Compact and portable “skin lab” continuously monitors glucose, alcohol and lactate

The device can be worn on the upper arm while the user goes about their day. Credit: Nanobioelectronics Laboratory/UC San Diego

Imagine being able to measure your blood sugar levels, know if you’ve had too much alcohol, and track your muscle fatigue during a workout, all in a small, skin-worn device. Engineers at the University of California, San Diego (UCSD) have developed a prototype of such a wearable device that can continuously monitor various health statistics (glucose, alcohol, and lactate levels) simultaneously in real time.

“This is like a complete lab on the skin.” — jose wang

The multitasking device is only the size of a six-quart stack. It is applied to the skin through a Velcro-like patch of microscopic needles, or microneedles, that are about one-fifth the width of a human hair. Using the device is painless: the microneedles barely penetrate the skin’s surface to detect biomolecules in the interstitial fluid, which is the fluid that surrounds cells under the skin. The device can be worn on the upper arm and wirelessly sends data to a custom smartphone app.

Researchers at the UC San Diego Wearable Sensor Center describe their device in a paper published today (May 9, 2022) in the journal Nature Biomedical Engineering.

The device can be worn on the upper arm and wirelessly sends data to a custom smartphone app. Credit: Nanobioelectronics Laboratory/UC San Diego

“This is like a whole lab on the skin,” said center director Joseph Wang, a professor of nanoengineering at UC San Diego and a co-author of the paper. “It is capable of continuously measuring multiple biomarkers at the same time, allowing users to monitor their health and wellness while going about their daily activities.”

Most commercial health monitors, such as continuous glucose monitors for diabetes patients, only measure one signal. The problem with that, the researchers said, is that it leaves out information that could help people with diabetes, for example, manage their disease more effectively. Monitoring alcohol levels is helpful because drinking alcohol can lower glucose levels. Knowing both levels can help people with diabetes prevent their blood sugar from dropping too low after having a drink. Combining information on lactate, which can be monitored during exercise as a biomarker of muscle fatigue, is also useful because physical activity influences the body’s ability to regulate glucose.

“With our wearable device, people can see the interaction between their glucose spikes or drops with their diet, exercise, and alcohol consumption. That could also increase your quality of life,” said Farshad Tehrani, a Ph.D. in nanoengineering. student in Wang’s lab and one of the study’s co-first authors.

Microneedles fused with electronics

The wearable device consists of a microneedle patch attached to an electronics box. Different enzymes at the tips of the microneedles react with glucose, alcohol, and lactate in the interstitial fluid. These reactions generate tiny electrical currents, which are analyzed by electronic sensors and communicated wirelessly to an app the researchers developed. Results are displayed in real time on a smartphone.

Disposable Microneedle Patch

The disposable microneedle patch is separated from the reusable electronic box. Credit: Nanobioelectronics Laboratory/UC San Diego

An advantage of using microneedles is that they sample directly from interstitial fluid, and research has shown that the biochemical levels measured in that fluid correlate well with levels in the blood.

“We’re starting out in a really good place with this technology in terms of clinical validity and relevance,” said Patrick Mercier, a professor of electrical and computer engineering at UC San Diego and a co-author of the paper. “That lowers the barriers to clinical translation.”

The microneedle patch, which is disposable, can be removed from the electronic box for easy replacement. The electronics box, which is reusable, houses the battery, electronic sensors, wireless transmitter, and other electronics. The device can be recharged on any wireless charging pad used for smart phones and watches.

Wearable Refill Multitasking Microneedle

The device can be recharged on a ready-to-use wireless charging pad. Credit: Nanobioelectronics Laboratory/UC San Diego

Integrating all of these components into a small, wireless handheld device was one of the team’s biggest challenges. It also required clever design and engineering to combine the reusable electronics, which must stay dry, with the microneedle patch, which is exposed to biological fluids.

“The beauty of this is that it’s a fully integrated system that anyone can use without being tied to a desktop computer,” said Mercier, who is also co-director of the UC San Diego Center for Wearable Sensors.

Tests

The wearable device was tested on five volunteers, who wore the device on their upper arms while exercising, eating, and drinking a glass of wine. The device was used to continuously monitor the volunteers’ glucose levels simultaneously with their alcohol or lactate levels. Glucose, alcohol, and lactate measurements taken by the device closely matched measurements taken, respectively, by a commercial blood glucose monitor, a breathalyzer, and blood lactate measurements made in the laboratory.

Next steps

Farshad Tehrani and fellow co-author Hazhir Teymourian, a former postdoctoral researcher in Wang’s lab, co-founded a startup company called AquilX to further develop the technology for commercialization. The next steps include testing and improving how long the microneedle patch can last before being replaced. The company is also excited about adding more sensors to the device to monitor patients’ medication levels and other signs of health.

Reference: “An Integrated Portable Microneedle Array for Continuous Monitoring of Multiple Biomarkers in Interstitial Fluid” May 9, 2022, Nature Biomedical Engineering.
DOI: 10.1038/s41551-022-00887-1

Funding: NIH/National Institute of Neurological Disorders and Stroke

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