On the failure and fracture of hydrogels for cartilage replacement

The failure and fracture properties of hydrogels and hydrogel composites are considered in the contexts of applicable fracture mechanics and biomaterials engineering. Distinction is made between material failure properties, characterized by a work of failure independent of mechanism, and fracture properties, characterized by fracture resistance that requires clear identification of crack propagation. Although advanced hydrogels can exhibit very large works of failure relative to conventional single-network hydrogels, they do so only at large strains and are not well characterized by fracture properties alone. The large failure strains are not obviously relevant to many biomaterial applications such as cartilage replacement, for which the engineering requirements involve limited physiological strains. An example is given of fiber-reinforced hydrogel composites that demonstrate increased work of failure at small strains.