Sustainable, biodegradable, flexible piezoelectric quaternary ammonium chitosan film pressure sensors for human motion detection and human-computer interaction

Abstract

The coexistence of increasingly severe environmental issues and bio-signal sensing systems necessitates comfortable and safe wearable devices for continuous human health monitoring. Bio-based piezoelectric materials that are environmentally friendly, biocompatible, and high-performing show great potential in health monitoring and human-computer interaction. Chitosan, a deacetylated product of chitin, is one of the natural piezoelectric biopolymer materials. Due to its complete degradability, excellent film-forming properties, and renewability, it has garnered significant attention in the field of piezoelectric sensing. Here, we explored the impact of different degrees of deacetylation on the crystal structure of chitosan and found that chitosan with a deacetylation degree of 70 % (CS−70) has the highest content of the β−phase. On this basis, 2,3-epoxypropyl trimethyl ammonium chloride (GTMAC) was grafted onto the amino groups of chitosan to induce the formation of the β−phase. It was proven that the proportion of the β−phase increased from 41.16 % to 56.46 %. By employing a simple processing method, we manufactured the quaternary ammonium chitosan film flexible pressure sensors. When the material ratio was 1:1, it produced the highest piezoelectric output of 0.325 V, with a sensitivity of 25.64 ± 1.22 (mV/kPa), which is 1.67 times and 2.3 times higher that of the original chitosan, respectively, and also possesses a high linearity characteristic (adjusted R²=0.99). Moreover, the flexible piezoelectric sensors were successfully applied to human motion detection, physiological signal detection, and human-computer interaction. Considering their scalability and ease of manufacturing, this study provides a new reference for the development of green, flexible, and high-performance electronic devices.