3D Printed Flexible Piezoelectric Sensor with Enhanced Performance for Gait Recognition

While wearable piezoelectric sensors are highly desirable for their reliable service in human–machine interfaces, substantial challenges remain in improving their electrical performance and structural design. Herein, a flexible and sensitive piezoelectric sensor is developed through electro-assisted fused deposition modeling (E-FDM) 3D printing, incorporating carbon nanotubes (CNTs) into a polyvinylidene fluoride (PVDF) matrix. The addition of CNTs and the applied external electric field during 3D printing significantly increase the content of the β-phase in PVDF, thereby improving the electrical output. Moreover, the unique grid structures are of great importance in enhancing the piezoelectric performance of PVDF-based piezocomposites. As a result, the 3D printed piezoelectric sensors demonstrate a high sensitivity of 65.8 mV kPa–1, rapid response time <30 ms, and outstanding cyclic stability of 100,000 cycles. Finally, the 3D Printed piezoelectric sensor is integrated into an intelligent insole system for real-time gait recognition. An impressive recognition accuracy of up to 97.25% is achieved for classifying various motions of patients with Parkinson’s disease (PD), including walking, limping, staggering, and falling, with the assistance of machine learning. 3D printing is a powerful tool in manipulating a barrier-free piezoelectric sensor with enhanced electrical performance for gait recognition and offers broad application prospects in intelligent sensing.