Ultra stretchable, tough and self-healable poly(acrylic acid) hydrogels cross-linked by self-enhanced high-density hydrogen bonds

Abstract

Hydrogen bond cross-linked hydrogels are generally not able to combine ultra-high stretchability and toughness, because water molecules can weaken the strength of hydrogen bonds. Herein, we report a strategy of introducing high-density hydrogen-bonded micelles to prepare poly(acrylic acid) (PAA) hydrogels named PAA/LTL/MT hydrogel. The micelle cross-linker (assembled from triblock polymer, LTL) was composed of dense hydrogen bond core: Poly(ether-thioureas) with triethylene glycol, and hydrophilic shell: Poly(L-lysine). Meanwhile, methacrylized poly(ether-thioureas) (MT) was embedded in the micelles to further increase the density of hydrogen bond. As a result, the micelle cross-linked hydrogels exhibited remarkable mechanical performance, including ultra stretchability and toughness, the maximum fracture strain, true fracture stress and toughness were 7800%, 4.80 MPa and 1.73 MJ/m3, respectively. Moreover, the dense hydrogen bonds endow hydrogels with great self-healing ability and good conductivity. The combined properties of PAA/LTL/MT hydrogel endow it to be a promising candidate for bio-sensors.