July 22, 2009: Scientists at the U. of Michigan have devised a microfluidic device incorporating a pneumatic system that requires no electromechanical valves, instead powered by sound waves. And they show how it works using the school’s fight song.
To use a typical “lab-on-a-chip” microfluidic device in an experiment (e.g. test for germs, contaminants, gases, etc.), tiny drops of fluid are moved, mixed, and split by air hoses, valves, and electrical connections to a computer. But the ultimate goal of the tiny device is its flexibility — “You’d really like to see something the size of an iPhone that you could sneeze onto and it would tell you if you have the flu,” notes Mark Burns, professor and chair of U-M’s Department of Chemical Engineering and prof. in biomedical engineering, in a statement. “What hasn’t been developed for such a small system is the pneumatics — the mechanisms for moving chemicals and samples around on the device.”
In their work, published online by the Proceedings of the National Academy of Sciences, describe how they use a pneumatic system that replaces the hoses, valves, and electrical connections with resonance cavities, tubes that amplify particular sounds. The cavities are connected on one end to the microfluidic channels, and the other end to a speaker connected to a computer. Notes or chords are generated and amplified through the cavities, and the sound waves push air pressure through holes in the cavities to the channels, which manipulates the droplets.
From the PNAS abstract:
The device consists of a bank of 4 uniquely tuned resonance cavities (404, 484, 532, and 654 Hz), each being responsible for the actuation of a single droplet, 4 identical flow-rectification structures, and a single acoustic source. Cavities selectively amplify resonant tones in the input signal, resulting in highly elevated local cavity pressures. Fluidic-rectification structures then serve to convert the elevated oscillating cavity pressures into unidirectional flows. The resulting pressure gradients, which are used to manipulate fluids in a microdevice, are tunable over a range of ≈0–200 Pa with a control resolution of 10 Pa.
Essentially the resonance cavities amplify specific tones and convert them into air pressure; if one note is played, one droplet moves, a three-note chord moves three droplets, etc., explained U-M chemical engineering doctoral student Sean Langelier. The cavities don’t communicate with each other, so strength of individual notes can be varied in strength to move drops faster or slower, he said.
The new system is still external to the chip, but the researchers are working to shrink it to integrate on a microfluidic device. Possible application, for example, is the aforementioned smartphone-sized home flu test.
Watch a video of the sound moving, splitting, and sorting droplets. Watch a video of droplets moving through a microfluidic device, to the tune of U-M’s fight song “Hail to the Victor.” (A computer-tonal version, not the collegiate football band grand spectacular…use your imagination)