Engineers at the University of California San Diego have developed a prototype of a wearable that can continuously monitor several health stats such as glucose, alcohol and lactate levels simultaneously in real time.

This means users can measure blood sugar levels, know if they’ve had too much to drink, and track muscle fatigue during a workout, all in one small device worn on the skin.

The device is about the size of a stack of six coins. It is applied to the skin through a Velcro-like patch of microscopic needles, or microneedles, that are each about one-fifth the width of a human hair. Wearing the device is not painful; the microneedles barely penetrate the surface of the skin to sense biomolecules in interstitial fluid, which is the fluid surrounding the cells beneath the skin. The device can be worn on the upper arm and sends data wirelessly to a custom smartphone app.

Researchers at the UC San Diego Center for Wearable Sensors described their device in a paper published this month in Nature Biomedical Engineering.

“This is like a complete lab on the skin,” said centre director Joseph Wang, a professor of nanoengineering at UC San Diego. “It is capable of continuously measuring multiple biomarkers at the same time, allowing users to monitor their health and wellness as they perform their daily activities.”

Most commercial health monitors, such as continuous glucose monitors for patients with diabetes, only measure one signal. The problem with that, the researchers say, is that it leaves out information that could help people with diabetes, for example, manage their disease more effectively. Monitoring alcohol levels is useful 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 about lactate, which can be monitored during exercise as a biomarker for muscle fatigue, is also useful because physical activity influences the body’s ability to regulate glucose.

“With our wearable, people can see the interplay between their glucose spikes or dips with their diet, exercise and drinking of alcoholic beverages,” said Farshad Tehrani, a nanoengineering PhD student in Wang’s lab. “That could add to their quality of life as well.”

The wearable consists of a microneedle patch connected to a case of electronics. Different enzymes on the tips of the microneedles react with glucose, alcohol and lactate in interstitial fluid. These reactions generate small electric currents, which are analysed by electronic sensors and communicated wirelessly to an app that the researchers developed. The results are displayed in real time on a smartphone.

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

“We’re starting at 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. “That lowers the barriers to clinical translation.”

The microneedle patch, which is disposable, can be detached from the electronic case for easy replacement. The electronic case, which is reusable, houses the battery, electronic sensors, wireless transmitter and other electronic components. The device can be recharged on any wireless charging pad used for phones and smartwatches.

Integrating all these components together into one small, wireless wearable was one of the team’s biggest challenges. It also required some clever design and engineering to combine the reusable electronics, which must stay dry, with the microneedle patch, which gets exposed to biological fluid.

“The beauty of this is that it is a fully integrated system that someone can wear without being tethered to benchtop equipment,” said Mercier, who is also the co-director of the UC San Diego Center for Wearable Sensors.

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

Farshad Tehrani and fellow co-first author Hazhir Teymourian, who is a former postdoctoral researcher in Wang’s lab, have co-founded a start-up company called AquilX to develop the technology for commercialisation. Next steps include testing and improving on how long the microneedle patch can last before being replaced. The company is also excited about the possibility of adding more sensors to the device to monitor medication levels in patients and other health signals.