Controlled degradation of micro and nanogels can be utilized in numerous applications, ranging from drug delivery applications to facilitating tissue engineering. As drug or biomolecules release from the hydrogels can be regulated via controlled degradation, further advancements in these applications would benefit from a clearer understanding of the hydrogel network degradation process. To this end, we have developed a Dissipative Particle Dynamic (DPD) method utilizing a stochastic approach to simulate the degradation of tetra-arm polyethylene glycol based nanogels. During degradation, clusters break off from the nanogel particle. We measure the cluster sizes in terms of the number of DPD beads in each cluster and track the distribution of these sizes along with the radius of gyration of the nanogel particle. We also track weight average degree of polymerization in these degrading systems. Our simulation approach allows us to probe the effects of degradation rate constant, polymer-solvent affinity, crosslink density, and initial nanogel size on the dynamics of the degradation process. Our results indicate that an increase in the particle size results in greater variance in the size of the clusters, provided that initial crosslink density remains constant. Further, we show that at the initial stages of the degradation process an increase in the radius of gyration of the nanogel is observed due to the decrease of a number of elastically active polymer strands resulting in gel swelling; we quantify this increase as a function of initial crosslink density. Specifically, we show that this effect is more pronounced for the loosely crosslinked gels. At late times, nanogels undergo reverse gelation and then complete disintegration to tetra-arm precursors.

Mesoscale modeling of nanogel degradation: Effect of crosslink density and particle size

ACS Spring Meeting 2021

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