Tiny robots flex their plastic muscles

By BBC News Online science editor Dr David Whitehouse

Miniscule submersible robots may soon cruise through your bloodstream looking for misbehaving cells or even man the production lines of miniature factories.

Swedish researchers have made crude micro-robots that are shorter than this hyphen - and no wider than the full stop at the end of this sentence.

Unlike many previous designs, the robots can function in different kinds of liquid, such as blood, urine, and the media used to culture cells. This could make them very useful to biotechnologists.

"Being able to manipulate many individual cells at the same time is becoming increasingly important in many areas of science," says Edwin Jager, of Sweden's Linköpings Universitet, lead author of a paper on the robots which appears in the journal Science.

"We think that these micro-robots would be helpful for fundamental studies, or for manufacturing other small devices, especially if we set up arrays of them."

Shrink and swell

The Swedish team speculate that the robots' miniature hands might someday pick up single cells or bacteria and transfer them to analysis stations.

The micro-robots have a silicon framework encased in layers of gold and a conducting polymer, such as polypyrrole.

A micro-robot shifts a bead to different tracks

The polymer can be forced to shrink and swell by subjecting it to spurts of positive and negative ions. This makes segments of the robot bend.

And by carefully controlling which particular segements bend and when, the researchers can simulate the action in their robots of elbows, wrists, hands, and even fingers.

Previous micro-robots have included electronic devices featuring rods and levers, artificial wings and legs. But, "none of these operate in water, and would not be suitable for the manipulation of cells," Jager says.

'Factory workers'

Submerged in an electrolyte solution, several robots were wired to an electrical source and videotaped as they hoisted glass beads.

By stimulating the micro-robots' fingers, wrists and elbows, the researchers made their mini-machines move the beads a distance 0.25 millimetres (0.01 inches).

The robots also managed to transfer the beads from one miniature conveyor belt or "track" to another, proving their potential as tiny factory workers.

The scientists say that if treated with adhesion molecules, the robot's fingers might select particular cells or bacteria from a sample.

The micro-robots could be positioned at the end of a catheter to assist surgical procedures.