Nanofibers — strands of material only a couple hundred nanometers in diameter — have a huge range of possible applications: scaffolds for bioengineered organs, ultrafine air and water filters, and lightweight Kevlar body armor, to name just a few. But so far, the expense of producing them has consigned them to a few high-end, niche applications.
MIT has a new system for spinning nanofibers that should offer significant productivity increases while drastically reducing power consumption.
Using manufacturing techniques common in the microchip industry, the MTL researchers built a one-square-centimeter array of conical tips, which they immersed in a fluid containing a dissolved plastic. They then applied a voltage to the array, producing an electrostatic field that is strongest at the tips of the cones. In a technique known as electrospinning, the cones eject the dissolved plastic as a stream that solidifies into a fiber only 220 nanometers across.
In their experiments, the researchers used a five-by-five array of cones, which already yields a sevenfold increase in productivity per square centimeter over even the best existing methods. But, Velásquez-García says, it should be relatively simple to pack more cones onto a chip, boosting productivity even more. Indeed, he says, in prior work on a similar technique called electrospray, his lab was able to cram almost a thousand emitters into a single square centimeter. And multiple arrays could be combined in a panel to further increase yields.
They believe that they can increase yields by ten times over what is available now.
The group’s results depend not only on the design of the emitters themselves, but on a precise balance between the structure of the cones and their textured coating, the strength of the electrostatic field, and the composition of the fluid bath in which the cones are immersed.
“Fabricating exactly identical emitters in parallel with high precision and a lot of throughput — this is their main contribution, in my opinion,” says Antonio Luque Estepa, an associate professor of electrical engineering at the University of Seville who specializes in electrospray deposition and electrospinning. “Fabricating one is easy. But 100 or 1,000 of them, that’s not so easy. Many times there are problems with interactions between one output and the output next to it.”