Single Gyroid and Inverse b.c.c. Photonic Crystals in Bird Feathers

Vivid, saturated structural colors are a conspicuous and important aspect of the appearance of many organisms. A huge diversity of underlying 3D ordered biophotonic nanostructures has been documented, for instance, within the chitinaceous exoskeletons of insects. Here, we report diverse, highly ordered, intracellular, 3D biophotonic crystals in vivid plumages from three families of birds, which have each evolved independently from quasi-ordered (glassy) ancestral states. These morphologies include exotic bi-continuous single gyroid {beta}-keratin and air networks, inverse b.c.c. and inverse opal (r.h.c.p.) close-packings of air spheres in the medullary {beta}-keratin of feather barbs. These self-assembled avian biophotonic crystals may serve as biomimetic inspiration for advanced multi-functional applications, as they suggest alternative routes to the synthesis of optical-scale photonic crystals, including the experimentally elusive single gyroid. Field CodesMaterials Science and Evolutionary Biology One Sentence SummaryEvolutionary disorder-order transitions in bird feathers suggest direct optical scale self-assembly of photonic crystals