Freezing-Induced Cross-Linking Strategy Constructing Antiswelling Porous Composites for Underwater Piezoresistive Sensing

Flexible piezoresistive sensors hold significant application demand in the fields of tactile perception and wearable electronics. However, developing flexible piezoresistive sensors capable of stable operation underwater remains a challenge. This difficulty primarily originates from signal drift and structural instability caused by the swelling effect of hydrogel matrices. To address this issue, we propose a freezing induced cross-linking strategy to fabricate a disintegration-resistant porous composite denoted as MSB-Ag, composed of microfibrillated cellulose (MFC), sodium alginate (SA), and silver nanoparticles (AgNPs). This method exploits the freezing concentration effect to during the freezing process to promote effective interactions between the polymer skeleton and the cross-linker, which consequently forms a robust porous structure. The prepared porous composite exhibit excellent mechanical properties with a compressive modulus of 510 kPa and a toughness of 187.0 kJ m–3. Furthermore, the material demonstrates superior strain sensitivity with a gauge factor (GF) of 4.66 and antiswelling performance with a mass swelling ratio of 10%. It retains substantial sensing capabilities even after working in an underwater environment for 50 days and can detect minute strains as low as 0.1%. In an air environment, the sensor can be used for the real-time monitoring of various human motions, including large-scale joint movements and subtle muscle vibrations. More importantly, the MSB-Ag porous composite soaked in an underwater environment for 50 days has been successfully employed as a strain sensor for both underwater motion detection and communication. This demonstrates its promising potential for application in underwater sensing.