A biopolymer that switches from rigid to flexible has been created by Case Western University researchers. It mimics the structure of sea cucumbers, which are able to change their skin from soft and flexible (for getting through narrow spots) to hard and rigid(armor to protect them from predators).

    It is known that sea cucumbers have skin composed of very finecellulose fibers. When attacked, surrounding cells secretemolecules that cause these "whiskers" to bind together,forming a kind of protective armor. When relaxed, other cellsrelease plasticizing proteins to loosen the fibers, allowing thecreatures to flow easily through crevices.

    Researchers isolated the cellulose fibers from the surface ofcreatures similar to sea cucumbers. The researchers then combinedthe fibers with a rubbery polymer mixture. The fibers formed a akind of mesh through the body of the material, reinforcing thesofter polymer. The fibers hold it together, creating an inflexiblematerial. "It's like a three-dimensional web in which thesenanofibers overlap at certain points, and wherever they overlap,they stick to each other," say researchers.

    It is hoped that this rigid-yet-flexible material could be used in biomedical applications, like implantable electrodes that could record brain activity over long periods oftime, without the scarring produced by conventional metal electrodes. This material is a variation on the idea ofshear-thickening fluids used in applications as varied as body armor and rehabilitative exoskeletons .