Plants That Can Move İnspire New Adaptive Structures

The Mimosa plant, which folds its leaves when they're touched, is inspiring a new class of adaptive structures designed to twist, bend, stiffen and even heal themselves. University of Michigan researchers are leading their development. Mechanical engineering professor Kon-Well Wang will present the team's latest work Feb. 19 at the American Association for the Advancement of Science's 2011 Annual Meeting in Washington D.C. He will also speak at a news briefing earlier that day. Wang is the Stephan P. Timoshenko Collegiate Professor of Mechanical Engineering and chair of the Department of Mechanical Engineering.

"This is quite different from other traditional adaptive materials approaches," Wang said. "In general, people use solid-state materials to make adaptive structures. This is really a unique concept inspired by biology."

Researchers at U-M and Penn State University are studying how plants like the Mimosa can change shape, and they're working to replicate the mechanisms in artificial cells. Today, their artificial cells are palm-size and larger. But they're trying to shrink them by building them with microstructures and nanofibers. They're also exploring how to replicate the mechanisms by which plants heal themselves.

"We want to put it all together to create hyper-cellular structures with circulatory networks," Wang said.

The Mimosa is among the plant varieties that exhibit specialized "nastic motions," large movements you can see in real time with the naked eye, said Erik Nielsen, assistant professor in the U-M Department of Molecular, Cellular and Developmental Biology.

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.

It's hydraulics, the researchers say.

"We know that plants can deform with large actuation through this pumping action," Wang said. "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."

Nielsen believes nastic movements might be a good place to start trying to replicate plant motions because they don't require new growth or a reorganization of cells.