Ultra-Stretchable and Skin-Conformal Piezoelectric Electronic Skin for Self-Powered Human Motion Monitoring.

Soft piezoelectric electronic skins are expected to work reliably under repeated joint bending, where both stretchability and stress transfer efficiency are important. In this work, a BaTiO3/PDMS piezoelectric electronic skin, denoted as BPPE-skin, was prepared by a blade-coating method. Rather than only increasing the amount of piezoelectric filler, this study focuses on how the PDMS matrix composition affects the mechanical deformation and electrical response of the composite. The PDMS base-to-curing-agent ratio was adjusted from 5:1 to 30:1, and the BaTiO3 loading was varied from 10 to 90 wt%. Tensile tests show that increasing the base-to-curing-agent ratio reduces the elastic modulus and improves stretchability, while excessive softening weakens effective stress transfer. As a result, the voltage output reaches its highest value at a 10:1 ratio. Increasing the BaTiO3 content further enhances the output, mainly because more active piezoelectric particles participate in electromechanical conversion. The optimized film, containing 90 wt% BaTiO3 with a 10:1 PDMS ratio, maintains good flexibility and can be attached conformally to different body joints. Tests on the knee, elbow, wrist, and fingers produce distinct voltage patterns during bending motions, indicating the potential of BPPE-skin for wearable, self-powered human motion monitoring.