Muscle-inspired anisotropic conductive foams with low-detection limit and wide linear sensing range for abnormal gait monitoring

A small-strain sensitive and highly compressible strain sensor is urgently required to handle external complex pressure environments in wearable applications and artificial intelligence. Therefore, the development of a reasonable sensor structure to achieve low detection limitation and wide linear detection range is significant and challenging. Herein, a muscle-inspired anisotropic conductive polydimethylsiloxane (PDMS)/carbon black (CB)/thermoplastic polyurethane (TPU) foam (PCTF) was prepared by directional freezing and ultrasonic-dipping method. The density and porosity of PCTF are 0.18 g cm-3 and 85.5%, respectively. Benefiting from the unique oriented structure, PCTF possesses good strain sensing performances, including ultra-low detection limit (0.002% strain), wide linear detection range (up to 82% strain and pressure over 500 kPa, logistic function R2=0.997), short response time (70 ms) and excellent sensing stability. In addition, PCTF demonstrates excellent properties as triboelectric nanogenerator (TEN(G) (2.5 × 3 cm2), including high triboelectric output (open-circuit voltage VOC=56 V) and high sensitivity (2.0 mV Pa-1), endowing PCTF with the motion state and running posture detecting ability. Moreover, PCTF-based strain sensors consisting of a plantar array can be employed to detect abnormal gait, including supination and pronation, providing a feasible strategy for training and personalized rehabilitation of the athletes.