Are plant hydraulics a path to adaptive dream machines?

Airplanes might soon have flexible wings like birds and robots could change shape as they please thanks to research under way on mimosa plants, researchers said.

The shrub's leaves, which can retract at the slightest of touches, could inspire a new class of structures that can twist, bend, harden and even repair themselves, explained University of Michigan professor of mechanical engineering Kon-Well Wang.

"This and several other characteristics of plant cells and cell walls have inspired us to initiate ideas that could concurrently realize many of the features that we want to achieve for adaptive structures," he said Saturday at an annual meeting of the American Association for the Advancement of Science.

"The phenomenon is made possible by osmosis, the flow of water in and out of plants' cells. Triggers such as touch cause water to leave certain plant cells, collapsing them. Water enters other cells, expanding them. These microscopic shifts allow the plants to move and change shape on a larger scale," he said.

The mimosa is a type of plant able to move itself in a way that is visible to the naked eye in real time. The plant's "hydraulic system" makes that "nastic motion" possible.

"Triggers such as touch cause water to leave certain plant cells, collapsing them. Water enters other cells, expanding them. These microscopic shifts allow the plants to move and change shape on a larger scale," the researcher explained.

Observing the process can be a gateway to designing cells with special mechanical properties, he believes.

"This and several other characteristics of plant cells and cell walls have inspired us to initiate ideas that could concurrently realize many of the features that we want to achieve for adaptive structures," Wang said.

"We can design those cells according to our needs. We can put those cells into structure, control them in different sequences," he explained.

"Currently we are looking at basic research only, but there are some applications that we have in mind," Wang said.

He mentioned the notions for example of planes able to change the shape of their wings while in flight as birds do; and other machines that change their shape perhaps to go under a bridge.

"You cannot make a plane wing deform to be able to achieve optimum flight condition in different scenario," he said. But "this kind of technology could help that because we can make the wing active and change its mechanical properties."

Meanwhile, auditory sensory cells that help humans hear and give them various detection capabilities are another source of inspiration from nature to develop more sophisticated technologies.

Chang Liu, professor of mechanical engineering at the University of Michigan (north), led a research group that produced artificial hair cells.

"The hair cell is interesting because biology uses this same fundamental structure to serve a variety of purpose," he told a press conference. "This differs from how engineers typically design sensors, which are often used for a specific task."

In creating these artificial cells with the use of nanotechnology, researchers have significantly improved the sensitivity of the sensors while understanding better how various animals use them.

And all fish are equipped with lateral auditory cells as well.

However, amphibians are not equipped with such sensors, which provide still more information about the movement of water, said Chang Liu.

For now, he is focusing on medical applications as sensors of fluid in the apparatus or at the end of a catheter.