Tech Briefs Magazine - January 2024 - 29

A Precision Arm for Mini Robots
An ultrasonically actuated glass needle attached to a robotic arm can perform a wide range
of tasks in microrobotic and microfluidic applications.
Swiss Federal Institute of Technology Zurich, Switzerland
U
ntil recently, microscopic robotic systems have had to make do
without arms. Now, a team at ETH Zurich has developed an ultrasonically
actuated glass needle that can be attached to a robotic
arm. This lets them pump and mix minuscule amounts of liquid
and trap particles.
Prior to the team's breakthrough, miniature systems that transport
miniscule amounts of liquid through fine capillaries have
had little association with such robots. Such systems are known as
microfluidics or lab-on-a-chip and generally make use of external
pumps to move the liquid through the chips. To date, such systems
have been difficult to automate, and the chips have had to be
custom-designed and manufactured for each specific application.
The device, which was reported in Nature Communications,
can be attached to a robotic arm, is suitable for performing a
wide range of tasks in microrobotic and microfluidic applications,
and can be used to automate such applications.
The device comprises a thin, pointed glass needle and a
piezoelectric transducer that causes the needle to oscillate. It's
akin to transducers used in loudspeakers, ultrasound imaging,
and professional dental cleaning equipment. The researchers
can vary the oscillation frequency of their glass needle; by dipping
the needle into a liquid they create a 3D pattern composed
of multiple vortices. Since this pattern depends on the
oscillation frequency, it can be controlled accordingly.
The team was able to use this to demonstrate several applications.
First, they were able to mix tiny droplets of highly
viscous liquids.
" The more viscous liquids are, the more difficult it is to mix
them, " said Professor Daniel Ahmed. " However, our method
succeeds in doing this because it allows us to not only create a
single vortex, but to also efficiently mix the liquids using a complex
3D pattern composed of multiple strong vortices. "
Second, they were able to pump fluids through a mini-channel
system by creating a specific pattern of vortices and placing
the oscillating glass needle close to the channel wall.
Third, they succeeded in using their robot-assisted acoustic
device to trap fine particles present in the fluid. This works
because a particle's size determines its reaction to the sound
waves. Relatively large particles move toward the oscillating
glass needle, at which they accumulate. The researchers
demonstrated how this method can capture not only inanimate
particles but also fish embryos. They believe it should also be
capable of capturing biological cells in the fluid.
" In the past, manipulating microscopic particles in three dimensions
was always challenging. Our microrobotic arm makes
it easy, " said Ahmed. " Until now, advancements in large, conventional
robotics and microfluidic applications have been made
separately. Our work helps to bring the two approaches together. "
As a result, future microfluidic systems could be designed similarly
to today's robotic systems. An appropriately programmed
single device would be able to handle a variety of tasks.
" Mixing and pumping liquids and trapping particles - we can do
it all with one device, " said Ahmed. This means tomorrow's microfluidic
chips will no longer have to be custom-developed for each specific
application. The researchers would next like to combine several
glass needles to create even more complex vortex patterns in liquids.
In addition to lab analysis, Ahmed can envisage other applications
for microrobotic arms, such as sorting tiny objects. The arms
could conceivably also be used in biotechnology as a way of introducing
DNA into individual cells. It should ultimately be possible
to employ them in additive manufacturing and 3D printing.
For more information, contact ETH Zurich media relations
at mediarelations@hk.ethz.ch; +41 44-632-4141.
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Tested in the following acids for over
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Part A: 3,000-6,000 cps at 75°F
Part B: 4,000-6,000 cps at 75°F
Using a glass needle made to oscillate with the assistance of ultrasound,
liquids can be manipulated and particles can be trapped. (Image: ETH Zurich)
Tech Briefs, January 2024
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