Biodegradable and Transparent Soft Piezoelectret Film with an Artificially Foamed Air Cell for Sustainable Bioelectronics

Piezoelectric functional films based on biomass materials are attractive due to their promising sustainable applications in wearable/implantable sensors, actuators, and energy harvesters, especially for biological systems. However, their widespread use is often hampered by the high stiffness and weak piezoelectricity of the involved biomaterials. In addition, the introduction of optical transparency is highly desirable, which can lead to the integration of tactile and visual intelligence in a piezoelectric sensor/actuator system. Herein, by leveraging space charge injection and a microstructural engineering strategy, biodegradable and transparent soft piezoelectret (BTSP) sensors from PLA films with artificially formed air cells were proposed. Artificial air cells drastically reduce the compressive modulus of elasticity of BTSP (∼0.02 MPa), resulting in a high longitudinal piezoelectric <i>d</i>₃₃ coefficient (∼6000 pC/N), which is 2 to 3 orders of magnitude larger than that of conventional biodegradable piezoelectric material counterparts. Additionally, a large transverse piezoelectric coefficient (<i>d</i>₃₁ ∼-10 pC/N) and exceptional electromechanical sensing stability determined by performing 70,000 mechanical loading cycles are simultaneously combined with the high resolution in terms of pressure and location. Thus, the presented BTSP has significant advantages over conventional biodegradable piezoelectric materials as they possess both high out-of-plane/in-plane piezoelectric coefficients and remarkable flexibility. This work paves the way for a simple but effective method to fabricate high-performance biodegradable piezoelectric materials and promotes their practical applications in the field of biological and medical microdevices.