Evaporation Gives Spores Energy - Cherry Blossom Inc.

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Up. Down. Up. Down. ((Show the lifting video))That's the power of evaporation — and SPORES.These spores are dormant, dried out bacteria that expand with moisture and contract when dry. Each is about a micron long — that's one twenty-five thousandth of an inch.To harness these tiny engines scientists at Columbia University made a liquid paste of spores and painted it on thin plastic tape.As the spores absorb and lose water that comes from evaporation, the sections of tape act like muscles. They can lift weight or open and close small shutters. They can even power a wheel. Spore muscles hold tiny blue weights away from the wheel's axis when they expand in a moist chamber.They bring them closer when they shrink in dry air. The shift in weight drives the wheel. Although the car they powered with this system is a toy, the idea is big. And eventually, the machines could be too.

By James Gorman

Science is always looking for new ways to exploit natural sources of energy — better windmills, new solar panels, geothermal heat pumps for houses.

But scientists at Columbia University have come up with something truly unusual: a method for using tiny bacterial spores to harness a process of energy transfer that, on a grand scale, is a hugely important factor in the planet's climate and weather — namely, evaporation.

The spores are dry, dormant bacteria. They expand when they absorb moisture and contract when they lose it. The researchers saw that if they could control evaporation, then they could control the expansion and contraction of the spores, which could be used like little muscles.

The problem is that they are very, very small. Each spore is about a micron long. Twenty-five thousand of them laid end to end would stretch about an inch. What the scientists did was devise a way to bridge the gap between the impossibly tiny and the merely small, to power devices like a toy car to demonstrate that their method can work.

Ozgur Sahin, the biologist who is the senior author of a report on the new work in Nature Communications, said this was only a way to prompt others to take the next leap. He said the process that Xi Chen and others in his laboratory developed can work on a much bigger scale. Imagine something the size of a windmill, but run by evaporation. Call it a moisture mill.

Manu Prakash, a biophysicist at Stanford University, who had no connection to the research, said, "What's beautiful is this notion of turning something that's bacterial, one micron, into a common, day-to-day material that I can design with."

The research grew out of an earlier project in which Dr. Ozgur's lab was investigating the properties of bacterial spores for other reasons. The team calculated the energy involved in expanding and contracting, and thought they ought to try to harness that energy.

"But how to use it?" he recalled wondering at the time. One spore was of no value, and millions were needed in some practical form. What the team did was to mix the spores with diluted glue, creating a kind of paste, which they applied to thin plastic tape on which the paste dried.

Sections of the tape functioned as artificial muscles, expanding and contracting with changes in humidity. Using the tape in different setups, Dr. Sahin's team made small gadgets to lift weights, open and close shutters, and even to power a toy car.

The lab used spores of common soil bacteria that are ubiquitous and harmless. They could theoretically return to active life, but Dr. Sahin said: "Spores wake up when there is a trigger, certain chemicals or nutrients. None of these are present," in the experiments. Water by itself is not a trigger.

If, as Dr. Sahin hopes, entrepreneurs and engineers are intrigued enough by the process to pursue practical applications, the bacteria could be genetically engineered to make it even less likely they would wake up.

Not that living soil bacteria would pose a hazard, but because they would lose the rigid shell that keeps them as spores, a bacterial resurrection would make any device using spore power less efficient.

Dr. Prakash said he saw "a lot of biological inspiration" in the research. Plants use evaporation in various ways — to pump water up giant trees, for example, and to power explosive seed dispersal when pods dry out.

The Columbia group, he said, used the power of evaporation combined with the unusual expanding material of the spores to create something completely new.

"Evaporation is beautiful," he said.