Ultrasensitive wearable strain sensor for promising application in cardiac rehabilitation

Real-time physiological signal monitoring is very essential to evaluate the function recovery, and the construction of ultrasensitive strain sensor has become the key technique and research hotspot in cardiac rehabilitation. Here, piezoresistive conductive polymer composites (CPCs)–based strain sensor, of which the conductive MXene/AgNW composite film served as the sensing materials and the flexible and stretchable thermoplastic polyurethane (TPU) acted as the supporting layer, was developed and further pre-strain treated to construct the ultrasensitive microcrack structure. Importantly, changing the mass percentage of MXene, sample thickness, and pre-strain amplitude can effectively tune the microcrack structure to achieve the optimization of strain-sensing performance of the sensor. As a result, the prepared strain sensor exhibits an ultrahigh sensitivity (gauge factor (GF) = 602), wide working range (90% strain), low detection limit (0.2%), rapid response and recovery time (60 ms/70 ms), and long-term durability over 1000 cycles. As a proof of concept, it can accurately monitor the pulse rate and respiration rate under different sports states and the simulated breathing modes, which will undoubtedly provide strong guarantee for the real-time health monitoring during the treadmill exercise and assessment of cardiac status. This work will undoubtedly possess a great guidance in the evaluation of cardiac rehabilitation.