Electrospinning is a fiber production method which uses electric force to draw charged threads of polymer solutions or polymer melts up to fiber diameters in the order of some ten nanometers. Electrospinning shares characteristics of both electrospraying and conventional solution dry spinning of fibers. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This makes the process particularly suited to the production of fibers using large and complex molecules. Electrospinning from molten precursors is also practiced; this method ensures that no solvent can be carried over into the final product.

The standard laboratory setup for electrospinning consists of a spinneret (typically a hypodermic syringe needle) connected to a high-voltage (5 to 50 kV) direct current power supply, a syringe pump, and a grounded collector. Apolymersolution, 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. Alternatively, the droplet at the tip of the spinneret can be replenished by feeding from a header tank providing a constant feed pressure. This constant pressure type feed works better for lower viscosity feedstocks.

Electrospinning Nanofibers Fibers can be made much thinner through electrospinning than other methods. A solution of liquid polymer fluid is put through a capilary device to produce a droplet. Next a voltage is applied to the droplet, which reduces the surface tension, resulting in a very thin fiber being drawn out. The voltage applied is very high. Typical values range from 8 to 25 kilo- volts. The diamiter of the fiber is inversly proportional to the applied voltage. The fiber is then drawn towards a collection plate by gravitational and electrostatic forces. The fibers become randomly arranged on the collection plate forming a mesh network.

The nonwoven industry generally considers nanofibers as having a diameter of less than one micron, although the National Science Foundation (NSF) defines nanofibers as having at least one dimension of 100 nanometer (nm) or less. The name derives from the nanometer, a scientific measurement unit representing a billionth of a meter, or three to four atoms wide. NANOFIBERS ARE AN EXCITING NEW CLASS OF MATERIAL USED FOR SEVERAL VALUE ADDED APPLICATIONS SUCH AS MEDICAL, FILTRATION, BARRIER, WIPES, PERSONAL CARE, COMPOSITE, GARMENTS, INSULATION, AND ENERGY STORAGE. SPECIAL PROPERTIES OF NANOFIBERS MAKE THEM SUITABLE FOR A WIDE RANGE OF APPLICATIONS FROM MEDICAL TO CONSUMER PRODUCTS AND INDUSTRIAL TO HIGH-TECH APPLICATIONS FOR AEROSPACE, CAPACITORS, TRANSISTORS, DRUG DELIVERY SYSTEMS, BATTERY SEPARATORS, ENERGY STORAGE, FUEL CELLS, AND INFORMATION TECHNOLOGY [1,2]. Generally, polymeric nanofibers are produced by an electrospinning process (Figure 1). Electrospinning is a process that spins fibers of diameters ranging from 10nm to several hundred nanometers. This method has been known since 1934 when the first patent on electrospinning was filed. Fiber properties depend on field uniformity, polymer viscosity, electric field strength and DCD (distance between nozzle and collector). Advancements in microscopy such as scanning electron microscopy has enabled us to better understand the structure and morphology of nanofibers. At present the production rate of this process is low and measured in grams per hour.

SEM image of a Random 10% PLGA nanofiber deposition. Electrospun 10% PLGA nanofiber diameter was 679nm ± 60 nm. Scale bar = 100 μm SEM image of a Aligned 10% PLGA nanofiber deposition. Electrospun 10% PLGA, nanofiber diameter was 679nm ± 60 nm. Scale bar = 20 μm Confocal image of 10% PLGA nanofibers

Fluid is pumped through a syringe with an automatic syringe pump The syringe needle is positively charged using a voltage supply (Several kV potential used) The resulting electric field causes fibers to be pulled from the droplet at the end of the syringe tip and onto a grounded metal collector

Electrospinning of Core-Shell FibersStandard Electrospinning Process

Nanofiber Applications Application in life science drug delivery carrier hemostatic devices wound dressing Nanosensors thermal sensors piezoelectric sensor biochemical sensor fluorescence optical chemical sensor Military protective clothing minimum impedance to air efficiency in trapping aerosol particles anti-bio-chemical gases Cosmetic skin masks Skin cleansing skin healing Skin therapy Tissue engineering scaffolding porous membrane for skin tubular shape for blood vessels and nerve regeneration three dimensional scaffolds for bone and cartilage regeneration Filter media liquid filtration gas filtration molecule filtration Other electronic applications micro/nanoelectronic devices electronic dissipation electromagnetic interference shielding photovoltaic devices LCD devices ultra-lightweigt spacecraft materials high efficient and functional catalysts Polymer Nanofibers

Drug delivery system: - Encapsulation of the drug inside the electrospun fiber - Improve therapeutic efficacy due to the high surface area and safety of drugs (Dissolution rate of a particulate drug increases with increasing surface area of both the drug and the corresponding carrier if needed.) Wound dressing: Novel polymeric composite materials that have antimicrobial properties and variable surface properties that can reduce attachment and adhesion to the wound. - Wound dressings having antibacterial properties would be highly desirable for wounded personnel

Percentage release of tetracycline HCl from films and nanospun mats vs. time Drug deliveryTissue engineeringWound dressing

Protective Clothing

A conceptual image of a nanofibrous wound dressing is shown. The electrospun polymer fibers would be attached to the dressing material to make direct contact with the wound. Novel polymeric composite materials that have antimicrobial properties and variable surface properties that can reduce attachment and adhesion to the wound. Wound dressings having antibacterial properties would be highly desirable for wounded personnel both in the field and in a clinical setting