A light weight, portable nanofiber fabrication device could one day be used to dress wounds on a battlefield or dress shoppers in customizable fabrics. There are many ways to make nanofibers. These versatile materials – whose target applications include everything from tissue engineering to bullet-resistant vests – have been made using centrifugal force, capillary force, electric field, stretching, blowing, melting, and evaporation.

A schematic of the pull spinning apparatus with a side view illustration of a fiber being pulled from the polymer reservoir. The pull spinning system consists of a rotating bristle that dips and pulls a polymer jet in a spiral trajectory.
Illustration courtesy of Leila Deravi/Harvard University; Spinning gif: Video courtesy of Harvard University

Each of these fabrication methods has pros and cons. For example, rotary jet-spinning (RJS) and immersion rotary jet-spinning (iRJS) are manufacturing techniques developed in the Disease Biophysics Group at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering. RJS and iRJS dissolve polymers and proteins in a liquid solution and use centrifugal force or precipitation to elongate and solidify polymer jets into nanoscale fibers.

These volumes are great for producing large amounts of a range of materials – including DNA, nylon, and even Kevlar – but until now, they haven’t been particularly portable.

The Disease Biophysics Group recently announced the development of a hand-held device that can quickly produce nanofibers with precise control of fiber orientation. Regulating fiber alignment and deposition is crucial when building nanofiber scaffolds that mimic highly aligned tissue in the body.

“Our main goal for this research was to make a portable machine that you could use to achieve controllable deposition of nanofibers,” says Nina Sinatra, a graduate student in the Disease Biophysics Group and co-first author of the paper. “To develop this point-and-shoot device, we needed a technique that could produce highly aligned fibers with a reasonably high throughput.”

The new fabrication method, pull spinning, uses a high-speed rotating bristle that dips into a polymer or protein reservoir and pulls a droplet from solution into a jet. The fiber travels in a spiral trajectory and solidifies before detaching from the bristle and moving toward a collector. Unlike other processes, which involve multiple manufacturing variables, pull spinning requires only one processing parameter – solution viscosity – to regulate nanofiber diameter. Minimal process parameters translate to ease of use and flexibility.

A scanning electron microscopy image of nanofibers woven into threads.

Pull spinning works with a range of polymers and proteins. The researchers demonstrated proof-of-concept applications using polycaprolactone and gelatin fibers to direct muscle-tissue growth and function on bioscaffolds.

Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS)
www.seas.harvard.edu

Wyss Institute for Biologically Inspired Engineering
www.wyss.harvard.edu

This research, published recently in Macromolecular Materials and Engineering, was coauthored by Nina Sinatra, Leila F. Deravi, Christophe O. Chantre, Alexander P. Nesmith, Hongyan Yuan, Sahm K. Deravi, Josue A. Goss, Luke A. MacQueen, Mohammad R. Badrossamy, Grant M. Gonzalez and Michael D. Phillips.