Biocompatible polysaccharide ionic hydrogel as ultra-stretchable and multifunctional wearable sensor

Due to their promising applications in health monitoring, wearable flexible sensors based on hydrogel have gained considerable attention as modern medicine advances. However, it is still challenging for hydrogel-based wearable flexible sensors to be integrated with high stretchability, multifunctionality, and biocompatibility. Herein, we designed novel flexible multifunctional sensors based on ionic conductive double-network (DN) hydrogels composed of poly (acrylamide- co -acrylic acid) (P(AM- co -AAc)), sodium alginate (SA), and calcium chloride (CaCl 2 ) by simple two-step method of copolymerization and soaking. Abundant carboxyl groups on SA and P(AM- co -AAc) chains and their capacity to bind with Ca 2+ were utilized to design a double network, providing the hydrogels with high stretchability and toughness. Ca 2+ endowed the hydrogels with enhanced conductivity and sensitivity, while P(AM- co -AAc) enabled the hydrogels to respond to multi-stimuli. The SA/P(AM- co -AAc)/Ca 2+ hydrogels presented outstanding mechanical properties (elongation at break of 2626%, tensile strength of 372 kPa), great sensitivity (gauge factor up to 7.1), and excellent durability (1000 stretching-releasing cycles). It could detect human movements, touch, physiology (temperature and sweat), pH changes, and organic solvents. Besides, the hydrogel sensors displayed great biocompatibility. Therefore, this work extends the design and preparation of highly stretchable and multifunctional hydrogels to facilitate the applications of skin-friendly wearable sensors. Graphical abstract