May 2010
Over The Wire Tissue Edition
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Super Tissue Strong as Kevlar

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A soft "tissue paper" made from normally brittle germanium and silicon contains individual fibers as strong as bulletproof Kevlar. Woven into traditional fabric or embedded in hard plastics, the new nanowires could stop bullets, harvest solar energy, or perform dozens of other tasks, according to a recent report in's Discovery News.

"Paper is made of wood fibers compressed together," said Brian Korgel, a scientist at the University of Texas at Austin and co-author of a new paper in ACS Nano that describes the germanium nanowires. "In this case, we took bulk semiconductors, turned them into nanowires and compressed them together to make a material with a tissue paper consistency." Germanium is usually quite hard and brittle. "When I handle a block of the bulk material, I have to handle it very carefully so it doesn't break," said Korgel.

Unlike bulk germanium, however, germanium tissue paper is flexible and won't break when bent. The individual nanowires that make up the tissue paper are also incredibly strong, having a similar strength-to-weight ratio as Kevlar. They can even absorb blows that would ordinarily shatter a block of germanium, the Discovery report explains. The germanium wires have the strength of Kevlar, but that doesn't mean they will make ordinary clothing bulletproof -- at least not immediately. Kevlar stops bullets because not only are individual fibers strong, but so are the bonds between the fibers. However, individual germanium nanowires are not there yet.

Korgel compares the bonds between his strong germanium nanowires with the proteins spiders use to make drag line silk as strong as steel. "Scientists know how to make the proteins spiders use in test tubes," said Korgel. "But you have to take those proteins and spin them into a web to match their mechanical properties."



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