People are increasingly using personalized wearable devices to monitor their health. From watches to patches and other types of sensors, these smart devices monitor heart activity, inflammation levels, and more, allowing patients to better manage their health at home. Now, a new type of wearable device has been added to the list: a high-tech paper mask that monitors your breathing.
Caltech Professor of Medical Engineering Wei Gao and his colleagues have developed a prototype smart mask that can be used to monitor a range of medical conditions, including respiratory illnesses such as asthma, COPD (chronic obstructive pulmonary disease), and post-COVID-19 infections. In contrast to other smart masks in development that monitor physical changes such as temperature, humidity, and breathing rate, this mask, called EBCare, can analyze chemicals in exhaled breath in real time. (“EBC” is an acronym used in the field for “exhaled breath condensate.”) For example, the mask can monitor levels of nitrite, a chemical that indicates airway inflammation in asthma patients.
“Monitoring a patient's breath is routinely done, for example to evaluate asthma and other respiratory diseases, but it requires the patient to visit a clinic to take a sample and then wait for the test results,” said Gao, lead researcher of the new study describing the mask in Science magazine. “Since COVID-19, people have started wearing masks. We can leverage this increased use of masks for remote, individual monitoring, giving people real-time feedback on their health at home or in the office. For example, we could use this information to evaluate how well a medical treatment is working.”
Gao, a Heritage Institute for Medical Research investigator, Ronald and Joan Willens Scholar, and faculty member at the Tianqiao and Chrissie Chen Neuroscience Institute, has already developed a number of wearable biosensors that analyze human sweat to measure levels of metabolites, nutrients, hormones, and proteins. In this case, his goal was to monitor breathing, but that came with new challenges.
To selectively analyze chemicals and molecules in a person's breath, researchers must first cool the breath vapor into a liquid. In a clinical setting, this cooling step is done separately from the analysis. Moist breath samples are cooled in buckets of ice or large refrigerated coolers. In contrast, Gao's new mask is self-cooling. The breath is cooled by a passive cooling system that integrates evaporative and radiative cooling of a hydrogel, effectively cooling the breath on the facemask.
“This mask represents a new paradigm for respiratory and metabolic disease management and precision medicine because it allows for easy collection of breath samples and real-time analysis of exhaled chemical molecules through a routinely worn mask,” said Wen-zheng Heng, lead author of the study and a graduate student at Caltech. “The exhaled breath condensate contains not only soluble gases but also non-volatile substances in the form of aerosols and droplets, including metabolic substances, inflammatory indicators, and pathogens.”
Once your breath is converted into liquid, a series of capillaries belonging to a device called bioinspired microfluidics transports the liquid right to a sensor for analysis. “We learned how to transport water from plants,” Gao says. “Plants use capillary force to pull water up from the ground.”
The analysis results are then sent wirelessly to an individual's phone, tablet, or computer. “The smart mask can be made relatively cheaply,” Gao says. “We've designed it so that the materials cost is only around $1.”
To test the mask, the team conducted a series of human studies, primarily with patients with asthma or COPD. Specifically, they monitored the patients' exhaled breath for nitrite, a biomarker of inflammation in both diseases. The results showed that the mask accurately detected biomarkers indicative of inflammation in the patients' airways.
In a separate study, the team demonstrated that the masks accurately detected subjects' blood alcohol concentration, suggesting that they could potentially be used for field DUI checks and other alcohol consumption monitoring.
The researchers also explored how the mask could be used to assess blood urea levels in the monitoring and management of kidney disease. As kidney function declines, protein metabolic by-products such as urea build up in the blood. At the same time, urea in saliva increases, which breaks down into ammonia gas, leading to elevated ammonium concentrations in breath condensate. The new study showed that the smart mask can accurately detect these ammonium concentrations, closely reflecting the urea levels in the blood.
“These initial studies are proof of concept,” Gao says, “and we aim to expand this technology to incorporate different markers associated with different health conditions. This will serve as the basis for creating a mask that can act as a versatile general health monitoring platform.”
Regarding mask comfort, participants reported positive experiences, including those with respiratory problems.
“Our smart mask platform for EBC collection and analysis represents a major advance in the potential for real-time monitoring of lung health,” said co-author Harry Rossiter, a research associate at Harbor-UCLA's Lundquist Institute for Biomedical Innovation and a professor of medicine at UCLA's David Geffen School of Medicine. “This notion that biosensors for a wide range of compounds could be added in the future highlights the groundbreaking potential of smart masks for health monitoring and diagnostics.”
The study, titled “Smart Mask for Exhaled Breath Condensate Collection and Analysis,” was funded by the National Institutes of Health, the National Science Foundation, the Tobacco-Related Disease Research Program, and the U.S. Army Medical Research Procurement Activity. Other Caltech authors include graduate students Shuqun Yin (Kevin), Canlan Wang, Hong Han, Jiahong Li, and postdoc Jihong Min, as well as former Caltech postdocs Efsan Shirzaei Sani and Yu Song.
