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This temporary tattoo can listen to your heart

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This new wearable is a stick-on stethoscope that’s smaller than a penny

Jeong Lab, University of Colorado Boulder

A new stick-on wearable sensor uses the symphony of internal rumblings, whooshing, gurglings, and cracklings to help doctors diagnose different conditions. And this souped-up, miniaturized stethoscope could one day be a way for clinicians to continuously monitor patients outside of the clinic. So far it’s been tested on chicken breasts and a very small group of people.

This wearable, smaller than a penny, can hear the beat of your heart, the sound of your voice, and even the whirr of an implantable heart pump, according to a paper published today in the journal Science Advances.

It sticks to the skin like a temporary tattoo. Inside the device, there’s an extremely sensitive accelerometer that can pick up the motion of sound waves as they travel through the flesh and fluids of the body. An electrode measures the electrical signals that nerves send to muscles to tell them to squeeze. These components lie sandwiched between layers of silicone and elastic that at their thickest point are only about two millimeters tall — about the thickness of your driver’s license stacked on top of your credit card. Right now, the device communicates with a computer via a wire, but the team is working on adding Bluetooth to connect it to a smartphone.

The device isn’t commercially available yet, but its potential applications include letting doctors monitor heart patients from afar, or listen for snoring during sleep studies. Because the wearable can also measure throat vibrations when a person is talking, the researchers are also planning trials that incorporate the wearable into speech therapy. Athletes or patients in physical therapy could use it to monitor blood flow and muscle contractions.

“This opens up a whole additional realm of measurement,” says John Rogers at the University of Illinois at Urbana Champaign. Rogers and Jae-Woong Jeong at the University of Colorado Boulder were senior authors on the study. “The skin is serving as the window for measurements of underlying body processes.” It can potentially expand clinical trials, which are often difficult and costly for patients to participate in. And for patients who live far from the closest specialist for their condition, it may be able to give them added peace of mind — their doctor is still checking in, just remotely.

Jeong Lab, University of Colorado Boulder

There are a couple advantages of a stick-on wearable over something like a Fitbit, says Howard Liu, a graduate student at the University of Illinois at Urbana Champaign and the lead scientist on the study. For one thing, the air gap between flesh and a Fitbit or another similar wearable makes it difficult to detect the simple beat of a pulse, let alone subtle body sounds or electrical signals. After all, when doctors measure the electrical activity of your heart with an electrocardiogram, they stick the electrodes to you — they don’t just drape them on your body. Plus, it’s flexible, stretchable, and lets sweat evaporate from underneath it, which means it’s more comfortable than a bulky bracelet.

Rogers’ team has been leading the way in developing wearable medical instruments, says George Malliaras, who is a professor of bioelectronics in France at the engineering graduate school MINES Saint-Etienne. (He wasn’t involved in the study.) “I was very happy when I read this work,” he says. “It advances the state of the art very much, and it allows us to monitor human health in a non-invasive fashion.”

Today’s paper was largely a description of the prototype device that still needs more testing in clinical settings. But the researchers did try it out in a couple of different applications. The first required a trip to the grocery store — since the experimental material was a chicken breast. Liu and his colleagues vibrated chopped up bits of chicken to test how well vibrations traveled through flesh. Malliaras, in the south of France, said this is actually standard for the field — though in France, “We use steak,” he says.

Courtesy of Jae-Woong Jeong

The researchers tried the device out on people, too, monitoring the heart sounds of eight elderly patients with heart conditions. The idea is that the wearable functions kind of like an autonomous stethoscope-electrocardiogram combo — monitoring the heart’s sounds and electrical activity. And in the future, the scientists think this device could also be used to keep tabs on internal devices like heart pumps that are hard to monitor because they’re out of sight. Liu and his colleagues weren’t able to test the wearable on heart pumps inside patients. But when they tested it on a pump outside of the body in the laboratory, the researchers could “hear” when a blood clot (made from cow’s blood) passed through it. “That’s a life supporting device,” Liu says. “If you don’t know whether that’s failing, then your life is in danger every second.”

The team also used the device to communicate with a computer and control a PacMan running around the screen by using the commands “Left,” “Right,” and “Up.” Rogers anticipates the criticism that any old microphone and voice-recognition software can do that, too. But because this wearable detects throat vibrations rather than spoken words, it’s immune to ambient noise, he says. That means it could be used as a way for security teams to quietly communicate with each other in noisy environments.

Liu says he and his colleagues might consider a spinoff company, but the wearable isn’t commercially available yet — and it’ll need a lot more testing and approval before anyone can sell it as a medical device. But when that time comes, there’s another, major advantage to a wearable that attaches to your skin: it will be a lot harder than a Fitbit to forget on the bathroom counter every single day.