Improving hydrogels' toughness by increasing the dissipative properties of their network.

The weak mechanical performance and fragility of hydrogels limit their application as biomaterials for load bearing applications. The origin of this weakness has been explained by the low resistance to chains breakage composing the hydrogel and to the cracks propagation in the hydrogel submitted to loading conditions. These low resistance and crack propagation were in turn related to an insufficient energy dissipation mechanism in the hydrogel structure. The goal of this study is to evaluate the dissipation mechanism in covalently bonded hydrogels so that tougher hydrogels can be developed while keeping for the hydrogel a relatively high mechanical stiffness. By varying parameters such as cross-linker type or concentration as well as water ratio, the dissipative properties of HEMA-based hydrogels were investigated at large deformations. Different mechanisms such as special friction-like phenomena, nanoporosity, and hydrophobicity were proposed to explain the dissipative behavior of the tested hydrogels. Based on this analysis, it was possible to develop hydrogels with increased toughness properties.