Electrospinning traces its roots to electrostatic spraying, which was first described more than 100 years ago. In electrostatic spraying, charge is injection into a liquid, typically 5-30 kV, from an electrode. The charged liquid is separated some distance from a second electrode (target) of opposite polarity to establish a static electric field. A so-called Taylor Cone forms due to the competing forces of the static electric field and the liquid's surface tension. For liquids with a finite conductivity, charged droplets are dispersed from the tip of the Taylor Cone and are delivered to the target. If the liquid consists of a polymer melt or a polymer in solution and the concentration of that polymer is sufficiently high to cause molecular chain entanglement, a fiber, rather than a droplet, is drawn from the tip of the Taylor cone.   A basic electrospinning system (Figure below on left) consists of a charged polymer solution (or melt) that is fed through a small opening or nozzle (usually a needle or pipette tip). Because of its charge, the solution is drawn toward a grounded collecting plate (usually a metal screen, plate, or rotating mandrel), typically 5 - 30 cm away, as a jet. During the jet's travel, the solvent gradually evaporates, and a charged polymer fiber is left to accumulate on the grounded target. The charge on the fibers eventually dissipates into the surrounding environment. The resulting product is a non-woven fiber mat that is composed of tiny fibers with diameters between 50 nanometers and 10 microns. This non-woven mat forms the foundation of the scaffold. If the target is allowed to move with respect to the nozzle position, specific fiber orientations (parallel alignment or a random) can be achieved. Previous work has shown that the mechanical properties of the scaffold can be varied by varying the fiber diameter and orientation. Appplication: Electrospinning uses an electrical charge to form a mat of fine fibers. Electrospinning shares characteristics of both the commercial electrospray technique and the commercial spinning of fibers. The standard setup for electrospinning consists of a spinneret with a metallic needle, a syringe pump, a high-voltage power supply, and a grounded collector. A polymer, sol-gel, composite solution (or melt) is loaded into the syringe and this liquid is driven to the needle tip by a syringe pump, forming a droplet at the tip. When a voltage is applied to the needle, the droplet is first stretched into a structure called the Taylor cone. If the viscosity of the material is sufficiently high, varicose breakup does not occur (if it does, droplets are electrosprayed) and an electrified liquid jet is formed. The jet is then elongated and whipped continuously by electrostatic repulsion until it is deposited on the grounded collector. Whipping due to a bending instability in the electrified jet and concomitant evaporation of solvent (and, in some cases reaction of the materials in the jet with the environment) allow this jet to be stretched to nanometer-scale diameters. The elongation by bending instability results in the fabrication of uniform fibers with nanometer-scale diameters. 
Schematic of an electrospinning setup shown without a syringe pump.
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