Fabrication of fatigue-resistant hydrogel via annealing-assisted salting-out method as flexible strain sensors

Hydrogels exhibit unique properties such as softness, biocompatibility, and responsiveness, which render such types of materials widely applicable in wearable devices. Although the toughness of hydrogels has been significantly improved over the past years to resist fracture deformations under the application of a single mechanical cyclic load, the already existing tough hydrogels are still prone to fatigue fracture when they are subjected to multiple cyclic mechanical loads. In this work, an annealing-assisted salting-out method was used to fabricate microcrystalline areas within the hydrogel to prepare anti-fatigue P(AAm-co-MPC)/PVA hydrogels. Interestingly, the fatigue threshold of these materials reaches the value of 480 J m −2 , much higher than that of the conventional synthetic hydrogel (1–100 J m −2 ). In addition, the proposed hydrogel structures exhibit excellent sensing performance, with a conductivity value of 0.42 S m −1 , and a long-term stable strain-current response (2500 cycles). The applicability of this technique is not limited only to conductive hydrogels, but can also be extended to enhance other functional hydrogels with poor fatigue resistance properties.