Chitosan-assisted dispersion of carbon nanotubes for high-performance conductive ink in wearable electronics.

Wearable sensors have emerged as a promising technology for continuous health monitoring. However, challenges related to the dispersion stability of carbon nanotubes (CNTs) in aqueous solutions and the development of conductive inks for sensor applications persist. Specifically, CNT-based inks often suffer from poor dispersion, leading to aggregation and reduced performance. In this study, we address these challenges by using chitosan (CS) as a dispersant for multi-walled carbon nanotubes (MWCNTs), aiming to improve dispersion stability and enhance the performance of conductive inks for wearable sensors. We demonstrate that CS significantly enhances the dispersion stability of MWCNTs, achieving a dispersion rate of 90.5 %, as confirmed by UV-visible spectroscopy and thermogravimetric analysis. These analyses indicate improved dispersion and thermal stability. Furthermore, the CS/MWCNT-based inks exhibit superior electrical conductivity, with a measured conductivity of 1171.0 S/m, underscoring their potential for sensor applications. Our results also show that CS/MWCNT-based inks are highly biocompatible, with no significant toxicity observed in plant models and L929 mouse fibroblast cells. Additionally, we successfully fabricated flexible, skin-conforming strain sensors using the CS/MWCNT ink. These sensors exhibited high sensitivity and accurately detected dynamic human movements, such as finger bending and muscle activity in various body parts. The sensors demonstrated a maximum resistance change of 1.6 % and 0.4 % in response to facial and calf movements, respectively. These findings suggest that CS/MWCNT-based inks hold great potential for developing sustainable, biocompatible, and efficient wearable sensors for health monitoring and other applications.