Mesoscale modeling of stress-strain behavior of tetra-PEG networks

We focus on hydrogels formed by end-linking of four-arm polyethylene glycol precursors with photolabile groups and characterize stress-strain behavior in these systems during photodegradation. We use our recently developed dissipative particle dynamics framework that captures bond scission and diffusion at the mesoscale. Breaking elastically active network strands during degradation leads to a decrease in elastic modulus and introduces structural and dynamic heterogeneities. We quantify the structural and dynamic heterogeneities upon approaching the reverse gel point. We apply strain with the constant strain rate and calculate the tensile stress via the respective pressure tensor components, which include contributions from the velocities of the beads and from the conservative forces. We characterize stress-strain curves for virgin hydrogels, which correspond to ideal tetra-functional networks, and for a range of hydrogel samples with various fractions of bonds broken during controlled degradation. Our results allow one to quantify stress-strain behavior of degrading hydrogel material and could provide guidelines for future design of degrading materials with dynamically controlled mechanical properties.