STANFORD, Calif., Mar 22, 2001 (United Press International via COMTEX) -- A microjet capable of precisely cutting tissue using minuscule pulses of liquid might one day replace some types of surgical lasers. The device could also one day painlessly and continuously inject medication through a patient's skin.

Surgeons often use pulsed lasers to cut through soft tissue during angioplasty and other kinds of surgeries. But the energy of the lasers creates vapor bubbles in the liquids in tissue -- often damaging tissue surrounding the point of incision.

"This so-called collateral damage reduces precision when you are trying to dissect soft tissue," said D. V. Palanker, the co-inventor of the microjet technique and a surgeon at the department of ophthalmology at Stanford University Medical Center in Stanford, Calif.

Palanker said the challenge for any surgical device is delivering enough power to disrupt tissue without radically expanding the liquid around the point of incision. So far, he has only used the microjet in a gel with physical qualities like that of soft tissue, but the tests were promising.

In a paper co-written by Dr. D.A. Fletcher, also of Stanford, in latest issue of Applied Physics Letters, Palanker said the microjet is driven by an electric discharge that creates vapor bubbles inside a micronozzle approximately 30 microns in diameter (30 millionths of a meter). The vapor bubbles create a jet effect by forcing out pulses of

liquid measuring only 100 picoliters in volume (100 trillionths of a liter) and also measuring 30 microns in diameter. The pulses reach a peak velocity of 90 meters per second.

Because the device is pulsed, any potentially damaging bubbles are given time to dissolve. Moreover, the liquid pulses are so small and delivered so rapidly; they do not damage blood vessel walls or skin, Palanker said.

"The microjet could also be used for injections in addition to cutting tissue," he added. "The standard technique of course is introducing a needle or micropipette into tissue and pushing liquid through. It's invasive because you are piercing tissue and in many cases causing bleeding. But it could also be possible to use the microjet to inject

medicines such as insulin without using needles." He added that, theoretically, tiny jets could even be installed into wristwatchs to shoot the desired amount of medication whenever required.

"Whether the microjet would do less collateral damage than a laser depends on what kinds of lasers you're talking about," said Denise Caldwell, a program director at the National Science Foundation. She said the microjet, in principal, might inflict less damage that some lasers but the NSF is funding research into new types that operate in

the picosecond (one trillionth of a second) and femtosecond (one quadrillionth of a second) levels. These tend cause much less damage than many contemporary techniques.

She said femtosecond lasers, which deliver bursts at one quadrillionths of a second, cause less damage because there is so little time for the energy to diffuse in the surround medium. "Essentially the energy doesn't have time to migrate and it's the energy that causes the damage," she said. "I would image they could eventually be used in various forms of eye surgery such as refractive surgery and corneal transplants."

A patent is pending for the microjet device.

(Reported by Technology Writer KELLY HEARN in Washington)

Copyright 2001 by United Press International.

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