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Feeding Silkworms Carbon Nanotubes and Graphene Makes Super-Tough Silk

A diet rich in graphene or carbon nanotubes causes the creatures to produce a fiber twice as strong as normal silk

Silkworm cocoons (Wikimeida Commons/Biswarup Ganguly)
smithsonian.com

Silk is pretty amazing stuff. The fiber, spun from the cocoons of the silkworm Bombyx mori, which munches exclusively on mulberry leaves, is lightweight, soft and has a beautiful sheen. It's also surprisingly strong for a natural fiber, but researchers have found a way to make it even stronger, opening the door to new applications for silk.

Scientists at Tsinghua University in Beijing began feeding silkworms mulberry leaves covered in a 0.2 percent solution of carbon nanotubes or graphene. The result, reports Bob Yirka at Phys.org, was silk that could withstand 50 percent more stress than the standard material. It also conducted electricity when heated to 1,922 degrees Fahrenheit. The results appear in the journal Nano Letters.

Discovered in 2004, graphene is a wonder material made of single layer of pure carbon atoms. It is the thinnest material possible to produce—200 times stronger than steel yet still very flexible. Carbon nanotubes, which are essentially sheets of graphene rolled into a cylinder, have a huge potential to strengthen other materials, serve as conductors and transistors and even to clean or desalinate water. It is so revolutionary that the engineers that discovered this amazing material won the Nobel prize in 2010

This latest find is another impressive application of the versatile material. But there's much more to know about the process. The researchers still haven't figured out  how the material is incorporated into the silk proteins, what percentage of the nanotubes make it into the silk and whether the nanotubes have adverse effects on the caterpillars themselves. That’s a project for biologists, lead researcher Yingying Zhang tells Prachi Patel for Chemical & Engineering News. However, this new process is likely more environmentally friendly than trying to spray or coat the silk with nanotubes after production, Patel reports.

But the technique has been tried before. In 2014, researchers at Donghua University produced silk with a 25 percent boost in strength by feeding the worms multi-walled carbon nanotubes. Yaopeng Zhang, also of Donghua, also tried feeding silk worms titanium dioxide nanoparticles to try to improve their strength and resistance to ultraviolet light.

Yirka says the new silk could lead to stronger medical implants and clothes embedded with electronics. The silk also has the potential to produce some of the first commercially available graphene-based products. “For many years people have been looking for graphene applications that will make it into mainstream use,” Ravi Silva, a graphene researcher at the University of Surrey, tells Anthony Cuthbertson at Newsweek. “We are finally now getting to the point where these applications are going to happen.”

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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