Cambridge, Mass. - August 30, 2012 Captivated by a strange coiling behavior in the grasping tendrils of the cucumber plant, researchers at Harvard University have characterized a new type of spring that is soft when pulled gently and stiff when pulled strongly.
Instead of unwinding to a flat ribbon under stress, as an untwisted coil normally would, the cucumber's tendrils actually coil further. Understanding this counterintuitive behavior required a combination of head scratching, physical modeling, mathematical modeling, and cell biologynot to mention a large quantity of silicone.
The result, published in the August 31 issue of Science, describes the mechanism by which coiling occurs in the cucumber plant and suggests a new type of bio-inspired twistless spring.
Led by principal investigator L. Mahadevan, Lola England de Valpine Professor of Applied Mathematics at the Harvard School of Engineering and Applied Sciences (SEAS), Professor of Organismic and Evolutionary Biology and Professor of Physics at Harvard, and a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering at Harvard, the researchers were motivated by simple curiosity about the natural world.
"Nature has solved all kinds of energetic and mechanical problems, doing it very slowly and really getting it right," says lead author Sharon Gerbode, a former postdoctoral fellow at SEAS who has now advanced to a faculty position in the physics department at Harvey Mudd College. "But few people have studied biological mechanisms from the point of view of a physicist or an engineer. We barely had to scratch the surface with this question about the cucumberhow does it coil? What could be a simpler question? And what we actually found was this new kind of spring that no one had characterized before."
Well known to botanists and gardeners, the coiling tendrils of climbing plants like cucumbers, sweet peas, and grape vines allow the
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