Bioinspired Soft Composites with Deformation-induced Coloration*

Fast dynamic control of skin coloration in the animal kingdom inspires soft robotic materials that can vibrantly adapt to their environment. Nature’s soft experts such as cephalopods and some fish species rely on iridescent cells called iridophores for camouflage and communication. The nanostructure of iridophores formed by alternating stacks of thin crystalline platelets and cytoplasm sheets disrupts the incident light and selectively reflects specific colors. Here, we draw a high-level inspiration from active iridophores and introduce an architected soft composite material that can reversibly change its color under pure deformation. The soft composite consists of an elastomer matrix filled with reflective ceramic platelets that are magnetized with iron oxide nanoparticles and aligned in a low magnetic field. We exploit shear instabilities to reversibly tilt reflective platelets upon stretching and dramatically change the appearance of the material even with a low concentration of platelets. Deformation-induced coloration in soft materials enables visual signaling and stress mapping at the material level that is suitable for sensing and feedback control of soft robots.