Tech Briefs Magazine - July 2021 - 30

Materials & Coatings
local
gel microenvironment, allowing
swelling and de-swelling of materials via
chemo-mechanical stresses in an auton -
omous manner. This generated dynamic
morphological change including periodic
oscillations reminiscent of heartbeats
found in living systems.
The team designed a chemical-re -
sponsive polymeric shell meant to mimic
living matter. They applied the waterbased
mechanical properties of the
hydrogel shell to a chemical species - a
chemical substance that produces specific
patterned behavior (in this case, wavelike
oscillations) - located within the
shell. After conducting a series of reduction-oxidation
reactions - a chemical
reaction that transfers electrons between
two chemical species - the shell generated
microcompartments capable of ex -
panding, contracting, or inducing buckling-unbuckling
behavior when mechan -
ical instability was introduced.
If the level of chemicals goes past a
certain threshold, water gets absorbed,
swelling the gel. When the gel swells, the
chemical species gets diluted, triggering
chemical processes that expel the gel's
water, therefore contracting the gel.
The model could be used as the basis
to develop other soft materials demonstrating
diverse, dynamic morphological
changes. This could lead to new drug
delivery strategies with materials that
enhance the rate of diffusion of compartmentalized
chemicals or release cargos at
specific rates. The work could also inform
the future development of soft materials
with robot-like functionality that operate
autonomously. These soft robotics have
emerged as candidates to support chemical
production, tools for environmental
technologies, or smart biomaterials for
medicine. Yet the materials rely on external
stimuli, such as light, to function.
The new soft material operates auton -
omously, so there is no external control
involved.
For more information, contact Julianne
Hill at julianne.hill@northwestern.edu; 847467-1194.
Nature-Inspired,
Manufactured, Non-Cuttable Material
The material could be used in security, health, industrial, and safety applications.
Durham University, Durham, United Kingdom
ngineers, inspired by nature, created
what is claimed to be the first manufactured
non-cuttable material. The idea
for the new lightweight material came
from the tough cellular skin of the
grapefruit and the fracture-resistant
shells of the abalone sea creature.
Called Proteus, the material is made
from alumina ceramic spheres encased
in a cellular aluminum metallic foam
structure and works by turning back the
force of a cutting tool on itself. In tests,
Proteus could not be cut by angle
grinders, drills, or high-pressure water
jets. The architected material is both
highly deformable and ultra-resistant to
dynamic point loads.
E
Metal powder +
foaming agent
The bio-inspired metallic cellular structure
has only 15% steel density. The
architecture derives its extreme hardness
from the local resonance between the
embedded ceramics in a flexible cellular
matrix and the attacking tool, which produces
high-frequency vibrations at the
interface. When cut with an angle grinder
or drill, the interlocking vibrational connection
created by the ceramic spheres
inside the casing blunts the cutting disc or
drill bit. The ceramics also fragment into
fine particles that fill the cellular structure
of the material and harden as the speed of
the cutting tool is increased
Essentially, cutting the material is like
cutting through jelly filled with nuggets
Mixing Pressing Extrusion
Preparation
- after getting through the jelly and hitting
the nuggets, the material vibrates in
such a way that it destroys the cutting
disc or drill bit. Water jets are also ineffective
because the curved surfaces of
the ceramic spheres widen the jet to substantially
reduce its speed and weaken its
cutting capacity.
Proteus could be used to make bike
locks, lightweight armor, and in protective
equipment for people who work
with cutting tools.
Watch Proteus in action on Tech Briefs TV
at www.techbriefs.com/tv/no-cut-material.
For more information, contact Dr. Stefan
Szyniszewski at stefan.t.szyniszewski@
durham.ac.uk; +44 (0) 191 33 42479.
Foaming
Cooling
Manufacturing steps include mixing metal powder with a small amount of foaming agent, followed by pressing the mix and extrusion into preform
shapes. The compressed powder bars enable precise placement of ceramic segments in the orthogonal pattern and manufacturing of the end product
in an industrial furnace. (Photo courtesy of the researchers)
30
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Tech Briefs, July 2021

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Tech Briefs Magazine - July 2021

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