High-Sensitivity Flexible Strain Sensor Based on MWCNTs/HNTs Nanocomposites for Physiological and Handwriting Monitoring

Abstract

With the rapid development of flexible electronics and human–computer interaction technologies, the demand for high-performance flexible strain sensors for human motion and physiological signal monitoring has grown sharply. This study developed a sandwich-structured flexible strain sensor based on multi-walled carbon nanotube/halloysite nanotube (MWCNT/HNT) nanocomposites. A polydopamine (PDA) modification layer was first formed on the polydimethylsiloxane (PDMS) film via in situ polymerization of dopamine (DA), which significantly improved the surface hydrophilicity and enhanced interfacial adhesion between PDMS and the subsequent conductive layer. The MWCNT/HNT mixed conductive layer was then uniformly sprayed onto the PDA@PDMS film, followed by PDMS encapsulation to form the final structure. The sensor integrates the excellent conductivity of MWCNTs and the mechanical reinforcement capability of HNTs, achieving a wide strain-sensing range, high sensitivity with GF values of 14.46 at 0–40% strain and 35.55 at 40–85% strain, fast response/recovery times of 250/300 ms, and excellent cyclic stability over 7500 cycles. It can sensitively detect physiological signals such as swallowing, pulse and breathing, as well as motion signals including joint bending and mouse clicking. Moreover, it can distinguish subtle finger movements during English letter writing, showing broad application potential in wearable healthcare devices and human–computer interaction systems.