Highly stretchable, transparent and conductive double-network ionic hydrogels for strain and pressure sensors with ultrahigh sensitivity

Abstract

Ionic conductive hydrogels have attracted much attention in artificial electronic skins and wearable strain sensors. However, most of the hydrogel-based sensors exhibit poor mechanical properties and limited sensitivity. Herein, a highly stretchable and transparent ionic conductive hydrogel was fabricated by one-step polymerization to assemble sensors based on the dynamic crosslinked network, which consists of long polyacrylamide (PAM) chains as a skeleton and dialdehyde β-cyclodextrin (O-β-CD) cross-linked gelatin (Gel) as a sacrificial network. Dynamic chemical and physical cross-linking can endow the hydrogel with remarkable stretchability (>1200%) and good self-recovery properties. The excellent ionic conductivity (53.3 mS cm⁻¹) was realized mainly due to the integration of sodium chloride (NaCl). Notably, the hydrogel exhibits ultrahigh strain/pressure sensitivity (GF are 4.58 and 0.56 kPa⁻¹, respectively), a broad working range (0–1200%, and 0–250 kPa), and appealing repeatability (output signal remains almost constant over 500 cyclic tensile and compression tests), which can be used as a wearable sensor to monitor human motions including a variety of joint movements, and even subtle motions such as pulse and speaking. Therefore, the hydrogels have great potential to be further developed in human health monitoring, human-machine interaction, and skin-like electronics in the future.