Review anti-swelling hydrogels from natural polysaccharide polymers: Emerging core materials for underwater wearable motion sensors.

Owing to the rapid advancement of wearable electronics and soft robotics, anti-swelling hydrogels have attracted considerable interest for underwater motion sensing because of their outstanding stability under aqueous conditions. Herein, this review first catalogues polysaccharide-based building blocks employed to engineer anti-swelling hydrogels, then systematically discuss structural design strategies and review recent advances in their application to motion sensing. This review first summarizes the use of natural polysaccharides-including chitosan and sodium alginate-for preparing anti-swelling hydrogels. Subsequently, three pivotal construction strategies are critically examined: (i) molecular engineering grounded in swelling-equilibrium theory, exemplified by non-covalent cross-linking; (ii) hierarchical network regulation via dual or supramolecular networks; and (iii) biomimetic strategies inspired by skin-like structures. Finally, the synergistic interplay between conventional approaches (e.g., nanofiber reinforcement) and emerging technologies is systematically compared. These hydrogels simultaneously retain high water content and exhibit superior mechanical robustness, electrical conductivity, and biocompatibility, rendering them ideal candidates for wearable underwater motion sensors. Nevertheless, critical challenges-including long-term stability under aqueous conditions, scalable manufacturing, and economic viability-remain unresolved. Future investigations must therefore prioritize the rational design of multifunctional hydrogels that satisfy escalating industrial and clinical requirements.