Shine on you crazy gyroid: Lessons from birds, butterflies and beetles.

A rich diversity of complex 3D photonic nanostructures produce vivid structural colors in the integument of many animals that are used prominently in communication and camouflage. Using synchrotron Small Angle X-ray Scattering (SAXS), we have unambiguously elucidated the nanoscale organization of biophotonic nanostructures across hundreds of species and discovered the enigmatic single network gyroid photonic crystals within wing scales of butterflies¹, beetles² and more recently in the feather barbs of some birds³. Insects grow these nanostructures by the complex invagination of lipid bilayer membranes with associated cuticle in a templated fashion that is eerily reminiscent of current engineering approaches¹. Whereas leafbirds appear to develop single gyroids in a bottom-up fashion via phase separation of feather keratins - a process that has no parallel in physics or biology³. We juxtapose the development of keratinaceous vs. chitinaceous single gyroids and discuss how self-assembled organismal single gyroids especially in feather barbs may suggest facile routes to materials synthesis at mesoscopic/optical length scales, which has hitherto remained experimentally elusive.