Tech Briefs Magazine - June 2023 - 22

Mechanical & Fluid Systems
Hydrodynamic Effect Helps Motorized Objects
Navigate Inclines
The tiny motors mimic how rock climbers navigate inclines.
New York University, NY
S
cientists have uncovered how heavy,
motorized objects climb steep slopes
- a newly discovered mechanism that
also mimics how rock climbers navigate
inclines. The finding stems from a series
of experiments in which motorized objects
were placed in liquid and then
moved up tilted surfaces. These " micro-swimmers "
are about 20 times heavier
than the fluid they swim in but they were
able to climb almost vertical steep slopes.
Gravitaxis - directional movement in
response to gravity - is a vital phenomenon
not only in engineering but also in
medicine and pharmaceutical development.
It explains, in part, how bacteria
move through the body and provides insights
into ways to create more effective
drug-delivery mechanisms.
The motorized swimmers, or nanorods,
are roughly 1/40th the width of
a strand of human hair and were tasked
with moving up an inclined surface while
im mersed in a liquid solution within a
walled container. The swimmers were
composed of two types of metal: gold
and rhodium as well as gold and platinum
- a make-up that gave them unbalanced
densities given the varying weights
of these metals. The swimmers' composition,
liquid environment, and juxtaposiHeavy
metallic microswimmers, made of rhodium (purple) and gold, swim around in a liquid solution.
When confronting a sloped wall, each rod-like swimmer will reorient its body upward due to
its density imbalance and swim up like a rock climber against gravity. A hydrodynamic effect helps
to amplify the action in its reorientation. (Image: Jun Zhang, NYU's Courant Institute and NYU's
Department of Physics)
tion of surfaces enabled them to move
upward, despite their significant weight.
The motors reorient themselves upward
against gravity thanks to their density
imbalance, much like a seesaw reorients
itself in response to the movement
and weight of its riders. A hydrodynamic
effect amplifies this movement - swimming
next to a wall yields a bigger torque
in repositioning the motors' bodies upwards.
Future motors will be de signed to
reach targeted locations and to perform
designated functions.
For more information, contact James
Devitt at james.devitt@nyu.edu; 212998-6808.
Chemically
Driven Wheels " Morph " Into Gears
A catalytic reaction causes a two-dimensional, chemically coated sheet to spontaneously
morph into a three-dimensional gear.
University of Pittsburgh, PA
T
22
he gear is one of the oldest mechanical
tools and led to ma chines
ranging from early irrigation systems
and clocks, to modern engines and robotics.
Researchers have utilized a catalytic
reaction that causes a two-dimensional,
chemically coated sheet to
spontaneously " morph " into a
three-dimensional gear that performs
sustained work.
The findings indicate the potential
to develop chemically driven ma chines
that do not rely on external power but
simply require the addition of reactants
to the surrounding solution.
Computational modeling has shown
that chemo-mechanical transduction
(conversion of chemical energy into
mo tion) at active sheets presents a
novel way to replicate the behavior of
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gears in environments without access
to traditional power sources.
In the simulations, catalysts are
placed at various points on a two-dimensional
sheet resembling a wheel
with spokes, with heavier nodes on the
sheet's circumference. The flexible
sheet, approximately a millimeter in
length, is then placed in a fluid-filled
microchamber. A reactant is added to
Tech Briefs, June 2023

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Tech Briefs Magazine - June 2023

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