Scientific American - 04.2020

ADVANCES

18 Scientific American, April 2020

FROM “BIOINSPIRED DESIGN OF FLEXIBLE ARMOR BASED ON CHITON SCALES,” BY M. CONNORS ET AL.,

IN

NATURE

C

OMMUNICATIONS,

VOL. 10, ARTICLE 5413; DECEMBER 10, 2019

T E C H

Mollusk

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 Bushwick

Individual scale

Curve forms

hook shape

Chiton armor structure

3-D-printed armor design comes from the small plates encircling a chiton mollusk ( above ).

Illustration by Brown Bird Design

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