title: Geometry and mechanics in the opening of chiral seed pods.
abstract: 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.
authors.affiliation: Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Shahaf
authors.initials: S
authors.lastname: Armon
authors.forename: Efi
authors.initials: E
authors.lastname: Efrati
authors.forename: Raz
authors.initials: R
authors.lastname: Kupferman
authors.forename: Eran
authors.initials: E
authors.lastname: Sharon
mesh_terms: D036481:Bauhinia / Q000033:anatomy & histology* / Q000502:physiology; D040761:Biomimetic Materials; D004548:Elasticity; D007840:Latex; D055641:Mathematical Concepts; D008954:Models, Biological; D055585:Physical Phenomena; D012639:Seeds / Q000033:anatomy & histology* / Q000502:physiology*
chemical_list: D007840:Latex