Say that five times fast. Harvard Gazette wraps its tendrils around a new way to build springs based on the coiling shoots of cucumber vines:
Harvard researchers, captivated by a strange coiling behavior in the grasping tendrils of the cucumber plant, 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 physical and mathematical modeling and cell biology — not to mention a large quantity of silicone.
The result, published in the Aug. 31 issue of Science, describes the mechanism by which coiling occurs in the cucumber plant and suggests a new type of twistless spring.…
A fibrous ribbon, made of threadlike cells called gelatinous fiber (g-fiber) cells, runs the length of each tendril. Two cell layers thick, this ribbon appears to provide the force required for the tendril to form a helix without the benefit of muscle. If the cells on one side of such a ribbon were to contract, the researchers thought, it would force the ribbon to curve and coil.
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“The inner cell layer of the tendril has more lignin in it, which is a sort of glue that gives cell walls stiffness and holds together the cellulose microfibrils, which are like rebar in the cells,” says [co-author Joshua] Puzey. “We thought this stiffness must be related to the coiling somehow.”
To test the idea, [lead author Sharon] Gerbode and Puzey glued a fabric ribbon to one side of their silicone model and a copper wire to the other side. At last, the silicone strip formed a pair of helices that overwound, just like the cucumber tendril.