Electrospinning

Electrospinning was described already in the early 19th century (39,40). Details of modem electrospirming techniques have been described (41,42). 

The process of electrospinning in an intermediate of dry spinning and electrospraying. Typically, draw very fine fibers can be fabricated in the range of micrometers and nanometers. 

Electrospinning techniques are used to form particles and fibers as small as one nanometer in a principal direction. The phenomenon of electrospray involves the formation of a droplet of polymer melt at an end of a needle, the electric charging of that droplet, and an expulsion of parts of the droplet because of the repulsive electric force due to the electric charges. In electrospraying, a solvent present in the parts of the droplet evaporates and small particles are formed but not fibers. The electrospinning technique is similar to the electrospray technique. However, in electrospinning and during the expulsion, fibers are formed from the liquid as the parts are expelled (41). 

Biological materials and biocompatible materials that can be elec-troprocessed have been described (43 5). 

The electrospinning method is used to generate a nonwoven web of micro- or nanofibers. In this method, high voltage electricity is applied to the liquid solution and a collector, which lets the solution extrude from a nozzle forming a jet. The jet formed fibers during drying and deposited these on the 

Important parameters in electrospinning are not only potymer and solution properties such as molecular weight, viscosity, conductivity and surface tension but also electrospinning conditions such as applied electric voltage, tip-collector distance, and feeding rate (Ceng et al., 2005). 

The parameters impacting the electrospinning process can be categorized into solution parameters (surface tension, concentration, viscosity and conductivity), processing conditions (voltage, distance from needle to collector, type of collector, flow rate) and ambient conditions (humidity, pressure and temperature) [90, 91]. Based on the interaction of all these factors, the morphology and size of resultant nanofibers can be changed. 

It is worth noting that new types of materials known as composite or hybrid nanofiber using electrospinning of CNC and different polymers such as polyethylene oxide (PEO) [108], polyvinyl alcohol (PVA) [109] and polymethyl methacrylate (PMMA) [45] have been fabricated. 

In 1951, a process to degrade cellulosic fibers with H SO was introduced by Ranby for the first time [111]. Since then a series of attempts have been taken to prepare CNC from various cellulosic fibers such as curaua fibers [117], coconut husk [118], cotton and tunicates [119], sugarcane bagasse [120], and wood [ 121 ]. In the acid hydrolysis process a suspension with specific acid concentration for a particular time and temperature based on various sources of fibers is mechanically stirred. Then the reaction is quenched with cold water. Subsequently, the washing process is conducted 

CHT/MWNT composite nanofihres can be fabricated by electrospinning. In our experiments, different solvents, including acetic acid (1-90%), formic acid and trifluoroacetic acid (TFA)/dichloromethane (DCM) were tested for the electrospinning of CHT/CNT. No jet was seen when applying a high voltage (even above 25 kV), with 1-30% acetic acid and formic acid as solvent for the CHT/CNT nanocomposite. 

TFA/DCM (70 30) was the only solvent that resulted in the production of CHT/CNT composite nanofibres during electrospinning. The scanning electron microscopic images showed homogenous fibres with an average diameter of 455 nm prepared by dispersing the CHT/CNT in TFA/DCM 70 30. These nanofibres have potential 

The idea of using an electric field for the production of textile fibers from a polymer melt or solution was conceived in the early 30s [1], In 1969, Taylor conducted a study of a drop of polymer on the tip of a capillary in an electrospinning equipment. This study led to a greater understanding of the behavior of polymer solutions ejected from a capillary [2], 

In a typical electrospinning process, high voltage between 5 and 50 kV is used to create an electric field between a drop of polymer solution at the tip of a capillary tube and a collector plate, as exemplified in Fig. 4.1. 

Nanofibers and webs are capable of delivering medicines directly to internal tissues. Anti-adhesion materials made of cellulose are already available from companies such as Johnson Johnson and Genzyme Corporation [19]. Namekawa etal. [20] developed a zeolite-polymer composite nanofiber mesh to remove uremic toxins for blood purification. The nanofiber is composed of blood compatible poly(ethylene-co-vinyl alcohol) (EVOH) as the primary matrix polymer and zeolites which are capable of selectively adsorbing uremic toxins such as creatinine. It was suggested that the proposed composite fibers have the potential to be utilized as a new approach to removing nitrogenous waste products from the bloodstream without the requirement of specialized equipment [21]. Kidney failure patients can have an alternative to dialysis in the form of nanofiber mesh which is portable and wearable. 

Under suitable conditions, an oriented filament can also be obtained (Fig. 3.7c and d). Oriented fiber mats can be obtained by using a rotating mandrel. Porous fibers can be obtained via phase separation process and selective extraction. Hollow fibers can be obtained by co-spinning two polymers followed by extraction of the core material. Additional advances in the technique have produced innovative architecture in these electrospun mats [10]. 

Some of the processing parameters are the nature of the solvent (polarity, conductivity, solubility, rate of evaporation), polymer concentration (viscosity, surface 

An important commercial application of the nondegradable electrospun fibers is high-efficiency particulate absorption (HEPA) filters for air purification. In biomedical area, electrospinning is used to fabricate tissue engineering scaffolds to mimic ECM function, in which the cell response of the mat can be tuned by tuning fiber diameter and mesh size. 

A typical electrospinner is made up of four main components (1) DC power supply capable of supplying greater 

FIGURE 14.19 Comparison of diameter and surfaee area of fibers produeed different processes. 

In view of the toxicity of the solvents used for dissolving PLA, several studies successfully electrospun PLA from the melt phase. Zhou et al. [110] deployed an electrospinning setup where the polymer was held in a heated reservoir maintained at 200°C, while the nozzle of the spinneret was 

This method was expanded to composite formulations with carbon nanotubes (CNTs) or inorganic nanoparticles, such as Ti02 and ZnO, added to the polymer solution. The polymer can be removed by thermal treatment afterward, leading to purely inorganic fibers. The major issues with this technique are that the fibers are randomly oriented and that once the fibers are collected, their structure is fixed as they are difficult to handle (their diameter is in the range of A few nanometers to A few micrometers). 

1 A First Case TI02 Fibers for Dye-Sensitized Solar Cells 

Titanium dioxide (Ti02) is a typical n-type semiconductor that has been widely used in industry due to its unique and various properties such as its antibacterial properties, its stability, its super hydrophilic behavior under radiation, and its photocatalytic properties [55]. This material is found in applications such as photovoltaic cells with dye-sensitized solar cells (DSSCs), sensors, self-cleaning coatings, painting, and air and water depollution (heterogeneous catalysis). 

DSSC technology was introduced by O Regan and Gratzel in 1991, and can be described as artificial photosynthesis [56]. Typically, the working electrode of a DSSC is made of a Ti02 nanoparticle-based (—20 nm diameter) mesoporous 

Most current reports dealing with inorganic fibers derived from electrospinning deal with electrospun suspensions of premade inorganic particles or inorganic precursors diluted in a polymer solution that provide suitable viscoelastic properties for the electrospinning process. The polymer acts as a support and is removed afterward by calcination to yield the fully inorganic ID object. This approach has been very successful for many systems [62,63], but 

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Kwon and coworkers prepared a series of nano- to microstmctured biodegradable PCLA porous fabrics by electrospinning. The nanoscale-fiber porous fabrics were electrospun with PCLA (1 1 mole ratio, approximately 0.3-1.2 mm in diameter) using l,l,l,3,3,3-hexafluoro-2-propanol as a solvent. 

Bedford, N.M. and Steckl, A.J. (2010) Photocatalytic self cleaning textile fibers by coaxial electrospinning. ACS Applied Materials ej Interfaces, 2, 2448-2455. 

Electroslag remelting, 23 255 Electroslurry process, 23 576 Electrospinning, 11 186 Electrospray ionization, liquid chromatography, 4 625 Electrospray ionization source, 15 654-658 Electrostatic atomization, in spray coating, 7 72-73... 

Viswanathan G, Murugesan S, Pushparaj V, Nalamasu O, Ajayan PM, Linhardt RJ (2006) Preparation of biopolymer fibers by electrospinning from room temperature ionic liquids. Biomacromolecules 7 415 418. 

To prepare nano-fibers of polymers, electrospinning is developed... 

McKee MG, Elkins C, Long TE. Influence of self-complementary hydrogen bonding on solution rheology/electrospinning relationships. Polymer 2004 45 8705-8715. 

Electrospinning is a method allowing creation of polymer fibers with diameters in the range between a few tens of nanometers to a few micrometers, starting from a solution of preformed polymer. MIP nanoparticles have been included into nanofibers by electrospinning [126, 127], In another case, the nanofibers were directly produced by electrospinning and polymerizing an MIP-precursor solution [128]. Such MIP fibers can then be used, for example, for the preparation of affinity separation materials [129] or as affinity layers in biosensors [127, 130]. 

Keywords Bioactive Biomaterials Biomimetic Cellular infiltration Electrospinning Extracellular matrix Hydrogels Nanofibers Polymer scaffolds Tissue... 

Fig. 2 Scaffold architecture affects cell binding and spreading. The examples were obtained by (a) phase separation/leaching combination and (b-d) electrospinning. Porosity data was roughly estimated note that classic nanofiber structure is <100 nm, but here is <1000 nm, as found commonly in biomedicine. Scale bars (a) 500 pm, (b-d) 10 pm. Top row. adapted from [12] bottom row. reprinted, with permission, from [47] copyright (2004) Elsevier [48] copyright (2010) Wiley-VCH...

Although the principle of this technique is quite old, electrospinning (ES) has been developed as a powerful tool for the design of fiber meshes with fiber diameters ranging from 10 pm down to a few nanometers, mesh porosities of <90%, and pore sizes of < 1 to 100 pm [156, 157],... 

Zarkoob et al. (1998, 2004) were the first to report on the electrospinning of silkworm silk and Nephila clavipes dragline protein. They used an HFIP solution of protein as the spinning dope. The resulting fibers had a wide distribution in diameter and the continuity during spinning could be significantly improved. 

In order to improve the properties and the spinnability, fibroin sometimes has been electrospun together with other natural or synthetic polymers (Jin et al., 2002 Park et al., 2004, 2006 Wang et al., 2004, 2006). For instance, Jin et al. (2002) developed an aqueous process for silk electrospinning in combination with PEO. More recently, Cao (2008) used PVA/Silk Fibroin (SF), Gelatin/SF, and Hydroxyapatite (HAP)/SF to produce double-layered (core-shell) nanofibers (mats) by coelectrospinning. 

Table 5 Some fibroin electrospinning results using different solution system...

Chen, C., Cao, C.B., Ma, X.L., Tang, Y., and Zhu, H.S. "Preparation of non-woven mats from all-aqueous silk fibroin solution with electrospinning method". Polymer 47(18), 6322-6327 (2006a). 

Sukigara, S., Gandhi, M., Ayutsede, J., Micklus, M., and Ko, F. "Regeneration of Bombyx mori silk by electrospinning - part 1 Processing parameters and geometric properties". Polymer 44(19), 5721-5727 (2003). 

Wang, H., Shao, H.L., and Hu, X.C. "Structure of silk fibroin fibers made by an electrospinning process from a silk fibroin aqueous solution". J. Appl. Polym. Sci. 101(2), 961-968 (2006). 

Wang, M., Yu, J.H., Kaplan, D.L., and Rutledge, G.C. "Production of submicron diameter silk fibers under benign processing conditions by two-fluid electrospinning". Macromolecules 39(3), 1102-1107 (2006). 

Yu Y, Gu L, Zhu C, Van Aken PA, Maier J. Tin nanoparticles encapsulated in porous multichannel carbon microtubes preparation by single-nozzle electrospinning and application as anode material for high-performance Li-based batteries. J Am Chem Soc. 2009 131 15984-5. 

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