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Evolutionary-Optimized Photonic Network Structure in White Beetle Wing Scales.

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Holler, Mirko 
Diaz, Ana 
Guizar-Sicairos, Manuel 


Most studies of structural color in nature concern periodic arrays, which through the interference of light create color. The "color" white however relies on the multiple scattering of light within a randomly structured medium, which randomizes the direction and phase of incident light. Opaque white materials therefore must be much thicker than periodic structures. It is known that flying insects create "white" in extremely thin layers. This raises the question, whether evolution has optimized the wing scale morphology for white reflection at a minimum material use. This hypothesis is difficult to prove, since this requires the detailed knowledge of the scattering morphology combined with a suitable theoretical model. Here, a cryoptychographic X-ray tomography method is employed to obtain a full 3D structural dataset of the network morphology within a white beetle wing scale. By digitally manipulating this 3D representation, this study demonstrates that this morphology indeed provides the highest white retroreflection at the minimum use of material, and hence weight for the organism. Changing any of the network parameters (within the parameter space accessible by biological materials) either increases the weight, increases the thickness, or reduces reflectivity, providing clear evidence for the evolutionary optimization of this morphology.



X-ray ptychography, arthopods, biophotonic structures, light scattering, nanotomography, Animals, Coleoptera, Color, Models, Theoretical, Photons, Wings, Animal

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Adv Mater

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Biotechnology and Biological Sciences Research Council (BB/K014617/1)
European Research Council (639088)
PXCT measurements were performed at the cSAXS beamline at the Swiss Light Source, Paul Scherrer Institut, Switzerland. The OMNY instrumentation was supported by the Swiss National Science Foundation SNSF (Funding scheme RQUIP, Project number 145056). This research was financially supported through the National Centre of Competence in Research Bio-Inspired Materials, the Adolphe Merkle Foundation (to B.D.W. and U.S.), a BBSRC David Phillips fellowship (BB/K014617/1), the European Research Council (ERC-2014-STG H2020 639088, to O.O. and S.V.), and the Ambizione program of the Swiss National Science Foundation SNSF (168223, to B.D.W.). The authors acknowledge support from the Winton Programme for the Physics of Sustainability.