From micelle-like aggregates to extremely-stretchable, fatigue-resistant, highly-resilient and self-healable hydrogels

The applications of hydrogels can be greatly expanded by the improvement of extensibility and toughness. Despite remarkable efforts in tough hydrogels, little is known about the fracture strain above 100 mm/mm due to the inhomogeneous chemical networks and inefficient energy-dissipative mechanism. Herein, micelle-like aggregates were obtained from the self-assembly of dually alkyl-modified polyethylene glycol (PEG) in water, serving as dynamic junctions to fabricate hydrogel via the aqueous radical polymerization of acrylamide (AM) monomers in water with the assistance of methylene bisacrylamide. Unlike hairy micelles, interactions of aggregates and hydrogel framworks were improved obviously through pronounced entanglements between PEG and PAM macromolecules. Meanwhile, the reversible break/reformation of micelle-like aggregates upon stretching empowered the gel an efficient energy-dissipative mechanism. Therefore, hydrogels with extreme stretchability (tensile strain = 150 mm/mm) and high toughness (toughness = 24.8 MJ/m3) were generated. Remarkably, their mechanics could be easily modulated by varying alkyl terminals and molecular weights of PEG to control the strength of hydrophobic domains and physical entanglements, respectively. Two examples were displayed: ultra-sensitive gels for wearable sensors and mechano-responsive molecule release. Impressively, the gauge factor was 60.29 under large deformation (strain > 20 mm/mm), outperforming most conductive hydrogels. As the first research to tune the macroscopic property of the hydrogel by delicately adjusting the microstructures of micelles, and interactions between micelles and gel network, this work not only expands the applications of soft materials but also sheds light on fabricating super-stretchable matters, making it promising candidates for flexible sensors, artificial skins, and drug delivery systems.