposition by electroblowing of PVA (polyvinyl alcohol)

Electrospinning provides a relatively versatile method of creating a variety of ultrathin nanofibers. One of the well known problems in electrospinning is low productivity. To increase the inherently low productivity in electrospinning, an assembly of multi-needles has been widely introduced. This process may be enhanced by introducing the electroblowing process that combines air blowing and electrospinning. In this study, the effect of electroblowing on web deposition was explored via the simultaneous and separate application of two forces: an electrostatic force and an air blowing-induced shear force, which are adjusted by the applied voltage and the air blowing pressure, respectively. The image filtering technology was used to evaluate the web deposition. The application of the shear force significantly affected the web deposition, especially at low voltage.     

A review: carbon nanofibers from electrospun polyacrylonitrile and their applications

Carbon nanofibers with diameters that fall into submicron and nanometer range have attracted growing attention in recent years due to their superior chemical, electrical, and mechanical properties in combination with their unique 1D nanostructures. Unlike catalytic synthesis, electrospinning polyacrylonitrile (PAN) followed by stabilization and carbonization has become a straightforward and convenient route to make continuous carbon nanofibers. This paper is a comprehensive and state-of-the-art review of the latest advances made in development and application of electrospun PAN-based carbon nanofibers. Our goal is to demonstrate an objective and overall picture of current research work on both functional carbon nanofibers and high-strength carbon nanofibers from the viewpoint of a materials scientist. Strategies to make a variety of carbon nanofibrous materials for energy conversion and storage, catalysis, sensor, adsorption/separation, and biomedical applications as well as attempts to achieve high-strength carbon nanofibers are addressed.     

Needle-disk electrospinning inspired by natural point discharge

Point discharge is a natural phenomenon which principle and application are both under active investigation. In this work, a needle-disk electrode spinneret was designed through the combination of the point discharge concept and the merits of typical needleless electrospinning (disk as spinneret). The desired outcome for point electrode system is to produce a controllable process of jet formation, with respect to the control of jet site and amount of jets under a lower applied voltage value. Two comparisons were used: (i) in comparison to the typical needleless electrospinning method (disk electrospinning), the needle-disk electrospinning produce finer and more uniform nanofibers. Further numerical simulation results confirmed that the needle-disk electrode induced electric field intensity which is 5.33 times higher than that of disk electrode under the same parameters; (ii) both the numerical simulation and experimental results showed that needle-disk electrospinning can produce competitive quality of nanofibers accompanied by enhanced throughput, compared with the traditional single-needle electrospinning method. Finally, we demonstrate that needle-disk electrospinning produces nanofiber with super-high throughput of 13.5 g/h, which is 183 times higher than traditional electrospinning under similar spinning conditions.     

Electrospun porous nanofibers for electrochemical energy storage

The demand for energy storage systems is rising due to the rapid development of electric transportation vehicles, and this demand is stimulating research on the next generation of high-performance, high-density energy storage devices. In this work, nanomaterials with excellent electrochemical properties are of particular significance. This review summarizes a variety of methods based on electrospinning techniques for the preparation of porous nanofibers with controllable morphologies. An emphasis is placed on methods involving polymer templates and polymer blend templates, hard templates, and on solvent-induced, nonsolvent-induced or activation methods. As a simple and cost-effective method for preparing one-dimensional nanomaterials, the electrospinning technique is of special significance in the energy storage field, because the as-prepared porous nanofibers exhibit large specific surface areas and interconnected micro-/meso-/macroporous structures. Both of these features enable greater energy storage. Furthermore, this review presents several suggestions for meeting the challenges involved in the preparation and industrial application of electrospun porous nanofibers for advanced energy storage systems.     

静电纺丝法制备陶瓷中空纳米纤维的研究进展

陶瓷中空纳米纤维具有特殊的纳米一维管式结构, 在微电子、应用催化、气体传感器和光电转换等领域具有良好的应用前景。本文综述了静电纺丝法制备陶瓷中空纳米纤维的最新研究进展, 主要包括同轴静电纺丝法、单针头静电纺丝法以及后处理法在制备陶瓷中空纳米纤维方面的发展趋势, 重点介绍了单针头静电纺丝法在制备中空纳米结构上存在的相转化、气体挥发和柯肯达尔效应等机理, 并且对于陶瓷中空纳米纤维的应用前景以及不足进行了展望与总结。     

Preparation of short submicron-fiber yarn by an annular collector through electrospinning

Electrospinning is known to be a unique method to prepare continuous nanofibers. Its brevity and extensive application in obtaining non-woven membrane, nanofiber bundle or yarn have attracted increasing attention throughout the world. Especially, how to obtain aligned nanofiber array by a modified electrospinning process has been a hot topic in recent years. An annular collector with the cross-section of circle to obtain fibrous yarn through electrospinning, pre-drafting, and subsequent twisting was reported in this investigation. Fiber arrangement in bundle and mechanical properties of the yarn were given by scanning electron microscope and strength tester. Results showed that the pre-drafted bundle consisted of highly-aligned submicron fibers with the diameter from 750 to 1000 nm. In addition, it was found that the yarn is unsuitable for clothing, but may be applied in many other fields, such as composites, tissue engineering, and catalyst materials.     

A new nanofiber fabrication technique based on coaxial electrospinning

In tissue engineering, nanofibrous scaffolds can achieve better biological responses than microfibrous scaffolds and electrospinning is a common method for producing fibrous scaffolds. However, not all biopolymers can be made into nanofibers through conventional electrospinning. The current investigation developed an innovative nanofiber fabrication technique based on coaxial electrospinning and used poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) as an example for achieving nanofibers. For obtaining PHBV nanofibers, core-shell structured fibers were fabricated first via coaxial electrospinning, with PHBV being the core and chitosan being the shell. The chitosan shell was then removed by washing electrospun scaffolds with water, leading to the formation of nanofibrous PHBV scaffolds. The PHBV nanofiber diameter was affected by the inner polymer (i.e., PHBV) solution concentration during coaxial electrospinning, which can be explained in terms of the coaxial electrospinning process and polymer solution viscosity. Compared to the approach of using a conductivity-enhancing salt in polymer solution to produce polymer nanofibers, the new technique not only eliminates the biocompatibility concerns but also provides a more effective way of reducing fiber diameters to the nano-size range.     

Smoothening electrospinning and obtaining high-quality cellulose acetate nanofibers using a modified coaxial process

The present research investigates a modified coaxial process for smoothening electrospinning of cellulose acetate (CA) and obtaining its nanofibers with high quality. With 11 w/v% CA in mixed solvent of acetone and N,N-dimethylacetamide (DMAc) (v:v, 3:1) as electrospinnable core fluid, different solvents (acetone, DMAc and their mixture) are taken as sheath fluids to conduct the modified process. SEM observations demonstrate that the modified process is effective in retarding the clogging of spinneret for a smooth electrospinning and in obtaining high quality CA nanofibers in terms of structural uniformity, diameters, and their distributions. The mechanism about the influence of sheath fluid on the process and the formation of nanofibers is discussed. The key for the modified coaxial process is the reasonable selection of sheath fluids and a sheath-to-core flow rate ratio matching the drawing process of core CA fluid during the electrospinning. The present paper provides a simple method to implement the modified coaxial process for smoothening the electrospinning and obtaining polymer nanofibers with high quality.     

Preparation of photocrosslinkable polystyrene methylene cinnamate nanofibers via electrospinning

Nanoscaled photocrosslinkable polystyrene methylene cinnamate (PSMC) nanofibers were fabricated by electrospinning. The PSMC was prepared by the modification of polystyrene as a starting material via a two-step reaction process, chloromethylation and esterification. The chemical structure of PSMC was confirmed by 1H NMR and Fourier transform infrared spectroscopy (FT-IR). The photosensitivity of the PSMC was investigated using ultraviolet (UV) spectroscopic methods. Electrospun PSMC nanofiber mat showed excellent solubility in many organic solvents. UV irradiation of the electrospun mats led to photodimerization to resist dissolving in organic solvents. The morphology of the nanofiber was observed by scanning electron microscopy (SEM) and the result indicated that the average diameter of nanofibers is 350 nm and the crosslinked nanofibers were not collapsed after dipping into organic solvent showing good solvent-stability. This photocrosslinked nanofibers has the potential application in filtration, catalyst carrier and protective coating.     

Electrospun composite nanofibers for tissue regeneration

Nanotechnology assists in the development of biocomposite nanofibrous scaffolds that can react positively to changes in the immediate cellular environment and stimulate specific regenerative events at molecular level to generate healthy tissues. Recently, electrospinning has gained huge momentum with greater accessibility of fabrication of composite, controlled and oriented nanofibers with sufficient porosity required for effective tissue regeneration. Current developments include the fabrication of nanofibrous scaffolds which can provide chemical, mechanical and biological signals to respond to the environmental stimuli. These nanofibers are fabricated by simple coating, blending of polymers/bioactive molecules or by surface modification methods. For obtaining optimized surface functionality, with specially designed architectures for the nanofibers (multi-layered, core-shell, aligned), electrospinning process has been modified and simultaneous 'electrospin-electrospraying' process is one of the most lately introduced technique in this perspective. Properties such as porosity, biodegradation and mechanical properties of composite electrospun nanofibers along with their utilization for nerve, cardiac, bone, skin, vascular and cartilage tissue engineering are discussed in this review. In order to locally deliver electrical stimulus and provide a physical template for cell proliferations, and to gain an external control on the level and duration of stimulation, electrically conducting polymeric nanofibers are also fabricated by electrospinning. Electrospun polypyrrole (PPy) and polyaniline (PAN) based scaffolds are the most extensively studied composite substrates for nerve and cardiac tissue engineering with or without electrical stimulations, and are discussed here. However, the major focus of ongoing and future research in regenerative medicine is to effectively exploit the pluripotent potential of Mesenchymal Stem Cell (MSC) differentiation on composite nanofibrous scaffolds for repair of organs.     

Near-field electrospinning

A near-field electrospinning (NFES) process has been developed to deposit solid nanofibers in a direct, continuous, and controllable manner. A tungsten electrode with tip diameter of 25 microm is used to construct nanofibers of 50-500 nm line width on silicon-based collectors while the liquid polymer solution is supplied in a manner analogous to that of a dip pen. The minimum applied bias voltage is 600 V, and minimum electrode-to-collector distance is 500 microm to achieve position controllable deposition. Charged nanofibers can be orderly collected, making NFES a potential tool in direct write nanofabrication for a variety of materials.     

Effect of heating rate on morphology and structure of CoFe2O4 nanofibers

Electrospinning is a novel technique used to fabricate nanometers to micrometers diameter polymeric and ceramic fibers. The morphology and structure of fibers which would be dominated by electrospinning process parameters and calcinations conditions are important when considering practical applications. This paper involves an investigation of how heating rate influence morphology and structure of CoFe₂O₄ nanofibers. The morphology of CoFe₂O₄ nanofibers changes from a continuous fibrous structure for low heating rate to a winding and packed crystallites nature for high heating rate, increasing heating rate also causes an increase in diameter. FTIR and XRD results demonstrate that PVP/CoFe₂O₄ composite nanofibers for all heating rate form CoFe₂O₄ cubic phase with very high crystallinity after calcinations.     

In-situ growth of titania nanoparticles in electrospun polymer nanofibers at low temperature

In-situ growth of titania nanoparticles in poly (ethylene terephthalate) (PET) nanofibers has been successfully achieved by combining sol-gel method and electrospinning process. Titania precursor, tetra-n-butyl titanate (TBT), was firstly hydrolyzed in trifluoroacetic acid (TFA), and then blend with a solution of PET in mixture of trifluoroacetic acid/dichloromethane (TFA/DCM) to form a homogeneous solution for electrospinning. Titania nanoparticles in-situ generated in the electrospun nanofibers via a hydrothermal treatment process at 70 °C-90 °C. The morphology and crystallinity of PET/TiO₂ hybrid nanofibers were investigated using TEM and DSC. The results showed that titania nanoparticles of anatase phase with an average diameter of about 10 nm in-situ generated both inside and on the surface of PET electrospun nanofibers. The reversible networks formed between titania nanoparticles and PET macromolecular chains led to considerable decrease of PET crystallinity.     

静电纺丝复合纳米纤维研究进展

静电纺丝是一种利用聚合物溶液或熔体在强电场中进行喷射纺丝的加工技术,是获得纳米尺寸纤维的有效方法之一。然而单一组分的纳米纤维已经难以满足应用的需求,而采用两种或两种以上的聚合物(或聚合物/填料颗粒)进行静电纺丝得到的复合纳米纤维逐渐受到了人们的关注。文中总结了由静电纺丝技术制备的复合纳米纤维及其性能等方面的研究进展。主要包括复合物/碳复合纳米纤维、聚合物/金属复合纳米纤维、聚合物/粘土复合纳米纤维、共混物复合纳米纤维、装饰型复合纳米纤维等。