Biological Applications of Micromachined Ultrasonic Flexural Plate-Wave Technology

The micromachined acoustic flexural plate-wave (FPW) device has many applications in biological research and medical diagnostics. In order to safely use the FPW device for these applications, we studied the effects of ultrasound produced with the device on biological samples of interest. Using gel electrophoresis as  an assay, we have shown that 4300-bp DNA molecules were not subject to strand breakage as a result of exposure to ultrasound generated by the FPW device.
As another application of the FPW device, we developed an in vitro cell growth sensor that is continuous and capable of automation for high-throughput screening. Density sensing was achieved by measuring the frequency shift caused by mass loading of the FPW membrane. Changes in the liquid density of the cell suspension were used to track growth. Experiments were performed to sense growth in suspensions of mammalian cells. Results show the expected correlation between changes in cell number and frequency measurements.
We developed an acoustically driven micropump offering the advantages of low operating voltages, gentle pumping, and no limitations on the electrical conductivity of liquid that can be pumped. A novel combination of unidirectional transducers and focused flow resulted in a micropump that achieved flow speeds up to 1.15 mm per second, two times higher than flow speeds previously obtained. In addition, the curved transducers focused 2 micron polystyrene spheres into a stream with a beam waist smaller than 100 microns. The pump was characterized using laser diffraction and particle image velocimetry.
We demonstrated a non-contact method of concentrating particles using acoustic radiation pressure to manipulate biological cells and polystyrene spheres in an EPW device. Using different transducer configurations, we have shown particle concentration in a grid pattern, moving and trapping particles in both the x and y directions and completely localizing even one single particle within the fluid. We studied the effects of input voltage and particle size on the speed and degree of trapping. We have shown controlled transport of a single trapped particle, allowing a sample to be positioned for analysis. The FPW device thus functions as an acoustical tweezer suitable for many applications in a microfluidic system.
Audra Hsien-I Meng
Rajendra Bhatnagar
Publication date: 
December 31, 1999
Publication type: 
Ph.D. Dissertation
Meng, A. H. (1999). Biological Applications of Micromachined Ultrasonic Flexural Plate-wave Technology. United States: University of California, Berkeley, with University of California, San Francisco.

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