Living organisms in nature have amazing control over their color, shape, and morphology in response to environmental stimuli for camouflage, communication, or reproduction. Inspired by the camouflage of the octopus via the elongation or contraction of its pigment cells, oblate cholesteric liquid crystal droplets are dispersed in a polymer matrix, serving as the role of pigment cells and showing structural color due to selective Bragg reflection by their periodic helical structure. The color of 3D-printed biomimetic systems can be tuned by changing the helical pitch via the chiral dopant concentration or temperature. When the oblate liquid crystal droplets are heated up to isotropic, the opaque and colored biomimetic systems become transparent and colorless. Meanwhile, the isotropic liquid crystal droplets tend to become spherical, causing volume contraction along the film plane and volume dilation in the perpendicular direction. The internal strain combined with the gradient distribution of the oblate isotropic liquid crystal droplets result in corresponding shape transformations. The camouflage of a biomimetic octopus and the blossom of a biomimetic flower, both of which show synergetic color and shape responses, are demonstrated to inspire the design of functional materials and intelligent devices.
Keywords: 3D printing; biomimetics; droplets; liquid crystals; stimulus response.
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