The chiral structure of porous chitin within the wing-scales of Callophrys rubi

Theoretische Physik I, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen, Germany
Journal of Structural Biology (Impact Factor: 3.23). 05/2011; 174(2):290-295. DOI: 10.1016/j.jsb.2011.01.004
Source: PubMed

ABSTRACT The structure of the porous three-dimensional reticulated pattern in the wing scales of the butterfly Callophrys rubi (the Green Hairstreak) is explored in detail, via scanning and transmission electron microscopy. A full 3D tomographic reconstruction of a section of this material reveals that the predominantly chitin material is assembled in the wing scale to form a structure whose geometry bears a remarkable correspondence to the srs net, well-known in solid state chemistry and soft materials science. The porous solid is bounded to an excellent approximation by a parallel surface to the Gyroid, a three-periodic minimal surface with cubic crystallographic symmetry I4132, as foreshadowed by Stavenga and Michielson. The scale of the structure is commensurate with the wavelength of visible light, with an edge of the conventional cubic unit cell of the parallel-Gyroid of approximately 310 nm. The genesis of this structure is discussed, and we suggest it affords a remarkable example of templating of a chiral material via soft matter, analogous to the formation of mesoporous silica via surfactant assemblies in solution. In the butterfly, the templating is achieved by the lipid–protein membranes within the smooth endoplasmic reticulum (while it remains in the chrysalis), that likely form cubic membranes, folded according to the form of the Gyroid. The subsequent formation of the chiral hard chitin framework is suggested to be driven by the gradual polymerisation of the chitin precursors, whose inherent chiral assembly in solution (during growth) promotes the formation of a single enantiomer.

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Available from: Gerd E Schröder-Turk, Sep 27, 2015
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    • "With recent technologies and advancements in manufacturing techniques, TPMS- IPCs can be manufactured and analyzed utilizing the techniques mentioned in Cooke et al. (2003), Schröder-Turk et al. (2011). However, while researchers can come up with hierarchical structures in the design of new materials, going from a computer model to the production of physical artifacts has been a persistent challenge. "
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    • "The use of Ω is motivated by the scaling properties of the Maxwell equations 3 stating that the photonic response of a frequency independent material as a function of Ω is conserved under a change of the lattice parameter a → r × a (i.e. an affine rescaling of the structure size with a real number r): A nano-structure with lattice parameter r × a has the same response for incoming light of wavelength r×λ as a similar structure with lattice parameter a has to incoming light with wavelength λ. In Figs. 5 to 7, we have set to a = 311 nm in line with experimental data from [16] "
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    ABSTRACT: The single Gyroid, a triply-periodic ordered chiral network of cubic symmetry, appears as a nanostructure in the green-colored wing scales of various butterflies. In lossless and perfectly ordered single Gyroid materials, the structural chirality leads to circularly polarized reflections from crystals oriented in the [100] direction. Here we report a circular polarisation study of the macroscopic reflections of the wing scales of Callophrys rubi and Teinopalpus imperialis that reveals no circular dichroism, that is, we find no significant difference in the reflectance values for left- and right-circularly polarized light. The reasons for the absence of circularly polarized reflections is likely to be a compound effect of various factors, including crystallite orientation, presence of both left- and right-handed single Gyroid enantiomers, and structural disorder. Each of these factors weakens, but does not fully extinguish, the circular polarisation signal. We further find a substantial amount of blue-absorbing pigment in those wing scales of C. rubi that are structured according to the single Gyroid. Numerical simulations demonstrate that absorption, while evidently reducing overall reflectance, does generally not reduce the circular dichroism strength. The experimental findings of this paper, however, clearly demonstrate that circular dichroism is absent from the reflections of the butterfly wing scale. Henceforth, the chiro-optical response of the idealised structure does not fulfil a biological photonic function.
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    • "The main advantage of minimal surface scaffolds is the open cell structure, deemed to facilitate cell migration and vitalization, while retaining a high degree of structural stiffness . The occurrence of minimal surface geometries in in-vivo biological tissue, such as in beetle shells, weevils, butterfly wingscales and crustacean skeletons [16] [17] [18] [19] [20], further hints at their usefulness as biomimetic scaffold designs. "
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