"Green" is a ubiquitous label that is even creeping into nanotechnology. But to engineer designs so small they can only be seen through the most powerful microscopes - plus use renewable materials and no harmful processing chemicals - is no easy feat, Renzo Shamey and Khaled El-Tahlawy discovered.
The two chemists at N.C. State University's College of Textiles set out to spin cornstarch into nanofibers that are porous and could, for example, carry medicines.
But the nanofibers continued to break. So Shamey and El-Tahlawy decided to regroup rather than resort to solvents long used in the spinning process. Instead of making fibers, they decided to produce starch-based foam particles that are smaller than a bacterium, light and environmentally friendly.
"It's very simple, but it has a lot of potential applications," El-Tahlawy said.
Researchers have been working for more than 15 years to conserve chemicals and energy and cut down on waste, said Barbara Karn, a green nanotechnology expert at the Environmental Protection Agency's National Center for Environmental Research in Washington, D.C. "Green chemistry has been around for a while," Karn said.
But what Shamey and El-Tahlawy are doing, she said, is "green engineering."
Shamey and El-Tahlawy went beyond conservation, designing the starch-based nanoparticles to have certain properties. Depending on the intended use, they could absorb or repel water. Then, El-Tahlawy went to work in the lab, dissolved starch in water, cooked the mixture and through a series of chemical reactions produced copies of the designs.
Fresh out of the lab, the nanoparticles look and feel like very fine powder or talc.
The air pockets enlarge the particles' surface area, which scatters light better and holds a larger load. Mixed into paint, the powder could replace titanium dioxide, a chemical that is added to make paint and milk snowy white and give sunscreen its protection against ultraviolet light. As a filler, the powder could make automotive and airplane parts lighter. And in medicine, the nanoparticles could be used to make bone replacements or to deliver medicine inside cells.