Double Network Alginate Hydrogel with Gold Nanoparticles and Reduced Graphene Oxide for Wearable Medical Devices

Herein, we present a double-network hydrogel synthesized from a polysaccharide, sodium alginate (Alg), and acrylamide (AAm) via a “one-pot” preparation process. The hydrogel utilized N,N′-methylenebis(acrylamide) (MBAA) as a cross-linker, while ammonium persulfate (APS) and N,N,N′,N′-tetramethylethylenediamine (TEMED) served as a combined initiator system to enhance gelation and structural uniformity. To improve its mechanical and electrical properties, gold nanoparticles (AuNPs) or reduced graphene oxide (rGO) was incorporated into the Alg-co-AAm hydrogel. The hydrogel features both chemical cross-linking, achieved through radical graft polymerization facilitated by MBAA, and physical cross-linking via coordination bonds between AuNPs and amide groups, alongside π–π interactions and hydrogen bonding from rGO. The resulting hydrogel exhibits remarkable mechanical properties, with a toughness of 1.10 MJ/m3 and strains over 832%, as well as a conductivity of 2.52 × 10–8 S/m and a capacitance of 6.70 mF. These characteristics make it ideal for applications in capacitive strain sensors and wearable electronics, particularly for functional electrical stimulation (FES) devices. The hydrogel effectively detects diverse human motions, distinguishing low-strain activities such as walking from high-strain activities such as running, highlighting its potential in flexible wearable medical monitoring devices.