High Fracture Efficiency and Stress ConcentrationPhenomenon for Microgel-Reinforced Hydrogels Based on Double-NetworkPrinciple.

Double-network hydrogels (DN gels)have aroused considerable interestbecause of their excellent mechanical strength and toughness, lowsliding friction, good biocompatibility, as well as wide tunabilityin components. By revisiting DN gels, we provide an ingenious wayto fabricate a kind of strong and tough microgel-reinforced hydrogels(MR gels), that densely cross-linked polyelectrolyte microgels ofpoly(2-acrylamido-2-methylpropanesulfonic sodium) (PNaAMPS) (replacingthe densely cross-linked PNaAMPS macro-network for conventional DNgels) are incorporated into sparsely cross-linked neutral polyacrylamide(PAAm) matrix. The structure of MR gels can be considered as a two-phasecomposite, where the disperse phase is the rigidDNmicrogels, and the continuous phase is the softPAAmmatrix. Similar to DN gels, MR gels show the irreversible energy dissipationin the hysteresis measurement, demonstrating the permanent fractureof the brittle PNaAMPS phase. Thus, the discontinuous brittle phasealso serves as sacrificial bonds. Through quantitativecomparison of the hysteresis curves with DN gels and monitoring themorphology change of the embedded microgels in MR gels during thereal-time stretching process, we conclude that the DN microgels inMR gels show four times higher in fracture efficiency of the sacrificialbonds than bulk DN gels at the same strain, as a result of the stressconcentration around the microgels. [ABSTRACT FROM AUTHOR]