Medical Design Briefs - June 2021 - 22

Cohesive Circuit Protection for Wearable Electronics
The cellulose nanofiber
coating counters bending
damage and retains
electrode function under
water.
Osaka University
Osaka, Japan
No
Most electronic devices aren't waterproof,
much to your irritation if a sprinkler
suddenly sprays you while you're talking
outside on your cellphone. Some electronics
can be made at least water-resistant
by, for example, using special glues to fuse
outer components together. Flexible electronics
are another story. Their sealant
materials must be able to bend, yet with
current technology it's inevitable that
eventually such a sealant will crack or separate
from the device - and there goes
your water-resistant coating.
Researchers are determined to come
up with a solution. Cellulose nanofibers
are a proposed polymer coating for flexible
electronics. These fibers are made
from renewable resources and are environmentally
friendly. However, they usually
absorb water - commonly thought
to be a fatal limitation for imparting
water resistance.
In a study recently published in ACS
Applied Nanomaterials, researchers from
Osaka University developed self-healing
cellulose nanofibers that slightly disperse
in water and act to protect a copper
electrode, enabling the electrode to
function for an extended period. The
researchers' flexible circuit protection
mechanism retains electrode function
underwater and can undergo hundreds
of bending cycles.
" In our initial work, an unprotected
copper electrode failed after 5 minutes
of dripping water onto it, " says Takaaki
Kasuga, lead author. " Remarkably, a cellulose
nanofiber coating prevented failure
over at least a day of the same water
challenge. "
Why is this? Remember that cellulose
fibers don't repel water. Instead, this
polymer coating migrates in the electrode
in such a way to prevent formation
of conductive metal filaments that cause
short-circuits. The electrodes even maintained
their function after the cellulose
coating was scratched to simulate bending
damage.
22
Cov
Water
CNF coating
Shortcircuit
With
CNF coating /1 h
-
Electronic circuit
+
Shortcircuit
Without
coating /1 min
130 °C
100.0 °C
5 mm
10 °C
130 °C
23.9 °C
Conductive Line
(copper)
Substrate
5 mm
10 °C
Fig. 1 - Water is detrimental to electronic devices because it easily causes short circuits and accidents,
such as overheating/ignition. By coating electronic circuits with cellulose nanofibers (CNFs),
it is possible to prevent water-induced short circuits in a completely different approach compared
with conventional waterproofing coatings.
Conventional waterproof coating
+
-
+
Damaged
and
submerged
-
2 mm
Short-circuit in a short time
Damaged
and
submerged
-
2 mm
No Short-circuit even after 24 h
Fig. 2 - Water inevitably penetrates waterproof coatings if they are damaged, and water can easily
cause malfunctions due to dendrite growth. Cellulose nanofibers (CNFs) migrate toward the anode
and gel, thus inhibiting short circuits even if the CNF coating film is damaged.
" Our results aren't attributable to simple
ion-exchange or nanofiber length, "
explains Masaya Nogi, senior author.
" The nanofibers aggregate in water into
a protective layer made cohesive by
locally acidic conditions and polymer
cross-linking. "
A more rigorous test of the polymer
coating was its performance after 300
cycles of bending underwater over the
course of an hour. A conventional polymer
coating usually failed, but the cellulose
nanofibers continued to power LEDs.
" You'll be able to stretch, bend, and
fold electronics with our coating, and
they'll still retain their water resistance, "
says Kasuga. " This is critical for use in
applications under extreme conditions
www.medicaldesignbriefs.com
ToC
where device failure is unacceptable -
for example, medical devices used in
emergency disaster response. "
In preliminary work, even an ultrathin
polymer coating thickness of only 1.5
μm, and some other polymers, performed
similarly to the originally tested
setup. They'll become a staple of wearable
electronics, and perhaps even medical
devices, in the coming years.
The article, " Cellulose nanofiber coatings
on Cu electrodes for cohesive protection
against water-induced short-circuit
failures, " was published in ACS
Applied Nanomaterials at DOI: https://
doi.org/10.1021/acsanm.1c00267.
For more information, visit https://resou.
osaka-u.ac.jp.
Medical Design Briefs, June 2021
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+
+
CNF Coating
https://www.doi.org/10.1021/acsanm.1c00267 https://https://resou.osaka-u.ac.jp http://www.medicaldesignbriefs.com

Medical Design Briefs - June 2021

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

Medical Design Briefs - June 2021 - Intro
Medical Design Briefs - June 2021 - Cov4
Medical Design Briefs - June 2021 - Cov1a
Medical Design Briefs - June 2021 - Cov1b
Medical Design Briefs - June 2021 - Cov1
Medical Design Briefs - June 2021 - Cov2
Medical Design Briefs - June 2021 - 1
Medical Design Briefs - June 2021 - 2
Medical Design Briefs - June 2021 - 3
Medical Design Briefs - June 2021 - 4
Medical Design Briefs - June 2021 - 5
Medical Design Briefs - June 2021 - 6
Medical Design Briefs - June 2021 - 7
Medical Design Briefs - June 2021 - 8
Medical Design Briefs - June 2021 - 9
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Medical Design Briefs - June 2021 - 18
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Medical Design Briefs - June 2021 - 100
Medical Design Briefs - June 2021 - Cov3
Medical Design Briefs - June 2021 - CovIV
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