Hydrogel-Based Autonomously Responsive Synthetic Chromatophores with Pattern Control Capabilities

Materials capable of rapid changes in color and appearance are of great interest in several application spaces, such as display technology, wearable devices, encryption, and sensing. However, modern chromogenic materials lack the microscale architecture and compliance needed to cover non-planar areas and undergo deformation, for example in autonomous color-changing skins. In nature, cephalopods can rapidly change their appearance through radial activation of chromatophore cells containing pigment sacs. Our recent work in the fabrication of microscale hydrogel arrays on soft, elastomeric supports is well suited to mimic this process, wherein individual microgels act as a class of stimuli-sensitive synthetic chromatophores. We employed dye-stained thermally responsive hydrogels which undergo radial contraction above a threshold temperature, resulting in a decrease in surface coverage and sample color intensity. The macroscopic absorbance of these synthetic chromatophores decreased by up to four-fold when gels were in a contracted state. We constructed a model which allows prediction of the surface fill fraction of gels in a sample using experimentally measured absorbance or vice-versa. The synthetic chromatophores were rendered air-stable by encapsulation in a UV-curable silicone, allowing them to report temperature changes on different surfaces (e.g., walls, windows, or skin) in ambient conditions. Finally, we investigated pattern control by layering multiple samples, which resulted in dynamic Moiré patterns for gels in a contracted or swollen state.