Double-network sodium carboxymethyl cellulose/Fe³⁺ hydrogel with enhanced mechanical properties and sensing performance for human motion monitoring and Morse code transmission

With advances in flexible electronics, hydrogels have found increasing use in applications such as wearable devices, soft robotics, and medical rehabilitation. However, conventional hydrogel synthesis methods remain complex and often yield structurally defective materials, hindering the optimal balance between high stretchability and high sensitivity. This limitation represents a major obstacle to practical applications. To overcome this challenge, we developed a PMVFC hydrogel featuring a double-network structure that leverages synergistic effects from three types of non-covalent bonds. The hydrogel comprised a dual-network framework of P(AM-co-VEImBr) and CMCNa, in which MBAA served as a covalent crosslinker to bridge the networks and establish a three-dimensional architecture. The carboxyl groups on CMC-Na formed hydrogen bonds with amide groups on the P(AM-co-VEImBr) backbone and also coordinated with Fe³⁺ ions to generate stable ionic crosslinks. This synergistic interaction resulted in significantly enhanced mechanical properties (Stress = 0.65 MPa, Strain = 1425 %), along with improved tensile sensing performance (GF₁ = 12.27, GF₂ = 6.25, GF₃ = 5.94) and pressure sensing capability (S₁ = 0.3963 kPa^-1, S₂ = 0.0568 kPa^-1, S₃ = 0.0085 kPa^-1). Sensors fabricated from this hydrogel successfully detected limb motion and transmitted signals using Morse code. Additionally, we created an array sensor based on the PMVFC hydrogel, providing a viable technical pathway for the development of high-performance human-machine interfaces and intelligent emergency response systems.