Off the scales: Fish armor both tough and flexible

Date:
June 18, 2020
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
Humans have drawn technological inspiration from fish scales going
back to ancient times: Romans, Egyptians, and other civilizations
would dress their warriors in scale armor, providing both protection
and mobility.

Now, using advanced X-ray imaging techniques, scientists have
characterized carp scales down to the nanoscale, enabling them
to understand how the material is resistant to penetration while
retaining flexibility.



FULL STORY ========================================================================== Humans have drawn technological inspiration from fish scales going
back to ancient times: Romans, Egyptians, and other civilizations
would dress their warriors in scale armor, providing both protection
and mobility. Now, using advanced X-ray imaging techniques, Lawrence
Berkeley National Laboratory (Berkeley Lab) scientists have characterized
carp scales down to the nanoscale, enabling them to understand how the
material is resistant to penetration while retaining flexibility.


==========================================================================
The researchers used powerful X-ray beams at Berkeley Lab's Advanced
Light Source (ALS) to watch how the fibers in carp scales react as stress
is applied.

As they wrote in their paper, published recently in the journal Matter,
what they found "may well provide further inspiration for the design
of advanced synthetic structural materials with unprecedented toughness
and penetration resistance." "The structure of biological materials is absolutely fascinating," said lead author Robert Ritchie, of Berkeley
Lab's Materials Sciences Division, who headed this work with Marc Meyers,
a professor of nanoengineering and mechanical engineering at UC San
Diego. "We like to mimic these properties in engineering materials, but
the first step is to see how nature does it." Fish scales have a hard
outer shell with a softer inner layer that is tough and ductile. When
something like a predator's teeth try to sink into the scales, the outer
shell resists the penetration but the inner has to absorb all the excess
load to keep the scale in one piece. How does it do this? It turns out
that the fibers in the scale, which is made up of collagen plus minerals,
are in a twisted orientation, called a Bouligand structure. When stress
is applied to the material, the fibers rotate in sequence in order to
absorb the excess load.

"It's called adaptive reorientation. It's like a smart material," said
Ritchie, who is also a professor of materials science and engineering
at UC Berkeley.

"Using a technique called small angle X-ray scattering, we can follow
that in real time using the synchrotron. We irradiate it with X-rays,
and we can actually see the fibers rotating and moving." The collagen
that makes up human skin, on the other hand, is "all messed up like
a bowl of spaghetti, but it can unravel and align to absorb energy,
which makes skin incredibly resistant to tearing," Ritchie said. The
Bouligand structure in the carp scale is much more organized but still
makes for a very effective toughening mechanism.

The other noteworthy characteristic of a carp scale is the gradient
between the hard and soft layers. "If we were making that as armor,
we would have an interface between the hard and soft material. The
interface is invariably a location where cracks and failures start,"
said Ritchie, an expert in how materials fail. "The way nature does it:
Instead of having these interfaces where there's discontinuity between
one material and another, nature makes a perfect gradient from the
hard to the soft (tougher) material." Working in collaboration with
the researchers at UC San Diego, the team has previously studied the
arapaima, an Amazonian freshwater fish whose scales are so tough they
are impenetrable to piranha, as well as other species. For this study
they chose the carp, a modern version of the ancient coelacanth fish,
also known for having scales that act as armor.

Now that the deformation and failure mechanisms of carp scales have been characterized, trying to reproduce these properties in an engineering
material is the next challenge. Ritchie noted that advances in 3D
printing could provide a way to produce gradients the way nature does,
and thus make a material that is both hard and ductile.

"Once we get a better handle on how to manipulate 3D printing, we can
start to make more materials in the image of nature," he said.

The ALS is a Department of Energy Office of Science user facility. The
study was supported by a grant from the Air Force Office of Scientific Research.


========================================================================== Story Source: Materials provided by
DOE/Lawrence_Berkeley_National_Laboratory. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Haocheng Quan, Wen Yang, Marine Lapeyriere, Eric Schaible, Robert O.

Ritchie, Marc A. Meyers. Structure and Mechanical Adaptability of
a Modern Elasmoid Fish Scale from the Common Carp. Matter, 2020;
DOI: 10.1016/j.matt.2020.05.011 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200618102416.htm

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