Bismuth Sodium Titanate-Enhanced Microfibrillated Cellulose/Poly(acrylic acid) Double-Network Piezoelectric Hydrogel for a Self-Powered, Flexible, and Durable Strain Sensor

Hydrogel sensors based on piezoelectric nanomaterials have emerged as a promising technology, which has the advantages of being lightweight, flexible, and able to conform to irregular surfaces and can accurately sense various physiological signals of the human body without the need for external power. However, most piezoelectric hydrogels suffer from poor toughness, low sensitivity, and complex preparation processes, which seriously hinder their practical applications. This work reports a self-powered hydrogel with excellent stretchability and toughness for use as a strain sensor. Using a simple one-pot method, a composite piezoelectric hydrogel was synthesized with microfibrillated cellulose (MFC) and poly(acrylic acid) (PAA) as the hydrogel matrix and surface-modified Na_0.5Bi_0.5TiO₃ (TBNT) nanoparticles as high-performance piezoelectric fillers, and its potential application for human motion detection was explored. The MFC/PAA/TBNT composite hydrogel exhibits excellent mechanical properties with a fracture stress of 1.4 MPa and an elongation of 740%, due to the well-designed dual-network hydrogel structure and the good compatibility between TBNT nanoparticles and hydrogel matrices. With the TBNT-enhanced piezoelectricity, the MFC/PAA/TBNT hydrogel sensor realizes an excellent mechanical–electric response performance (GF is 19.07 mV under small compressive strain) and superior durability (∼209 mV during 1000 s stress–discharge cycles). The obtained sensor can be conveniently attached to the human body, demonstrating high accuracy and stability in real-time monitoring of human motions. Therefore, the flexible hydrogel sensors based on piezoelectric TBNT nanoparticles will have broad application prospects in the field of wearable health monitoring.