Electrospinning

Electrospinning uses an electrical charge to draw very fine (typically on the micro or nano scale) fibers from a liquid. Electrospinning shares characteristics of both electrospraying and conventional wet spinning of fibers.

Process

The standard laboratory setup for electrospinning consists of a spinneret (typically a hypodermic syringe needle) connected to a a high-voltage (5 to 50 kV) direct current power supply, a syringe pump, and a grounded collector plate. A polymer solution, sol-gel, particulate suspension or melt is loaded into the syringe and this liquid is extruded from the needle tip at a constant rate by a syringe pump, forming a droplet at the tip. When a voltage is applied to the needle, the flowing liquid is stretched into a Taylor cone. If the molecular cohesion of the material is sufficiently high, stream breakup does not occur (if it does, droplets are electrosprayed) and a charged liquid jet is formed. The jet is then elongated by a whipping process caused by electrostatic repulsion initiated at small bends in the fibre, 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.D. Li, X. Xia. Electrospinning of Nanofibers: Reinventing the Wheel?. Advanced Materials. 2004, 16, 1151-1170.]

History

This process was patented by J.F Cooley in February 1902 (US Patent|692631) and by W.J. Morton in July 1902 (US Patent|0705691. Further developments were made by Anton Formhals, described in a sequence of patents from 1934 (US Patent|1975504) to 1944 (US Patent|2349950) for the fabrication of textile yarns. Electrospinning from a melt rather than a solution was patented by C.L Norton in 1936 (US Patent|2048651) using an air-blast to assist fibre formation.

There was not much interest in the process from this period until the early 1990s, when several research groups demonstrated that many organic polymers could be electrospun into nanofibers. Since then, the number of publications about electrospinning has been increasing exponentially every year..

Uses

Textile manufacturing

Electrospinlacing is the use of electrospinning to combine different fibers and coatings to form three dimensional shapes, such as clothing.S. Lee, S.K. Obendorf. Use of Electrospun Nanofiber Web for Protective Textile Materials as Barriers to Liquid Penetration. Textile Research Journal. Sep 2007.]

Electrospinning can produce seamless garments by integrating advanced manufacturing with fiber electrospinning. This would introduce multi-functionality (flame, chemical, environmental protection) by blending fibers into electrospinlaced layers in combination with polymer coatings.Yu-jun Zhang, Yu-dong Huang, Feng-fu Li, Lei Wang, Zhen-hao Jin. Electrospun non-woven mats of EVOH. Discharges and Electrical Insulation in Vacuum. 2004, 1, 106-109.]

High-tech applications for multifunctional fabrics warrant the investigation of novel textile manufacturing technologies, such as electrospinning, which has the capability of lacing together numerous types of polymers and fibers in a direct one step operation to produce ultrathin layers of protection.

Tissue Engineering

Electrospinning is currently being investigated as a source of cost-effective, easy to manufacture scaffolds for the production of artificial human tissues. These scaffolds fulfill a similar purpose as the extracellular matrix in natural tissue. Biodegradable polymers, such as polycaprolactone, are typically used for this purpose. These fibers are then coated with collagen to promote cell attachment, although collagen has successfully been spun directly into membranes. [Matthews JA, Wnek GE, Simpson DG, Bowlin GL. Electrospinning of collagen nanofibers. Biomacromolecules. 2002 Mar-Apr;3(2):232-8.]

Catalysts

Electrospun fibers may have potential as a surface for enzymes to be immobilized on. These enzymes could be used to break down toxic chemicals in the environment, among other things.

Filtration

Polymeric nanofibers have been used in air filtration applications for more than a decade. Due to poor mechanical properties of thin nanowebs, they were laid over a substrate suitable enough to be made into a filtration medium. The small fiber diameters cause slip flows at fiber surfaces, causing an increase in the interception and inertial impaction efficiencies of these composite filter media. The enhanced filtration efficiency at the same pressure drop is possible with fibers having diameters less than 0.5 micrometre. The potential for using nanofiber webs as a filtering medium is highly promising. Knowing that the essential properties of protective clothing are high moisture vapor transport, increased fabric breathability, and enhanced toxic chemical resistance, electrospun nanofiber membranes have been found to be good candidates for these applications.Thandavamoorthy Subbiah, G. S. Bhat, R. W. Tock, S. Parameswaran, S. S. Ramkumar. Electrospinning of Nanofibers. Journal of Applied Polymer Science. June 2004. Volume 96, Issue 2 (p 557-569) ]

References

External links

* [http://fluid.ippt.gov.pl/nanofibres/Welcome.html Polish Academy of Science's page on electrospinning]