Geometry and Mechanics in the Opening of Chiral Seed Pods

We studied the mechanical process of seed pods opening in Bauhinia variegate and found a chirality-creating mechanism, which turns an initially flat pod valve into a helix. We studied configurations of strips cut from pod valve tissue and from composite elastic materials that mimic its structure. Th...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2011-09, Vol.333 (6050), p.1726-1730
Main Authors: Armon, Shahaf, Efrati, Efi, Kupferman, Raz, Sharon, Eran
Format: Article
Language:English
Subjects:
Anisotropy
Bauhinia - anatomy & histology
Bauhinia - physiology
Bending
Biological and medical sciences
Biomimetic Materials
Curvature
Elasticity
Environmental Influences
Fracture mechanics
Fundamental and applied biological sciences. Psychology
Geometry
Handedness
Helical
Latex
Macromolecules
Mathematical analysis
Mathematical Concepts
Mathematical models
Mechanical properties
Mechanics
Mechanics (Process)
Models, Biological
Molecular structure
Physical Phenomena
Plant physiology and development
Residual stress
Seed pods
Seeds
Seeds - anatomy & histology
Seeds - physiology
Self assembly
Strip
Tensors
Valves
Vegetative and sexual reproduction, floral biology, fructification
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Summary:We studied the mechanical process of seed pods opening in Bauhinia variegate and found a chirality-creating mechanism, which turns an initially flat pod valve into a helix. We studied configurations of strips cut from pod valve tissue and from composite elastic materials that mimic its structure. The experiments reveal various helical configurations with sharp morphological transitions between them. Using the mathematical framework of "incompatible elasticity," we modeled the pod as a thin strip with a flat intrinsic metric and a saddle-like intrinsic curvature. Our theoretical analysis quantitatively predicts all observed configurations, thus linking the pod's microscopic structure and macroscopic conformation. We suggest that this type of incompatible strip is likely to play a role in the self-assembly of chiral macromolecules and could be used for the engineering of synthetic self-shaping devices.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.1203874