Imagine being able to measure your blood sugar, know if you’ve had too much to drink, and track your muscle fatigue during a workout, all in one small device worn on your skin. Engineers at the University of California, San Diego have developed a prototype of such a wearable that can continuously monitor multiple health stats – glucose, alcohol and lactate levels – simultaneously in real time.
The device is about the size of a six-quart stack. It is applied to the skin through a Velcro-like patch of microscopic needles, or micro-needles, which are each about one-fifth the width of a human hair. Wearing the device is not painful – the micro-needles barely penetrate the surface of the skin to detect biomolecules in the interstitial fluid, which is the fluid surrounding the cells under the skin. The device can be worn on the upper arm and sends data wirelessly to a custom smartphone app.
Researchers from the UC San Diego Center for Wearable Sensors describe their device in an article published May 9 in Nature Biomedical Engineering.
“It’s like a complete lab on the skin,” said center director Joseph Wang, a professor of nanoengineering at UC San Diego and co-corresponding author of the paper. “It is able to continuously measure multiple biomarkers at the same time, allowing users to monitor their health and well-being as they go about their daily activities.”
Most commercial health monitors, such as continuous glucose monitors for diabetic patients, only measure a single signal. The problem with this, 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 helpful because drinking alcohol can lower glucose levels. Knowing the two levels can help people with diabetes prevent their blood sugar from dropping too low after having a drink. The combination of 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 devices, people can see how their glucose spikes or drops interact with their diet, exercise, and alcoholic beverage consumption. It could also improve their quality of life,” said Farshad Tehrani, incumbent. a doctorate in nano-engineering. student in Wang’s lab and one of the study’s co-first authors.
Micro-needles fused with electronics
The wearable consists of a micro-needle patch connected to an electronic box. Different enzymes on the microneedle tips react with glucose, alcohol and lactate in the interstitial fluid. These reactions generate small electrical currents, which are analyzed by electronic sensors and communicated wirelessly to an application developed by the researchers. The results are displayed in real time on a smartphone.
An advantage of using microneedles is that they sample the interstitial fluid directly, and research has shown that the biochemical levels measured in this fluid correlate well with levels in the blood.
“We are starting at a very good place with this technology in terms of clinical validity and relevance,” said Patrick Mercier, professor of electrical and computer engineering at UC San Diego and co-corresponding author of the paper. “It reduces barriers to clinical translation.”
The microneedle patch, which is disposable, can be detached from the electronics box for easy replacement. The electronics box, which is reusable, houses the battery, electronic sensors, wireless transmitter and other electronic components. The device can be charged on any wireless charger used for phones and smart watches.
One of the team’s biggest challenges was integrating all of these components into a single, small, wireless wearable. It also took clever design and engineering to combine the reusable electronics, which must remain dry, with the microneedle patch, which is exposed to biological fluid.
“The beauty of this is that it’s a fully integrated system that someone can wear without being tethered to benchtop equipment,” said Mercier, who is also 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 continuously monitor volunteers’ glucose levels simultaneously with their alcohol or lactate levels. The glucose, alcohol, and lactate measurements taken by the device closely matched the measurements taken by a commercial glucometer, the breathalyzer, and the blood lactate measurements taken in the laboratory, respectively.
Farshad Tehrani and his co-first author Hazhir Teymourian, who is a former postdoctoral researcher in Wang’s lab, co-founded a startup called AquilX to further develop the technology for commercialization. Next steps include testing and improving the life of the microneedle patch before it is replaced. The company is also excited about the possibility of adding more sensors to the device to monitor patient drug levels and other health signals.