ROSSLYN, Va., March 20, 1997 -- Biomedical engineers have built a prototype drug pump the size of a contact lens, a miniature, closed-loop implant that could monitor its own flow rate to ensure a steady stream of medicine.
The pump is still considered large as a microelectromechanical system, in which sensors, actuators and electronics are merged onto a single silicon wafer. The next step will be to shrink the device so it can be mass produced like a computer chip.
The research, in the laboratory of Whitaker Investigator Michael Huff at Case Western Reserve University, is driven partly by managed health care, which wants to keep people out of hospitals, and partly by the needs of diabetics and other patients on regular, intravenous medication.
Huff, who himself is diabetic, 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 patients blood glucose level and change the dose of insulin accordingly," said Huff, who has begun with a pump and a flow sensor to ensure a constant pumping rate. An insulin sensor would have to be added later.
Huffs 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 F.). "When these materials recover their shape, they can produce very large displacements and forces," Huff said.
To operate the pump, rhythmic pulses of mild electrical current are
passed directly through the alloy, setting up a cycle of heating and
cooling that causes the metal 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 valv
Contact: Frank Blanchard