Medical invention of the day: Roboscallop drug delivery device.

A device that mimics a sea scallop -- propelling itself by alternately sucking and blowing -- could one day carry drugs to hard-to-reach parts of the human body.

"Our motor has no moving parts and can be powered remotely with no connecting wires," says Claus-Dieter Ohl, a physicist at the University of Twente in the Netherlands who led the team that built the device.

The so-called "roboscallop" consists of a tube a few millimetres long and about 750 microns in diameter that is closed at one end and contains a bubble of air. Submerging the tube in fluid and bombarding it with sound waves causes the bubble to expand and contract, alternately sucking and blowing liquid from one end of the tube. The process generates thrust because fluid enters the tube from a wide angle but is expelled as a narrow jet.

"It's how a scallop moves," explains team member Rory Dijkink. "When you watch our device, it looks as if it is making two steps forward and one step back."