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Press Release 10-040
Spider Silk Reveals a Paradox of Super-strength

Research finds weakest chemical bonds produce materials stronger than steel

Illustration showing the nanoscale structure of silks.

Research finds weak hydrogen bonds contribute to the amazing strength of silk.
Credit and Larger Version

March 16, 2010

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.

The journal Nature Materials reported the findings online March 14.

-NSF-

Media Contacts
Bobbie Mixon, NSF, (703) 292-8485, bmixon@nsf.gov

Program Contacts
Jorn Larsen-Basse, NSF, (703) 292-7088, jlarsenb@nsf.gov

Principal Investigators
Markus Buehler, Massachusetts Institute of Technology, (617) 452-2750, mbuehler@mit.edu

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2014, its budget is $7.2 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives about 50,000 competitive requests for funding, and makes about 11,500 new funding awards. NSF also awards about $593 million in professional and service contracts yearly.

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Image showing breaking mechanisms of silk nanocrystals as a function of crystal size.
Hydrogen bonds show an ability to self-heal, making up for lost strength when other bonds break.
Credit and Larger Version

Image showing structure of silk.
The size of beta-sheet crystals determines silk's high performance properties.
Credit and Larger Version



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