Saturday, July 12, 2014

Wind-powered plectoneme actuators

A plectoneme. Image quoted from B.C. Daniels et al., "Discontinuities at the DNA Supercoiling Transition."

I am working on a proposal for an artwork at World Maker Fair New York that uses wind-powered plectoneme actuators. A plectoneme is the twist instability that forms a hairpin side branch on a highly twisted fiber. As has been discovered in DNA biomechanics, when a twisted fiber forms a plectoneme it becomes the mechanical equivalent of a threaded screw: additional twisting at constant tension shortens the length of the fiber. The shortening continues to nearly full contraction of the fiber as demonstrated in my video on "writhing thread" actuators. That demo used a high-current pulse to drive a cellphone vibrator motor to lift a weight weighing about 30 times the motor's weight to almost 100% contraction of the fiber.

After plectonemes form, further twisting of a fiber under constant tension is converted into linear motion. Image quoted from S. Forth et al., "Abrupt Buckling Transition Observed during the Plectoneme Formation of Individual DNA Molecules."

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