The air pressure or vacuum, respectively, push or pull air through channels in the bottom layer, transmitting pressure or suction through the middle-layer membrane to push or draw fluids through channels in the upper layer.
While an outside air pump or vacuum is needed to run the device, Gale says the membrane is, in effect, the pump because a pump creates a pressure difference, which is what the membrane does to move fluids.
Because gas, not fluid, flows through the middle layer, liquid in the upper-layer microchannels can flow into and fill dead-end channels or chambers without trapping air. That allows the pump to carry samples like blood or fluids with protein or DNA through the microchannels to dead-end chambers that contain chemicals needed for a test.
The outside device to run the lab-on-a-chip – including air pressure or a vacuum to run the micropumps – "would be as big your wallet, and the chip would be like a credit card that goes in your wallet," Gale says.
Each micropump can produce a flow of up to 200 nanoliters of fluid per minute. A nanoliter is one-billionth of a liter, and a liter is less than 1.1 quarts.
"If you had a drop on the end of a pin, that would be five times as much fluid as this pump would move in a minute," Gale says. "In some respects, we are bragging that's a large flow" for such a tiny pump. Yet the flow could be slowed considerably if the pump was used to deliver drugs, he adds.
Of Micropumps and Miniature Laboratories
The idea of a lab-on-a-chip is to reduce the price and time for lab tests and to conduct them where patients are treated. On such a chip, micropumps replace the large equipment normally used to move blood and other samples through a laboratory test.
The first micropumps were developed 20 years ago, and some are used commercially now, particularly for various sensor devices and for cooling computer chips, Gale says. "But almost all the micropumps you find in the last 15 or 20 years are complicated, multilayered devices not conducive to inexpensive manufacturing, and you can't put a whole bunch of them on a chip," he adds.
Gale says there are at least 20 categories of micropumps, including ones that move fluids using piston-like devices, magnets, pressure from silicone membranes and electrical charges.
"Compared with our pump, existing micropumps are difficult to make and more expensive," Gale says. "They are bulky, and it is difficult to integrate thousands of them simultaneously into a lab-on-a-chip."
Another advantage of the new micropump is that the mechanical air pressure device or vacuum that powers the pump never contacts blood or other medical samples.
"Most of these biological fluids are very sensitive," Gale says. "If you have a medical sample, you don't want to contaminate it. We've removed the complexity of the pump from the microdevice to an external location."
Eddings says only three or four steps are required to make the new micropump, compared with many steps for existing models.
The new micropump – known technically as a "PDMS-based gas permeation pump" – was developed for about $20,000 at the university's Center for Biomedical Fluidics, part of Utah's Centers of Excellence program, Gale says. The National Science Foundation also helped fund the research.
"This pump would not ever be sold as an independent system," Gale says. "It would be integrated directly into the device you are making."
Gale says he is working to develop a lab-on-a-chip that would test the blood of multiple sclerosis patients to determine if they are developing resistance to a new MS drug.
He also is developing a lab-on-a-chip blood test that would detect genes that affect how quickly various patients break down blood-thinning drugs used to treat heart disease. The test would be used by doctors to decide the right dose for each individual patient, something done now by trial and error, he says.
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