Juliane R. Sempionatto

Could This Sensitive Patch be a Key to Precision Medicine?

Next-generation wearable sensors will combine biochemical and physiological metrics.

Though new developments are announced almost daily, wearable sensors promising to customize medicine by constantly monitoring people’s vital signs as they go about their daily routines have yet to fully hit their stride. That could finally change with the efforts of a group of researchers from the University of California, San Diego led by Nanoengineering professor Joseph Wang. Thanks to their work, health professionals who aspire to tailor treatment to a person based on their vital data—not just heart rate, but cholesterol levels, glucose, caffeine, lactates, erythrocytes, white blood cell counts, and blood pressure—could soon have access to an all-in-one patch capable of collecting and conveying these signals in real time. 

“We can establish correlations between your daily activities, seeing if your blood pressure goes up or down when you’re drinking alcohol, a cup of coffee, doing exercise or when you’re eating a meal,” says Lu Yin, the co-author of a new study describing the wearable device. “This patch will allow us to study your body’s response to these activities more closely and in real time. Observing how the dynamics of biochemical and biophysical data correlate to each other, we can not only understand how people react to what they eat and to environmental conditions but also become aware of subclinical manifestations which may lead to an eventual disease.” Because it can be worn on the wrist or the neck and can potentially communicate wirelessly with off-the-shelf digital devices, like smart watches and laptops Yin says, the device promises to have applications in other fields, like sport and entertainment, for monitoring athletic performance and fatigue.

Professor Wang’s research in wearables began in 2016. That year, his laboratory introduced a proof-of-concept wearable array, dubbed Chem-Phys, to detect biometric information. It demonstrated that packing several bulky sensors onto one miniaturized patch without having the signals interfere is possible. But while the idea seemed sound in 2016, the engineering wasn’t there yet for scale-up. 

“This is the first time that biometric and biological sensors are packed on the same patch.”

Recently, however, Wang and his team advanced the technology further by developing a skin-like wearable patch, which is both pliable and elastic and can monitor cardiovascular signals and multiple biochemical metrics like lactate, glucose, and alcohol in the body at the same time. “This is the first time that biometric and biological sensors are packed on the same patch,” Yin says. 

To design a functional patch that actually works required resolving several technical problems, chief among them the issue of cross talk among biodynamic sensors such as heart rate and blood pressure monitors with biochemical sensors for glucose, alcohol, caffeine, and lactate. To combine rigid ultrasonic transducers with electrochemical sensors, they were using a liquid ultrasound gel. But if the gel leaked and met other sensors, it caused interference. So they used a solid ultrasound gel that performs well but does not generate electromagnetic interference. They also had to calculate the optimal distance between the blood pressure sensor and the chemical sensors. They found that 1 cm of spacing was enough to prevent signal leakage while still keeping the device small enough to wear comfortably. 

Tensile pliability and stability were another two issues to resolve. Once applied to a subject’s epidermis, the chemical sensor’s impedance and the the contact resistance of the ultrasonic transducers could be affected by torsion and pressure, which normal body movement can produce through bending and flexing. 

They overcame this obstacle by mounting and gluing the ultrasonic transducers on a plastic substrate while wetting the surfaces of the printed electrodes with toluene, an industrial solvent. “This has meant that stretching and other deformations do not affect the form of the waves recorded by the ultrasound transducer,” Lin says.

“These systems will allow a physician to monitor patients’ vitals closely, pretty much as a mechanic does today with a car from its dashboard.”

During the test, the subjects wore the patch on their necks while performing various tasks in sequence, including eating a sugary meal, riding a stationary bike, and drinking alcoholic and caffeinated beverages. The patch produced measurements that clearly matched those obtained with traditional monitoring devices such as a breathalyzer, a blood pressure cuff, a blood lactate meter, and a glucometer. Laboratory analyses of the subjects’ sweat were instead used to confirm the levels of caffeine measured by the sensor.

“There’s no doubt that biosensors like those of UC San Diego will advance telemedicine and prevention,” observes Michael Snyder, director of the Stanford Center for Genomics and Personalized Medicine, who was not involved in the research. “These systems will allow a physician to monitor patients’ vitals closely, pretty much as a mechanic does today with a car from its dashboard.”

He added, however, that problems of signal resolution and functionality, such as wearability and cumbersomeness, still hamper their use in non-institutional settings. This patch is still a long way from being as elegant and wearable as an Apple Watch or an Oura ring. Even so, Snyder believes that Chem-Phys or something like it will become a single biometric device people will wear to stream all sorts of real-time remote feedback on the state of their health to their physicians, to the flight deck, or ultimately to their trainers, personal chefs, and therapists. But the first goal is to allow doctors to discover and prevent adverse events earlier, improving the health of their patients and saving lives. 

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