ical data on where this particular information was
sensed,” says lead researcher Ken Shepard, Ph.D.,
professor of electrical engineering and biomedical
engineering at Columbia.
The motes’ data transmission and power are
both wireless. The interface that connects the
human to the technology is integrated on the chip
itself. And the device is small enough to be unobtru
sive and amenable to the human body.
To power the chips, the scientists apply ultra
sonic waves. (The motes run only when activated
by an ultrasound machine.) Ultrasonic wavelengths
are much smaller than the radio wavelengths used
for most wireless communication, allowing the
chip’s extremely small size.
The chips are built with the same complemen
tary metaloxidesemiconductor (CMOS) process
used in chips for computers, cars, and smartphones.
CMOS chips are made with a pair of semiconduc
tors attached to a secondary voltage source so that
they work at opposite times; when one transistor is
switched on, the other is switched off.
To have the chips communicate with ultrasound
technology, researchers added a microscale piezo
electric transducer. It converts mechanical sound
waves from the ultrasound machine into electri
cal signals and vice versa. It’s covered with a small
layer of gold on both sides to enhance connectivity.
The motes also feature a layer of special conductive
film and a thin sheet of copper.
“These are added after we get the chips back
from the commercial foundry,” Shepard says. “In
addition, we have to etch and thin the chips to these
very small form factors and coat them with a kind
of plastic for biocompatibility.”
So far, the Columbia University team has suc
cessfully demonstrated the use of motes to monitor
body temperature in rats—injecting the chips into
the rodents’ brains and hind legs to evaluate the
chips’ temperaturesensing performance—but
human use will require considerable testing and
FDA regulation.
Shepard and his team believe the motes will even
tually prove useful in monitoring data other than
temperature, from respiratory conditions to blood
pressure. He says this could streamline the way we
diagnose and treat diseases. In the future, implant
able tech might be how your vitals are taken before
a surgery or how tumors are located in a specific
organ, or they might even be used in therapeutic set
tings to help treat chronic illnesses.A BRIEF
HISTORY OF
REVOLUTIONARY
MEDICAL
IMPLANTS
THE MOTES ARE THE SIZE
O F D U S T M I T E S, M E A S U R I N G
L E S S T H A N O N E-T E N T H O F A C U B I C
MILLIMETER.
1949 / The intraocular lens
replaces a natural lens in a
human eye. These artificial
lenses help patients suffering
from cataracts by similarly
refracting light that enters the
eye to help implant recipients
focus and see again.1960 / The first clinically successful
pacemaker is implanted. This pace
maker used a mercury battery that
powered transistors and a transformer
on a circuit that was all set within
epoxy resin and attached to electrodes
that were placed within heart muscle
tissue.1977 / The modern cochlear
implant is implanted to give
patients with hearing loss
a new sense of sound. This
neuroprosthesis replaces the
acoustic hearing process with
electric signals that stimulate
the auditory nerve.22 November/December 2021
FROM LEFT: GIPHOTOSTOCK/GETTY IMAGES; CHARLES O'REAR/GETTY IMAGES; WESTEND61/GETTY IMAGESBioengineering
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