Wearable Sensor Patch Records Multiple Health Measures

Multi-functional sensor patch (Wang lab, Univ. of California in San Diego)

16 Feb. 2021. An engineering team developed a transparent thin film sensor patch that measures several vital signs for monitoring heart disease and diabetes. The patch is the work of labs in the Center for Wearable Sensors at University of California in San Diego and described in yesterday’s issue of the journal Nature Biomedical Engineering.

Patients with chronic disorders like heart disease and diabetes need to keep track of multiple health indicators, often requiring separate devices in a clinic, with trained staff to take and record measurements. With more use of mobile devices, efforts are underway to further miniaturize medical devices that connect to phones and tablets, and can be used at home. However, most miniaturized and networked devices of this kind are still made to capture and record single vital signs or measures. The UC San Diego researchers sought instead to design a wearable device that measured several functions, relieving the need for multiple devices.

The team led by Joseph Wang, director of the Center for Wearable Sensors, and electrical and bioengineering professor Sheng Xu. Wang’s nanobiolelectronics lab studies nanoscale components and systems, such as sensors, for measuring health indicators, including blood glucose levels needed by people with diabetes. Xu’s research group investigates ways to add more functions to stretchable and wearable electronics for monitoring a person’s health, while keeping down the amount of real estate these devices occupy.

The UC San Diego team designed a set of electronic and chemical sensors built into a thin transparent film worn on the skin. The film is made from a stretchable styrene-ethylene-butylene-styrene or SEBS polymer with electrodes screen-printed on the surface. The patch, worn on the neck over the carotid artery, measures blood-pressure with a set of ultrasound transducers that beam sound waves into the artery. The transducers are powered by piezoelectric electricity generated by stretching motions, with a corresponding sensor to read the ultrasound echoes for measuring dilation and contraction of the artery.

Glucose, lactate, caffeine, and alcohol

The patch also has electrodes for measuring glucose in interstitial fluid that flows between cells. An electrode emits a mild electrical impulse into the skin to produce interstitial fluid on the skin surface. Another set of electrodes measures lactate, caffeine, and alcohol in the wearer’s sweat. Lactate, or lactic acid, is produced by cells while metabolizing food into energy, particularly when exercising. The patch releases a drug on the skin called pilocarpine used to treat dry mouth, but can also induce sweat, for measuring these chemicals. Spacing the sensors and hydrogel insulation limits sensor signal interference.

“Each sensor provides a separate picture of a physical or chemical change,” says Xu in a university statement. “Integrating them all in one wearable patch allows us to stitch those different pictures together to get a more comprehensive overview of what’s going on in our bodies.”

The team tested measurement of each function separately in the lab, validated with conventional techniques, then together to reveal any interference of signals from the different sensors. The researchers also recruited volunteers to test the prototype sensor patch in various real-life scenarios: after eating, drinking, exercise, or fasting. The results show the patch can capture various health indicators, including production of glucose following food digestion.

The prototype sensor patch described in the paper is hard-wired to a receiving system. The researchers are working on a wireless patch, as well as adding more functions, while further miniaturizing the patch itself.

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