An international team of scientists is developing what they say will be the world's first microrobot -- as wide as two human hairs -- that can swim through the arteries and digestive system.

The scientists are designing the 250-micron device to transmit images and deliver microscopic payloads to parts of the body outside the reach of existing catheter technology.

It will also perform minimally invasive microsurgeries, said James Friend of the Micro/Nanophysics Research Laboratory at Australia's Monash University, who leads the team. The researchers hope the device will reduce the risks normally associated with delicate surgical procedures.

While others have tried and failed to create microrobots for arterial travel, Friend believes his team will succeed because they are the first to exploit piezoelectric materials -- crystals that create an electric charge when mechanically stressed -- in their micromotor design.

"People have tried various techniques, including electromagnetic motors," Friend said. "But at this scale, electromagnetic motors become impractical because the magnetic fields become so weak. No one has taken the trouble to build piezoelectric motors at the same scales, for this kind of application."

Funded by the Australian Research Council, Friend's team is tweaking larger versions of the device, and expects to have a working prototype later this year and a completed version by 2009.

The scientists say stroke, embolism and vascular-disease patients should be the first to benefit from the new technology.

The tiny robot, small enough to pass through the heart and other organs, will be inserted using a syringe. Guided by remote control, it will swim to a site within the body to perform a series of tasks, then return to the point of entry where it can be extracted, again by syringe.

For example, the microrobot might deliver a payload of expandable glue to the site of a damaged cranial artery -- a procedure typically fraught with risk because posterior human brain arteries lay behind a complicated set of bends at the base of the skull beyond the reach of all but the most flexible catheters. There's a high risk of puncturing one of these arteries, which almost always results in the death of the patient.

Other regions of the body are completely outside the reach of current technology, including congenital arteriovenous malformations, or AVMs, which recently afflicted South Dakota Sen. Tim Johnson.

The microrobot's design is based on the E. coli bacterium, complete with flagella that will propel it through the body. Scientists will make the flagella out of human hair in the preliminary research stages, and eventually they want to try using Kevlar.

The theory behind the microrobot's propulsion system is modeled after turbine and helicopter blades, Friend said.

"In and of itself, the idea is not especially new, but it has always fallen down around the propulsion system," he said.

The piezoelectric materials vibrate a twisted microstructure inside the robot at ultrasonic frequencies. When the twisted structure is compressed against the rotor, it untwists and the rotor turns. As the compression is released, the twisted structure unwinds back to its original shape, while the rotor slides.

Working with the flagella, the tiny propulsion system creates enough power to carry the device through the viscous, fluid environment inside the human body, Friend said.