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environmental engineering at MIT, and gradu-
ate student Hyunwoo Yuk, is currently looking
to adapt hydrogel robots for medical applica-
tions.
¡°Hydrogels are soft, wet, biocompatible, and
can form more friendly interfaces with human
organs,¡± Zhao says. ¡°We are actively collabo-
rating with medical groups to translate this
system into soft manipulators such as hydro-
gel ¡®hands,¡¯ which could potentially apply more
gentle manipulations to tissues and organs in
surgical operations.¡±
Zhao and Yuk have published their results
this week in the journal Nature Communica-
tions. Their co-authors include MIT graduate
students Shaoting Lin and Chu Ma, postdoc
Mahdi Takaffoli, and associate professor of
mechanical engineering Nicholas X. Fang.
Robot recipe
For the past five years, Zhao¡¯s group has been
developing ¡°recipes¡± for hydrogels, mixing
solutions of polymers and water, and using
techniques they invented to fabricate tough
yet highly stretchable materials. They have
also developed ways to glue these hydrogels
to various surfaces such as glass, metal, ce-
ramic, and rubber, creating extremely strong
bonds that resist peeling.
The team realized that such durable, flexible,
strongly bondable hydrogels might be ideal
materials for use in soft robotics. Many groups
have designed soft robots from rubbers like
silicones, but Zhao points out that such mate-
rials are not as biocompatible as hydrogels.
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The Good News
2017 February/March
Pg 3 - The Sunshine Express
combination of extreme strength and light weight.
¡°You could either use the real graphene material or
use the geometry we discovered with other materials,
like polymers or metals,¡± Buehler says, to gain similar
advantages of strength combined with advantages in
cost, processing methods, or other material properties
(such as transparency or electrical conductivity).
¡°You can replace the material itself with anything,¡±
Buehler says. ¡°The geometry is the dominant factor.
It¡¯s something that has the potential to transfer to
many things.¡±
The unusual geometric shapes that graphene naturally
forms under heat and pressure look something like
a Nerf ball ¡ª round, but full of holes. These shapes,
known as gyroids, are so complex that ¡°actually mak-
ing them using conventional manufacturing methods
is probably impossible,¡± Buehler says. The team used
3-D-printed models of the structure, enlarged to thou-
sands of times their natural size, for testing purposes.
For actual synthesis, the researchers say, one possibil-
ity is to use the polymer or metal particles as tem-
plates, coat them with graphene by chemical vapor
deposit before heat and pressure treatments, and then
chemically or physically remove the polymer or metal
phases to leave 3-D graphene in the gyroid form. For
this, the computational model given in the current
study provides a guideline to evaluate the mechanical
quality of the synthesis output.
The same geometry could even be applied to large-
scale structural materials, they suggest. For example,
concrete for a structure such as a bridge might be
made with this porous geometry, providing comparable
strength with a fraction of the weight. This approach
Stronger Than Steel (continued from page 1)
Hydrogel Robots Invented
Transparent, gel-based robots can catch
and release live fish; Made from hydrogel,
robots may one day assist in surgical
operations, evade underwater detection
Jennifer Chu, MIT News Office, February 1,
2017: Engineers at MIT have fabricated trans-
parent, gel-based robots that move when water
is pumped in and out of them. The bots can
perform a number of fast, forceful tasks, includ-
ing kicking a ball underwater, and grabbing and
releasing a live fish.
The robots are made entirely of hydrogel, a
tough, rubbery, nearly transparent material
that¡¯s composed mostly of water. Each robot
is an assemblage of hollow, precisely designed
hydrogel structures, connected to rubbery tubes.
When the researchers pump water into the
hydrogel robots, the structures quickly inflate in
orientations that enable the bots to curl up or
stretch out.
The team fashioned several hydrogel robots,
including a finlike structure that flaps back and
forth, an articulated appendage that makes kick-
ing motions, and a soft, hand-shaped robot that
can squeeze and relax.
Because the robots are both powered by and
made almost entirely of water, they have similar
visual and acoustic properties to water. The re-
searchers propose that these robots, if designed
for underwater applications, may be virtually
invisible.
The group, led by Xuanhe Zhao, associate pro-
fessor of mechanical engineering and civil and
would have the addition-
al benefit of providing
good insulation because
of the large amount of
enclosed airspace within
it.
Because the shape is
riddled with very tiny
pore spaces, the material
might also find applica-
tion in some filtration
systems, for either water
or chemical processing.
The mathematical de-
scriptions derived by this
group could facilitate the
development of a vari-
ety of applications, the
researchers say.
¡°This is an inspiring
study on the mechanics
of 3-D graphene assem-
bly,¡± says Huajian Gao, a
professor of engineering
at Brown University, who
was not involved in this
work. ¡°The combination
of computational model-
ing with 3-D-printing-
based experiments used
in this paper is a pow-
erful new approach in
engineering research.
It is impressive to see
the scaling laws initially
derived from nanoscale
simulations resurface in
macroscale experiments
under the help of 3-D
printing,¡± he says.
This work, Gao says,
¡°shows a promising
direction of bringing the
strength of 2-D materials
and the power of mate-
rial architecture design
together.¡±
The research was sup-
ported by the Office of
Naval Research, the
Department of Defense
Multidisciplinary Univer-
sity Research Initiative,
and BASF-North Ameri-
can Center for Research
on Advanced Materials.
(source: http://news.
mit.edu/2017/3-d-gra-
phene-strongest-lightest-
materials-0106)