The breathable material from a team at North Carolina State University (NC State) provides comfort by allowing sweat and volatile organic compounds to evaporate away from the skin. Their findings are published in ACS Nano.
"The gas permeability is the big advance over earlier stretchable electronics," said Yong Zhu, co-corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at NC State. "But the method we used for creating the material is also important because it's a simple process that would be easy to scale up."
According to NC State, the researchers used the so-called breath figure method to create a stretchable polymer film featuring an even distribution of holes. The film is coated by dipping it in a solution containing silver nanowires. The material is then heat-pressed to seal the nanowires.
"The resulting film shows an excellent combination of electric conductivity, optical transmittance and water-vapour permeability," Zhu said in a statement. "And because the silver nanowires are embedded just below the surface of the polymer, the material also exhibits excellent stability in the presence of sweat and after long-term wear."
"The end result is extremely thin - only a few micrometres thick," said Shanshan Yao, co-author of the paper and a former postdoctoral researcher at NC State. "This allows for better contact with the skin, giving the electronics a better signal-to-noise ratio.
"And gas permeability of wearable electronics is important for more than just comfort," Yao added. "If a wearable device is not gas permeable, it can also cause skin irritation."
To demonstrate the material's potential for use in wearable electronics, the researchers developed and tested prototypes.
The first consisted of skin-mountable, dry electrodes for use as electrophysiologic sensors that have potential applications in measuring electrocardiography (ECG) and electromyography (EMG) signals.
The second gas permeable prototype demonstrated textile-integrated touch sensing for human-machine interfaces. The authors used a wearable textile sleeve integrated with the porous electrodes to play computer games such as Tetris.
"If we want to develop wearable sensors or user interfaces that can be worn for a significant period of time, we need gas-permeable electronic materials," Zhu said. "So this is a significant step forward."
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