Molecular biomimetics involves the design of optical materials based on specific molecules and/or macromolecules to induce coloration. Pigment-inspired materials aiming for specific molecular light absorption have been developed as for example melanin-inspired films prepared by polymerization of melaninprecursors such as dopamine and 5,6-dihydroxyindole to provoke color saturation. Materials based on the multi-layer stacking of guanine molecular crystals found in living organisms have been proposed as potential reflective coatings and solar reflectors. Protein-based optical materials, for instance self-assembling reflectin proteins found in cephalopods and silk, have incited interest in artificial materials for camouflage systems, electronic paper and biomedical applications. Non-protein biological macromolecules such as DNA have also been utilized for bio-inspired optics. The most abundant biopolymer on earth, cellulose, has been also utilized as a principal component for bio-optics. Modification of wood or other cellulose sources can mitigate scattering and absorption of light leading to optically interesting materials such as transparent wood and paper.
Bioinspired periodic/aperiodic structures
is a type of coloration that arises from the interaction of light with nano-sized structures. This interaction is possible because these photonic structures are of the same size as the wavelength of light. Through a mechanism of constructive and destructive interference, certain colors get amplified, while others diminish. Photonic structures are abundant in nature, existing in a wide range of organisms. Different organisms use different structures, each with a different morphology designed to obtain the desired effect. Examples of this are the photonic crystal underlying the bright colors in peacock feathers or the tree-like structures responsible for the bright blue in some Morpho butterflies. An example of bio-inspired photonics using structures is the so-called moth eye. Moths have a structure of ordered cylinders in their eyes that do not produce color, but instead reduce reflectivity. This concept has led to creation of antireflective coatings.
