Geometry and mechanics in the opening of chiral seed pods

Shahaf Armon, Efi Efrati, Raz Kupferman, Eran Sharon*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

584 Scopus citations


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.

Original languageAmerican English
Pages (from-to)1726-1729
Number of pages4
Issue number6050
StatePublished - 23 Oct 2011


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