How does the MoCA system mimic butterfly wing structures?

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MoCA System Mimics Butterfly Wing Structures Through Dual-Colour Micro-Concavities

The MoCA system replicates the colour-changing properties of butterfly wings by mimicking their unique structural composition. Specifically, it reproduces the dual-colour micro-concavities found on butterfly wings, which are tiny pits that interact with light to produce different colours depending on the viewing angle. These micro-concavities are arranged in regular patterns, forming what are known as photonic crystals, a structure that MoCA emulates.
Reproduction of Photonic Crystal Structures

MoCA's design incorporates a photonic crystal elastomer actuator (PC-EA) film, mirroring the photonic crystal arrangement observed in nature. This film, composed of an elastomer layer (GPDMS) and a hydrogel layer (pNIPAM), is engineered to create morphable concavities. When ethanol is introduced to the hydrogel layer, it causes swelling, which in turn pulls the elastomer layer into a dish-like concave shape within a hole array. This controlled deformation is the fundamental mechanism by which MoCA manipulates light to change colour, akin to how photonic crystals on butterfly wings function.
Mechanism of Colour Change

The colour alteration in MoCA is achieved by altering the local morphology of its pixels, specifically through the transition between flat and concave states. This is distinct from other colour-changing systems that may rely on different principles. In the MoCA system, the creation of a concave shape blocks certain wavelengths of light, causing a visible colour shift. This process directly mimics the function of the dual-colour micro-concavities on butterfly wings, where similar pits interact with light to generate vibrant, iridescent hues.
Bio-Inspired Design Principles

The inspiration for MoCA stems directly from the dual-colour micro-concavities present on butterfly wings. These naturally occurring structures are described as tiny pits that selectively block specific wavelengths of light, resulting in colours that vary with the angle of light incidence and the observer's perspective. By recreating this fundamental principle of structural colouration, the HKU researchers have developed a novel pixelated system that harnesses biological design for advanced optical applications.

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How does the MoCA system mimic butterfly wing structures?

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