Parameters

• Molecular weight, molecular-weight distribution and architecture (branched, linear etc.) of the polymer
• Solution properties (viscosity, conductivity and surface tension)
• Electric potential, flow rate and concentration
• Distance between the capillary and collection screen
• Ambient parameters (temperature, humidity and air velocity in the chamber)
• Motion and size of target screen (collector)
• Needle gauge

Apparatus and range

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. 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.^[6] 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.

Scaling-up possibilities

• Alternating current electrospinning^{[7][8][9][10][11][12]}
• Needleless (also known as, nozzle-free) electrospinning ^[13][14]
• Multiplying the needles^[15]
• High-throughput roller electrospinning^[16]
• Wire electrospinning
• Bubble electrospinning^[17]
• Ball electrospinning^[18][19]
• High speed electrospinning^[20]
• Plate edge electrospinning^[21]
• Bowl electrospinning^[22]
• Hollow tube electrospinning^[23]
• Rotary cone electrospinning^[24]
• Spiral coil electrospinning^[25]
• Electroblowing^[26]

Co-axial electrospinning

A coaxial setup uses a dual-solution feed system which allows for the injection of one solution into another at the tip of the spinneret. The sheath fluid is believed to act as a carrier which draws in the inner fluid at the Taylor Cone of the electrospinning jet.^[27] If the solutions are immiscible then a core shell structure is usually observed. Miscible solutions however can result in porosity or a fiber with distinct phases due to phase separation during solidification of the fiber. For more advanced setups, a triaxial or quadaxial (tetra-axial) spinneret can be used with multiple solutions.

Emulsion electrospinning

Emulsions can be used to create core shell or composite fibers without modification of the spinneret. However, these fibers are typically more difficult to produce compared to coaxial spinning due to the greater number of variables which must be accounted for in creating the emulsion. A water phase and an immiscible solvent phase are mixed in the presence of an emulsifying agent to form the emulsion. Any agent which stabilizes the interface between the immiscible phases can be used. Surfactants such as sodium dodecyl sulfate, Triton X-100 and nanoparticles have been used successfully. During the electrospinning process the emulsion droplets within the fluid are stretched and gradually confined leading to their coalescence. If the volume fraction of inner fluid is sufficiently high, a continuous inner core can be formed.^[31]

Electrospinning of blends is a variation of this technique which uses the fact that polymers are generally immiscible with each and can phase segregate without the use of surfactants. This method can be simplified further if a solvent which dissolves both polymers is used.^[32]

Melt electrospinning

Electrospinning of polymer melts eliminates the need for volatile solvents in solution electrospinning.^[33] Semi crystalline polymer fibers such as PE, PET and PP, which would otherwise be impossible or very difficult to create using solution spinning, can be created. The setup is very similar to that employed in conventional electrospinning and includes the use of a syringe or spinneret, a high voltage supply and the collector. The polymer melt is usually produced by heating from either resistance heating, circulating fluids, air heating or lasers.^[34]

Due to the high viscosity of polymer melts, the fiber diameters are usually slightly larger than those obtained from solution electrospinning. The fiber uniformity upon achieving stable flow rates and thermal equilibrium, tends to be very good. The whipping instability which is the predominant stage in which the fiber is stretched for spinning from solutions can be absent from the process due to the low melt conductivity and high viscosity of the melt. The most significant factors which affect the fiber size tend to be the feed rate, the molecular weight of the polymer and the diameter of the spinneret. Fiber sizes ranging from ~250 nm to several hundreds of micrometers have been created thus far with the lower sizes being achieved using low molecular weight polymers.^[35]

Filtration

The use of nanofiber webs as a filtering medium is well established. Due to the small size of the fibers London-Van Der Waals forces are an important method of adhesion between the fibers and the captured materials. Polymeric nanofibers have been used in air filtration applications for more than seven decades.^[47][57] Because of poor bulk mechanical properties of thin nanowebs, they are laid over a filtration medium substrate. 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 micrometer. Since the essential properties of protective clothing are high moisture vapor transport, increased fabric breath-ability, and enhanced toxic chemical resistance, electrospun nanofiber membranes are good candidates for these applications.^[58]

Textile manufacturing

The majority of early patents for electrospinning were for textile applications, however little woven fabric was actually produced, perhaps due to difficulties in handling the barely visible fibers. However, electrospinning has the potential to produce seamless non-woven garments by integrating advanced manufacturing with fiber electrospinning. This would introduce multi-functionality (flame, chemical, environmental protection) by blending fibers into electrospinlaced (using electrospinning to combine different fibers and coatings to form three-dimensional shapes, such as clothing)^[59] layers in combination with polymer coatings.^[60]

Medical

Electrospinning can also be used for medical purposes.^[61] The electrospun scaffolds made for tissue engineering applications can be penetrated with cells to treat or replace biological targets.^[62] Nanofibrous wound dressings^[63] have excellent capability to isolate the wound from microbial infections.^[64][65] Other medical textile materials such as sutures are also attainable via electrospinning.^[66] Through the addition of a drug substance into the electrospinning solution or melt^[33] diverse fibrous drug delivery systems (e.g., implants,^[67] transdermal patches,^[68] oral forms^[69]) can be prepared. Electropsun propolis nanofibrous membrane showed an antiviral effect against the SARS-CoV-2 virus, and an antibacterial effect against Staphylococcus aureus and Salmonella enterica bacteria.^[70] Interestingly, electrospinning allows to fabricate nanofibers with advanced architecture ^[71] that can be used to promote the delivery of multiple drugs at the same time and with different kinetics.^[72][73]

Cosmetic

Electrospun nanomaterials have been employed to control their delivery so they can work within skin to improve its appearance.^[74] Electrospinning is an alternative to traditional nanoemulsions and nanoliposomes.

Pharmaceutical manufacturing

The continuous manner and the effective drying effect enable the integration of electrospinning into continuous pharmaceutical manufacturing systems.^[75] The synthesized liquid drug can be quickly turned into an electrospun solid product processable for tableting and other dosage forms.

Composites

Ultra-fine electrospun fibers show clear potential for the manufacture of long fiber composite materials.^[76]

Application is limited by difficulties in making sufficient quantities of fiber to make substantial large scale articles in a reasonable time scale. For this reason medical applications requiring relatively small amounts of fiber are a popular area of application for electrospun fiber reinforced materials.

Electrospinning is being investigated as a source of cost-effective, easy to manufacture wound dressings, medical implants, and 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^[77] and polysaccharides,^[78] are typically used for this purpose. These fibers may then be coated with collagen to promote cell attachment, although collagen has successfully been spun directly into membranes.^[79]

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.^[5]