Fatigue Behaviors of Anisotropic Hydrogels with a Macroscopic Lamellar Bilayer Structure and Swelling Effects

The application of soft materials for long-term use requires a profound understanding of their fatigue mechanisms and structural evolution under cyclic loading conditions. In this work, we studied the fatigue resistance behaviors of an anisotropic hydrogel composite consisting of periodically stacked, polymerized bilayers embedded in an elastic hydrogel matrix. The hydrogel composite exhibits high toughness and self-resilience under monotonic loading due to efficient energy dissipation from the lamellar bilayers, which act as reversible sacrificial bonds. We found that at a loading rate similar to the monotonic loading test, bilayers only modestly enhance the fatigue threshold itself but significantly suppress the fatigue crack extension rate above the fatigue threshold. Specifically, the fatigue crack extension length per cycle is only 1/10,000 that of the pristine elastic hydrogel. This enhancement in fatigue fracture resistance is only modestly reduced in the fully swollen sample.