Hydrophobic Association Hydrogels Reinforced with Carboxymethyl Cellulose-Grafted-Acrylamide for Flexible Strain Sensor

A macromolecular cross-linker, acryloylated carboxymethyl cellulose (CMA), was successfully composited and integrated with acrylamide (AM) and hexadecyl methacrylate (HMA) to construct a composite hydrogel (CMA/P(HMA-AM)) combining hydrophobic association and chemical cross-linking for flexible strain sensing applications. Specifically, the macromolecular cross-linker was composited by grafting acrylamide onto carboxymethyl cellulose (CMC) via an acylation reaction, thereby introducing vinyl double bond groups onto the CMC backbone. These functional groups served as cross-linking junctions within the hydrogel network. Notably, the cross-linker exhibited inherent biocompatibility and biodegradability, making it suitable for biomedical applications. Therefore, relying on the synergistic effect of macromolecular cross-linking agent CMA and hydrophobic association, CMA/P(HMA-AM) hydrogel exhibits impressive mechanical properties. The maximum fracture stress is 1.25 MPa, the elongation at break is 3020.91%, and the toughness is 14.64 MJ/m3. In addition, the hydrogel also exhibits good self-recovery (75% modulus recovery) and fatigue resistance (hysteresis curve overlaps in repeated loading–unloading cycles). Besides, the hydrogel displayed highly sensitive strain-dependent conductivity with a gauge factor (GF) of 5.82 within the 400–1000% strain range. Furthermore, the CMA/P(HMA-AM) hydrogel effectively monitored human joint movements through stable electrical signal transduction, validating its potential as a high-performance flexible wearable strain sensor. In conclusion, this work integrates CMA-mediated chemical networks with AM-based hydrophobic associations to establish a dual-cross-linked hydrogel strategy, providing a solution for advancing hydrogel-based sensing materials toward applications in next-generation wearable electronics and intelligent robotics.