Polysaccharide-based hydrogel strain sensors: Materials design, sensing mechanisms, applications, and challenges

Polysaccharide-based hydrogel strain sensors have attracted significant interest for wearable electronics, biomedical monitoring, and human-machine interfaces owing to their flexibility, ionic conductivity, and biocompatibility. Although numerous reviews have discussed hydrogel-based strain sensors, most provide broad overviews of sensing materials or device performance without critically linking polysaccharide chemistry to hydrogel material design, signal transduction, and sensing functionality. This review systematically summarizes recent progress in polysaccharide-based hydrogel strain sensors, focusing on alginate, chitosan, starch, hyaluronic acid, cellulose, and their derivatives. Unlike existing reviews, it establishes clear structure-property-performance relationships by correlating polysaccharide molecular characteristics, crosslinking strategies, network architectures, and ion/electron transport pathways with strain-sensing behavior. Crosslinking strategies, mechanical reinforcement, electrolyte engineering, and conductive functionalization strategies are critically discussed to elucidate their roles in achieving high sensitivity and signal stability. A distinctive feature of this review is the comparative analysis of sensing mechanisms and fabrication strategies, providing a unified understanding of material design and device performance. Emerging functionalities, including self-healing, adhesion, and anti-freezing properties, are highlighted alongside key challenges related to dehydration and durability. By integrating materials chemistry, sensing mechanisms, device engineering, and future perspectives, this review provides a practical platform for development of sustainable, multifunctional, and biocompatible strain sensors.