In high performance scenarios, your skin will sweat. The sticky pads of the electrodes rub off, compromising their biometric accuracy. And the metal-skin interface of your typical smartwatch, while impressive, can do a lot – often falling short on key data points, e.g. calorie content expenses. So how should anyone be the most the best (as no one has ever been) under these conditions?
An international team of scientists, including researchers from Penn State, MIT and China’s Suzhou Institute of Biomedical Engineering and Technology, happened to develop the answer: a safe and reliable polymer electrode that can be painted directly onto the skin. According to their new paper, published In Monday’s Proceedings of the National Academy of Sciences (PNAS), these “biocompatible” paintable electrode assemblies excel at tracking muscle activity, heart rate and brain waves, and pass numerous safety tests. In electrocardiogram (ECG) tests with a subject running on a treadmill, the electrodes actually achieved 95.1% consistency “before and after light sweating,” they write.
The researchers believe their design could be tweaked to form more permanent electrode “tattoos,” cyborg human-machine interfaces, and plant biometrics to help achieve agricultural goals. But they were excited about the paintable electrodes’ ability to make life easier for children who need long-term medical monitoring.
“For example, electrodes could be designed with cartoon patterns, which could reduce anxiety and improve acceptance among child users, making EP (electrophysiology) monitoring less intimidating,” they suggested in their study.
“Such personalization not only improves physiological comfort, but also increases social acceptance,” they noted. (I can think of several Electric-type Pokemon that would be particularly good for this.)
Fresh paint
Penn State mechanical engineering professor Huangyu Chen and his collaborators incorporated several complex compounds to make this ultra-flexible electrode paint with unique adhesion. The electrical conductivity of the material was achieved by using a material called poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) or PEDOT:PSS. Another additive, 4-dodecylbenzenesulfonic acid, or DBSA, did double duty as an electrically conductive additive and plasticizer, helping to make the finished product more flexible to the movements of the human body. Finally, a mixture of water, ethanol, and a soft plastic polymer known as polyvinyl alcohol (PVA) completed the recipe, which the team graciously shortened to WE-PPD (for “water-ethanol-PVA/PEDOT:PSS/DBSA”).
“Long-term use of skin electrodes relies on high water vapor permeability to increase body comfort and improve adhesion even in the presence of sweat, while minimizing skin irritation,” the team noted in their study.
Cheng and his colleagues tested the breathability of the paintable electrodes at two temperatures, 71.6 degrees Fahrenheit (22 degrees Celsius) and 98.6 degrees Fahrenheit (37 degrees Celsius), to see how easily water vapor could pass through them. The results compared to traditional Tegaderm medical film were impressive: WE-PPD was able to let through almost five times more water vapor at this milder temperature and more than ten times more at 98.6 degrees.
These electrodes were also able to “stretch up to ∼170% before failure,” the team reported, when combined with a porous silver fabric to connect them to biomonitoring devices.
Skin in the game
While the researchers documented “no adverse skin effects” after subjects wore the WE-PPD for a full 24 hours, they acknowledge that this and their modest set of toxicity tests are just the beginning of the safety mechanisms needed for real-world use of these electrodes.
One particular challenge, they noted, will be validating these dyed electrodes for multimodal magnetic resonance imaging (MRI), where the technology has passed preliminary MRI compatibility, but may cause unwanted side effects.
“Future studies should systematically investigate radio frequency (RF)-induced heating, specific absorption rate, and electromagnetic interactions under different MRI operating conditions and pulse sequences,” they noted. (In other words, the last thing you want is a super-sticky device that suddenly gets very hot and won’t come off.)
So the technology is promising, but it may be a while before you get to flaunt paint electrodes like Pikachu or Raichu.
