Imagine being able to measure your blood sugar levels, see if you have too much to drink, and track your muscle fatigue during exercise, all in a small device worn on your skin. Engineers at the University of California, San Diego, have developed a prototype of such a wearable device that can continuously monitor several health stats—; glucose, alcohol and lactate levels-; simultaneously in real time.
The device is the size of a six-quarter stack. It is applied to the skin through a Velcro-like patch of microneedles, or microneedles, which are each about one-fifth the width of a human hair. Wearing the device is not painful; Micro-needles penetrate the surface of the skin to sense biomolecules in the interstitial fluid, which is the fluid surrounding cells under the skin. The device can be worn in the upper arm and sends data wirelessly to a dedicated smartphone app.
Researchers at the Center for Wearable Sensors at the University of California, San Diego describe their devices in a research paper published May 9 in The nature of biomedical engineering.
“This is like an entire skin lab,” said center director Joseph Wang, a professor of nanoengineering at the University of California, San Diego and co-author of the paper. “It is able to continuously measure multiple vital signs at the same time, allowing users to monitor their health and wellness as they go about their daily activities.”
Most commercial health monitors, such as continuous glucose monitors for diabetics, measure only one signal. The problem with this, 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 diabetics prevent their blood sugar from dropping too low after drinking a drink. The combination of information about lactate, which can be monitored during exercise as a biomarker of muscle fatigue, is also useful because physical activity affects the body’s ability to regulate glucose.
“Through the wearable devices, people can see the interaction between glucose highs or lows with their diet, exercise and drinking alcohol. This can add to their quality of life as well,” said Farshad Tehrani, Ph.D. in nanoengineering. A student in Wang’s lab and one of the study’s co-authors.
Microneedles merged with electronics
The wearable consists of a microneedle patch attached to a box of electronics. Various enzymes on the tips of the microneedles react with glucose, alcohol, and lactate in the interstitial fluid. These interactions generate tiny electric currents, which are analyzed by electronic sensors and wirelessly delivered to an application developed by the researchers. Results are displayed in real time on a smartphone.
The advantage of using fine needles is that they take a sample directly from the interstitial fluid, and research has shown that the biochemical levels measured in this fluid correlate well with the levels in the blood.
We’re starting in a really good place with this technology in terms of clinical validity and relevance. This reduces barriers to clinical translation. “
Patrick Mercier, Professor of Electrical and Computer Engineering at the University of California, San Diego and co-author of the paper
The disposable micro-needle patch can be separated from the electronic case for easy replacement. The electronic enclosure, which is reusable, contains the battery, electronic sensors, radio transmitter, and other electronic components. The device can be recharged on any wireless charging pad used for phones and smartwatches.
Incorporating all of these components together into a small, wearable wireless device was one of the team’s biggest challenges. It also required some clever design and engineering to combine reusable electronics, which must be kept dry, with a microneedle patch, which is exposed to biological liquid.
“The beauty of this is that it’s a fully integrated system that anyone can wear without being restricted to tabletop 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 the volunteers’ glucose levels simultaneously with their alcohol or lactate levels. Measurements of glucose, alcohol, and lactate taken by the device closely matched those taken consecutively by a commercial blood glucose monitor, alcohol analyzer, and blood lactate measurements taken in a laboratory.
Farshad Tehrani and fellow co-first author Hazir Timurian, 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 optimizing how long the micro-needle patch can last before it is replaced. The company is also excited about the possibility of adding more sensors to the device to monitor patients’ drug levels and other health signals.
University of California – San Diego
Tehrani, F.., et al. (2022) Integrated wearable microneedle array for continuous monitoring of various biomarkers in interstitial fluid. The nature of biomedical engineering. doi.org/10.1038/s41551-022-00887-1.