Eco-friendly in-situ gap generation of no-spacer triboelectric nanogenerator for monitoring cardiovascular activities

Monitoring cardiovascular activities plays a critical role in predicting and preventing cardiovascular diseases. Flexible and biosafe sensors that can provide complementary information about cardiovascular activity beyond the traditional electrocardiogram (ECG) are in great demand. Here, a novel eco-friendly in-situ gap-generation method by vaporizing soaked distilled water is developed to fabricate a no-spacer triboelectric nanogenerator (NSTENG). This NSTENG reveals more uniform stress/strain distributions and undergoes larger displacement compared with the traditional TENG with spacer under the same pressure; and it obliterates the obstruction on detection of subtle movements near spacer. The unique fabrication method also guarantees biological safety and avoids air contamination in vivo. The established wireless mobile system based on the NSTENG can precisely detect the full pulse waveforms and display them on the phone screen in real time. By mounting onto the rat's heart, it can monitor normal heart motion and the measured heart rate has an accuracy of up to 99.73%. Moreover, the NSTENG can monitor abnormal heart motion and detect subtle heart movements that fail to be captured by the ECG. This work provides a new strategy that promotes the innovation of biosafe and new-structure TENGs, and offers new insights into developing wearable and implantable sensors.