A dual-mode wearable sensor with electrophysiological and pressure sensing for cuffless blood pressure monitoring†

Wearable cuffless blood pressure sensing is essential for the monitoring of hypertension and its related cardiovascular diseases in an on-demand, timely, and comfortable manner. Measurement of the pulse transit time (PTT) has been the most employed technique to monitor blood pressure due to its noninvasiveness, low cost, and ease of device miniaturization. However, the existing PTT measurements rely on analyzing pulse and electrophysiological signals using discrete sensors that complicate the circuit design and signal processing. Herein, we report a wearable dual-mode sensor that can simultaneously monitor both the electrocardiogram and arterial pulse to simplify the measurement of the PTT. This was achieved by encapsulating a liquid metal pressure sensing circuit within the adhesive and conductive ionogel. The ionogel can not only be used for encapsulation but also as ionotronic electrodes for electrocardiogram recording, thus eliminating the use of multiple sensors in PTT sensing. We also integrated the dual-mode sensor into a printed circuit board to achieve wireless signal transmission based on Bluetooth. Upon wearing it on the wrist, the electrocardiogram and arterial pulse can be simultaneously collected. Based on these two signals, the PTT was measured to predict blood pressure, and the predicted results agree well with those of the commercial sphygmomanometer.