Polyelectrolyte Hydrogel with Piezoelectricity and Adhesion for Soft Electronics

Flexible and piezoelectric hydrogels show great potential in the fields of wearable sensors, soft robotics, and the human–machine interface. However, these existing piezoelectric hydrogel sensors lack adhesive properties to the skin, limiting their further application. Here, by introducing the methacryloxyethyltrimethylammonium chloride (DMC) and the sodium p-styrenesulfonate (NaSS) into the polyacrylonitrile (PAN) piezoelectric hydrogel, a polyelectrolyte hydrogel (PNxDyAz) was prepared through the electrostatic interaction between the polyelectrolytes. The obtained hydrogels exhibited good mechanical properties (fracture stress and fracture strain were 140.65 ± 4.52 kPa and 499 ± 9.54%, respectively) and excellent adhesion (adhesion to pig skin surface was 22.78 kPa), excellent mechanical-electric response performance, and could produce stable electrical signal output (∼65 mV) during 3000 stress-discharge cycles. When used as a flexible strain sensor, the PNxDyAz hydrogel accurately monitors a variety of body signals and exhibits excellent biocompatibility. Therefore, the flexible and piezoelectric PNxDyAz hydrogel will have broad application prospects in the field of soft electronics.