Medical Design Briefs - January 2025 - 28

Wearable Device for Cells Could Help Restore
Brain Function
The devices could
help scientists probe
subcellular regions of
the brain.
MIT, Cambridge, MA
Wearable devices like smartwatches
and fitness trackers interact with parts of
our bodies to measure and learn from internal
processes, such as our heart rate or
sleep stages. Now, MIT researchers have
developed wearable devices that may be
able to perform similar functions for individual
cells inside the body.
These battery-free, subcellular-sized devices,
made of a soft polymer, are designed
to gently wrap around different
parts of neurons, such as axons and dendrites,
without damaging the cells, upon
wireless actuation with light. By snugly
wrapping neuronal processes, they could
be used to measure or modulate a neuron's
electrical and metabolic activity at a
subcellular level.
Because these devices are wireless and
free-floating, the researchers envision
that thousands of tiny devices could
someday be injected and then actuated
noninvasively using
This image shows the researchers' subcellular-sized devices, which are designed to gently wrap around different
parts of neurons, such as axons and dendrites, without damaging the cells. The devices could be used to measure
or modulate a neuron's electrical activity. (Credit: Pablo Penso, Marta Airaghi)
light. Researchers
would precisely control how the wearables
gently wrap around cells, by manipulating
the dose of light shined from outside
the body, which would penetrate the
tissue and actuate the devices.
By enfolding axons that transmit electrical
impulses between neurons and to
other parts of the body, these wearables
could help restore some neuronal degradation
that occurs in diseases like multiple
sclerosis. In the long run, the devices
could be integrated with other materials
to create tiny circuits that could measure
and modulate individual cells.
" The concept and platform technology
we introduce here is like a founding
stone that brings about immense possibilities
for future research, " says Deblina
Sarkar, the AT&T career development
assistant professor in the MIT
Media Lab and Center for Neurobiological
Engineering, head of the NanoCybernetic
Biotrek Lab, and the senior
author of a paper on this technique.
Sarkar is joined on the paper by lead
author Marta J. I. Airaghi Leccardi, a for28
mer
MIT postdoc who is now a Novartis
Innovation Fellow; Benoît X. E. Desbiolles,
an MIT postdoc; Anna Y. Haddad
'23, who was an MIT undergraduate researcher
during the work; and MIT graduate
students Baju C. Joy and Chen
Song. The research appears in Nature
Communications Chemistry.
n Snugly Wrapping Cells
Brain cells have complex shapes,
which makes it exceedingly difficult to
create a bioelectronic implant that can
tightly conform to neurons or neuronal
processes. For instance, axons are slender,
tail-like structures that attach to the
cell body of neurons, and their length
and curvature vary widely.
At the same time, axons and other cellular
components are fragile, so any device
that interfaces with them must be
soft enough to make good contact without
harming them.
To overcome these challenges, the
MIT researchers developed thin-film
devices from a soft polymer called azobenzene
that don't damage cells they
enfold.
Due to a material transformation, thin
sheets of azobenzene will roll when exposed
to light, enabling them to wrap
around cells. Researchers can precisely
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control the direction and diameter of
the rolling by varying the intensity and
polarization of the light, as well as the
shape of the devices.
The thin films can form tiny microtubes
with diameters that are less than a
micrometer. This enables them to gently,
but snugly, wrap around highly curved
axons and dendrites.
" It is possible to very finely control the
diameter of the rolling. You can stop if
when you reach a particular dimension
you want by tuning the light energy accordingly, "
Sarkar explains.
The researchers experimented with
several fabrication techniques to find a
process that was scalable and wouldn't
require the use of a semiconductor
cleanroom.
n Making Microscopic Wearables
They begin by depositing a drop of
azobenzene onto a sacrificial layer composed
of a water-soluble material. Then
the researchers press a stamp onto the
drop of polymer to mold thousands of
tiny devices on top of the sacrificial layer.
The stamping technique enables them
to create complex structures, from rectangles
to flower shapes.
A baking step ensures that all solvents
are evaporated and then they use etchMedical
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