Engineers get under the skin of ionic skin

Date:
April 28, 2022
Source:
University of British Columbia
Summary:
In the quest to build smart skin that mimics the sensing
capabilities of natural skin, ionic skins have shown significant
advantages. They're made of flexible, biocompatible hydrogels that
use ions to carry an electrical charge. These hydrogels can generate
voltages when touched, but scientists did not clearly understand
how -- until a team of researchers devised a unique experiment.



FULL STORY ==========================================================================
In the quest to build smart skin that mimics the sensing capabilities
of natural skin, ionic skins have shown significant advantages. They're
made of flexible, biocompatible hydrogels that use ions to carry an
electrical charge.

In contrast to smart skins made of plastics and metals, the hydrogels
have the softness of natural skin. This offers a more natural feel to
the prosthetic arm or robot hand they are mounted on, and makes them comfortable to wear.


========================================================================== These hydrogels can generate voltages when touched, but scientists did
not clearly understand how -- until a team of researchers at UBC devised
a unique experiment, published today in Science.

"How hydrogel sensors work is they produce voltages and currents in
reaction to stimuli, such as pressure or touch -- what we are calling
a piezoionic effect.

But we didn't know exactly how these voltages are produced," said the
study's lead author Yuta Dobashi, who started the work as part of his
master's in biomedical engineering at UBC.

Working under the supervision of UBC researcher Dr. John Madden, Dobashi devised hydrogel sensors containing salts with positive and negative
ions of different sizes. He and collaborators in UBC's physics and
chemistry departments applied magnetic fields to track precisely how
the ions moved when pressure was applied to the sensor.

"When pressure is applied to the gel, that pressure spreads out
the ions in the liquid at different speeds, creating an electrical
signal. Positive ions, which tend to be smaller, move faster than
larger, negative ions. This results in an uneven ion distribution which
creates an electric field, which is what makes a piezoionic sensor work."
The researchers say this new knowledge confirms that hydrogels work in a similar way to how humans detect pressure, which is also through moving
ions in response to pressure, inspiring potential new applications for
ionic skins.



==========================================================================
"The obvious application is creating sensors that interact directly
with cells and the nervous system, since the voltages, currents and
response times are like those across cell membranes," says Dr. Madden,
an electrical and computer engineering professor in UBC's faculty of
applied science. "When we connect our sensor to a nerve, it produces a
signal in the nerve. The nerve, in turn, activates muscle contraction."
"You can imagine a prosthetic arm covered in an ionic skin. The skin
senses an object through touch or pressure, conveys that information
through the nerves to the brain, and the brain then activates the
motors required to lift or hold the object. With further development
of the sensor skin and interfaces with nerves, this bionic interface
is conceivable." Another application is a soft hydrogel sensor worn on
the skin that can monitor a patient's vital signs while being totally unobtrusive and generating its own power.

Dobashi, who's currently completing his PhD work at the University
of Toronto, is keen to continue working on ionic technologies after
he graduates.

"We can imagine a future where jelly-like 'iontronics' are used for body implants. Artificial joints can be implanted, without fear of rejection
inside the human body. Ionic devices can be used as part of artificial
knee cartilage, adding a smart sensing element. A piezoionic gel implant
might release drugs based on how much pressure it senses, for example."
Dr. Madden added that the market for smart skins is estimated at $4.5
billion in 2019 and it continues to grow. "Smart skins can be integrated
into clothing or placed directly on the skin, and ionic skins are one of
the technologies that can further that growth." The research includes contributions from UBC chemistry PhD graduate Yael Petel and Carl Michal,
UBC professor of physics, who used the interaction between strong magnetic fields and the nuclear spins of ions to track ion movements within the hydrogels. Ce'dric Plesse, Giao Nguyen and Fre'de'ric Vidal at CY Cergy
Paris University in France helped develop a new theory on how the charge
and voltage are generated in the hydrogels.


========================================================================== Story Source: Materials provided by University_of_British_Columbia. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yuta Dobashi, Dickson Yao, Yael Petel, Tan Ngoc Nguyen, Mirza Saquib
Sarwar, Yacine Thabet, Cliff L. W. Ng, Ettore Scabeni Glitz, Giao
Tran Minh Nguyen, Ce'dric Plesse, Fre'de'ric Vidal, Carl A. Michal,
John D. W.

Madden. Piezoionic mechanoreceptors: Force-induced current
generation in hydrogels. Science, 2022; 376 (6592): 502 DOI:
10.1126/science.aaw1974 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220428142837.htm

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