## 1 Introduction  
The efficient delivery of drug molecules within the recommended therapeutic level to the target cell, tissue or organ for a defined period of time at a required dose and rate as well as the distribution of associated drugs using appropriate drug carriers to provide sustained release systems are the basic goals of drug-delivery systems (DDS) [1]. The concept has encouraged active and intensive studies to design biodegradable materials as a carrier. Recent efforts have led to the development of a new approach in the field of controlled transdermal drug delivery systems (TDS) with the creation of nano-sizedbiodegradable polymeric carriers [2; 3]. The maintenance of sustained plasma therapeutic concentration, minimized adverse effects, lesser dose and dosing frequency and ease of use are the advantages of TDS [4]. Electrospun nanofibers from a wide variety of polymers and polymer blends have been developed and gained attention as the potential carriers for drugs in wound-dressing materials, medical, biotechnological applications and TDS [5; 6; 7; 8]. Also, electrospun nanofibers have been used in smart DDS as a novel and hot topic with the aim of combining smart stimuli-responsive plasmonic hydrogel with nanofibers [9; 10]. Nanofibrous TDS have outstanding characteristics including large surface-to-volume ratio, high porosity, effective and proper relationship without irritation or adhesion to the skin due to the passage of air through its porous structure [11]. Versatility, simplicity, low star-up cost, continuous unit operation process and easy to scale-up make the electrospinning method an economically viable alternative method to produce continuous nanofibers [12]. Various nanofibrous TDS have been developed based on the encapsulation of a pharmaceutical compound within electrospun nanofibers [13; 14]. The method comprises mixing the drugs into the polymer solution to be electrospun. Drug loaded nanofibrous TDS have the advantage of enhancing drug solubility and bioavailability, modifying the dissolution rate of drug and active substances [15], enhancing therapeutic effects and lowering the toxicity of conventional dosage forms [16; 17]. High surface-area-to-volume ratios, high porosity and the possibility of controlling the crystalline-amorphous phase transition in nanofibers can improve drug dissolution behavior to formulate new TDS for small molecules with poor solubility [13]. Immediate release and controlled release over a period of a few minutes to a few weeks can be achieved using nanofibrous TDS [18]. Recently, [PERSON] et al. used nanofibrous TDS with controlled release behavior and good mucoadhesive strength for the treatment of periodontitis. Their study resulted in the selectivity of the developed therapy with reduced side effects [19]. A wide range of synthetic, natural and blends of polymers have been used in electrospinning including chitosan, fibrinogen, cellulose triacetate [20], poly acrylic acid (PA), poly(vinyl chloride) (PVC), polyurethane (PU) poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) among others, opening new ways for developing effective therapeutic carriers [14; 21]. PVP is an amorphous synthetic polymer with a high affinity for water and good adhesion; it is one of the most important materials used in biomedical and pharmaceutical applications because of its low chemical toxicity and biocompatibility [22]. PVP films have high potential as a new wound-dressing material because they maintain the moisture around wounds preventing dehydration and scab formation [23]. PVP nanofibers are widely used as a polymer carrier for the fabrication of various drug-delivery systems (Table 1) [24; 25; 26; 27; 28; 29; 30; 31; 32]. The studies conducted thus far show that PVP nanofibers have the immediate release of water-soluble drug due to high porosity, high surface-to-volume ratio and the high solubility of the polymer in water [24].