Spider Silk Reveals A Paradox Of Super-Strength

There should be an image here!Since its development in China thousands of years ago, silk from silkworms, spiders and other insects has been used for high-end, luxury fabrics as well as for parachutes and medical sutures. Now, National Science Foundation-supported researchers are untangling some of its most closely guarded secrets, and explaining why silk is so super strong.

Researchers at the Massachusetts Institute of Technology’s Center for Materials Science and Engineering say the key to silk’s pound-for-pound toughness, which exceeds that of steel, is its beta-sheet crystals, the nano-sized cross-linking domains that hold the material together.

Markus Buehler, the Esther and Harold E. Edgerton Associate Professor in MIT’s department of civil and environmental engineering, and his team recently used computer models to simulate exactly how the components of beta sheet crystals move and interact with each other. They found that an unusual arrangement of hydrogen bonds — the “glue” that stabilizes the beta-sheet crystals — play an important role in defining the strength of silk.

They found that hydrogen bonds, which are among the weakest types of chemical bonds, gain strength when confined to spaces on the order of a few nanometers in size. Once in close proximity, the hydrogen bonds work together and become extremely strong. Moreover, if a hydrogen bond breaks, there are still many hydrogen bonds left that can contribute to the material’s overall strength, due to their ability to “self-heal” the beta-sheet crystals.

The researchers conclude that silk’s strength and ductility — its ability to bend or stretch without breaking — results from this peculiar arrangement of atomic bonds. They say controlling the size of the area in which hydrogen or other chemical bonds act can lead to significantly enhanced properties for future materials, even when the initial chemical bonds are very weak.

Bobbie Mixon @ National Science Foundation

[Photo above by Luc Viatour / CC BY-ND 2.0]

[awsbullet:spider silk strength]

Cotton Is The Fabric Of The Future

There should be an image here!Consider this T-shirt: It can monitor your heart rate and breathing, analyze your sweat and even cool you off on a hot summer’s day. What about a pillow that monitors your brain waves, or a solar-powered dress that can charge your ipod or MP4 player? This is not science fiction — this is cotton in 2010.

Now, the laboratory of Juan Hinestroza, assistant professor of Fiber Science and Apparel Design, has developed cotton threads that can conduct electric current as well as a metal wire can, yet remain light and comfortable enough to give a whole new meaning to multi-use garments. This technology works so well that simple knots in such specially treated thread can complete a circuit — and solar-powered dress with this technology literally woven into its fabric will be featured at the annual Cornell Design League Fashion Show on Saturday, March 13 at Cornell University’s Barton Hall.

Using multidisciplinary nanotechnology developed at Cornell in collaboration with the universities at Bologna and Cagliari, Italy, Hinestroza and his colleagues developed a technique to permanently coat cotton fibers with electrically conductive nanoparticles. “We can definitively have sections of a traditional cotton fabric becoming conductive, hence a great myriad of applications can be achieved,” Hinestroza said.

“The technology developed by us and our collaborators allows cotton to remain flexible, light and comfortable while being electronically conductive,” Hinestroza said. “Previous technologies have achieved conductivity but the resulting fiber becomes rigid and heavy. Our new techniques make our yarns friendly to further processing such as weaving, sewing and knitting.”

This technology is beyond the theory stage. Hinestroza’s student, Abbey Liebman, was inspired by the technology enough to design a dress that actually uses flexible solar cells to power small electronics from a USB charger located in the waist. The charger can power a smartphone or an MP3 player.

“Instead of conventional wires, we are using our conductive cotton to transmit the electricity — so our conductive yarns become part of the dress,” Hinestroza said. “Cotton used to be called the ‘fabric of our lives’ but based on these results, we can now call it ‘The fabric of our lights.'”

Joe Schwartz @ Cornell University

[Photo above by Carol Von Canon / CC BY-ND 2.0]

[awsbullet:alternative energy fuel]