Electrospinning

Among different fiber manufacturing techniques, electrospinning has been widely used in the manufacture of tissue scaffolds with an average fiber diameter at micrometer or nanometer scales due to its relatively simple and easy control of critical process parameters [227, 228]. In the past decade, different natural materials, like collagen and chitosan, and synthetic polymers, like PLA, polyglycolic acid, poly- caprolactone, etc. can be electrospun into fibers with different diameters from nanoscale to microscale for the development of tissue scaffolds [229, 230]. As the most commonly used technique, it also plays an important role in the manufacture of scaffolds for tissue engineering, and its application examples are numerous.

Basically, in electrospinning, a high voltage is used to produce an electrically charged jet of polymer solution or melt that forms polymer fibers after drying or solidification [73, 230, 231]. This process is controlled by a high intensity electric field between two electrodes having an opposite polarity charge. One electrode is placed in the polymer solution, and the other is placed in a collector. Typically, the polymer solution is pumped as a result to form a drop of solution. Afterward, an electric field is generated and intended to produce a force caused by the droplet to overcome the surface tension of the solution. A jet of the polymer is ejected to produce the fibers while the solvent begins to evaporate due to the jet formation and continues after the nanofibers are deposited to the collector (Fig. 2.11). The electrospinning can produce fibers with diameters in the range of 100 nm to several micrometers, and the fibers have special orientation, high aspect ratio, high surface area and controllable pore geometry, which are favorable for better cell adhesion, cell expression, and transportation of oxygen and nutrients to the cells. The factors that influence the electrospinning process are the physical properties of polymer

Fig. 2.11 Electrospinning of polymeric fibers that are drawn under an applied electric field and deposited on a surface to form a fibrous scaffold [73] (Adapted with permission from Ref. [73]. Copyright 2013 Elsevier Ltd)

(e.g., viscosity, electrical conductivity and surface tension), the applied electric field, the polymer flow rate and the distance between the jet and the collector.

This technique, as one of the main processing methods, has been applied to fabricate the reinforced composites for various scaffolds in tissue engineering. There are countless examples of this technique used for the reinforced scaffolds. Kang et al. [113] found that MWCNTs embedded in the silk fibroin nanofibers by electrospinning were well aligned along the nanofibers axis. Cont et al. [82] designed a novel composite scaffolds consisting of long continuous bidirectional fibers embedded in an electrospun matrix for the purpose of using them in soft tissue engineering applications. He et al. [232] prepared all-cellulose nanocomposite nanofibers reinforced with cellulose nanocrystals by electrospinning. Yang et al. [233] developed an electrospun-aligned nanoyarn-reinforced scaffold for tendon tissue engineering to improve mechanical strength and cell infiltration. Rui et al. [234] fabricated anisotropically aligned nanofibrous scaffolds reinforced with cellulose nanocrystals for tendon tissue engineering by electrospinning. Eslami et al. [235] integrated electrospun poly(glycerol sebacate) (PGS)- PCL microfiber scaffolds for heart valve engineering.

The advantages of electrospinning for scaffold fabrication are relative simple and have the possibility of enlarging and effectively controlling critical process parameters such as flow rate and voltage. However, the disadvantages of the technique are that it is difficult to create complex 3D scaffold shapes and internal pore networks, and the average fiber diameter is usually on the larger side of the ECM fibers and sometimes falls within micrometer range.

 
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