As technical devices become smaller, basic processes like fluid flow become more difficult. University of Arkansas researcher Steve Tung is creating a novel solution to this problem by incorporating living bacteria into microelectromechanical systems (MEMS) to form living motors for pumps and valves. These tiny bioMEMS devices could be used in systems for drug delivery or DNA sequencing.

"It is hard to move fluid on a micro scale because it takes a lot of pressure," explained Tung, associate professor of mechanical engineering. "Current systems are expensive and inefficient, requiring high voltage or very good seals."

MEMS devices are machines so small they cannot be seen by the unaided human eye. With gears no bigger than a grain of pollen, they range in size from micrometers to a millimeter. MEMS combine electrical and mechanical components into an integrated micro device or systems that can function individually or in groups to sense, control and actuate larger devices.

The tiny devices have a big impact on both the consumer and defense industries. The market for MEMS devices was estimated at more than $8 billion in 2001, and it is growing rapidly.

BioMEMS use a specific type of bacteria, which has a tendency to attach itself to a surface by one of its many flagella, the long filaments that protrude from its surface. Bacteria use the whip-like motion of their flagella to move about. While each flagellum normally turns counter-clockwise about 80 percent of the time, it is possible to introduce a mutation that will lock the motors in one direction of rotation, either clockwise or counterclockwise, according to Tung.

While several MEMS-based pumps have been developed, non-mechanical designs have limited applications because they rely on the electrical properties of the fluids. Mechanical micro pumps require a very large pressure drop, which severely limits their performance.