Flexible sensor based on Hair-like microstructured ionic hydrogel with high sensitivity for pulse wave detection

• Hair-like tunable unstable microstructures were fabricated using modified lithography technology. • The microstructured ionic hydrogels could be assembled as flexible sensors. • Enhanced large-range sensitivity derived from unstable microstructures. • Detecting pulse wave both without external pressure and under cuff compression. • The ionic hydrogels could be collected, recycled and re-assembled as new sensors. Flexible sensors will be widely used in wearable pulse wave detection. However, there are few reports that can be used as pulse wave detection both without external pressure and under large pressure. Because it is difficult for flexible pressure sensor with centrosymmetric microstructures to further improve the sensitivity and broaden the pressure range. Based on the modified lithography processes, the PVA-H 3 PO 4 ionic hydrogel film with hair-like tunable microstructures can be synthesized. The flexible sensor with hair-like unstable microstructures achieve high sensitivity of 2296 kPa −1 at 0∼4 kPa, 1167 kPa −1 at 4∼40 kPa and 511 kPa −1 at 40∼100 kPa, respectively. Moreover, the sensor shows low detect limit (∼3.9 Pa), rapid response time (37 ms), long loading/unloading times (2900 cycles) and accurate dynamic response to follow the pressure change. The flexible sensors can monitor the pulse waves both without external pressure and under cuff compression. Not only different arterial pulse waves and heart rate can be detected with no pressure, but also pulse waves can be monitored under different static pressure, which enables the blood pressure measuring. In addition, ionic hydrogels can be collected and reproduced for environmental protection and resources utilization.