Tech Briefs Magazine - February 2022 - MD-12

Mobile Molecular Robots Swim in Water
Synthesized micro-robots can convert their mechanical motion into a means of self-propulsion in water.
Hokkaido University, Sapporo, Japan
C
reating molecular microrobots that
mimic the abilities of living organisms
has a number of challenges. One
of the most significant of these is the
creation of directed self-propulsion in
water. There are two major challenges
to achieving this: the first is to make a
molecular robot that can reciprocally
deform and the second is converting
this deformation into propulsion of the
molecular robot.
A team of scientists has created a microcrystal
that utilizes self-continuous reciprocating
motion for propulsion. The
team built on their previous research
that had solved the challenge of creating
molecular robots that can reciprocally
deform. However, tiny objects cannot convert
their reciprocal motion into progressive
motion, in general. In the current
study, the scientists succeeded in realizing
self-propulsion of the molecular robot in
an experimental system where motion was
confined to two dimensions - in this system,
viscous resistance acts anisotropically,
making it negligibly weak.
The microrobot was powered by blue
light, which drove a series of reactions
leading to the fin flipping and the propulsion.
Due to the nature of the reactions,
the motion was not continuous but
occurred intermittently. In addition, the
molecular robots exhibited one of three
different styles of propulsion: a " stroke "
Flapping
0 sec
3 sec
6 sec
100 µm
100 µm
Time
100 µm
Time
(Top) A series of light micrographs showing the movement of one of the synthesized microrobots in this study.
(Bottom) A representation of the movement of the fin over time. (Photo: Kazuma Obara, Yoshiyuki Kageyama,
Sadamu Takeda)
style, with the fin in front; a " kick " style,
with the fin behind; or a " side-stroke "
style, with the fin to one side. The nature
of mobility was affected by the area of the
fin and its angle of elevation; individual
crystals propelled themselves in different
directions and styles.
The scientists then created a computational
minimum model to understand
the variables that affected the propulsion
in a two-dimensional tank. They
were able to determine that fin length,
fin ratio, and elevation angle were the
key variables affecting the direction and
the pace of propulsions.
For more information, contact Assistant
Professor Yoshiyuki Kageyama at y.kageyama@
sci.hokudai.ac.jp; +81-11-706-3532.
Micro-Robots Propelled by Air Bubbles and Ultrasound
A remotely controlled microswimmer could navigate the human body and aid in drug delivery.
Cornell University, Ithaca, NY
A
team led by Mingming Wu, professor
of biological and environmental
engineering in the College of
Agriculture and Life Sciences, created
cell-size robots that can be powered and
steered by ultrasound waves. Despite
their tiny size, these micro-robotic swimmers
- whose movements were inspired
by bacteria and sperm - could one day
be a formidable new tool for targeted
drug delivery.
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For more than a decade, Wu's lab has
been investigating the ways microorganisms,
from bacteria to cancer cells,
migrate and communicate with their environment.
The ultimate goal was to create
a remotely controlled micro-robot
that could navigate in the human body.
Wu's research team initially tried to
design and 3D print a micro-robot that
mimicked the way bacteria use flagellum
to propel themselves. However, like the
early aviators whose cumbersome airplanes
were too birdlike to fly, that effort
collapsed. When Luo joined Wu's lab,
they began exploring a less literal approach.
The primary hurdle was how to
power it. As a person must crawl before
they can walk, a micro-robot needs to be
energized before it can swim.
The team hit upon the idea of using
high-frequency sound waves. Because
ultrasound is quiet, it can be easily used
Motion Design, February 2022
MD Tech Briefs 0222_1.indd 12
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Propulsion

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Tech Briefs Magazine - February 2022

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