Utah Dobashi, a graduate of UBC’s master’s program in biomedical engineering, and faculty advisor to Dr. John Madden, professor of electrical engineering and computer engineering at UBC’s Faculty of Applied Sciences. Credit: Kai Jacobson / UBC Faculty of Applied Sciences

Ionic skins have demonstrated significant benefits in efforts to create intelligent skin that matches the sensory capabilities of real skin. They consist of biocompatible, flexible hydrogels that use ions to transport an electric charge. Unlike smart leathers made of plastic and metals, hydrogels are as soft as real leather. This provides a more natural feel to the prosthesis or robot arm on which they are mounted and makes them comfortable to wear.

These hydrogels can generate touch voltage, but scientists have not figured out how – until a team of researchers from the University of British Columbia (UBC) came up with a unique experiment, published on April 28, 2022 in the journal science.

“How hydrogel sensors work, they produce voltages and currents in response to stimuli such as pressure or touch – what we call piezoionic effect. But we didn’t know exactly how these stresses were produced, “said study lead author Utah Dobashi, who began work as part of his master’s degree in biomedical engineering at UBC.

Utah Dobashi

The study’s lead author, Utah Dobashi, began work as part of his master’s degree in biomedical engineering at UBC. Credit: Photo by Kai Jacobson / UBC Faculty of Applied Sciences

Working under the supervision of UBC researcher Dr. John Madden, Dobashi created hydrogel sensors containing salts with positive and negative ions of various sizes. He and UBC’s physics and chemistry staff apply magnetic fields to track exactly how ions move when pressure is applied to the sensor.

“When pressure is applied to the gel, this pressure disperses the ions in the liquid at different speeds, creating an electrical signal. Positive ions, which are usually smaller, move faster than larger negative ions. This results in an uneven distribution of ions, which creates an electric field that causes the piezo ion sensor to operate. “

Researchers say this new knowledge confirms that hydrogels work in a similar way to the way humans detect pressure, which is also through moving ions in response to pressure, inspiring potential new applications for ionic skins.

Hydrogels with jelly ions

Researchers use a jelly dessert to demonstrate how ions move in hydrogels. Credit: Photo by Kai Jacobson / UBC Faculty of Applied Sciences

“The obvious application is to create sensors that interact directly with cells and the nervous system, because the voltages, currents and response times are similar to those in cell membranes,” said Dr. Madden, a professor of electrical and computer engineering at the Faculty of Applied Sciences. sciences at UBC. “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 prosthesis on the arm covered with ionic skin. The skin senses an object by touch or pressure, transmits this information through the nerves to the brain, and then the brain activates the motors needed to lift or hold the object. With the further development of sensory skin and nerve interfaces, this bionic interface is possible. “

Another application is a soft hydrogel sensor that is worn on the skin, which can monitor the patient’s vital signs, while being completely unobtrusive and generating its own power.

Dobashi, who is currently completing his doctorate at the University of Toronto, wants to continue working in ion technology after graduation.

“We can imagine a future in which 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 the artificial cartilage of the knee, adding a smart sensor element. A piezoionic gel implant can release drugs based on how much pressure it feels, for example.

Dr Madden added that the smart leather market is valued at $ 4.5 billion in 2019 and 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 contribute to this growth.”

Reference: Piezoionic Mechanoreceptors: Force-Induced Current Generation in Hydrogels by Utah Dobashi, Dixon Yao, Yael Petel, Tan Ngoc Nguyen, Mirza Sakib Sarwar, Yassin Tabet, Cliff L.V. Ng, Ettore Scabeni Glitz, Nguy Pleen S., Frédéric Vidal, Carl A. Michal and John DW Madden, 28 April 2022, science.
DOI: 10.1126 / science.aaw1974

The study, published in science, includes contributions from UBC PhD student in chemistry Jael Petel and Carl Michal, a professor of physics at UBC, who used the interaction between strong magnetic fields and nuclear ion rotations to track ion movements in hydrogels. Cédric Plesse, Giao Nguyen and Frédéric Vidal of CY Cergy Paris University in France helped develop a new theory of how charge and voltage are generated in hydrogels.

Ionic Skin: Engineering Smart Skin That Mimics the Sensing Capabilities of Natural Skin

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