A SCUM-DWELLING pond microbe is the inspiration for minute springs that bioengineers hope will operate tomorrow鈥檚 miniaturised devices.
Danielle France at the Massachusetts Institute of Technology is studying a protozoan called Vorticella convallaria, which can attach itself to rocks, lily pads and even other creatures in the plankton using a stalk called a spasmoneme. When the protozoan is disturbed, the spasmoneme contracts abruptly, like a stretched telephone lead springing back into a coiled shape. 鈥淲e think that it operates on stored energy,鈥� says France.
鈥淚t is like a stretched telephone lead springing abruptly back into a coiled shape鈥�
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This striking behaviour was first observed by the inventor of the microscope, Anton van Leeuwenhoek, in 1676. But only now have France and her colleagues revealed how this spring-like structure works 鈥� and just how powerful it is.
France told the American Society for Cell Biology meeting in San Francisco last week about experiments in which she spun Vorticella cells on a revolving microscope stage, exposing them to accelerations of 10,000g. Even working against the colossal resulting forces the cells could still contract their spasmonemes. The researchers calculate that a contracting spasmoneme exerts a force of at least 300 nanonewtons. That might not sound like much, but France says that, for its size, Vorticella鈥榮 spasmoneme is more powerful than a car engine.
The mighty nanospring is triggered by the release of calcium ions from the cell. The spasmoneme contains six proteins from a family called the centrins. By using antibodies to disable each centrin in turn, France and her colleagues have identified one, called centrin 5, that seems especially responsive to the calcium signal.
At the same time as investigating the natural fibres, the team is also trying to build artificial nanosprings by cross-linking centrins to fibres of polyethylene oxide. She suggests that centrin-triggered springs could one day form part of miniature probes that would deliver drugs deep inside the body.
