Wearable and flexible materials are replacing conventional solid-state sensors in different biomedical applications. Flexible sensor must provide unrestricted geometrical designs, appropriate mechanical properties and low power consumption. Hydrogel-based sensing elements offer several appealing inherent properties such as tissue-resembling elasticity, accessibility for modification and robust mechanical performance. Their widely available and affordable raw components in addition to a straightforward synthesis and modification approach make hydrogels appealing material for flexible and wearable sensors in biomedical applications. This work demonstrates the development of new and sensitive material for strain sensing using polyvinyl alcohol (PVA) and κ-carrageenan (κCA) hydrogel comprising conductive polyaniline nanofibers (PANI NFs). Double-network hydrogel was produced via chemical crosslinking of PVA with Glutaraldehyde (GA) and physical crosslinking of κCA with potassium ions in a binary solvent system of deionized water and glycerol. PANI NFs were then embedded in hydrogel matrix via the interfacial polymerization (IP) method of polyaniline nanofibers to significantly enhance the material properties and strain sensitivity of the pristine hydrogel. The obtained hydrogel has been involved in rigorous material characterization and sensing capability evaluation. The produced hydrogel demonstrated a high-water content (86.6%), high swelling percentage in acidic solutions, mechanical compressibility up to 60% at 400 kPa, high electrical conductivity of 2.11 S/m, and thermal stability ranging from -26.9 to 120 oC. The characteristics peaks of UV-vis at 299, 402, and 800 nm proved successful polymerization of aniline monomers to acquire conductive and high dispersed polyaniline nanofiber with diameter ranged between 13 and 40 nm. The hydrogel resulted in a linear response in its sensing performance of the applied stress (R2=0.99). Also, the developed composite demonstrated a sensitivity of 1.5 mV/kPa in stress range from zero up to 170 kPa with response and recovery times of ~300 ms and 500 ms, respectively.
