Three-dimensional Molecular Geometry of PEG Hydrogels by an Expansion-Contraction Method through Monte Carlo Simulations

Three-dimensional (3-D) coarse-grained Monte Carlo algorithms were used to simulate the conformations of swollen hydrogels formed by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The simulation consists of three successive steps including diffusion, cross-linking and relaxation. The cross-linking of multifunctional reaction sites is simulated instantly followed by fast crosslinking. In order to explore the validity of this approach pristine poly(ethylene glycol) (PEG) hydrogels with tri- and tetra-functional reaction sites (G3 and G4 respectively) were prepared and characterized. The data from the simulations were found to be in good agreement with experimental results such as PEG lengths between crosslinks, pore volume and pore radius distribution, indicating the validity of the modeling algorithm. The calculated PEG lengths in G3 and G4 networks are close (approximate to 4.6 nm). The 3-D visual topological structure of the hydrogel network suggests that the ideal hydrogel is far from cubic, diamond or any well defined structures of regular repeating cells.