This soft and elastic patch can monitor the user’s blood pressure and biochemical levels at the same time.
Engineers at the University of California at San Diego have developed a soft, elastic skin patch that can be used on the neck to continuously monitor blood pressure and heart rate while measuring the user’s glucose levels, as well as lactate, alcohol or caffeine. It is the first wearable device that monitors cardiovascular signals and various biochemical levels in the human body at the same time.
“This type of wearable would be very useful for people with underlying medical conditions to monitor their own health regularly,” said Lu Yin, a Ph.D. in nanoengineering. UC San Diego student and co-first author of the study published on February 15 in Nature Biomedical Engineering. “It would also serve as a great tool for remote patient monitoring, especially during the COVID-19 pandemic, when people are minimizing personal visits to the clinic.”
This device can benefit individuals who control hypertension and diabetes – individuals who are also at high risk of becoming seriously ill with COVID-19. It can also be used to detect the onset of sepsis, which is characterized by a sudden drop in blood pressure accompanied by a rapid increase in the level of lactate.
A soft skin patch that can do everything would also be a convenient alternative for patients in intensive care units, including babies in the NICU, who need continuous monitoring of blood pressure and other vital signs. Currently, these procedures involve inserting catheters into patients’ arteries and tying patients to multiple hospital monitors.
“The novelty here is that we take completely different sensors and merge them into a single small, stamp-sized platform,” said Joseph Wang, professor of nanoengineering at UC San Diego and corresponding co-author of the study. “We can collect so much information with this wearable and do it in a non-invasive way, without causing discomfort or interruptions in daily activities.”
The new patch is the product of two pioneering efforts at UC San Diego’s Wearable Sensor Center, of which Wang serves as director. Wang’s lab has developed wearables capable of monitoring multiple signals simultaneously – chemical, physical and electrophysiological – in the body. And in the laboratory of nanoengineering professor at the University of California, San Diego, Sheng Xu, the researchers developed soft, elastic electronic skin patches that can monitor blood pressure inside the body. By joining forces, the researchers created the first flexible and extensible wearable device that combines chemical detection (glucose, lactate, alcohol and caffeine) with blood pressure monitoring.
“Each sensor provides a separate image of a physical or chemical change. Integrating them all into a wearable patch allows us to sew these different images together to get a more comprehensive overview of what is happening in our bodies, ”said Xu, who is also a corresponding co-author on the study.
Patch of All Trades
The patch is a thin sheet of elastic polymers that adapt to the skin. It is equipped with a blood pressure sensor and two chemical sensors – one that measures lactate levels (a biomarker of physical effort), caffeine and alcohol in sweat and another that measures glucose levels in interstitial fluid.
The patch is capable of measuring three parameters at the same time, one for each sensor: blood pressure, glucose and lactate, alcohol or caffeine. “Theoretically, we can detect all of them at the same time, but that would require a different sensor design,” said Yin, who is also a Ph.D. student in Wang’s lab.
The blood pressure sensor is located near the center of the patch. It consists of a set of small ultrasound transducers that are welded to the patch by a conductive paint. A voltage applied to the transducers causes them to send ultrasound waves to the body. When the ultrasound waves reflect on an artery, the sensor detects echoes and translates the signals into a blood pressure reading.
The chemical sensors are two electrodes that are printed on canvas in the conductive paint patch. The electrode that detects lactate, caffeine and alcohol is printed on the right side of the sticker; it works by releasing a drug called pilocarpine into the skin to induce sweat and detect chemicals in sweat. The other electrode, which detects glucose, is printed on the left side; it works by passing a moderate electric current through the skin to release interstitial fluid and measure the glucose in that fluid.
The researchers were interested in measuring these specific biomarkers because they affect blood pressure. “We chose parameters that would give us a more accurate and reliable blood pressure measurement,” said co-author Juliane Sempionatto, Ph.D. in nanoengineering. student in Wang’s lab.
“Let’s say you are monitoring your blood pressure and see spikes during the day and think that something is wrong. But reading a biomarker can tell if these spikes were caused by drinking alcohol or caffeine. This combination of sensors can provide that kind of information, ”she said.
Wearing the patch on the neck provides an ideal reading.
In the tests, participants wore the patch on their neck while performing various combinations of the following tasks: exercise on an exercise bike; eat a meal rich in sugar; drinking an alcoholic beverage; and drink a caffeinated drink. The adhesive measurements are similar to those collected by commercial monitoring devices, such as a blood pressure meter, blood lactate meter, glucometer and breathalyzer. Measurements of users’ caffeine levels were verified with measurements of sweat samples in the laboratory enriched with caffeine.
Engineering Challenges
One of the biggest challenges when making the patch was to eliminate interference between the signals from the sensors. To do this, the researchers had to find the ideal spacing between the blood pressure sensor and the chemical sensors. They found that an inch of spacing resolved, keeping the device as small as possible.
The researchers also had to figure out how to physically protect the blood pressure sensor’s chemical sensors. The latter is usually equipped with a liquid ultrasound gel to produce clear readings. But the chemical sensors are also equipped with their own hydrogels, and the problem is that if any liquid gel from the pressure sensor comes 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 found to work as well as the liquid version, but without the leak.
“Finding the right materials, optimizing the overall layout, integrating the different electronics in a seamless way – these challenges took a long time to overcome,” said co-first author Muyang Lin, Ph.D. in nanoengineering. student in Xu’s lab. “We are fortunate to have this great collaboration between our laboratory and Professor Wang’s laboratory. It was so fun to work with them on this project. “
Next steps
The current prototype of the patch needs to be connected with cables to a bench machine and power supply.
The team is already working on a new version of the patch, with even more sensors. “There are opportunities to monitor other biomarkers associated with various diseases. We want to add more clinical value to this device ”, said Sempionatto.
The work in progress also includes the reduction of the electronic components of the blood pressure sensor. At the moment, the sensor needs to be connected to a power source and a bench machine to display its readings. The ultimate goal is to patch it all up and make everything wireless.
“We want to make a complete system that is fully usable,” said Lin.
Paper: “An epidermal patch for simultaneous monitoring of hemodynamic and metabolic biomarkers. “
This research was supported by the UC San Diego Wearable Sensor Center and the National Institutes of Health (grant # 1R21EB027303-01A1).
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