A highly stretchable and sensitive carboxymethyl chitosan-based hydrogel for flexible strain sensors

Abstract

It is essential to diagnose Parkinsonism at an early stage to prevent functional impairments in patients and improve their level of healthcare. However, low electrical signal transmission and poor stretchability limit the application of flexible hydrogel sensors in the early diagnosis of Parkinsonism. CGTX-IX composite hydrogels were prepared using carboxymethyl chitosan (CMCS), glyoxal, tannic acid (TA), and ionic liquid ([BMIM][Cl]). The CGTX-I3 composite hydrogel has reversible dynamic chemical bonds, such as imine and hydrogen bonds, and physical interactions. It exhibits good mechanical properties (elongation at break of 112.5% and tensile strength of 284.4 kPa) and excellent electrical conductivity (1.16 × 10⁻³ S cm⁻¹). Moreover, CGTX-I3 composite hydrogels have excellent adhesion to commonly used substrate materials, especially human skin (130.9 kPa). The CGTX-I3 hydrogel can also detect the deformation caused by an external force and human movements, such as finger bending, elbow movement, wrist movement, ankle movement, and other subtle human actions (such as swallowing and smiling). After 1000 cycles, the sensor can still maintain a stable sensitivity factor (GF = 2.14).