Ultrasoft Conducting Polymer Hydrogels with Large Biaxial Strain and Conformal Adhesion for Sensitive Flexible Sensors

Conducting polymer hydrogels have been considered as promising materials for flexible sensors. The integrated performances of ultrasoftness, high deformation, mechanical robustness, conformal adhesion, and high sensitivity are of great importance for their applications in wearable sensors but still remains challenging. Herein, a highly deformable conducting polymer hydrogel with ultrasoftness, tear resistance, and self-adhesiveness is fabricated by incorporating poly(3, 4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) and silk sericin (SS) into a covalently cross-linked polyacrylamide (PAM) network. Owing to abundant noncovalent interactions among the folded SS chains, PAM chains, and PEDOT:PSS, the obtained hydrogel shows a low modulus (10.3 kPa), ultrastretchability (>2000%), particularly large biaxial strain (an areal strain of 1700%), high toughness (tearing energy of 2.5 kJ/m²), and good conformal adhesion. As a result, this hydrogel demonstrates superior strain-sensitivity (gauge factor = 13.8) in a broad strain range (2000%) and excellent sensing reproducibility. The hydrogel-based wearable sensor can be used for accurately monitoring large and tiny human movements in real time and serves as bioelectrodes for precise gathering of electrocardiography and electromyography signals, showing great potential for applications in flexible sensing devices.