The technique, which is reported in the journal Nanotechnology is claimed to be both cheaper and more reliable than existing processes for producing the materials, which have promising applications in areas ranging from tissue engineering, to body armour and solar cells.
The new device consists of an array of small nozzles through which a fluid containing particles of a polymer are pumped. The group claims that the technique matches the production rate and power efficiency of its best-performing predecessor - also developed at MIT - but significantly reduces variation in the fibres’ diameters and doesn’t require a clean-room environment to operate.
“In the next few years, nobody is going to be doing microfluidics n the clean room,” claimed Luis Fernando Velásquez-García, a principal research scientist in MIT’s Microsystems Technology Laboratories and senior author on the new paper. “3D printing is a technology that can do it so much better — with better choice of materials, with the possibility to really make the structure that you would like to make.”
Nanofibres are useful for any application that benefits from a high ratio of surface area to volume — such as solar cells, which try to maximise exposure to sunlight, or fuel cell electrodes, which catalyse reactions at their surfaces. They can also be used to produce materials that are permeable only at very small scales, such as water filters, or that are remarkably tough for their weight, such as body armour.
Velásquez-García added the new technology is more effective at achieving the regular diameters critical to many of these applications.
Because the group’s earlier device was etched in silicon, it was “externally fed,” meaning that an electric field drew a polymer solution up the sides of the individual emitters. The fluid flow was regulated by rectangular columns etched into the sides of the emitters, but it was still erratic enough to yield fibres of irregular diameter.
The new emitters, by contrast, are “internally fed”: They have holes bored through them, and hydraulic pressure pushes fluid into the bores until they’re filled. Only then does an electric field draw the fluid out into tiny fibres. Beneath the emitters, the channels that feed the bores are wrapped into coils, and they gradually taper along their length. That taper is key to regulating the diameter of the nanofibres, something that the group claims would be virtually impossible to achieve with clean-room microfabrication techniques.
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