Morphological Engineering of Sensing Materials for Flexible Pressure Sensors and Artificial Intelligence Applications

Abstract

Driven by market speculation, trends among youth, and massive funding, wearable technology has become a topic of interest in academia and industry because of broad applications in growing disruptive fields, such as wearable medical devices [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ], artificial intelligence (AI) [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], and the Internet of Things (IoT) [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. Flexible pressure sensors that convert pressure into electrical output are an essential part of flexible electronics. Due to rapidly advancing techniques in electrical sensing, material sciences, system engineering, and signal processing, flexible pressure sensors have been investigated in multiple disciplines because of their unique advantageous properties, such as outstanding flexibility, low cost, and compatibility with large-area processing techniques [ 25 , 26 , 27 , 28 , 29 ]. For example, flexible pressure sensors can be attached to the human body for real-time monitoring of different physiological parameters like blood pressure [ 2 , 30 ], blood flow [ 1 , 30 ], pulse beat [ 2 , 6 , 31 , 32 ], heartbeat [ 32 ], respiration [ 31 , 32 ], tremor [ 33 , 34 , 35 ], and body movement [ 36 , 37 , 38 , 39 ]. These parameters are of vital importance in biomedical research, disease diagnosis, and timely treatment. Interest in integrated networks of sensors has been motivated by promising applications in intelligent robotics [ 40 , 41 , 42 ], human–machine interactions (HMI) [ 34 , 35 , 43 , 44 ], biomimetic prostheses [ 4 , 45 , 46 , 47 ], smart homes [ 48 , 49 , 50 ], digitizing sports [ 20 , 21 , 51 , 52 ], wireless monitoring in security [ 17 , 23 , 44 , 53 ], and machine learning (ML)-enabled computational sensing platforms [ 54 , 55 , 56 , 57 , 58 , 59 , 60 ], promoting the advancement of AI systems. Substantial achievements have been made for pressure sensors, including but not limited to piezoresistive [ 37 , 61 , 62 , 63 ], piezocapacitive [ 64 , 65 , 66 ], transistor [ 48 , 67 , 68 ], piezoelectric [ 25 , 49 , 69 ], and triboelectric sensors [ 31 , 70 , 71 , 72 , 73 ].