Silk nanofibrous iontronic sensors for accurate blood pressure monitoring

• A highly sensitive and breathable silk-based nanofibrous iontronic sensor was fabricated. • The sensor exhibits great signal fidelity because of the high sensitivity and conformal contact. • The sensor shows long-term on-skin signal stability due to the high breathability and sweat tolerability. • The sensor can provide a cuff-less and continuous blood pressure monitoring with high accuracy and long-term stability. Continuous and cuff-less blood pressure (BP) monitoring based on pulse transit time has been extensively explored in wearable electronics. However, both the accuracy and wearing comfort are impeded by the limited sensitivity, skin conformability and breathability of conventional pulse sensors. Here, silk nanofibrous iontronic pressure sensors made entirely of biocompatible materials were demonstrated for accurate, skin-friendly and long-term BP measurement. The sensor achieved a high sensitivity (138.5 kPa -1 ) by incorporating ionic deep eutectic solvents (DES) and engineering micro-structured electrodes, which enables the accurate measurement of pulse waveforms. High flexibility and gas-permeability (2056 g m -2 h -1 ) of the sensor render a conformal contact with the skin and prevent the signal deterioration by sweat, thus improving the signal accuracy and stability during long-term on-skin BP monitoring. Together with the electrocardiogram, both systolic and diastolic BPs could be estimated with mean ± standard deviation of 0.6 ± 3.57 mmHg and 0.7 ± 3.72 mmHg, respectively, meeting the standard of Association for the Advancement of Medical Instrumentation.