Public Release: 

Mini Drug Pump Could Simplify Diabetics' Lives

Case Western Reserve University

Biomedical engineers at Case Western Reserve University have built a prototype drug pump the size of a contact lens. It is a miniature implant that could monitor its own flow rate to ensure a steady stream of medicine. The micropump is a closed-loop system, meaning that a flow sensor measures and adjusts the pumping rate to provide more accurate pumping.

The Whitaker Foundation awarded a three-year, $208,000 grant to support the research.

The pump is still considered large for a microelectromechanical system (MEMS), in which sensors, actuators, and electronics are merged onto a single silicon wafer.

Michael Huff, CWRU assistant professor of electrical engineering and applied physics, is an insulin-dependent diabetic himself. He hopes his device may be adapted as a closed-loop system for monitoring blood glucose levels and pumping just the right amount of insulin into the bloodstream.

"Ideally, an insulin-delivery pump would sense the patient's blood glucose level and change the dose of insulin accordingly," said Huff.

As a first step in designing the prototype, Huff has begun with a pump and a flow sensor to ensure a constant pumping rate. An insulin sensor would have to be added later.

Huff's prototype consists of a rectangular silicon chamber with one of the outer walls made of two thin layers of a titanium-nickel alloy sandwiched around a layer of silicon. The alloy forcefully changes shape when heated to around 60 degrees Celsius (140 degrees Fahrenheit).

"When these materials recover their shape, they can produce very large displacements and forces," Huff said.

To operate the pump, a staggered pulse of electrical current passes directly through the alloy, setting up a cycle of heating and cooling that causes it to flex. This forces the chamber to expand and contract. The expansion pulls fluid into the chamber through an intake valve, and the contraction expels the fluid through an exhaust valve.

The flow sensor is made up of a heater that raises the temperature of the fluid at one point in the flow stream. Two heat sensors downstream detect this hot spot as it passes by. Huff can calculate the flow rate from this measurement.

The device has been successfully tested in the laboratory and is being scaled down for mass production, Huff reported at the International Society for Optical Engineering's Smart Structures and Materials Symposium in March. The next step will be to shrink the device so it can be mass-produced like a computer chip.

The field of MEMS and micro fabrication research has led to the development of micro devices, which feature sizes down to a micrometer or less. The field, which developed from integrated circuit fabrication techniques, has recently expanded into the medical device market.

"No company wants to build hospital infusion pumps any longer, since the whole health care system is striving to keep people out of hospitals," Huff said. "Drug-delivery systems should be based on ambulatory delivery."

Medical care has already begun to feel the influence of MEMS. Disposable blood pressure instruments with microscopic pressure sensors costing about $10 are replacing conventional $600 devices that, while reusable, cost another $50 to sterilize and tune up before each use.

About 20 million miniature blood pressure sensors are now being used each year, in addition to other downsized pumps and sensors -- but there are still no closed-loop systems on the market that can regulate themselves without a physician's intervention.

Huff said that the pump could be used for many drugs which require light control and either implantible or ambulatory delivery, such as those used for chemotherapy, AIDS, and cardiovascular disease. The pump could be on the market in two years, following clinical testing and approval by the Federal Drug Administration (FDA).

Toni Searle, amf2@po.cwru.edu Editor, "Campus News, CWRU Phone: 216-368-4443 Fax: 216-368-3546

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