The extraordinary adaptations we can observe in every organism on Earth amount to an almost limitless assortment of useful things nature can teach us - and researchers from the University of Bristol are learning something particularly cool from the masters of camouflage, organisms such as the squid (order Teuthida) and zebrafish (Danio rerio). These animals use pigment-containing cells in order to mimic their surroundings, giving them rapidly adjustable natural camouflage the likes of which us as humans can only dream of. However, by creating artificial materials based on the same mechanisms seen in these organisms, we can bring it one step closer to reality.
In cephalopods such as the squid, cells called chromatophores sit immediately below the skin, filled with either yellow pigment (xanthophores), red pigment (erythrophores) or brown pigment (melanophores), and stacked vertically in that order with xanthophores uppermost. The pigment is held in small elastic sacs surrounded by 15-25 muscles, which when contracted, cause the sac to stretch to cover a larger surface area with colour; when relaxed, the pigment is contained in a tiny blob. The muscles are stimulated by nerves that are linked directly to the brain - every single cell is served by at least one nerve ending! This exquisite level of control means that highly complex patterns can be easily formed to closely match even the most variable of backgrounds.
Zebrafish use a slightly different mechanism in which a small reservoir of pigment travels up to the skin surface and spreads out in an ink-like manner when stimulated, usually by hormones rather than through the nervous system.
The researchers have made use of these mechanisms by creating artificial muscles that include smart materials that are responsive to an electric current - these are known as dielectric elastomers, or DEs. When the electric circuit is applied, the smart DEs expand; when short-circuited, they return to their original shape. In addition, a different pump-based system was produced using smart DEs that reflected the mechanism used by zebrafish. The end products can be made into a soft ‘skin’ which, with further development, could be used to make “smart clothes” that could allow us to mimic the camouflaging abilities seen in in nature.
Ref: Rossiter J., Yap B. & Conn A., 2012. Biomimetic chromatophores for camouflage and soft active surfaces. Bioinspiration & Biomimetics 7 036009 [link]
The Biomimicry Institute, 2011. Rapid color change used for protection: cuttlefish. The Biomimicry Institute [link]
Wood J. & Jackson K., 2004. How Cephalopods Change Color. The Cephalopod Page [link]