'Smart' face mask knows when CO2 limits are exceeded

Scientists and engineers at the University of Granada (UGR) have developed a ‘smart’ FFP2 face mask that notifies the user via their smartphone when the permitted carbon dioxide (CO₂) limits inside the mask are exceeded. Described in the journal Nature Communications, their advance addresses a problem that has been spotlighted since the COVID-19 pandemic began: that of the CO₂ that we rebreathe inside our face masks.

Wearing FFP2-type face masks for any length of time produces a concentration of CO₂ between the face and the mask that is higher than the normal atmospheric concentration (~0.04%), due to the gas we exhale when breathing. CO₂ rebreathing can cause adverse health effects, even in healthy people, such as general malaise, headaches, fatigue, shortness of breath, dizziness, sweating, increased heart rate, muscle weakness and drowsiness. Furthermore, these negative effects are known to be linked to both the duration of exposure and the concentration of the gas itself. Some health regulations recommend a maximum value of 0.5% CO₂ in the working environment (averaged over an 8-hour day), or that a 30-minute exposure to 4% CO₂ be considered very harmful to health.

The UGR face mask makes it possible to ascertain the level of CO₂ rebreathed in real time, using a simple, wearable gas-monitoring system combined with a smartphone application. While standard face masks simply act as air filters for the nasal and/or mouth passage, the inclusion of sensors to measure specific parameters of interest provides added value that improves their use and effectiveness, creating a new paradigm of smart face masks.

“The system we propose is based on inserting a flexible ‘tag’ into a standard FFP2 mask,” the study authors said. “This tag comprises an innovative, custom-developed opto-chemical CO₂ sensor, together with the necessary signal-processing electronics. Both the sensor and the circuitry are fabricated onto a lightweight, flexible polymeric substrate, forming the so-called ‘sensing tag’, which causes no discomfort to the wearer.”

The tag does not require batteries as it is powered wirelessly by the near-field communication (NFC) link of a smartphone, using an Android app; this lack of batteries makes it 100% environmentally friendly. The custom-developed app is also used for data processing, alert management, and display and sharing of results.

The scientists conducted preliminary tests of their face mask on both subjects conducting sedentary activity and those performing physical exercise. The authors said, “Our results, which are in line with previous clinical trials, present CO₂ values of between 2% during low-work-rate (sedentary) activities and a peak value of almost 5% during high-intensity physical exercise. These values are significantly higher than the typical range of 0.04%–0.1% of CO₂ found in atmospheric air or in typical work environments that are considered healthy. Although the performance tests we carried out do not constitute a formal clinical trial, they are intended to give an indication of the potential of this system in the field of wearable sensors for non-invasive health monitoring.”

The low-cost device has potential applications in the fields of non-invasive health monitoring, preclinical research and diagnostics using portable electronic devices, the scientists claim. Other sensors can also be included, to detect other gases of interest.

Image caption: The flexible sensing tag, inside and outside the FFP2 face mask.

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