Researchers from the University of Bristol
have created artificial muscles that can be transformed at the flick of a
switch to mimic the remarkable camouflaging abilities of organisms such as
squid and zebrafish.
They demonstrate two individual transforming
mechanisms that they believe could be used in ‘smart clothing’ to trigger
camouflaging tricks similar to those seen in nature.
The study is published in Bioinspiration
and Biomimetics.
“We have taken inspiration from nature’s
designs and exploited the same methods to turn our artificial muscles into
striking visual effects,” said lead author of the study Jonathan Rossiter.
The soft, stretchy, artificial muscles are
based on specialist cells called chromatophores that are found in amphibians,
fish, reptiles, and cephalopods, and contain pigments of colors that are
responsible for the animals’ remarkable color-changing effects.
The color changes in these organisms can be
triggered by changes in mood, temperature, stress, or something visible in the environment,
and can be used for camouflage, communication, or attracting a mate.
Two types of artificial chromatophores were
created in the study: The first based on a mechanism adopted by a squid and the
second based on a rather different mechanism adopted by zebrafish.
A typical color-changing cell in a squid has a
central sac containing granules of pigment. The sac is surrounded by a series
of muscles and when the cell is ready to change colour, the brain sends a
signal to the muscles and they contract. The contracting muscles make the
central sacs expand, generating the optical effect which makes the squid look
like it is changing color.
The fast expansion of these muscles was
mimicked using dielectric elastomers (DEs)—smart materials, usually made of a
polymer, which are connected to an electric circuit and expand when a voltage
is applied. They return to their original shape when they are short circuited.
In contrast, the cells in the zebrafish contain
a small reservoir of black pigmented fluid that, when activated, travels to the
skin surface and spreads out, much like the spilling of black ink. The natural
dark spots on the surface of the zebrafish therefore appear to get bigger and
the desired optical effect is achieved. The changes are usually driven by
hormones.
The zebrafish cells were mimicked using two
glass microscope slides sandwiching a silicone layer. Two pumps, made from
flexible DEs, were positioned on both sides of the slide and were connected to
the central system with silicone tubes; one pumping opaque white spirit, the
other a mixture of black ink and water.
“Our artificial chromatophores are both
scalable and adaptable and can be made into an artificial compliant skin which
can stretch and deform, yet still operate effectively. This means they can be
used in many environments where conventional ‘hard’ technologies would be
dangerous, for example at the physical interface with humans, such as smart
clothing,” continued Rossiter.
