Tough Hydrogels for Load-Bearing Applications

Tough hydrogels have emerged as a promising class of materials to target load-bearing applications, where the material has to resist multiple cycles of extreme mechanical impact. A variety of chemical interactions and network architectures have been used to enhance the mechanical properties and fracture mechanics of hydrogels. In recent years, the mechanical properties of high-performance hydrogels are benchmarked, however this is often incomplete as important variables like water content are largely ignored. In this review, we aim to clarify the reported mechanical properties of state-of-the-art tough hydrogels by providing a comprehensive library of fracture and mechanical property data. First, we briefly discuss modes of energy dissipation at work in tough hydrogels, which we use to categorize the individual data sets. Next, we introduce common methods for mechanical characterization of high-performance hydrogels, followed by a detailed analysis of the current materials and their (fracture) mechanical properties. Finally, we consider several current applications, compare high-performance hydrogels with natural materials, and discuss promising future opportunities of tough hydrogels.