Artificial Iridophores to Mimic the Color Change of Chameleon Skin

In nature, animals employ tunable structural colors for communication or camouflage through iridophores, which act as biological “pixel” units. Inspired by the cellular architecture of iridophores, this study introduced a rapid and straightforward process for fabricating microspheres with tunable structural color through the aggregation of poly(N-isopropylacrylamide-2-aminoethyl methacrylate hydrochloride) (PNIPAM-AEMA) nanogels. Unlike previous methods in which microspheres were obtained by physical attraction between the nanoparticles, the microspheres here were stabilized by cross-linking between nanogels. The microspheres were obtained by dripping a PNIPAM-AEMA nanogel emulsion containing glutaraldehyde into silicone oil to form spherical droplets. As water evaporated, the nanogels were concentrated and underwent cross-linking via glutaraldehyde, yielding PNIPAM-AEMA nanogel-based microspheres. When hydrated, these microspheres displayed dynamically tunable structural colors through temperature-dependent modulation of the PNIPAM-AEMA nanogel dimensions. Moreover, the resulting microspheres displayed an angle-independent structural color for the short-range ordered nanogels. Furthermore, bioinspired skin with spatially patterned and dynamically tunable colors could be engineered by integrating microspheres that contain PNIPAM-AEMA nanogels of different sizes. Such microspheres, possessing a tunable and reversible structural color, may offer potential applications in chemical/biological sensing, displays, encoding, and optical switching.