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Biomimetic design of patterned insect carapaces

Rules for an eco-design, with applications in cryptography

by WAROT Bénédicte - published on , updated on

Twisted cholesteric liquid crystal patterns are found in the iridescent tessellated cuticles of many insects and a few fruits. Their accurate replication is extremely difficult to achieve. A solution is demonstrated by addressing striped insect cuticles. Proof-of-concept prototypes of anti-counterfeiting tags are presented. The present eco-design involves a high versatility of chiral patterns unreached by the current manufacturing techniques.

The accurate replication of patterns found in the carapaces of many insects is extremely difficult since discontinuous patterns and colors must coexist in a single layer within continuous structures.

We approach this problem of the high-fidelity capture of the structural complexity observed in nature by focusing on iridescent carapaces with a complex twisted organization of chitin fibers. At the micrometer and submicrometre scale, the helical pitch and orientation of the helical structure depend on the position in 3D, and the formation of periodic patterns is required at 2D. We used liquid crystal oligomers to mimic biological liquid crystals. Geometric constraints are met by controlling the thermal diffusion in a bilayer subjected to local changes in the molecular anchoring conditions. 

We attempted to reproduce the textural, structural and color properties at several length scales. The imaging of cross-sections of materials by transmission electron microscopy was performed at the Center for Integrative Biology in Toulouse (CNRS, University Paul-Sabatier).

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Biomimetic sample with a piece of carapace.

We made optimal use of resources, in the spirit of eco-design. By means of a single sequence based on self-organization, precise control of a single-piece sample structure composed of different colored patterns with the same unique pitch gradient was enabled. 

A multicriterion comparison reveals a very high level of biomimicry. 

Proof-of-concept prototypes of optical tags in cryptography are presented. The functionalities of biological and synthetic materials are both relevant to communication and camouflage. 

The present design involves a high versatility of chiral patterns unreached by the current manufacturing techniques such as metallic layer vacuum deposition, template embossing or lithography.

 

Publication : Biomimetic design of Iridescent Insect Cuticles with Tailored, Self-Organized Cholesteric Patterns, Adriana Scarangella, Vanessa Soldan and Michel Mitov, Nature Communications, 11, 4108 (2020). https://www.nature.com/articles/s41467-020-17884-0

ContactMichel Mitov     

 

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