Nanomaterials for Flexible Arterial Pulse Sensors

The acquisition of pulse pressure from various parts of the human body is an important diagnostic factor in both Western and Chinese medicine (CM). To ensure a full and accurate recording of a pulse pressure induced by blood vessel contraction and relaxation, a pulse sensor must be ideally flexible and stretchable to fit the irregular shapes and topographies of, for example, the human wrist and arteries, during daily movements. However, commercially available microelectromechanical system (MEMS)-based pressure/tactile sensors, most of which are based on silicon pressure-sensing diaphragms, have limited mechanical flexibility and sensor output sensitivity, which make them unsuitable for many wearable and healthcare electronics applications. Hence, the development of nanomaterial-based pressure sensors is extremely important for the eventual proliferation of micro-/nanosensors in wearable healthcare monitoring products. In this chapter, we present examples of fabrication processes for three prevalent types of nanomaterial-based flexible sensing devices: capacitive, piezoelectric, and piezoresistive sensors. Since piezoresistive sensors are easier to fabricate and require less stringent electrical configurations, we provide a more detailed overview of state-of-the-art piezoresistive pressure sensors, followed by a characterization of a specific flexible piezoresistive pressure sensor and its applications in monitoring human motion, healthcare, and electronic skin (e-skin). We have also included a table to summarize and compare the performance of many of the reported nanomaterial-based pressure sensors before providing conclusive remarks at the end. © 2020 World Scientific Publishing Co. Pte. Ltd.