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Scientists Use Bacteria to Power Microgears

Scientists at Northwestern University and the U.S. Department of Energy's Argonne National Laboratory have discovered that common bacteria can turn microgears when suspended in a solution, providing insights for the design of bio-inspired dynamically adaptive materials for energy.

The ability to harness and control the power of bacterial motion is an important requirement for further development of hybrid biomechanical systems driven by microorganisms.

The researchers placed microgears with slanted spokes in solution along with common aerobic bacteria, Bacillus subtilis. (The gears are a million times more massive than the bacteria.) They discovered that the bacteria appear to swim around the solution randomly, but occasionally the organisms will collide with the spokes of the gear and begin turning it in a definite direction.

The results are published online in the Proceedings of the National Academy of Sciences.

"While this work by itself certainly does not solve the grand energy challenge, it provides the first demonstration that useful energy can be harnessed from random and otherwise wasteful motions of bacteria," said Bartosz A. Grzybowski, a senior co-author of the paper and the Kenneth Burgess Professor of Physical Chemistry and Chemical Systems Engineering at Northwestern. "If this technology is further optimized, one could envision generating some useful power from bugs swimming in contaminated waters."

A few hundred bacteria work together in order to turn the gear. When multiple gears are placed in the solution with the spokes connected like in a clock, the bacteria will begin turning both gears in opposite directions, causing the gears to rotate in synchrony for a long time.

"There exists a wide gap between man-made hard materials and living tissues -- biological materials, unlike steel or plastics, are 'alive,'" said Igor Aronson, a physicist at Argonne and an adjunct professor of engineering sciences and applied mathematics at Northwestern. "Our discovery demonstrates how microscopic swimming agents, such as bacteria or man-made nanorobots, in combination with hard materials can constitute a 'smart material' that can dynamically alter its microstructures, repair damage or power microdevices."

The speed at which the gears turn also can be controlled through the manipulation of oxygen in the suspended liquid. The bacteria need oxygen in order to swim; if the amount of available oxygen is decreased, they will begin to slow down. If oxygen is eliminated completely, the bacteria go into a type of "sleep" and stop completely. Once oxygen is reintroduced into the system, the bacteria "wake up" and begin swimming once again.

The research at Argonne was supported by the U.S. Department of Energy's Office of Science. Work at Northwestern was supported as part of the Non-equilibrium Energy Research Center, an Energy Frontier Research Center also funded by the DOE Office of Science.

The title of the paper is "Swimming Bacteria Power Microscopic Gears." In addition to Grzybowski and Aronson, other authors of the paper are Mario M. Apodacac of Northwestern and Andrey Sokolov of Princeton University.

- Megan Fellman