Squid turn skin into living jewels

Lots of animals have sparkly skin, but squid are one of few that can change the colour of their shimmer.

Now Trevor Wardill and colleagues at the Marine Biology Laboratory in Woods Hole, Massachusetts, are getting new insight into how they do it by zapping their skin with electricity.

In this video, iridescent patches of skin change hue when nerves near the fin are stimulated. The signal travels through a network of nerves in the skin, allowing the squid to cycle through a range of hues from blue to red in about 15 seconds.

They also change colour via a similar mechanism that alters pigment-containing cells, but the animals are able to display different opaque hues much faster.

The experiment shows that rather than being a local reflex, the central nervous system controls changes in shimmer. But how squid pick and maintain their skin colour is still a mystery.

The hue of the shimmer helps the animals camouflage themselves - but they are colour blind, so scientists are puzzled by how they know they've got it right.

Magic Ink: Now available for full colour Printing

Borrowing an idea from nature could lead to technology capable of producing full-colour A4 prints in a fraction of a second, according to South Korean engineers.

Many insects and birds owe their bright colours to the interaction of light with finely-patterned surface textures, rather than relying on pigments. The iridescent colours of a peacock's tail are largely a result of the interaction of light with just one biological material – melanin rods.

Engineers have long experimented with replicating these so-called structural colours in synthetic materials, and now Sunghoon Kwon's team at Seoul National University in South Korea has managed it.

Their M-Ink can be used to produce any colour in the visible spectrum and could lead to a new method of cheap and fast full-colour printing, Kwon says.

Just add nanoparticles

M-Ink contains three ingredients: magnetic nanoparticles 100 to 200 nanometres across, a solvation liquid, and a resin.

The nanoparticles disperse throughout the resin, giving the ink a brown appearance. But when an external magnetic field is applied, the nanoparticles immediately snap to the magnetic field lines, forming chain-like structures.

The regularly-spaced nanoparticle chains interfere with incoming light, so that the light reflected from the surface is of a particular colour. Adjusting the magnetic field strength shifts the spacing of the field lines and changes the colour, says Kwon.