Silk, made from silkworms, spiders and other insects and developed in China, is well known as a high-end fabric. But its luxurious texture masks an extreme toughness.
Pound-for-pound, silk is stronger than steel. And because of its ability to bend and stretch without breaking, silk is used in parachutes, medical sutures and other life-saving devices.
But scientists are still unraveling the answers behind what makes the luxurious fabric so strong.
Now, researchers at the Massachusetts Institute of Technology’s Center for Materials Science and Engineering, with funding from the National Science Foundation, say they’ve found that silk’s strength comes from its beta-sheet crystals, the nano-sized cross-linking domains that hold the material together. Markus Buehler, of MIT’s civil and environmental engineering department, and his team reported their findings in a Nature Materials paper published online this month.
Using computer models to simulate how the components of beta-sheet crystals move and interact, the researchers found that the unique arrangement of hydrogen bonds plays a major role in silk’s toughness. The hydrogen bonds, which act as glue to stabilize the beta-sheet crystals, are among the weakest chemical bonds. But the hydrogen bonds gain strength when confined to spaces of just a few nanometers in size.
Added strength comes from the fact that if one hydrogen bond breaks, many more of the bonds remain to maintain the material’s overall toughness. The bonds can “self heal” the beta-sheet crystals, according to the researchers.
By determining that silk’s strength comes from this arrangement of hydrogen bonds, the researchers’ findings have implications for future materials. According to their work, controlling the size of the area in which chemical bonds act — even if the bonds are initially quite weak — can lead to significantly enhanced properties in other materials.
Image: Rendering of the nanoscale structure of silks with beta-sheet nanocrystals shown in yellowish color, including detailed view of the domains between the beta-sheet nanocrystals / M.J. Buehler (MIT)
