​Comfortable pajamas capable of detecting episodes of sleep apnea would be a huge improvement over the intrusive devices currently used to measure chest movements while the wearer is sleeping. The new printable, stretchable strain gauges were developed at CEA-Liten's structural electronics platform, which has been collaborating with CEA-Leti on wearable medical devices for years. This latest advance could soon make discreet wearables like sleep apnea pajamas a reality.

To be integrated into fabric, the strain gauges have to be flexible, of course. But above all, they have to be stretchable. Another challenge is that the gauges' electrical resistance has to vary as the device is stretched—but come back to normal after and do so reproducibly. CEA-Liten's extensive experience with printed electronics played a decisive role in selecting the right substrate and conductive ink. Graphene was also added to the technology stack to make the gauge less sensitive to temperature variations.

The sensor was integrated on fabric for characterization by Plux, a Portugal-based company, as part of the EU SmartEEs project. SmartEEs produced a 30% stretchable gauge that meets the requirements of a wearable breathing monitor. A more advanced version with other printed components will soon be produced. The goal is to make instrumented clothes that can provide more complete monitoring.