Stretchy Spider Silk Wires Flex Like Muscles

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Spider silk: its threads are stronger than steel of the same size, it can stretch and absorb water. Some kinds of spider silk can transmit light like optical fibers, or form fibers that can be woven into body armor. Now it's being turned into flexible electrical conductors.

Researchers at Florida State University's National High Magnetic Field Lab have found a way to coat spider silk with a very thin layer of carbon nanotubes, which are also stretchable and flexible but conduct electricity as well as a copper wire. Such a conductor could work as a sensitive pressure detector or be a component in electronics designed to be implanted in the body.

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The Florida State team have already built a heartbeat sensor as proof-of-concept, but postdoctoral researcher Eden Steven, the lead author of the study, published in this week's Nature, told DNews the coated silk could just as well work as an artificial muscle. "Earlier studies on lifting strength showed it is some fifty times stronger than muscle," he said.

Other research teams have tried mixing spider silk with metals to get electrical conductivity, but the silks don't stretch as far as pure silk. Coating the silk in metal also cuts off moisture, so it can't shrink or expand the way it normally does. Steven said he wanted a material that was porous enough to let water in, so he decided to try carbon nanotubes.

To make the conductive threads, the group collected threads from the webs of golden silk spiders Nephila clavipes, which are common orb weavers in the American south. The chief advantage of these spiders is that the webs are often large -- three feet across -- making it easy to gather the dragline silk, which is what anchors the web in place.

Next, they mixed the threads with dry nanotubes, which stuck to the threads, but not strongly. Adding drops of water to the bundles of the carbon-covered silk encouraged adhesion and then they pressed the wet threads between two Teflon sheets.

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