**1. Introduction**

Electrospinning is a fiber spinning technique that is able to produce continuous ultrafine fibers from sub-micrometer to nanometer diameters, which uses electrostatic forces. The original ideas of using electrical potentials on the surfaces of droplets, amount of charge required for the deformation of droplets, and also apparatus for spraying of liquids by use of electrical charges can be traced back more than 100 years [1–3]. However, Formhals was recognized as the father of the electrospinning and he was the first to describe the operation of electrospinning in 1934 for producing polymer filaments by electrostatic repulsions between surface charges [4].

Despite these early studies, researches in nanofibers and electrospinning have received a great deal of attention, after 1990s, especially after Doshi and Reneker [5], Srinivasan and

Reneker [6], and Reneker and Chun [7], spun various kinds of polymers including polyethylene oxide, nylon, polyimide, DNA, polyaramid, and polyaniline, and were able to characterize their properties. Afterward this old technology rediscovered, refined, and expanded into non-textile applications. Electrospinning process is unique among other nanofiber fabrication techniques in terms of ease of use, vast possibilities of material selection and combination, and it has a potential for scale-up. This has led to electrospinning being considered as a key platform technology that will be studied to develop products for a wide range including drug delivery, tissue scaffolding, wound dressing, electronics, chemical sensors, filtration, and so on [8]. This rediscovery and attention are partly the results of leading-edge technology, especially, scanning probe microscopy and high-resolution electron microscopy, which enable the exploration of the "nanodimension."
