Medical Design Briefs - August 2021 - 42

Sweat-Proof 'Smart Skin' Takes Reliable Vitals
The design could lead to
conformable wearable
monitors to track skin
cancer and other
conditions.
MIT
Cambridge, MA
MIT engineers and researchers in
South Korea have developed a sweatproof
" electronic skin " - a conformable,
sensor-embedded sticky patch that
monitors a person's health without malfunctioning
or peeling away, even when a
wearer is perspiring.
The patch is patterned with artificial
sweat ducts, similar to pores in human
skin, that the
researchers etched
through the material's ultrathin layers.
The pores perforate the patch in a
kirigami- like pattern, similar to that of
the Japanese paper-cutting art. The
design ensures that sweat can escape
through the patch, preventing skin irritation
and damage to embedded sensors.
The kirigami design also helps the patch
conform to human skin as it stretches and
bends. This flexibility, paired with the material's
ability to withstand sweat, enables it to
monitor a person's health over long periods
of time, which has not been possible
with previous " e-skin " designs. The results,
published in Science Advances, are a step
toward long-lasting smart skins that may
track daily vitals or the progression skin
cancer and other conditions.
" With this conformable, breathable
skin patch, there won't be any sweat accumulation,
wrong information, or detachment
from the skin, " says Jeehwan Kim,
associate professor of mechanical engineering
at MIT. " We can provide wearable
sensors that can do constant longterm
monitoring. "
Kim's co-authors include lead author
and MIT postdoc Hanwool Yeon, and
researchers in MIT's departments of
mechanical engineering and materials
science and engineering, and the
Research Laboratory of Electronics,
along with collaborators from cosmetics
conglomerate Amorepacific and other
institutions across South Korea.
■ A Sweaty Hurdle
Kim's group specializes in fabricating
flexible semiconductor films. The re -
searchers have pioneered a technique
called remote epitaxy, which involves growing
ultrathin, high-quality semiconductor
films on wafers at high temperature and
selectively peeling away the films, which
they can then combine and stack to form
sensors far thinner and more flexible than
conventional wafer-based designs.
Recently, their work drew the attention
of the cosmetics company Amorepacific,
which was interested in developing thin
wearable tape to continuously monitor
changes in skin. The company struck up a
collaboration with Kim to fashion the
group's flexible semiconducting films into
something that could be worn over long
periods of time.
Engineers have developed a sweat-proof " electronic skin " - a conformable, sensor-embedded sticky
patch that reliably monitors a person's health, even when a wearer is perspiring. The patch contains
artificial sweat ducts through the material's ultrathin layers, pictured. (Credit: Felice Frankel)
PI
Top PI layer
Au
Bottom PI layer
Sensor array
PDMS
PDMS adhesive
(40:1 ratio)
Schematic illustration of perforated e-skins. (Credit: MIT)
42
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But the team soon came against a barrier
that other e-skin designs have yet to
clear: sweat. Most experimental designs
embed sensors in sticky, polymer-based
materials that are not very breathable.
Other designs, made from woven nano -
fibers, can let air through, but not sweat.
If an e-skin were to work over the longterm,
Kim realized it would have to be
permeable not only to vapor but also to
sweat.
" Sweat can accumulate between the eskin
and your skin, which could cause skin
damage and sensor malfunctioning, " Kim
says. " So we tried to address these two
problems at the same time, by allowing
sweat to permeate through electronic
skin. "
■ Making the Cut
For design inspiration, the re searchers
looked to human sweat pores. They found
that the diameter of the average pore
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Medical Design Briefs - August 2021

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