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CeNS Colloquium

Place: Kleiner Physik-Hörsaal, Geschwister-Scholl-Platz
Date: 23.04.10, Time: 15:30 h

Actuating nanostructures in plants

Prof. Peter Fratzl
MPI für Kolloid- und Grenzflächenforschung, Golm

The secondary plant cell wall is a polymeric composite of cellulose nano-fibrils and a water-swelling matrix containing hemicelluloses and lignin [1]. Generally, the cellulose fibrils are arranged at an angle, the microfibril angle (MFA) with respect to the axis of the tube-like cells. Recent experiments showed that this swelling capacity helps generating growth stresses, e.g., in conifer branches or in the stem [2]. A similar mechanism also provides motility to wheat seeds [3]. A simple mechanical model for the cell wall predicts that primarily depending on the MFA swelling may lead either to significant compressive or tensile stresses or to large movements at low stresses [4]. The model reproduces most of the experimental observations in spruce wood and in the awns of wheat seeds. The general principle is based on the water-induced swelling of the matrix, whereby the MFA redirects the stresses and leads to the appropriate deformation. Tension wood in poplar [5] and in certain roots [6] contains a thick cellulose layer within the lumen of the cell wall which is proposed to enhance the tensile deformation by exerting an internal pressure to the cell. Ideas based on the isotropic swelling of a gel and a redirection of the stress by embedded oriented fibres or needles have already been used to design micro-actuators using a gel filled with parallel silicon needles [7]. More generally, actuation systems in plants provide guidelines for designing fibre architectures suitable to convert isotropic swelling into complex movements and forces of various kinds and directions [8,9].

 

References:

[1] P. Fratzl, R. Weinkamer, Prog. Mater. Sci. 52, 1263-1334 (2007)
[2] I. Burgert, M. Eder, N. Gierlinger, P. Fratzl, Planta 226, 981-7 (2007)
[3] R. Elbaum, L. Zaltzman, I. Burgert, P. Fratzl, Science 316, 8846 (2007)
[4] P. Fratzl, R. Elbaum, I. Burgert, Faraday Discussions 139, 275-282 (2008)
[5] L. Goswami, J.W.C. Dunlop, K. Jungnikl, M. Eder, N. Gierlinger, C. Coutand, G. Jeronimidis, P. Fratzl, I. Burgert, Plant J. 56, 531-8 (2008)
[6] N. Schreiber, N. Gierlinger, N. Pütz, P. Fratzl, C. Neinhuis, I. Burgert, Plant J. 61, 854-61 (2010)
[7] A. Sidorenko, T. Krupenkin, A. Taylor, P. Fratzl, J. Aizenberg, Science 315, 487-90 (2007)
[8] I. Burgert, P. Fratzl, Phil. Trans. R. Soc. A 367, 1541-57 (2009)
[9] P. Fratzl, F. G. Barth, Nature 462, 442-8 (2009)