This soft, stretchy patch can monitor the wearer’s blood pressure and biochemical levels at the same time.
Engineers at the University of California, San Diego have developed a soft, stretchy skin stain that can be worn around the neck to constantly monitor blood pressure and heart rate while measuring the wearer’s glucose level, as well as lactate, alcohol or caffeine. It is the first portable device that monitors cardiovascular signals and multiple biochemical levels simultaneously.
“This type of wearable material will be very useful for people with underlying medical conditions to monitor their own health regularly,” said Lu Yin, a doctor of nano-engineering. student at UC San Diego and co-author of the study published on February 15 in Natural Biomedical Engineering. “It will also serve as an excellent tool for remote patient monitoring, especially during the COVID-19 pandemic when people restrict visits to the clinic.”
Such a device could benefit individuals with high blood pressure and diabetes – individuals who are also at 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 coupled with a rapid rise in lactate levels.
One soft skin patch that can do it all also provides a convenient alternative for patients in intensive care units, including infants in the NICU, who need to monitor continuous blood pressure and other vital signs. These procedures currently involve inserting catheters deep into the patient’s veins and tying patients on multiple hospital monitors.
“The novelty here is that we take completely different sensors and merge them on a single small platform as small as a seal,” said Joseph Wang, a professor of nano-engineering at UC San Diego and co-author of the study , said. “We can gather so much information with this portable and do it in a non-intrusive way, without causing discomfort or interruptions to daily activities.”
The new patch is a product of two groundbreaking efforts at the UC San Diego Center for Wearable Sensors, for which Wang serves as director. Wang’s laboratory has developed wearable clothing that is capable of monitoring multiple signals simultaneously – chemically, physically and electrophysiologically – in the body. And in the laboratory of San Diego professor of nano-engineering, Sheng Xu, researchers have developed soft, stretchy electronic skin patches that can monitor blood pressure deep in the body. By joining forces, the researchers created the first flexible, stretchable portable device that combines chemical observation (glucose, lactate, alcohol and caffeine) with blood pressure monitoring.
‘Each sensor provides a separate image of a physical or chemical change. By integrating them all into one wearable cloth, we can put the different pictures together to get a more comprehensive overview of what’s going on in our body, ” 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 adhere to the skin. It is 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 glucose levels in interstitial fluid.
The patch can measure three parameters at once, one from each sensor: blood pressure, glucose and lactate, alcohol or caffeine. “Theoretically, we can all detect at the same time, but that requires a different sensor design,” says Yin, who also holds a Ph.D. student in Wang’s laboratory.
The blood pressure sensor sits near the center of the patch. It consists of a set of small ultrasound transducers that are welded to the patch by a conductive ink. A voltage applied to the transducers causes them to send ultrasound waves to the body. When the ultrasound waves bounce off an artery, the sensor detects the echoes and translates the signals into a blood pressure reading.
The chemical sensors are two electrodes shielded with conductive ink on the patch. The electrode that 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 cause sweating and to detect the chemicals in the sweat. The other electrode, which detects glucose, is depressed on the left side; it works by passing a light electric current through the skin to release interstitial fluid and measure the glucose in the 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, reliable blood pressure measurement,” said co-author Juliane Sempionatto, a doctor of nano-engineering. student in Wang’s laboratory.
‘Suppose you keep an eye on your blood pressure, and you see nails during the day and think something is wrong. But a biomarker reading can tell you if the spikes were due to alcohol or caffeine intake. This combination of sensors can give you that kind of information, ”she said.
Wearing the patch on the neck provides an optimal reading.
In tests, subjects wore the patch on their necks while performing various combinations of the following tasks: exercising on a stationary bicycle; eat a high sugar meal; drink an alcoholic beverage; and drinking a caffeinated beverage. Measurements from the patch are similar to those collected by commercial monitoring devices such as blood pressure cuff, blood lactate meter, glucometer and respirator. The measurement of the caffeine levels of the carriers was verified with the measurement of sweat samples in the laboratory caffeinated.
Engineering challenges
One of the biggest challenges in making the patch was eliminating the interference between the sensors’ signals. To do this, the researchers had to find the optimal space between the blood pressure sensor and the chemical sensors. They found that a space of one centimeter did the thing while keeping the device as small as possible.
The researchers also had to figure out how to physically protect the chemical sensors from the blood pressure sensor. The latter is usually equipped with a liquid ultrasound gel to provide clear measurements. But the chemical sensors are also equipped with their own hydrogels, and the problem is that if any liquid gel flows out of the blood pressure sensor and makes contact with the other gels, it will cause interference between the sensors. Instead, the researchers used a solid ultrasound gel, which they said works as well as the liquid version, but without the leak.
“Finding the right materials, optimizing the overall layout, seamlessly integrating the various electronics – these challenges took a lot of time to overcome,” said co-author Muyang Lin, a doctor of nano-engineering. . student in Xu’s laboratory. ‘We are fortunate to have this wonderful collaboration between our laboratory and Professor Wang’s laboratory. It was so nice to work with them on this project. ”
Next steps
The current prototype of the patch should be connected with cables to a table machine and power supply.
The team is already working on a new version of the patch, one with even more sensors. ‘There are opportunities to monitor other biomarkers related to different diseases. We want to add more clinical value to this device, ”said Sempionatto.
Ongoing work also includes shrinkage of the electronics for the blood pressure sensor. At present, the sensor must be connected to a power source and a table machine to display its readings. The ultimate goal is to put it all on the rag and make everything wireless.
“We want to create a complete system that is fully portable,” Lin said.
Question paper: “An epidermal patch for the simultaneous monitoring of hemodynamic and metabolic biomarkers. ”
This research was supported by the UC San Diego Center of Wearable Sensors and the National Institutes of Health (Grant No. 1R21EB027303-01A1).
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