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Braille pins control microf luidic flow e was fortunate to still have a 486-MHz computer at home. And it helped that he remembered how to use DOS. Because when Wei Gu, a senior at the University of Michigan, found a Braille display machine and tried to connect it to a microfluidic device, he quickly discovered that it was much too old to run on Windows. The idea was to program the Braille pins to move fluid through the microchip channels and thus eliminate the need for external pumps or Schematic of how Braille pins and microchannels can be valves. “We are interested in arranged to perform multiple laminar-flow experiments. microfluidic tissue engineering with little mixing between streams, and and cell culture,” says Gu’s research segmented flow of immiscible fluids in advisor, Shuichi Takayama. One of the one channel (Proc. Natl. Acad. Sci. U.S.A. bottlenecks has been the lack of a ro2004, 101, 15,861–15,866). In addition, bust, user-friendly system to do the they used the method to seed cells, divide pumping and valving, he says. them into distinct subpopulations, and To make it all work, Gu dusted off culture each subpopulation for up to his old computer and wrote a program that translates pumping speed into a line three weeks under constant perfusion. “In most systems, the chips are small of text. The Braille machine converts but the actuators are big and externally that text into pin movement. “You can connected by tubes. What is nice about program the pins to move fluid around this Braille system is [that] we don’t the channels however you want. So it’s need any external connections or tubing very flexible,” says Gu. for the actuation,” explains Takayama. The concept is quite simple. A miIn addition, “the basic Braille platform crochip, which is made out of PDMS, is well developed and engineered so that contains channels that are sealed with a it is robust and user-friendly,” he says. thin layer of PDMS. The chip is placed One of the challenges in making the on a Braille display that contains a grid Braille microfluidic system work was of 320 moving pins. When the pins getting the geometry of the channels move up, they squeeze the rubber miright, says Takayama. “It is crucial to crochannels shut, controlling the flow have the right cross-section channel of fluid. “It is like stepping on a hose, geometry to get good valving and chip except that you do it microscopically,” behavior. These channels can be tedious says Takayama. Using the new approach, the research- to make well, so we’ve developed a new, inexpensive, one-step method to generers demonstrated rapid mixing between two liquid streams, multiple laminar flows ate microchannels with bell-shaped cross © 2005 AMERICAN CHEMICAL SOCIETY
sections,” he says (Adv. Mater. 2004, 16, 1320–1323). The Braille system could be useful for numerous analytical applications, but the researchers are mostly interested in using it for cell culture. “Cells need constant perfusion to survive,” says Takayama. Programmable fluid flow makes it possible to put cells inside microscale devices and perfuse them for extended time periods, says Gu. During those long time spans, you also can arbitrarily deliver any reagent and change the fluid dynamics of the system however you want, he adds. One big advantage of the Braille device is that it is portable, say the researchers. Compared with other types of fluid control, “it would be easier to use something like this in a resource-poor environment,” says Gu. In addition, it is easy to move it around the lab between the cell-culture hood, the incubator, and the microscope, says Takayama. Some microfluidics experts are excited about the new approach. “Control of flow with Braille displays is novel and quite clever,” says Olgica Bakajin of the Lawrence Livermore National Laboratory. “It’s nice because it’s relatively cheap and compact and because all the valves can be independently actuated,” she says. The only limitations she sees are that the spacing between the valves cannot be arbitrarily small and that the method only works with elastic materials, such as PDMS. “Still, for most applications, the 2.5-mm spacing is good enough, and there are lots of applications where PDMS (or other elastomers) work,” she says. a —Britt E. Erickson NOBUYUKI FUTAI
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