Nanofibers are useful for any application that benefits from a high ratio of surface area to volume, such as solar cells that maximize exposure to sunlight, or fuel cell electrodes that catalyze reactions at their surfaces. Nanofibers can also yield materials that are permeable only at very small scales, such as water filters, or that are remarkably tough for their weight, such as body armor. Most such applications depend on fibers with regular diameters. But their commercialization has been hampered by inefficient manufacturing techniques.
A new device for producing nanofiber meshes was developed that matches the production rate and power efficiency of its best-performing predecessor, but significantly reduces variation in the fibers’ diameters. Whereas the predecessor device, produced by the same researchers, was etched into silicon through a complex process that required production in a cleanroom, the new device was built using a commercial 3D printer. The work thus points toward nanofiber manufacture that is not only more reliable, but also much less expensive.
The new device consists of an array of small nozzles through which a fluid containing particles of a polymer is pumped. As such, it is what's known as a microfluidic device. 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 fibers 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 fibers.
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 nanofibers, and it would be virtually impossible to achieve with clean-room microfabrication techniques.
In the new device, the nozzles are arranged into two rows that are slightly offset from each other because the device was engineered to demonstrate aligned nanofibers — nanofibers that preserve their relative position as they're collected by a rotating drum. Aligned nanofibers are particularly useful in applications such as tissue scaffolding. For applications in which unaligned fibers are adequate, the nozzles could be arranged in a grid, increasing output rate.
Besides cost and design flexibility, another advantage of 3D printing is the ability to rapidly test and revise designs. By deterministically engineering the position and size of electrospun fibers, the mechanical properties of materials made from the fibers may be controlled.