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What has soft matter physics got to do with butterfly colors?

The vivid, angle-dependent structural colors of some butterfly wing-scales are produced by light scattering from complex three-dimensional nanoscale structures. With intricate structural knowledge from synchrotron small angle x-ray scattering (SAXS), we hypothesize that the butterfly nanostructures develop by the self-organizing kinetics of cellular membranes, as with soft matter systems such as a soap film spanning a wire contour. Half of the space so templated gets filled with the protein chitin, while the rest of the scale cell degenerates leaving behind a single crystalline network of chitin and air. Butterfly biophotonic nanostructures that evolved over millions of years not only offer a biomimetic template for novel engineering applications, but also serve as a platform to advance our understanding of the physical principles guiding biological soft matter assembly.