Back in Sept. 2005 we reported about surgical micro-robots being developed by Prof. Bradley Nelson and Co. from the Institute of Robotics and Intelligent Systems at the Swiss Federal Institute of Technology in Zurich. The group of researchers came up with a bacteria-like propulsion system that is designed to drive micro-robots to perform specific predefined tasks.
A recent article at the MIT’s Tech Review explains the workings of this nanomotor:
Tests show that the tiny rotating nanocoils–just 27 nanometers thick and 40 micrometers long–are capable of spinning at 60 revolutions per minute and that it is possible to propel an object at nearly 5 micrometers per second…
Moving through fluids at the nanoscale can be a real challenge because of the viscosity of the liquid, says Sylvain Martel, an associate professor at the department of computer engineering at Montreal Polytechnique in Canada. As the size of an object is reduced, the force required to move it through a fluid does not reduce proportionally, Martel says.
For a bacterium trying to move around at the microscopic scale, this effect can be dramatic. “It’s like swimming through something thicker than molasses,” says Nelson, who carried out the work with graduate student Dominik Bell.
As a result, bacteria evolved the highly sophisticated flagellum. “Sperm just waggle their tails, but bacteria have a much more complicated mechanism,” says Nelson. A molecular motor that pumps protons across the cell’s membrane causes the helical filaments of the flagellum to rotate. This is carried out so efficiently that some flagella have been clocked spinning at speeds of up to 1,000 revolutions per minute.
Nelson’s nanocoils generate their motion using an external rotating magnetic field which causes them to move in much the same way as flagella. The nanocoil was made by fabricating two very thin strips of gallium arsenide on top of each other, using photolithographic techniques; the bottom layer is laced with indium. “The indium atoms in the lower layer induce a compressive stress,” says Bell. This causes it to curl up into a helix to release the stress, says Bell. “It’s like a corkscrew,” Nelson explains.
To make this helical nanocoil rotate, Nelson and his colleagues then created a set of four magnetic coils positioned so that they would produce an electromagnetic field that would rotate around a single axis. The coils were attached to small nickel plates, which acted as surrogate microrobots, and were placed in liquids to see if the coils could propel them. They could.