The first wearable device for simultaneous monitoring of cardiovascular signals and biochemical levels

Engineers at the University of California, San Diego wear a soft, stretchy skin patch that can be worn around the neck to continuously track blood pressure and heart rate while measuring the wearer’s glucose, lactic acid, alcohol, and caffeine levels. Developed. This is the first wearable device to monitor the human body’s cardiovascular signals and multiple biochemical levels simultaneously.

“This type of wearable is very helpful for people with underlying illnesses to regularly monitor their health,” said Lu Yin, Ph.D. in nanoengineering.A student at the University of California, San Diego, and co-lead author of a study published on February 15. Nature Biomedical Engineering.. “It will also serve as a great tool for remote patient monitoring, especially during the COVID-19 pandemic where people minimize direct visits to the clinic.”

Such devices may benefit individuals who manage hypertension and diabetes-; also individuals at high risk of becoming seriously ill with COVID-19. It can also be used to detect the development of sepsis, which is characterized by a sudden drop in blood pressure accompanied by a sharp rise in lactate levels.

One soft skin patch that can do it all is also a convenient alternative for patients in the intensive care unit, including NICU babies who require continuous monitoring of blood pressure and other vital signs. These procedures currently involve inserting a catheter deep into the patient’s arteries to connect the patient to multiple hospital monitors.

The novelty here is to use completely different sensors and merge them into a single small platform as small as a stamp. This wearable allows you to collect a lot of information in a non-invasive way without causing discomfort or interruption in your daily activities. “

Joseph Wang, Professor of Nanoengineering at the University of California, San Diego, and co-author of Study

The new patch is the result of two pioneering efforts at the UC San Diego Wearable Sensor Center, directed by Wang. Wang’s lab is developing wearables that can simultaneously monitor multiple signals (chemical, physical, electrophysiological) in the body. In Sheng Xu’s lab, a professor of nanoengineering at the University of California, San Diego, researchers are developing soft, stretchy electronic skin patches that can monitor deep blood pressure in the body. Together, the researchers have created the first flexible, stretchable wearable device that combines chemical sensing (glucose, lactate, alcohol, caffeine) with blood pressure monitoring.

“Each sensor provides a separate image of physical or chemical changes. By integrating them all into one wearable patch, you can stitch these different images together to better than what’s happening in your body. You can get a comprehensive overview, “said Xu. Co-author of research.

Patches for all transactions

A patch is a thin sheet of stretchable polymer that can adapt to the skin. It is equipped with a blood pressure sensor and two chemical sensors. One measures the levels of lactic acid (a biomarker of physical activity), caffeine, and alcohol in sweat, and the other measures the glucose levels of interstitial fluid.

The patch can measure three parameters at once: blood pressure, glucose, lactic acid, alcohol and caffeine. “Theoretically, we could detect them all at the same time, but that would require a different sensor design,” said Yin, who holds a PhD. A student in the King’s lab.

The blood pressure sensor is near the center of the patch. It consists of a series of small ultrasonic transducers welded to the patch with conductive ink. When a voltage is applied to the transducer, the transducer sends ultrasonic waves into the body. When the ultrasound bounces off the arteries, the sensor detects the echo and converts the signal into a blood pressure measurement.

Chemical sensors are two electrodes that are screen-printed on a patch from conductive ink. Electrodes that detect lactic acid, caffeine, and alcohol are printed on the right side of the patch. It works by releasing a drug called pilocarpine into the skin to induce sweat and detect the chemicals contained in the sweat. The other electrode that senses glucose is printed on the left. It works by passing a gentle electric current through the skin to release interstitial fluid and measuring the glucose in the fluid.

Researchers were interested in measuring these specific biomarkers because they affect blood pressure. “We have selected parameters that enable more accurate and reliable blood pressure measurements,” said Juliane Sempionatto, co-lead author with a PhD in nanoengineering. A student in the King’s lab.

“Suppose you’re monitoring your blood pressure and you see spikes during the day and you think something is wrong. But biomarker readings tell you if these spikes are due to alcohol or caffeine intake. With this combination of sensors, you have that kind of information, “she said.

In the test, subjects wore patches around their necks while performing various combinations of the following tasks: Exercise on an exercise bike. Eat a high-sugar diet. Drink alcoholic beverages; drink caffeinated drinks. The readings from the patch were in close agreement with those collected by commercially available monitoring devices such as blood pressure cuffs, blood lactate meters, glucose meters, and drinking detectors. Caffeine level measurements in the wearer were validated with caffeine-spiked lab sweat sample measurements.

Engineering challenges

One of the biggest challenges in creating patches was eliminating interference between sensor signals. To do this, researchers needed to understand the optimal spacing between blood pressure and chemical sensors. They found that they worked well at 1-centimeter intervals, keeping the device as small as possible.

Researchers also needed to understand how to physically protect chemical sensors from blood pressure sensors. The latter is usually equipped with a liquid ultrasonic gel to produce clear readings. However, the chemical sensor is also equipped with its own hydrogel, and if the liquid gel from the blood pressure sensor flows out and comes into contact with other gels, there is a problem that interference between the sensors occurs. Instead, the researchers used solid ultrasonic gels. It works like the liquid version, but I found it leak-free.

“Finding the right materials, optimizing the overall layout, and seamlessly integrating different electronics. It took a lot of time to overcome these challenges,” said co-lead author Nano. Muyang Lin, who holds a PhD in engineering, said. A student in Xu’s lab. “We are fortunate to have this wonderful collaboration between our lab and Professor Wang’s lab. It was a lot of fun to work with them on this project.”

Next step

The team is already working on a new version of the patch and has more sensors. “We have the opportunity to monitor other biomarkers associated with a variety of diseases. We aim to add more clinical value to this device,” says Sempionatto.

Work in progress also includes shrinking the blood pressure sensor electronics. At this time, you need to connect the sensor to the power supply and the benchtop machine to display the readings. The ultimate goal is to apply all of this to the patch and make it all wireless.

“I want to create a completely wearable system,” Lin said.