Sound waves transport droplets for rewritable lab-on-a-chip devices
Vibrating transducers create tunnels in a thin layer of oil to transport droplets across a chip without leaving a trace behind

Date:
June 11, 2020
Source:
Duke University
Summary:
Engineers have demonstrated a versatile microfluidic lab-on-a-chip
that uses sound waves to create tunnels in oil to digitally
manipulate and transport droplets. The technology could form the
basis of a small-scale, programmable, rewritable biomedical chip
that is completely reusable for disparate purposes from on-site
diagnostics to laboratory-based research.



FULL STORY ========================================================================== Engineers at Duke University have demonstrated a versatile microfluidic
lab-on- a-chip that uses sound waves to create tunnels in oil to
touchlessly manipulate and transport droplets. The technology could form
the basis of a small-scale, programmable, rewritable biomedical chip
that is completely reusable to enable on-site diagnostics or laboratory research.


==========================================================================
The results appear online on June 10 in the journal Science Advances.

"Our new system achieves rewritable routing, sorting and gating of
droplets with minimal external control, which are essential functions
for the digital logic control of droplets," said Tony Jun Huang,
the William Bevan Distinguished Professor of Mechanical Engineering
and Materials Science at Duke. "And we achieve it with less energy
and a simpler setup that can control more droplets simultaneously than
previous systems." Automated fluid handling has driven the development
of many scientific fields such as clinical diagnostics and large-scale
compound screening. While ubiquitous in the modern biomedical research
and pharmaceutical industries, these systems are bulky, expensive and
do not handle small volumes of liquids well.

Lab-on-a-chip systems have been able to fill this space to some
extent, but most are hindered by one major drawback -- surface
absorption. Because these devices rely on solid surfaces, the samples
being transported inevitably leave traces of themselves behind that can
lead to contamination.

The new lab-on-a-chip platform uses a thin layer of inert, immiscible oil
to stop droplets from leaving behind any trace of themselves. Just below
the oil, a grid of piezoelectric transducers vibrate when electricity
is passed through them. Just like the surface of a subwoofer, these
vibrations create sound waves in the thin layer of oil above them.



========================================================================== These sound waves form complex patterns when they bounce off the top
and bottom of the chip as well as when they run into one another. By meticulously planning the design of the transducers and controlling
the frequency and strength of the vibrations causing the waves, the
researchers are able to create vortices that, when combined, form tunnels
that can push and pull droplets in any direction along the surface of
the device.

"The new system uses dual-mode transducers, which can transport droplets
along x or y axis based on two different streaming patterns," said
Huang. "This is a big step up from our previous system, which simply
created a series of dimples in the oil to pass droplets along on a
single axis." Aiding Huang in the creation of this upgraded system
was Krishnendu Chakrabarty, the John Cocke Distinguished Professor of Electrical and Computer Engineering at Duke, and his PhD student Zhanwei
Zhong. The pair helped design the electronics at the heart of the new lab-on-a-chip demonstration, and greatly upgraded and miniaturized the
wire connections, controllers and other hardware used in the system.

By using dual-mode transducers, the researchers were able to move
droplets along two axes while simultaneously reducing the complexity of
the electronics four-fold. They were also able to reduce the operating
voltage of the transducers three-to-seven times lower than previous
system, which allowed it to simultaneously control eight droplets. And
by introducing a microcontroller to the setup, the researchers were able
to program and automate much of the droplet movement.

The researchers show off the capabilities of their new device in a series
of videos. In one, a droplet is quickly whisked around the exterior of
a square.

Others show droplets coming to a "T" intersection and turning right or
left, and the creation of a "logic gate" that can either interrupt a
droplet's movement along a corridor or allow it to pass through.

The ability to control droplets in a manner similar to the logic systems
found on a computer chip is essential to a wide variety of clinical and research procedures.

"Our next step is to combine the miniaturized radio-frequency power-supply
and control board designed by Professor Chakrabarty's team for large-scale integration and dynamic planning," said Huang. "We're also planning
to integrate the ability to split droplets into two without having to
touch them."

========================================================================== Story Source: Materials provided by Duke_University. Original written
by Ken Kingery. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Peiran Zhang, Chuyi Chen, Xingyu Su, John Mai, Yuyang Gu,
Zhenhua Tian,
Haodong Zhu, Zhanwei Zhong, Hai Fu, Shujie Yang, Krishnendu
Chakrabarty, Tony Jun Huang. Acoustic streaming vortices enable
contactless, digital control of droplets. Science Advances, 2020;
6 (24): eaba0606 DOI: 10.1126/sciadv.aba0606 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200611133107.htm

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