Flat polymer sheets bend themselves into 3D shapes - just add water

Flat polymer sheets bend themselves into 3D shapes - just add water:

When the petal of a flower is being formed, its shape is achieved by cells in one area expanding more than cells in an adjacent area. This uneven expansion causes the material to buckle, creating the desired curves and creases. Scientists from the University of Massachusetts, Amherst have taken that same principle, and applied it to flat polymer gel sheets that fold themselves into three-dimensional shapes when exposed to water. Some day, such sheets could serve a number of useful purposes...
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