University of Utah investigators, under Dr. Bruce Gale, an assistant professor of mechanical engineering, invented a novel method to move chemicals, blood or other bio samples through diagnostic chips.
Here’s how the university explains its technology:
While a lab-on-a-chip would have hundreds to thousands of micropumps–sets of tiny fluid and air channels and larger chambers in which samples were tested–Eddings and Gale demonstrated their invention by building an array of 10 of the tiny pumps.
They molded tube-like “microchannels” — each the width of a human hair — into the top and bottom layers of a three-layered piece of silicone polymer material about the size of a deck of playing cards. The polymer is named polydimethylsiloxane, or PDMS.
“It’s made out of bathroom caulk,” Gale quips. “It is very similar to the clear silicones you’d use to seal your bathtub.”
The card deck-sized array has three layers of rubbery PDMS:
A top fluid channel layer, with wells into which blood or other samples are placed, and microchannels through which they can flow toward small chambers. A crucial middle layer, a thin, permeable membrane of PDMS. Gas can pass through the caulk-like PDMS, while liquid cannot. A bottom control channel layer, with inlets and tiny channels through which air pressure or a vacuum is applied.
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.