Harnessing power from microscopic wind farms

Microbiologists are a clever bunch. A team from Oxford University has discovered that the natural movement of bacteria can be harnessed to assemble and power microscopic ‘wind farms’ or other man-made micromachines such as the components used in smartphones.

The study has been published in the journal Science Advances and uses computer simulations to demonstrate how this is possible. Dense active matter such as bacteria displays a natural chaotic swarming effect and the scientists believe that it can be organised to turn cylindrical rotors and to provide a steady power source. These miniature power plants could then be used as microscopic engines for tiny man-made devices that are self-assembled and self-powered.

Co-author Dr Tyler Shendruk, from Oxford University’s Department of Physics, said: “Many of society’s energy challenges are on the gigawatt scale, but some are downright microscopic. One potential way to generate tiny amounts of power for micromachines might be to harvest it directly from biological systems such as bacteria suspensions.”

Dense bacterial suspensions are the quintessential example of active fluids that flow spontaneously. While swimming bacteria are capable of swarming and driving disorganised living flows, they are normally too disordered to extract any useful power from.

But when the Oxford team immersed a lattice of 64 symmetric microrotors into this active fluid, the scientists found that the bacteria spontaneously organised itself in such a way that neighbouring rotors began to spin in opposite directions — a simple structural organisation reminiscent of a wind farm. The self-organisation was unexpected.

“The amazing thing is that we didn’t have to predesign microscopic gear-shaped turbines. The rotors just self-assembled into a sort of bacterial wind farm.

“When we did the simulation with a single rotor in the bacterial turbulence, it just got kicked around randomly. But when we put an array of rotors in the living fluid, they suddenly formed a regular pattern, with neighbouring rotors spinning in opposite directions,” said Shendruk.

Co-author Dr Amin Doostmohammadi, from Oxford University’s Department of Physics, said: “The ability to get even a tiny amount of mechanical work from these biological systems is valuable because they do not need an input power and use internal biochemical processes to move around.

“At micro scales, our simulations show that the flow generated by biological assemblies is capable of reorganising itself in such a way as to generate a persistent mechanical power for rotating an array of microrotors,” he said.

Senior author Professor Julia Yeomans, from Oxford University’s Department of Physics, said that the potential is enormous.

“Nature is brilliant at creating tiny engines, and there is enormous potential if we can understand how to exploit similar designs,” she said.