**2. Electrospinning**

The electrospinning process simply constituted of a high voltage power supply, a spinneret and a deposition area named as collector generally covered with an aluminum foil. The potential difference between the spinneret and the collector leads to the stretch of the polymeric solution and creates a thin nanofiber jet from solution toward to the deposition area. During this electrospinning process, the solvent evaporates and ultrafine fibers are collected [9, 10]. Main process equipments and setup are presented in **Figure 1**.

The electrospinning process has attracted a great deal of attention due to the ability to fabricate fibers with diameters on the nanometer scale [11, 12], vast possibilities for surface functionalization [13, 14] with high surface area to volume or mass ratio, small inter-fibrous pore size and high porosity [11, 15, 16]. Technically, almost any soluble polymer with a sufficiently high molecular weight can be electrospun, and [17] various polymers have been successfully electrospun into nanofibers cost-effectively compared to the other methods.

The method can be applied to synthetic and natural polymers, polymer blends, and polymers loaded with chromophores, nanoparticles, or active agents, as well as to metals and ceramics [18]. A large number of inorganic salts, inorganic and organic particles, and carbon nanotubes (CNTs), can also be immobilized in polymer fibers [19]. More than 100 different polymers have been successfully electrospun into ultrafine fibers using this technique [10] including synthetic polymers such as PU [20–29].
