Medical Design Briefs - April 2021 - 34

Silicone Membrane for Wearable Devices Is Comfortable
and Breathable
The membrane wicks
water away from the skin.
KAIST,
Daejon, Republic of Korea
A silicone membrane for wearable
devices is more comfortable and breathable thanks to better-sized pores made
with the help of citric acid crystals. The
new preparation technique fabricates
thin, silicone-based patches that rapidly
wick water away from the skin. The technique could reduce the redness and
itching caused by wearable biosensors
that trap sweat beneath them. The technique was developed by bioengineer and
professor Young-Ho Cho and his colleagues at KAIST and reported in the
journal Scientific Reports.
" Wearable bioelectronics are becoming
more attractive for the day-to-day monitoring of biological compounds found in
sweat, like hormones or glucose, as well as
body temperature, heart rate, and energy
expenditure, " Prof. Cho explains. " But
currently available materials can cause
skin irritation, so scientists are looking for
ways to improve them, " he adds.
Attachable biosensors often use a silicone-based compound called polydimethylsiloxane (PDMS), because it has a
relatively high water vapor transmission
rate compared with other materials.
Still, this rate is only two-thirds that of
skin's water evaporation rate, meaning
sweat still gets trapped underneath it.
Current fabrication approaches mix
PDMS with beads or solutes, such as sugars or salts, and then remove them to
leave pores in their place. Another technique uses gas to form pores in the material. Each technique has its disadvantages, from being expensive and complex to leaving pores of different sizes.
A team of researchers led by Cho from
the KAIST department of bio and brain
engineering was able to form small, uniform pores by crystallizing citric acid in
PDMS and then removing the crystals
using ethanol. The approach is significantly less costly than using beads and
leads to 93.2 percent smaller and 425
percent more uniformly sized pores compared to using sugar. Importantly, the
membrane transmits water vapor 2.2
times faster than human skin.

Polymer, Toluene,
Citric acid, and
Ethanol mixture

(a) Preparing mixture

(b) Evaporating Toluene
and Ethanol
(c)

Crystalized
citric acid
Polymer
(c) Crystalizing citric acid
in polymer

(d) Molding of polymer
and citric acid mixture
Ethanol
Porous
polymer

(e) Dissolving citric acid

(f) Porous polymer

Smaller, more uniformly sized pores are made in the PDMS membrane by mixing PDMS, toluene,
citric acid, and ethanol. Toluene dilutes PDMS so that it can easily mix with the other two constituents. Toluene and ethanol are then evaporated, which causes the citric acid to crystallize within
the PDMS material. The mixture is placed in a mold where it solidifies into a thin film. The crystals
are then removed using ethanol, leaving pores in their place. (Credit: Prof. Young-Ho Cho, KAIST)

The team tested their membrane on
human skin for seven days and found
that it caused only minor redness and no
itching, whereas a non-porous PDMS
membrane did.
" Our method could be used to fabricate porous PDMS membranes for skinattachable devices used for daily monitoring of physiological signals, " says Cho.

34

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ToC

" We next plan to modify our membrane so it can be more readily attached
to and removed from skin, " he adds.
This work was supported by the
Ministry of Trade, Industry, and Energy
(MOTIE) of Korea under the Alchemist
Project.
For more information, visit https://
news.kaist.ac.kr.
Medical Design Briefs, April 2021


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Medical Design Briefs - April 2021

Table of Contents for the Digital Edition of Medical Design Briefs - April 2021

Medical Design Briefs - April 2021 - Intro
Medical Design Briefs - April 2021 - Cov4
Medical Design Briefs - April 2021 - Cov1a
Medical Design Briefs - April 2021 - Cov1b
Medical Design Briefs - April 2021 - Cov1
Medical Design Briefs - April 2021 - Cov2
Medical Design Briefs - April 2021 - 1
Medical Design Briefs - April 2021 - 2
Medical Design Briefs - April 2021 - 3
Medical Design Briefs - April 2021 - 4
Medical Design Briefs - April 2021 - 5
Medical Design Briefs - April 2021 - 6
Medical Design Briefs - April 2021 - 7
Medical Design Briefs - April 2021 - 8
Medical Design Briefs - April 2021 - 9
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Medical Design Briefs - April 2021 - 14
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Medical Design Briefs - April 2021 - 33
Medical Design Briefs - April 2021 - 34
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Medical Design Briefs - April 2021 - 42
Medical Design Briefs - April 2021 - Cov3
Medical Design Briefs - April 2021 - Cov4
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