Spinning Nanofibers Like Cotton Candy

A new patent-pending invention literally spins, stretches and pushes out 100-nm-diameter, polymer-based threads using a rotating drum and nozzle — much like a cotton candy machine.

According to Mohammad Reza Badrossamay, lead author of a study published in the May 24 online edition of Nano Letters, the invention has potential applications ranging from artificial organ and tissue regeneration to clothing and air filter fabrication.

"This is a vastly superior method to making nanofibers as compared to typical methods, with production output many times greater," said co-author Kit Parker, Thomas D. Cabot Associate Professor of Applied Science and associate professor of bioengineering in the Harvard School of Engineering and Applied Sciences (SEAS). He is also a core faculty member of the Wyss Institute for Biologically Inspired Engineering at Harvard and a member of the Harvard Stem Cell Institute. "Our technique will be highly desirable to industry, as the simple machines could easily bring nanofiber production into any laboratory. In effect, with this technique, we can mainstream nanotextiles."

A diagram of the rotary jet spinner is shown on the left. On the upper right are the resulting "spun" nanofibers; on the bottom right are the nanofibers viewed at 10 µm. (Image: Kit Parker, Disease Biophysics Group at the Harvard School of Engineering and Applied Sciences)

By contrast, the most common method of creating nanofibers is through electrospinning, or sending a high-voltage electric charge into a droplet of polymer liquid to draw out long wisps of nanoscale threads. While effective, electrospinning offers limited control and low output of the desired fibers.

The Harvard researchers turned to a simpler solution using rotary jet spinning. Quickly feeding and then rotating the polymer material inside a reservoir atop a controllable motor offers more control and greater yield.

When spun, the material stretches much as molten sugar does as it begins to dry into thin, silky ribbons. Just as in cotton candy production, the nanofibers are extruded through a nozzle by a combination of hydrostatic and centrifugal pressure. The resulting pile of extruded fibers forms into a bagel-like shape about 10 cm in diameter.

"The new system offers fabrication of naturally occurring and synthetic polymers as well as a lot of control over fiber alignment and web porosity, hierarchical and spatial organization of fibrous scaffold and three-dimensional assemblies," said Badrossamay, a postdoctoral fellow in the Wyss Institute and a member of Parker's lab at SEAS.

The researchers tested the new device using a variety of synthetic and natural polymers such as polylactic acid in chloroform, a biodegradable polymer created from cornstarch or sugar cane that has been used in items such as disposable cups as an eco-friendly alternative to plastic

Moreover, the rapid spinning method provides a high degree of flexibility, as the diameter of the fibers can be readily manipulated and the structures can be integrated into an aligned three-dimensional structure or any other shape simply by varying how the fibers are collected.

The shape of the fibers can also be altered from beaded to textured to smooth.

Parker's Disease Biophysics Group (DBG), which has extensive expertise in cardiac tissue engineering, also used the technology to form tissue engineering scaffolds, or artificial structures upon which tissue can form and grow.

Heart tissue from rats was integrated and aligned with the nanofibers and, as seen in past studies, formed beating muscle.

"I was visiting the Society of Laparoscopic Surgeons a couple of years ago to look at the equipment demos, and it dawned on me that we needed to develop techniques to miniaturize scaffold production so we could do it in vivo. Our finding is the first step," explained Parker. "The initial testing suggests that our technique is incredibly versatile for both research and everyday applications. As rotary jet spinning does not require high voltage, it really brings nanofiber fabrication to everyone."

The researchers expect to further refine the process for tissue engineering applications and to look for opportunities to exploit the advance in other textile applications.

Badrossamay and Parker's co-authors include Holly Alice McIlwee, a bioengineering graduate student at SEAS, and Josue A. Goss, the DBG laboratory manager who built the machine with Badrossamay.

The researchers acknowledge the support of the Nanoscale Science and Engineering Center at Harvard; the Materials Research Science and Engineering Center at Harvard; and Center for Nanoscale Systems and the Wyss Institute for Biologically Inspired Engineering, both at Harvard. The work was funded in part also by the National Science Foundation.

For more information, visit: www.harvard.edu