Multi-scale mechanical and transport properties of a hydrogel

• A novel cross-linking method is used to create molecular structure of hydrogels.
• However, existing all-atom models cannot predict the actual mechanical properties of hydrogels.
• A novel Coarse-Grained (CG) model is proposed to capture the elastic properties more accurately.
• The CG model can also predict the transport properties, being verified with the all-atom model.
• The CG model predicts the optimal water content for hydrogel mechanical performance is about 40%.

In this paper, molecular dynamic simulation was used to study the effect of water on the equilibrated structure and mechanical properties of cross-linked hydrogel at multiple scales. The hydrogel consisted of Polyethylene glycol diglycidyl ether (PEGDGE) as epoxy and the Jeffamine, poly-oxy-alkylene-amines, as curing agent. The results for systems with various water contents indicated that the cross-links were more hydrophilic within the hydrogel structure. Effects of cross-linking on the transport properties were also investigated by computing diffusion coefficients of water molecules. A new Coarse-Grained (CG) scheme for hydrogels is proposed, and validated by comparing the transport properties with the all-atom method, demonstrating the capability of the model to capture the correct dynamic evolution of the system. The all-atom model of the hydrogel was mapped to the CG model using the MARTINI force field. This method resulted in a more realistic representation of the stiffness of the system, compared to the previous experimental studies in the literature. The variation of the stiffness of the hydrogel as a function of the water content showed that 40% water content is the optimal value for mechanical performance of the hydrogel.