Tiny Bubbles Deliver Drugs in Pump Prototype

Sometimes the best ideas are the simplest.

Researchers around the world have been trying to develop tiny pumps that could automatically supply medications such as insulin to a person suffering from diabetes, but most candidates are complex electro-mechanical devices that could be subject to early--and catastrophic--failure.

Now, engineers at Johns Hopkins University have come up with a potentially elegant solution. Their device creates microscopic bubbles to force fluid through a tube, one bubble at a time.

“It’s very different from having a pump with a valve that has to open and close,” said Andrea Prosperetti, professor of mechanical engineering at the university and the leader of the project. “With no moving parts, the bubble-powered pump’s prospects of failure are minimal.”

The university has applied for a patent for the device, and one unidentified firm already has expressed an interest in the technology, which was revealed only recently. The research is supported by the Air Force and the Defense Advanced Research Projects Agency.

Prosperetti sees a wide range of possible applications, ranging from environmental monitoring to pharmaceutical delivery systems small enough to be embedded in the patient’s body.

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So far, the university has developed only a prototype, and it is about the size of a paper clip, but the technology can be scaled down to very, very small devices, according to Hansan Oguz, a mechanical engineer who is working on the project.

The prototype consists of two narrow tubes, one about the diameter of the wire in a large paper clip, and the other somewhat narrower. The tubes are connected by a cone-shaped device that serves as the bubble chamber.

The device is filled with saltwater, which also serves as an electrical conductor. When a small current is applied, the water in the narrow section of the cone heats up because the current is “squeezed” as it passes through the narrow throat, the researchers said.

That causes the water to vaporize, creating a single bubble.

“The bubble expands toward the wider end [of the cone] because the surface tension is stronger at the narrow section than at the wider section,” Oguz said. In other words, the bubble moves toward the section of lower friction.

“This gives the bubble the preferential direction” needed to push the fluid forward, he said.

When the current is turned off, the bubble collapses in the larger tube, and “there has been a net displacement” of the fluid, he said. When the current resumes, another bubble forms in the cone’s throat, pushing the fluid along.

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The bubble pump is a very different approach than that taken by other researchers, including Michael Huff, a biomedical engineer at Case Western Reserve University in Cleveland. Huff, who has had diabetes all his life, has developed a small pump about the size of a contact lens to supply insulin to those suffering from the disease.

Huff’s system uses two thin layers of a titanium-nickel alloy sandwiched around a layer of silicon. Small electric pulses cause the alloy to flex, drawing fluid in one valve and then forcing it out another.

But the Johns Hopkins researchers believe any system that relies on a series of valves is likely to prove too vulnerable to mechanical failure.

The potential applications for any successful micropump are considerable. Micropumps could make it possible for pharmaceutical companies to test costly drugs with only minute samples, Prosperetti said. Or they could provide continuous monitoring of liquid pollutants produced by a factory.

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The Department of Defense is supporting the work because tiny pumps could be useful for the detection of chemical and biological weapons and possibly for advanced fuel-injection systems for high performance aircraft.

And maybe someday, they will be reliable enough to be embedded beneath the skin of a patient, providing just the right dosage whenever it is needed.

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Lee Dye can be reached at leedye@ptialaska.net.