Fatigue-resistant, single-phase stretchable materials via crack bridging

Stretchable materials such as elastomers and hydrogels are vulnerable to the growth of a crack under repeated cycles of stretch. This is because in single-network/phase materials, the crack can easily propagate by fracturing a single layer of polymer chains. Therefore, to improve the fatigue resistance of stretchable materials, current methods focus on blocking the crack front by another intrinsically high-energy phase. Such high-energy phases, however, are often limited to specific polymers or compromise other properties, limiting its extension to other fields. Single material approaches have been used in structural materials but considered inapplicable to soft materials. Here we challenge this acknowledgement by demonstrating the crack bridging effect in micropatterned elastomers. Instead of resisting in front of crack tips, micropatterns shield polymer chains by bridging behind the crack front. To utilize the bridging effect, we create composites with one material. They are structurally one piece of material but have molecularly separated fibers and matrices due to different curing mechanisms of components. Single-phase composites of polydimethylsiloxane (PDMS) made by this strategy have a fatigue threshold three times higher than that of PDMS-hydrogel composites designed based on the classic high-energy strategy. This crack bridging strategy does not rely on the inter- and intra-polymer interactions provided by specific materials, and thus have a general usefulness.