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, say researchers writing in Nature Materials.

Using computer models, researchers simulated 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.

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 study concludes that silk's strength and ductility--its ability to bend or stretch without breaking--results from this peculiar arrangement of atomic bonds. 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.

Citation: Keten et al., 'Nanoconfinement controls stiffness, strength and mechanical toughness of β-sheet crystals in silk', Nature Materials, March 2010; doi:10.1038/nmat2704