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Electronic Materials

Video: Breathable electronics could monitor our health long-term

Simple method makes conductive materials that stand up to sweat

by Tien Nguyen, special to C&EN
June 2, 2020

Credit: Tien Nguyen/ACS Nano/C&EN

Wearable electronics face a constant foe: sweat. To help sweat escape and reduce skin irritation caused by wearing devices for long periods, researchers have designed electrodes from porous materials, but they’re not always cheap and easy to make. Now, a team of scientists at the Institute of Advanced Materials and North Carolina State University have developed porous silver nanowire-based electrodes using a simple and cost-effective method (ACS Nano 2020, DOI: 10.1021/acsnano.0c00906). These ultrathin electrodes could be used to monitor health or even adapted into touch sensors for a game of Tetris.

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The following is the script for the video.

Tien Nguyen: This researcher looks like they’re putting on a temporary tattoo, but they’re actually applying an ultrathin electrode. Laced with conductive silver nanowires, this ultrathin electrode can be used to monitor heart signals or even play a game of Tetris.

Wearable electronics are in high demand for fitness tracking and virtual reality applications. In fact, the market for the devices is projected to hit almost $100 billion in sales by 2023. Most existing wearable electrodes use solid polymer scaffolds. But these solid materials aren’t completely breathable: they can trap sweat and irritate skin.

To make more breathable sensors, researchers have developed more porous materials but their fabrication requires complicated techniques like electrospinning.

Now, a team of scientists have developed a new, porous electrode that can be made using a cheap and simple method called the breath figure method. The process starts with spreading a thin layer of thermoplastic polyurethane dissolved in organic solvent on a glass surface. This layer is placed inside a high humidity chamber where water droplets form and deposit. These droplets push aside the polymer solution and then evaporate to leave behind pores. Finally, the film is dipped into a silver nanowire solution and heat-pressed under high pressure. This last step embeds the nanowires into the polymer, which is key for the film’s overall stability.

To test whether the electrodes really are breathable, the team soaked the material in saline solution to simulate sweat and found that after 100 hours it was still conductive with only a small change in resistance. To test how comfortable it was, lead author Weixin Zhou wore the electrode for an entire week and observed no skin irritation.

The team measured heart and nerve electrical signals from volunteers in the lab and found that the electrodes performed comparably to commercial gel devices.

Finally, the researchers turned their electrode into a touch sensor paired with a battery and a Bluetooth controller. With real-time responsiveness, the electrode let them play a game of Tetris by barely lifting a finger.

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