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Benjamin Shapiro
Fischell Department of Bioengineering
Joint appointment with:
Institute for Systems Research
2246 Kim Building
University of Maryland
College Park, MD 20742
Tel: (301) 405-4191
Fax: (301) 405-9953

Manipulating Objects (e.g. swimming cells, quantum dots) by Micro Flow Feedback Control
( vs ABEL trap, we did particle feedback control first.
Details/Documentation )

Students: Mike Armani, Satej Chaudhary, Zach Cummins, Roland Probst

We precisely control the surrounding fluid to accurately trap and steer multiple particles. If the particle is to the West of its desired position, we create a flow to move it East, if it is to the North, we create a correcting South flow. Our control algorithms are sophisticated enough to create correcting flows at multiple locations at once. In the past we achieved 1 µm steering and trapping accuracy (this accuracy was set by the resolution of our optical system). Now we can do steering of single quantum dots to 84 nm accuracy. Control is also possible by other forces, e.g. by electrical or magnetic forces using the same idea – always apply a force to move the object from where it is towards where it should be.

For some of our more recent results see the following projects:

      a: Steering and Trapping of Live Swimming Cells
      b: Manipulation of Single Quantum Dots to Nanometer Precision
      c: Flow Control of Object Positions and Orientations”


Below we show some movies that demonstrate our capabilities. For details on device fabrication, control algorithms, and capabilities, please see our published journal papers.

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Above: An early experiment, from 2004. Top view of a PDMS device zoomed to where the two channels cross. Two 10 micron beads are visible. The flow is controlled by 4 electrodes (not shown, 1 cm away) to steer one of the beads along the figure 8. The figure 8 is approximately 100 um long. Particle jitter is due to the bead sensing camera-frame 30Hz update rate.

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Above: Theoretical simulation for steering 8 particles at once,
to an accuracy of 1 mm.

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Above: Steering of one yeast cell along a UMD path,
to an accuracy of 1 mm.
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Steering of 3 yeast cells to an accuracy of 1 mm.


microfluidic devices
Above Left: Photograph of the microfluidic devices with the Cursive “UMD” path super-imposed on the image. The four control electrodes are located outside figure frame.   Above Right: The actual path of the yeast cell (white dot) in the feedback control experiment. The yeast cell is being steered to an accuracy of one micron. Any other cell that is small enough to act as a particle in the flow could also be steered in this way: the type of cell is not important from a flow control perspective.

Steering 4 particles
Steering 4 particles at once (top view): grey disks = electrodes; color field = electric potential; arrows = electric field; black circles = particles to be steered; black curves = actual particles paths (match desired paths).

Experimental results for steering three yeast cells to one micron accuracy by electroosmotic flow control

steering 3 yeast cell
Left: PDMS microfluidic device with 8 control electrodes (one in each of the lightbulb shaped reservoirs). Right: Steering of 3 cells at once along two circles and a UMD path by electroosmotic flow control. White traces shows path of the cells, arrows show current cell locations. Can also trap 1 or 2 cells while steering the others.


next project


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