Performance of piezoelectric and triboelectric transducers under gait loading for energy harvesting and load monitoring in total knee replacements.

This study investigates the energy harvesting and sensing capabilities of piezoelectric nanogenerators (PENG) and triboelectric nanogenerators (TENG) for long-term load monitoring in total knee replacement (TKR). Multi-layered polyvinylidene fluoride (PVDF) films and cuboid-patterned silicone rubber embedded with dopamine-coated BaTiO particles (SR/BT@PDA) TENG are compared as energy harvesting-based load sensors. Unlike prior studies relying on simplified harmonic loading, this work utilizes physiologically relevant gait cycles covering realistic force ranges to precisely evaluate electrical output, sensitivity, and activity recognition capabilities. Results indicate forward-polarized TENG samples and upward-polarized PVDF layers generate significantly higher outputs, indicating the importance of dipole alignment for enhanced sensor efficiency. The harvesters' outputs show that the SR/BT@PDA TENG achieves a maximum apparent power output of 6 W at 1.5GΩ, while the PVDF reaches 2.7 W at 200MΩ under normal walking conditions. The SR/BT@PDA TENG outperforms PVDF in energy harvesting, reaching 140 V in 26 gait cycles for a 10nF capacitor and powering 60 LEDs, while PVDF charges the same capacitor to 33 V in nearly 19 gait cycles, powering 14 LEDs. The TENG's micro-cuboid surface patterning and synergistic effects of embedded piezoelectric material (BaTiO) enhance its output power density, whereas the multi-layered PVDF demonstrates reliable performance under diverse load conditions. Both sensors effectively detect diverse activities, including walking, jogging, and stair climbing. Overall, PVDF provides precise load monitoring by tracking dynamic force profiles, while TENG outperforms in energy harvesting. This study evaluates the potential of integrating TENG and PENG into TKR as energy-harvesting solutions for joint load monitoring without relying on external power sources.