Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn

Abraham, Yael; Tamburu, Carmen; Klein, Eugenia; Dunlop, John W. C.; Fratzl, Peter; Raviv, Uri; Elbaum, Rivka

doi:10.1098/rsif.2011.0395

Cited by 93 publications

(77 citation statements)

References 33 publications

(37 reference statements)

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“…The mechanism of hygroscopic movement is a consequence of wetting and drying of tissue, which results in different anisotropic swelling in different regions of the tissue. Humidity-driven movement is not only shown in wheat awns, it is also reported for various other species [5][6][7][8][9]. This movement is interesting for the (bio)materials engineer as the movement occurs without an active metabolism and as such is controlled solely by the architectural arrangement of the different swellable tissues.…”

Section: Introductionmentioning

confidence: 54%

Finite Element Modeling of the Cyclic Wetting Mechanism in the Active Part of Wheat Awns

et al. 2012

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Many plant tissues and organs are capable of moving due to changes in the humidity of the environment, such as the opening of the seed capsule of the ice plant and the opening of the pine cone. These are fascinating examples for the materials engineer, as these tissues are non-living and move solely through the differential swelling of anisotropic tissues and in principle may serve as examples for the bio-inspired design of artificial actuators. In this paper, we model the microstructure of the wild wheat awn (Triticum turgidum ssp. dicoccoides) by finite elements, especially focusing on the specific microscopic features of the active part of the awn. Based on earlier experimental findings, cell walls are modeled as multilayered cylindrical tubes with alternating cellulose fiber orientation in successive layers. It is shown that swelling upon hydration of this system leads to the formation of gaps between the layers, which could act as valves, thus enabling the entry of water into the cell wall. This supports the hypothesis that this plywood-like arrangement of cellulose fibrils enhances the effect of ambient humidity by accelerated water or vapor diffusion along the gaps. The finite element model shows that a certain distribution of axially and tangentially oriented fibers is necessary to generate sufficient tensile stresses within the cell wall to open nanometer-sized gaps between cell wall layers.

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Section: Introductionmentioning

confidence: 54%

Finite Element Modeling of the Cyclic Wetting Mechanism in the Active Part of Wheat Awns

et al. 2012

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“…As the material dehydrates, the coil becomes tighter, storing more and more tension until the material eventually fractures. This has been successfully mathematically modelled by Aharoni et al [26] and in a simplified version reproduced in a physical model by Abraham et al [25]. This latter work demonstrates that one does not need to reproduce all the elegant details of the natural solution to draw on the concept.…”

Section: Cellulose Catapults: a Natural Examplementioning

confidence: 76%

“…Importantly, the axis of the helix is not aligned with the axis of the cell, causing the cell itself to bend such that it packs in a helical form. Thus, the off-axis alignment of the cellulose nanostructure instigates a similar directionality in the cellular alignment, which results in the macroscopic coiling effect seen [25]. As the material dehydrates, the coil becomes tighter, storing more and more tension until the material eventually fractures.…”

Section: Cellulose Catapults: a Natural Examplementioning

confidence: 91%

“…As seen with mimicry of the filaree awn [25], shape-change may be reproduced without using the same method seen in the natural example. Conversely, we will draw attention to some ways of reproducing the aligned or gradated structures that give rise to shape-changing properties in nature which have not yet been used to create synthetic shape-change.…”

Section: Beyond Isotropy: Modification Of Structurementioning

confidence: 96%

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Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

2016

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Shape-changing materials open an entirely new solution space for a wide range of disciplines: from architecture that responds to the environment and medical devices that unpack inside the body, to passive sensors and novel robotic actuators. While synthetic shape-changing materials are still in their infancy, studies of biological morphing materials have revealed key paradigms and features which underlie efficient natural shape-change. Here, we review some of these insights and how they have been, or may be, translated to artificial solutions. We focus on soft matter due to its prevalence in nature, compatibility with users and potential for novel design. Initially, we review examples of natural shape-changing materials-skeletal muscle, tendons and plant tissues-and compare with synthetic examples with similar methods of operation. Stimuli to motion are outlined in general principle, with examples of their use and potential in manufactured systems. Anisotropy is identified as a crucial element in directing shape-change to fulfil designed tasks, and some manufacturing routes to its achievement are highlighted. We conclude with potential directions for future work, including the simultaneous development of materials and manufacturing techniques and the hierarchical combination of effects at multiple length scales.

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“…At the macroscopic level of the bilayer, wetting/drying cycles correspond to an alternate bending/straightening motion, as predicted by the Timoshenko model of a two-material plate undergoing thermal deformations [11]. Another natural passive actuator exploiting the microscopic architecture of the cellulose fibrils is the awn of the stork's bill [12]. The macroscopic & 2014 The Author(s) Published by the Royal Society.…”

Section: Introductionmentioning

confidence: 99%

Pressurized honeycombs as soft-actuators: a theoretical study

Guiducci

Fratzl

Bréchet

et al. 2014

J. R. Soc. Interface.

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The seed capsule of Delosperma nakurense is a remarkable example of a natural hygromorph, which unfolds its protecting valves upon wetting to expose its seeds. The beautiful mechanism responsible for this motion is generated by a specialized organ based on an anisotropic cellular tissue filled with a highly swelling material. Inspired by this system, we study the mechanics of a diamond honeycomb internally pressurized by a fluid phase. Numerical homogenization by means of iterative finite-element (FE) simulations is adapted to the case of cellular materials filled with a variable pressure fluid phase. Like its biological counterpart, it is shown that the material architecture controls and guides the otherwise unspecific isotropic expansion of the fluid. Deformations up to twice the original dimensions can be achieved by simply setting the value of input pressure. In turn, these deformations cause a marked change of the honeycomb geometry and hence promote a stiffening of the material along the weak direction. To understand the mechanism further, we also developed a micromechanical model based on the Born model for crystal elasticity to find an explicit relation between honeycomb geometry, swelling eigenstrains and elastic properties. The micromechanical model is in good qualitative agreement with the FE simulations. Moreover, we also provide the force-stroke characteristics of a soft actuator based on the pressurized anisotropic honeycomb and show how the internal pressure has a nonlinear effect which can result in negative values of the in-plane Poisson's ratio. As nature shows in the case of the D. nakurense seed capsule, cellular materials can be used not only as low-weight structural materials, but also as simple but convenient actuating materials.

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Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn

Cited by 93 publications

References 33 publications

Finite Element Modeling of the Cyclic Wetting Mechanism in the Active Part of Wheat Awns

Finite Element Modeling of the Cyclic Wetting Mechanism in the Active Part of Wheat Awns

Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

Pressurized honeycombs as soft-actuators: a theoretical study

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