New skin patch brings us closer to portable, all-in-one health monitor

Engineers at the University of California, San Diego have developed a soft, stretchy skin patch that can be worn on the neck to continuously monitor blood pressure and heart rate while measuring the wearer’s glucose levels as well as lactate, alcohol or caffeine. It is the first portable device that monitors cardiovascular signals and multiple biochemical levels in the human body at the same time.

“This type of laptop would be very useful for people with underlying medical conditions to monitor their own health on a regular basis,” said Lu Yin, a PhD in nanotechnology. UC San Diego student and co-first author of the study published Feb.15 in Biomedical engineering of nature. “It would also be a great tool for remote monitoring of patients, especially during the COVID-19 pandemic when people minimize in-person clinic visits.

Such a device could benefit people with high blood pressure and diabetes – people who are also at high risk of becoming seriously ill with COVID-19. It could also be used to detect the onset of sepsis, which is characterized by a sharp drop in blood pressure accompanied by a rapid rise in lactate levels.

A soft skin patch that can do it all would also offer a convenient alternative for ICU patients, including NICU infants, who need continuous monitoring of blood pressure and other vital signs. These procedures currently involve inserting catheters deep into patients’ arteries and attaching patients to multiple hospital monitors.

“The novelty here is that we take completely different sensors and merge them onto a single little platform as small as a stamp,” said Joseph Wang, UC San Diego professor of nanotechnology and co-author. correspondent of the study. “We can collect so much information with this laptop and do it non-invasively, without causing discomfort or disruption to daily activity.”

The new patch is the product of two pioneering efforts at the UC San Diego Center for Wearable Sensors, of which Wang is a director. Wang’s lab has developed wearable devices that can simultaneously monitor multiple signals – chemical, physical, and electrophysiological – in the body. And in UC San Diego’s nanoengineering professor Sheng Xu’s lab, researchers have developed soft, stretchy electronic skin patches that can monitor blood pressure deep within the body. By joining forces, researchers created the first flexible and expandable portable device that combines chemical detection (glucose, lactate, alcohol and caffeine) with blood pressure monitoring.

“Each sensor provides a distinct image of a physical or chemical change. Incorporating them all into one wearable patch allows us to put these different images together to get a more complete picture of what’s going on in our bodies, ”said Xu, who is also a co-author of the study.

Patch of all trades

The patch is a thin sheet of stretchable polymers that can conform to the skin. It’s equipped with a blood pressure sensor and two chemical sensors – one that measures levels of lactate (a biomarker of physical exertion), caffeine, and alcohol in sweat, and another that measures levels of glucose in the interstitial fluid.

The patch is capable of measuring three parameters at a time, one from each sensor: blood pressure, glucose and either lactate, alcohol or caffeine. “Theoretically, we can detect them all at the same time, but that would require a different sensor design,” said Yin, also a PhD holder. student in Wang’s lab.

The blood pressure sensor is located near the center of the patch. It consists of a set of small ultrasonic transducers which are soldered to the patch by conductive ink. A voltage applied to the transducers causes them to send ultrasonic waves through the body. When ultrasound waves bounce off an artery, the sensor detects the echoes and translates the signals into a blood pressure measurement.

The chemical sensors are two electrodes screen printed on the patch from conductive ink. The electrode which detects lactate, caffeine and alcohol is printed on the right side of the patch; it works by releasing a medicine called pilocarpine into the skin to induce sweating and detect chemicals in sweat. The other electrode, which detects glucose, is printed on the left side; it works by passing a small electric current through the skin to release interstitial fluid and measuring the glucose in that fluid.

The researchers wanted to measure these particular biomarkers because they have an impact on blood pressure. “We chose parameters that would allow us to measure blood pressure more accurately and more reliably,” said co-first author Juliane Sempionatto, who holds a doctorate in nanotechnology. student in Wang’s lab.

“Let’s say you’re monitoring your blood pressure, seeing spikes during the day, and you think something’s wrong. But a biomarker reading could tell you if those spikes were due to alcohol or caffeine consumption. This combination of sensors can give you that kind of information, ”she says.

Wearing the patch on the neck allows optimal reading.

In testing, subjects wore the patch on their necks while performing various combinations of the following tasks: exercising on a stationary bike; eat a meal high in sugar; drink an alcoholic drink; and drink a drink containing caffeine. The patch’s readings closely matched those collected by commercial monitoring devices such as a blood pressure cuff, glucometer, and breathalyzer. Carrier measurements of caffeine levels were verified with measurements of caffeine-spiked laboratory sweat samples.

Engineering challenges

One of the biggest challenges in creating the patch was to eliminate interference between the signals from the sensors. To do this, the researchers had to determine the optimal spacing between the blood pressure sensor and the chemical sensors. They found that an inch of spacing did the trick while keeping the device as small as possible.

The researchers also had to figure out how to physically protect the chemical sensors in the blood pressure sensor. The latter is normally fitted with a liquid ultrasonic gel in order to produce clear readings. But chemical sensors also come with their own hydrogels, and the problem is if a liquid gel from the blood pressure sensor leaks out and comes in contact with the other gels, it will cause interference between the sensors. Instead, the researchers used a solid ultrasound gel, which they said works just as well as the liquid version, but without leaking.

“Finding the right materials, optimizing the overall layout, integrating the different electronic components together seamlessly – these challenges have taken a long time to overcome,” said co-first author Muyang Lin, who holds a PhD in nano-engineering. student in Xu’s lab. “We are fortunate to have this excellent collaboration between our laboratory and Professor Wang’s laboratory. It was so much fun working with them on this project.

Next steps

The current prototype of the patch must be connected with cables to a benchtop machine and a power source.

The team is already working on a new version of the patch, one with even more sensors. “There are opportunities to monitor other biomarkers associated with various diseases. We are looking to add more clinical value to this device, ”Sempionatto said.

Work in progress also includes shrinking the electronics of the blood pressure sensor. Currently, the sensor must be connected to a power source and a benchtop machine to display its readings. The ultimate goal is to put all of that on the patch and make everything wireless.

“We want to create a complete, fully portable system,” Lin said.

Paper: “An epidermal patch for the simultaneous monitoring of hemodynamic and metabolic biomarkers. “

This research was supported by the Center for Wearable Sensors at UC San Diego and the National Institutes of Health (Grant # 1R21EB027303-01A1).

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