The closing of pine cones in response to rain, and the reduction in the angle of the V shaped tops of wild wheat, have been observed for hundreds (or even thousands of years) – but it is only recently that scientists have begun to get to the bottom of why these phenomena occur.


In today’s plenary talk, Peter Fratzl (the director of the Max Plank Institute of Colloids and Interfaces in Potsdam, Germany) gave us an overview of this research field. The mechanical change in both the above examples arises from water causing a non-uniform swelling of the interfaces between the cells in the plant . The cell interfaces on the outer side of the area at the bottom on the V in the wheat plant, or the pine cone segments, swell more than those on the inside – pushing the V together and closing the pine cone needles shut.

Then Peter told us that researchers are in the early stages of copying this mechanism to make materials with anisotropically swelling matrices. One example is a flexible material that is straight when dry, and then reversibly curls up in to a perfect spiral when exposed to humidity. I wonder why nature didn’t design my hair like this – in humidity it turns into an uncontrolled wavy frizz (rather than perfect spiral curls), and it doesn’t go straight again when the humidity drops!

Nina Notman

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