Mesoscale modeling of erosion of polymer networks: characterizing mass loss via extent of reaction

Materials involving controlled erosion of polymer networks find numerous applications from the design of degradable plastics to the sequential release of encapsulated cells for tissue engineering. To further develop such applications, a better understanding of the physical processes occurring during erosion is essential. Herein, we present a Dissipative Particle Dynamics (DPD) based approach for modeling controlled degradation and erosion in polymer networks. We use the modified segmental repulsive potential (mSRP) DPD formulation to minimize unphysical bond crossings and include the effects of polymer chain entanglements in our model. We recently developed a LAMMPS-based custom framework that enables us to switch on and off the additional mSRP forces upon bond formation and breaking. We track the progress of degradation via measurement of the fraction of degradable bonds intact during degradation. The number and sizes of clusters of bonded beads formed during degradation allow us to calculate the weight-average degree of polymerization and predict a reverse gel point for the hydrogel films. These measurements depend on network parameters such as the hydrogel film thickness and crosslink density. Further, the spatial distribution of these clusters allows us to measure mass loss from the film. We show that along with the variations in network topology upon breaking, it is also necessary to account for the diffusion of clusters that broke off to comprehensively characterize the mass loss dynamic.