Tough hydrogels featuring low young's modulus and low mechanical hysteresis toward high-performance strain sensors

Numerous strategies have been developed to improve the mechanical strength of hydrogels, yet most inevitably compromise their intrinsic favorable properties, such as low Young's modulus and high resilience, which are important mechanical factors for stretchable electronics. Herein, a maleic anhydride-modified polyacrylamide hydrogel (PAM-MA-Fe) featuring a single network reinforced by robust ionic coordination interactions was successfully fabricated. This efficient toughening strategy significantly enhances hydrogel mechanical strength while excellently maintaining a low Young's modulus (106.2 kPa) and low mechanical hysteresis (7.3% at 1 mm/mm). In comparison, a conventional double-network hydrogel (PAM-SA-Fe) with integrated sodium alginate and polyacrylamide networks also achieves enhanced strength, but exhibits a sharply increased Young's modulus (692.5 kPa) and severely aggravated hysteresis (58.5% at 1 mm/mm). When applied in flexible strain sensors, PAM-MA-Fe endows devices with superior sensitivity and stable signals, whereas PAM-SA-Fe-based sensors require larger driving force and generate unstable sensing outputs.