Medical Design Briefs - June 2021 - 24

Tiny Wireless Implant Detects Oxygen Deep Within
the Body
The implant provides realtime
measurements of
tissue oxygen levels.
UC Berkeley
Berkeley, CA
Engineers at the University of California,
Berkeley, have created a tiny wireless
implant that can provide real-time measurements
of tissue oxygen levels deep
underneath the skin. The device, which is
smaller than the average ladybug and powered
by ultrasound waves, could help doctors
monitor the health of transplanted
organs or tissue and provide an early warning
of potential transplant failure.
The technology, created in collaboration
with physicians at the University of
California, San Francisco, also paves the
way for the creation of a variety of miniaturized
sensors that could track other key
biochemical markers in the body, such as
pH or carbon dioxide. These sensors
could one day provide doctors with minimally
invasive methods for monitoring
the biochemistry inside functioning or -
gans and tissues.
" It's very difficult to measure things
deep inside the body, " says Michel
Maharbiz, a professor of electrical engineering
and computer sciences at UC
Berkeley and a Chan Zuckerberg Biohub
Investigator. " The device demonstrates
how, using ultrasound technology coupled
with very clever integrated circuit
design, you can create sophisticated
implants that go very deep into tissue to
take data from organs. "
Maharbiz is the senior author of a new
paper describing the device, which appears
in the journal Nature Biotechnology.
Oxygen is a key component to cells'
ability to harness energy from the food
that we eat, and nearly all tissues in the
body require a steady supply in order to
survive. Most methods for measuring tissue
oxygenation can only provide information
about what is happening near
the surface of the body. That is because
these methods rely on electromagnetic
waves, such as infrared light, which can
only penetrate a few centimeters into
skin or organ tissue. While there are
types of magnetic resonance imaging
that can provide information about
24
Cov
This wireless implant, developed by engineers at the University of California, Berkeley, can measure the
oxygenation of living tissue deep below the surface of the skin. (Credit: UC Berkeley/Soner Sonmezoglu)
μLED
O2-sensing film
Piezo-crystal
IC
Optical filter
A schematic of the oxygen-detecting implant, which measures 4.5 mm long by 3 mm wide. The
μLED, O2-sensing film, and optical filter make up the oxygen sensor, and are controlled by an integrated
circuit (IC). The piezo-crystal converts an electronic signal from the IC into ultrasonic waves
that can be transmitted safely through living tissue. (Credit: UC Berkeley/Soner Sonmezoglu)
deep tissue oxygenation, they require
long scanning times, and so are unable
to provide data in real-time.
Since 2013, Maharbiz has been designing
miniaturized implants that use ultrasonic
waves to wirelessly communicate with
the outside world. Ultrasonic waves, which
are a form of sound too high in frequency
to be detected by the human ear, can travel
harmlessly through the body at much
longer distances than electromagnetic
waves and are already the basis of ultrasound
imaging technology in medicine.
One example of such a device is
Stimdust, designed in collaboration with
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ToC
UC Berkeley electrical engineering and
computer sciences assistant professor
Rikky Muller. Stimdust can detect and
stimulate electrical nerve firings in the
body. Soner Sonmezoglu, a postdoctoral
researcher in engineering at UC Berkeley,
led the effort to expand the implant's
capabilities to include oxygen sensing.
In corporating the oxygen sensor
involved integrating both an LED light
source and an optical detector into the
tiny device, as well as designing a more
complicated set of electronic controls to
operate and read out the sensor. The
team tested the device by monitoring the
Medical Design Briefs, June 2021

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Medical Design Briefs - June 2021

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