ADVANCES
18 Scientific American, April 2020FROM “BIOINSPIRED DESIGN OF FLEXIBLE ARMOR BASED ON CHITON SCALES,” BY M. CONNORS ET AL.,
INNATURECOMMUNICATIONS,VOL. 10, ARTICLE 5413; DECEMBER 10, 2019T E C HMollusk
Armor
Scaly sea creatures inspire
a flexible protective material Protective gear has come a long way since
the days of medieval armor. But engineers
still have trouble shielding joints like elbows
and knees, which requires material tough
enough to prevent injur y but flexible enough
to allow motion. Toward this end, research-
ers are imitating an inconspicuous sea ani-
mal whose covering strikes a remarkable
balance between protection and flexibility.
Certain species of marine mollusks
called chitons are encircled by girdles of
tough tissue capped with overlapping
scales of calcium carbonate, the rigid com-
pound that encases many shellfish. Scien-
tists analyzed this ocean armor to learn
how it provides freedom of movement
without compromising defense, then
3-D-printed protective gear based on its
shape. The work appeared last December
in Nature Communications.
“ We did a systematic study of the mate-
rial structure, from the nanometer to mac-
roscopic scale,” says study co-author Ling
Li, a mechanical engineer at Virginia Poly-technic Institute and State University. He
and his colleagues at multiple institutions
examined individual chiton scales’ chemical
composition, crystal structure and mechani-
cal properties, then zoomed out to study
how the scales worked together. The type
of chiton they studied is about the length of
a penny, and its largest scales are only a cou-
ple of millimeters wide—so the researchers
relied on high-resolution x-rays to image the
3-D geometry of the animals’ coverings.
They found the armor gains strength
from its interlocking structure. Each scale
has a diamond-shaped base that stretches
up to a smooth top surface, which curves
to hook the plate to its neighbor. When an
outside force pushes on one scale, it presses
against those next to it, distributing the
pressure to protect the organism under-
neath. Working with architectural design-
ers, the team 3-D-printed analogous scaled
armor for humans—including kneepads
that protect the wearer from broken glass.
The researchers could then run physi-cal tests on the scales’ behavior rather
than relying on computer simulations.
“This system with a lot of scales that con-
tact each other, that slide along one
another—if you try to capture this using
traditional computer models, then it
becomes a nightmare ver y fast,” says Fran-
cois Barthelat, a mechanical engineer at
the University of Colorado Boulder, who
was not involved in the study. Printing the
structures offers an efficient way to dem-
onstrate the principles involved, he adds.
Li’s team tested different scale configu-
rations and investigated how the synthetic
armor behaved under stress; he says it
could provide protection for athletes or for
scientists doing fieldwork. Barthelat notes
that it “seems to be pretty efficient at com-
bining flexibility with protection against
lacerations.” He suggests the armor could
cover any joints, including fingers, and
could, for example, help industrial workers:
“There’s a huge demand for this type of
flexible protection.” — Sophie BushwickIndividual scaleCurve forms
hook shapeChiton armor structure3-D-printed armor design comes from the small plates encircling a chiton mollusk ( above ).
Illustration by Brown Bird Design© 2020 Scientific American