Nanofiber systems with various composition and biological properties have been extensively studied for various biomedical applications. The electrospinning process has been regarded as one of the versatile techniques to prepare nano to microfibers. The electrospun nanofibers are being used especially in textile industries, sensors, filters, protective clothing, energy storage materials, and biomedical applications. In the last decade, electrospun nanofibers have been highly investigated for drug delivery systems to achieve a therapeutic effect in specifically targeted sites. Various drugs or biomolecules can be easily loaded into the electrospun nanofibers by direct or indirect methods. The proper selection of polymers (or blends of various polymers), drugs, solvents to prepare the composite nanofibers with desired morphology are the tools in enhancing the bioavailability, stability, and bioactivity of drugs.
TopIntroduction
Nanofibers were initially defined as fibers with a dimeter of less than 100 nm in a narrow sense. However, in a broad sense, the nanofibers refer to the fibers with a diameter below 1000 nm (or 1μm) (Kajdič, Planinšek, Gašperlin, & Kocbek, 2019; Roodbar Shojaei, Hajalilou, Tabatabaei, Mobli, & Aghbashlo, 2019; Rošic, Kocbek, Pelipenko, Kristl, & Baumgartner, 2013). By reducing the diameter of fiber from micrometer to nanometers, several amazing features, for example, high surface to volume ratio, superior mechanical performance, flexibility, etc appeared. These properties make the nanofibers a promising candidate for various applications such as biomedical, filtration, sensor, personal care, energy storage, wastewater treatment, etc (Bhattarai, Bachu, Boddu, & Bhaduri, 2019; Pant, Ojha, Kim, Park, & Park, 2019; Pant et al., 2013; Pant et al., 2012; Pant, Park, Ojha, Park, et al., 2018; Pant, Park, & Park, 2019a; T. Xu et al., 2020). There are several techniques to fabricate the nanofibers from various polymer solutions. The examples include phase separation, drawing, template synthesis, and electrospinning (Gugulothu, Barhoum, Nerella, Ajmer, & Bechelany, 2019). Among the various methods, electrospinning is the most popular approach for generating fibers from polymeric solutions due to its outstanding feathers such as simplicity, versatility, and cost-effectiveness (Pant, Park, et al., 2019a). So far a large number of natural and synthetic polymers as well as their blends have been electrospun into the nanofiber form for various applications, including biomedical (Agarwal, Wendorff, & Greiner, 2008; Lagaron, Solouk, Castro, & Echegoyen, 2017; Pant, Park, et al., 2019a).
History of Electrospinning
In 1745, Bose described that a high electric potential is required to generate aerosols from fluid drops (Bose, 1745). Later, in 1882, Lord Rayleigh calculated the quantity of charge required for overcoming the surface tension of a drop (Rayleigh, 1882). In 1902, Cooley patented (Patent No: 692631) electrospinning and described it as an apparatus for electrically dispersing fluids (Anton, 1934). Anton Formhals developed preparation methods and designed the apparatus (Formhals, 1934). He published a series of patents between 1934 and 1944. From 1964 to 1969, Sir Geoffrey Ingram Taylor brought a significant advancement in the theoretical understanding of electrospinning technique. Taylor defined the characteristic droplet shape, which is now known as the “Taylor cone” (Taylor, 1969). Later on (the late 1990s), several research groups, notably Ranker, popularized electrospinning to study the structural morphology of a wide variety of polymeric nanofibers (Bognitzki et al., 2001; Doshi & Reneker, 1995; Fong, Chun, & Reneker, 1999). Since then, the electrospinning technique has become popular for preparing nanofibers.