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A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 1 6
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AUXETIC MATERIAL COULD
REVOLUTIONIZE RUNNING
SHOES
Chemists at the University of Cal-
ifornia, San Diego created an “adap-
tive protein crystal” that acts like it is
opposite day. When stretched in one
direction, the material thickens in
the perpendicular direction—rather
than thinning, as is typical—and when
squeezed in one dimension, it shrinks in
the other, becoming denser. This coun-
terintuitive, auxetic behavior could
prove useful in the sole of a running
shoe that thickens for greater shock
absorption as a heel collides with pave-
ment, or in other applications, such as
body armor that strengthens when a
bullet strikes.
Akif Tezcan, professor of chemistry
and biochemistry, and his colleagues
created a sheet-like crystal made of
square-shaped RhuA proteins arranged
like tiles in a repeating pattern. “We
found a way to create strong, flexible,
reversible bonds to connect the protein
tiles at their corners,” he says.
The flexibility allows the tiles to
rotate to open spaces within the mate-
rial or to close up in a kind of adaptable
sieve. It is the rotation of the protein
tiles in unison that creates the auxetic
behavior of the material, which has not
been previously demonstrated at the
molecular level.
ucsd.edu.
TURTLE-INSPIRED SKIS
Researchers at the École Poly-
technique Fédérale de Lausanne (EPFL),
in conjunction with the Institute for
Snow and Avalanche Research and
the ski manufacturer Stöckli—all in
Switzerland—developed a new kind of
multi-function alpine ski. While downhill
experts require rigid skis that withstand
Strong, flexible bonds in these protein tiles allow them to rotate to open spaces.
Courtesy of UC San Diego.
EPFL researchers helped develop new
skis based on a mechanism that mimics
turtle scales.
BRIEF
The
U.S. Department of Defense
is contributing $75 million toward the establishment of
Advanced Functional
Fabrics of America,
a consortium of 89 companies, universities, researchers, and startups. The goal is to use flexible
integrated circuits, lights, and sensors to create fabrics that can see, hear, sense, communicate, store energy, monitor
health, and more. For example, running shoes using the new fabrics will be able to sense impact load for every step
and communicate data about their user’s physiological condition, and sensors woven into the nylon of parachutes
will be able to catch small tears that otherwise would expand in midair.
defense.gov.
the high pressures of turns, intermedi-
ate athletes look for the maneuverabil-
ity that comes with flexibility. The new
type of ski delivers both qualities due
to inspiration from the morphology of
turtle shells.
“The scales of a turtle interlock,
like a jigsaw puzzle, and are connected
by a polymer,” explains Véronique
Michaud, a researcher at EPFL’s Lab-
oratory of Polymer and Composite
Technology. “When turtles breathe, the
scales separate slightly, and the shell
becomes flexible. But when an exter-
nal shock occurs, the shell tightens and
stiffens.”
To replicate this quality in the skis,
aluminum plates with a snake-shaped
fissure are embedded at both ends.
When skis take the force of a turn,
plates on either side of the gap come
together and the ski stiffens, affording
the skier stability and precision. As the
skier comes out of the turn, the gap
reopens, rendering the ski flexible and
easier to maneuver. A special type of
rubber between the plates functions
like the polymer in the turtle shell.
www.epfl.ch.
EMERGING TECHNOLOGY