Anti-freezing, hybrid hyaluronate‑gold nanoparticles-polyacrylamide gel - synthesis, characterization and application as sensitive pressure sensor.

The composition of gel materials can be tailored to achieve desired properties and functions, making them suitable for applications as sensors and smart interfaces. In this work, the sodium hyaluronate (HA) polymer enables multiple functions as a reducing and stabilizing agent for gold nanoparticles; additionally, the hyaluronate chains enhance mechanical properties and improve interfacial adhesion. In the first step, the gold nanoparticles were formed by reduction with hyaluronate. Using this method, small AuNPs with a narrow size distribution can be obtained. Then, the HA/AuNPs solution was utilized to synthesize semi-interpenetrating polymer pAAm-sIPN-HA/AuNPs. The obtained material has mechanical properties similar to those of human skin, good adhesion, compression-dependent conductivity, and, due to the presence of glycerol, excellent anti-freezing properties. The pAAm-sIPN-HA/AuNPs hybrid gel exhibits a compressive strength of (120.2 ± 34.3) kPa, elongation at break of (620 ± 21) %, tensile strength of (22.9 ± 4.3) kPa, toughness of (71.3 ± 11.2) kJ·m-3, and adhesion strength to porcine skin of (6.03 ± 0.24) kPa. This soft nanocomposite gel can be applied as a pressure sensor for monitoring very subtle human motion; it possesses exceptional sensitivity - 0.0896 kPa-1 for low pressures in the range of 0-1 kPa, and in the range of 1-10 kPa - 0.0530 kPa-1, with fast response and recovery times of 200 ms. The pAAm-sIPN-HA/AuNPs sensor can be used to detect touch stimuli, as well as to detect Morse code signals.