Enhanced Piezoelectricity in Sustainable-By-Design Chitosan Nanocomposite Soft Thin Films for Green Sensors

Piezoelectricity, the generation of an electric charge in response to mechanical stress, is a key property in both natural and synthetic materials. This study significantly boosts the piezoelectric response of chitosan, a biodegradable biopolymer, by integrating chitin/surface-deacetylated chitin nanocrystals into natural chitosan-based thin films. The resulting materials, produced in our laboratories, achieve <i>d</i>₃₃ values of up to 18.7 ± 1.1 pm V^-1, a marked improvement over 8.9 ± 0.6 pm V^-1 observed in pure chitosan films, thanks to the increased crystallinity provided by the nanocrystals. We utilize piezoresponse force microscopy (PFM) to accurately measure the <i>d</i>₃₃ coefficient, employing an engineered extraction method that eliminates the electrostatic contribution, which can overestimate the piezoelectric response. This work introduces a soft, elastomer-like piezoelectric thin film entirely derived from upcycled biowaste. The chitosan-based films combine high elasticity (up to 40% strain) with a low Young's modulus (∼100 MPa), closely mimicking soft biological tissues. Unlike previously reported piezoelectric materials, which typically rely on synthetic or inorganic components, our films are fully biobased and mechanically compliant, making them ideal for applications in prosthetics, wearable devices, soft robotics, and sustainable energy harvesting.