Bio-Inspired Photonic Microcapsules that Change Colors via Reversible Osmotic Actuation

Animals have evolved complex and sophisticated mechanisms to control coloration, employing a combination of small molecules and nanostructured composites. Notably, chromatophores, specialized organs found in animals such as squids and octopuses, play a crucial role in dynamic color change. Chromatophores have the unique ability to modify their physical shape and size by expanding or contracting pigment-containing cells. This study introduces an artificial chromatophore system that uses osmotic annealing to trigger reversible color switching. To achieve this, we fabricate double emulsion droplets using polystyrene nanoparticles functionalized with the xanthommatin, the primary pigment found in the skin of cephalopods. The particle size and the pigment loading density into the system are influential factors in controlling the oscillation between pigmentary and structural colors which can be manipulated through annealing. We compared the reflectance spectra of photonic capsules from the presence and absence of pigments. Our findings highlight a distinctive and scalable approach for producing color-changing materials, providing a versatile range of tunable visible colors.