Previous efforts by MIT researchers to manufacture nanofibers relied on deep reactive-ion etching technology in a complex process that required an air-locked clean room. The same team recently assembled a new device that produces nanofibers using a $3,500 commercial 3D printer. The process is more economical and reliable, and reduces variation in the fibers’ diameters, an important consideration in most applications.
The etching scheme was “externally fed,” meaning that an electric field drew a polymer solution up the sides of 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 fibers of irregular diameter.
The new microfluidic system consists of an array of small nozzles through which fluid containing particles of a polymer are pumped. These emitters are “internally fed”: hydraulic pressure pushes fluid into bores until they’re filled, after which an electric field draws the fluid out into tiny fibers.
Channels that feed the bores are wrapped into coils and gradually taper along their length. This design is key to regulating nanofiber diameter of the nanofibers, which would be virtually impossible to achieve with clean-room microfabrication techniques.
“My personal opinion is that in the next few years, nobody is going to be doing microfluidics in the clean room,” said Luis Fernando Velásquez-García, a principal research scientist in MIT’s Microsystems Technology Laboratories. “There’s no reason to do so. 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. When you go to the clean room, many times you sacrifice the geometry you want to make. And the second problem is that it is incredibly expensive.”
Two rows of nozzles are slightly offset from each other in order to produce aligned nanofibers — nanofibers that preserve their relative position as they’re collected by a rotating drum. Aligned nanofibers are particularly useful in some applications, such as tissue scaffolding. For applications in which unaligned fibers are adequate, the nozzles could be arranged in a grid, increasing output rate. The 3D printing system also enables faster design revisions and testing.