The Rotor That Spins on a Bubble
By Celeste Biever
Posted on May 6, 2006
WHAT do you get if you take a set of miniature silicon helicopter
blades, drop them into a beaker of water and blast them with sound
waves? A remote-controlled underwater "bubble rotor" that could be used
to manipulate individual cells.
The rotor, developed by Daniel Attinger of Columbia University in New
York, consists of a piece of silicon, 60 micrometres wide, cut into two
crossed blades. It can be made to spin by placing it near a bubble of
air in water and hitting the bubble with ultrasound waves.
Although the bubble rotor itself is 100 times bigger than ordinary
cells, if you attach a carbon nanotube shaft to drill into individual
cells, you can learn more about how they respond to stimuli, Attinger
says. The rotor could also be used in microfabrication: hundreds of
spinning shafts could be assembled to form a moving "carpet" that guides
tiny mechanical parts around a surface.
Attinger and his colleagues discovered the bubble rotor by accident in
2004 while using ultrasound waves to make an underwater air bubble
expand and contract. The team was attempting to recreate a 2003
experiment by Philippe Marmottant at CNRS-Université Joseph Fourier in
France, in which he showed that the process produces a doughnut-shaped
whirlpool above the bubble. By creating this whirlpool near cells
suspended in water it is possible to trap and stretch the cells so that
the pores in their surface are wide enough to absorb certain drugs.
When Attinger repeated the experiment, he threw in tiny crushed plastic
pieces to help him see the vortex more easily. One of these pieces, a
round plastic disk, was much larger than the rest. He found that the
creation of the whirlpool sucked this plastic disk towards the
18-micrometre wide bubble, where it stuck to the top and started
rotating along with the whirlpool, just like a spinning dish balancing
on the end of a stick.
He has since built a helicopter rotor with four prongs, which he has
spun on the surface of a bubble. By varying the frequency of the
ultrasound, he can control the speed at which the rotor turns, up to a
maximum of 600 rotations per minute. Attinger will present his bubble
rotor on 8 May at Nanotech 2006 in Boston.
Story location: http://www.newscientisttech.com/…
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