Biomimetic Ultraflexible Piezoresistive Flow Sensor Based on Graphene Nanosheets and PVA Hydrogel

Flow sensors play a critical role in monitoring flow parameters, including rate, velocity, direction, and rotation frequency. In this paper, inspired by biological hair cells in the human vestibular system, an innovative flow sensor is developed based on polyvinyl alcohol (PVA) hydrogel nanocomposites with a maze-like network of vertically grown graphene nanosheets (VGNs). The VGNs/PVA hydrogel absorbs a copious amount of water when immersed in water, making the sensor highly sensitive to tiny stimuli underwater. The sensor demonstrates a high sensitivity (5.755 mV (mm s(-1))(-1)) and extremely low velocity detection (0.022 mm s(-1)). It also reveals outstanding performance in detecting low-frequency oscillatory flows down to 0.1 Hz, which make it suitable for many biomedical applications. As one of the potential applications of the sensor, it exhibits excellent performance in mimicking various physiological conditions of vestibular hair cells. To explain the experimental results, a complete finite element simulation is developed to model the piezoresistive effect of VGNs/PVA thin film structure. This is the first attempt to develop hydrogel-graphene nanosheet-based flow sensors, which creates the closest artificial sensor to vestibular hair cells. This miniaturized hair cell sensor paves the way for utilizing hydrogels to develop next-generation of ultrasensitive flow sensors for biomedical applications.