Medical Design Briefs - August 2021 - 43

measures about 100 µm, and that pores
are randomly distributed throughout skin.
They ran some initial simulations to see
how they might overlay and arrange artificial
pores, in a way that would not block
actual pores in human skin.
" Our simple idea is, if we provide artificial
sweat ducts in electronic skin and
make highly permeable paths for the
sweat, we may achieve long-term monitor -
ability, " Yeon explains.
They started with a periodic pattern of
holes, each about the size of an actual
sweat pore. They found that if pores were
spaced close together, at a distance smaller
than an average pore's diameter, the
pattern as a whole would efficiently permeate
sweat. But they also found that if
this simple hole pattern were etched
through a thin film, the film was not very
stretchable, and it broke easily when
applied to skin.
The researchers found they could
increase the strength and flexibility of
the hole pattern by cutting thin channels
between each hole, creating a pattern
of repeating dumbbells, rather
than simple holes, that relaxed strain,
rather than concentrating it in one
place. This pattern, when etched into a
material, created a stretchable effect,
similar to kirigami.
" If you wrap a piece of paper over a
ball, it's not conformable, " Kim says.
" But if you cut a kirigami pattern in the
paper, it could conform. So we thought,
why not connect the holes with a cut, to
have kirigami-like conformability on
the skin? At the same time, we can permeate
sweat. "
Following this rationale, the team fabricated
an electronic skin from multiple
functional layers, each of which they
etched with dumbbell-patterned pores.
The skin's layers comprise an ultrathin
semiconductor-patterned array of sensors
to monitor temperature, hydration,
ultraviolet exposure, and mechanical
strain. This sensor array is sandwiched
between two thin protective films, all of
which overlays a sticky polymer adhesive.
Perforated e-skin
Conventional e-skin
Perforated Conventional
Perforated
Conventional
The researchers tested the e-skin by sticking it to a volunteer's wrist and forehead for a week. The
volunteer wore the tape during sweat-inducing activities, such as running on a treadmill for 30 minutes
and consuming a spicy meal, pictured. (Credit: Video still courtesy of the researchers)
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Medical Design Briefs - August 2021

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