Improvement\nof Thermal\nStability of Charges in Polylactic\nAcid Electret Films for Biodegradable Electromechanical Sensors

Eco-friendly\nsensors fabricated from biocompatible and\nbiodegradable\nmaterials are promising candidates for wearable and implantable electronics\ndue to their environmental sustainability and biosafety. This article\nreports a fully biodegradable electromechanical sensor (FBES) utilizing\na sandwich structure with macro ripple structured polylactic acid\n(PLA) electret films acting as sensitive layers and molybdenum (Mo)\nsheets serving as electrodes for a wearable device application. The\nstability of the space charge stored within the PLA film has been\nenhanced by introducing an internal cellular structure and improving\nthe polarization process. A macro ripple structure of the PLA layer\nwith higher deformation is a great guarantee for boosting the pressure\nsensitivity. The results indicate that inserting cell microstructures\nand optimizing the polarization process significantly improve the\ncharge storage stability of PLA films by nearly 55%. This enhancement\nis attributed to several factors, including the extended charge drift\npath of the charges in cellular films, a synergy effect of surface\ncharges, and “macroscopic” dipole charges distributed\nin the cells. The fabricated sensor achieves a high sensitivity of\n1000 pC/kPa, a wide pressure detection range of 0.03–62.4 kPa,\nand satisfactory stability. Such sensors are not only sensitive to\nbody movements but also to subtle physiological signals, satisfying\nthe diverse needs of wearable healthcare. Importantly, all the composition\nmaterials of the sensor can be completely degraded after their service,\naligning with the environmentally friendly principles of green development.