FLEXIBLE AND BIODEGRADABLE PRESSURE SENSORS BASED ON CHITOSAN-GLYCINE REINFORCED WITH MXENE

As the demand for sustainable and eco-friendly electronics grows, biodegradable materials are receiving increasing attention for their potential in flexible sensing applications. This study focuses on the development of film composites based on chitosan (CH) and glycine (Gly), synthesized through a simple solution-casting method. Chitosan was first dissolved in a 1% v/v aqueous acetic acid solution, followed by the incorporation of glycine at varying weight ratios (CH:Gly = 1:0.2, 1:0.6, and 1:0.8). The thin films were characterized using optical imaging, atomic force microscopy (AFM), and X-ray diffraction (XRD) to assess their morphology and phase composition. Local mechanical and piezoelectric properties were evaluated through AFM-based techniques, including AM-FM viscoelastic mapping, PFM DARTSS, and PFM lateral DARTSS. These analyses confirmed that the CH:Gly compositions of 1:0.6 and 1:0.8 were suitable for use in pressure sensor applications, with potential for further modification. The resulting solution was cast and dried in a desiccator for 48 h, producing uniform, free-standing films. Additionally, free-standing films from CH:Gly = 1:0.6 and 1:0.8 compositions were further modified by incorporating low concentrations of Ti3C2Tx (MXene) sheets (5 and 25 μg/ml). While MXene is not a piezoelectric material itself, it offers unique properties such as a large specific surface area, high conductivity, excellent hydrophilicity, and adjustable surface functional groups. These characteristics make MXene an ideal candidate for enhancing the performance of flexible pressure sensors. Specifically, MXene was used as a 8th Conference of the Serbian Society for Ceramic Materials 109 nucleating agent to induce the β-phase polarity and enhance the piezoelectric output during compression by promoting electron transfer. Square samples (2.3 cm × 2.3 cm) were fabricated and equipped with copper electrodes (2 cm × 2 cm) on both sides, connected via wires and encapsulated in Kapton for mechanical and thermal protection. The electrical output of the films was measured using a custom-built laboratory apparatus under mechanical stress induced by finger taps. To ensure a more uniform distribution of mechanical stress, additional tests were performed using a Quartz Impulse Hammer (KISTLER, Italy) with a 2 cm rubber end. The CH-0.6Gly-25MXene film demonstrated strong and reproducible responses in both finger tapping and hammer impact tests, with a sensitivity of 40 mV/N. These results underscore the promising potential of CH-Gly-MXene composites as high-performance, flexible, biodegradable pressure sensors. They offer an optimal combination of high sensitivity, mechanical robustness, and environmental sustainability.