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Institute of Bioengineering



Prof. Peter Fratzl. Water as a fuel - the materials basis for passive plant movements.

Image: Peter Fratzl
Peter Fratzl

Date: 29 January 2014   Time: 15:00 - 16:00

Prof. Peter Fratzl

Dead plant bodies such as seed capsules are able to generate movement by the cyclic absorption of water from the environment. This is based on water swelling of the (secondary) plant cell wall, which is a composite of cellulose nano-fibrils and a matrix containing hemicelluloses and lignin. Cell-wall swelling helps generating growth stresses, e.g., in conifer branches or in the tree stem when subjected to loads. A simple mechanical model for the cell wall predicts that – depending on the detailed architecture of the cellulose fibrils – swelling may lead either to significant compressive or tensile stresses or to large movements at low stresses. A similar mechanism also provides motility to various seeds. The general principle is based on the modification of the isotropic swelling of a gel by embedded oriented fibres and a suitable spatial confinement. Actuation systems in plants provide guidelines for designing material architectures suitable to convert isotropic swelling into complex movements which might be useful for many applications, including soft robotics.

Location:  PP1 Lecture Theatre