Modeling Erosion of Polymer Networks with Stimuli-Responsive Degradable Bonds

Understanding and controlling degradation of polymer networks on the mesoscale is critical for a range of applications ranging from regulating growth of complex tissues and neural networks to controlled drug delivery. Degradation that can be controlled by external stimuli, for example photo-controlled degradation, permits spatially-resolved dynamic control of materials properties. We develop a dissipative particle dynamics (DPD) approach that captures degradation and erosion of hydrogels at the mesoscale. To overcome unphysical topological crossings of bonded polymer chains, we utilize a modified Segmental Repulsive Potential (mSRP) formulation. We focus on hydrogels formed by the end-linking of multi-arm polyethylene glycol macromolecular precursors. We track the degradation via measuring the fraction of the degradable bonds intact and spatial distributions of network fragments or clusters. We demonstrate that the dispersity and the fraction of broken-off fragments scales with the relative extent of reaction. Reduced weight average and reduced z-average degrees of polymerization allow us to identify the reverse gel point. We characterize the erosion process in solvents of various qualities via tracking the mass loss that accounts for the broken-off fragments remaining in contact with the percolated network. We quantify the dependence of the mass loss on the extent of reaction and on the hydrogel properties. These results elucidate the main features of degradation and erosion on the mesoscale and could provide guidelines for future design of degrading materials with dynamically controlled properties.