If you've never heard of electrospinning, you're not alone. It is a method that uses electric force to draw charged threads of polymer solutions into fibers that have a diameter of around 100 nanometers. A nanometer is one-billionth of a meter.
A polymer consists of very long chains of molecules that have many repeating sub units. Polymers include synthetic plastics such as polystyrene and natural biopolymers such as DNA. Polymers tend to be incredibly tough, and they generally have high elasticity.
What is electrospinning?
The first person to recognize electrospinning was the English physician and physicist William Gilbert, who died in 1603. Gilbert investigated both magnetic and electrostatic properties, and he noticed that when he brought an electrically charged piece of amber toward a droplet of water, that droplet would form a cone shape and tiny droplets would be ejected from the tip of the cone.
In the U.S., the electrospinning process was first patented in 1900, followed by a series of patents between the years 1934 and 1944 for the fabrication of textile yarns.
In 1938, two Russian scientists, Nathalie Rozenblum and Igor Petryanov-Sokolov, who were working at the Aerosol Laboratory of the Karpov Institute, created electrospun fibers that were used as filters called "Petryanov filters". These were used for filtering aerosols out of the air and other gasses, and by 1939, a Russian factory was creating electrospun smoke filters for use in gas masks.
Between 1964 and 1969, British physicist and mathematician Sir Geoffrey Ingram Taylor formulated the theoretical underpinnings of electrospinning. Taylor mathematically modeled the shape of the cone that forms when a liquid droplet is under the effect of an electric field. Today, that cone is called a "Tayor Cone".
How does electrospinning work?
When a sufficiently high electric voltage is applied to a droplet, the liquid becomes charged, and electrostatic repulsion counteracts the surface tension of the droplet. At that point, the droplet erupts into a stream of liquid.
As the stream of liquid dries in flight, the electric charge migrates to the surface of the droplet/fiber, and electrostatic repulsion causes the shape to elongate, before being deposited on a grounded collector. This elongation leads to the formation of uniform fibers that have nanometer diameters.
To do electrospinning yourself, you'll need the following. Also, since high voltages are involved, you should be sure you know what you're doing. Always take the proper precautions when working with high voltages.
- A needle, called a spinneret, which is typically a hypodermic syringe
- A high-voltage source of between 5 to 50 kV direct current, such as an old television, a cathode ray tube monitor, or a transformer
- An air pump, such as a bicycle pump
- A grounded collector, such as a metal plate
- A polymer solution, a sol-gel, or a particulate suspension
- A holding tank, such as a 2-liter soda bottle.
The polymer solution can vary by its molecular weight, viscosity, conductivity, surface tension, electric potential concentration, and flow rate. The electrospinning process is also affected by the ambient temperature, humidity, air velocity, gauge of the needle, and the needle's distance from the collection plate.
Uses for electrospinning products
By 1988, it was noted that electrospinning could be used to produce nano- and submicron-scale (a micron is one-millionth of a meter) polystyrene and polycarbonate fibrous mats. These mats could be used as cell substrates in cell cultures. If polycarbonate sounds familiar to you, it's because it's used to make eyeglass lenses.
Electrospun fibers make ideal wound dressings and sutures, and the fibers can also be impregnated with drugs, making them a drug delivery system. Electrospun fibers can also replace medical implants and fillers that are commonly used in cosmetic surgery procedures.
In the early 1990s, it was demonstrated that organic polymers could be electrospun into nanofibers. These fibers have high moisture vapor transport, increased fabric breathability, and enhanced toxic chemical resistance, making them ideal for use in sports or protective clothing.
Electrospinning also has the potential to produce seamless, non-woven clothing that would be flame-, chemical- and environmental hazard-resistant.
An open-source gift
Due to the COVID pandemic, N95 masks are hard to find, and wearers often complain that they are hot, moist, and uncomfortable to wear. To counter that, a group of researchers at Utah's Brigham Young University (BYU) has electrospun a nanofiber fabric that can be layered within a cloth face mask to block up to 99% of particles, such as those that carry the COVID-19 virus.
The BYU researchers, partnering with the Nanos Foundation, are using a homogenized polymer solution combined with a solvent, a soda bottle, and a simple bicycle pump.
This mesmerizing GIF shows a process called electrospinning. BYU engineering students + the Nanos Foundation are using it to turn liquid polymer into nanofibers, which, when added to a cloth mask, makes it just as effective as an N95 mask. #COVID19 https://t.co/FcqH4Per7C pic.twitter.com/ftOMMia7Vz— BYU (@BYU) October 21, 2020
Director of the Nanos Foundation, Will Vahle, recently told KSL-TV that, "Our nanofiber membranes are six times easier to breathe through than existing N95 masks, making them cooler, drier, and more comfortable."
A member of the BYU research team, a mechanical engineering senior Katie Varela, also told KSL that, “When they [virus particles] come close to your mask, they will be statically attracted to the mask and will not be able to go through it, and so it prevents you from inhaling viruses."
Rather than patenting their discovery, the BYU group plans to make their nanofiber mesh process open-source, meaning that anyone can use the group's design to create their own mask filters, and they are free to improve upon the process.
Even though it's hard to think about, COVID might be around for the foreseeable future, which means that we all might be wearing masks for a lot longer.