Effect of heterogeneities in controllably degrading hydrogels on its structural and mechanical properties

Photo-controlled degradation allows dynamic and localized tunning of materials properties, in particular mechanical properties of hydrogel-based materials. This work evaluates the structural and dynamic heterogeneities in degrading tetra-PEG hydrogels and their effect on mechanical properties, especially elastic modulus. We use our recently developed dissipative particle dynamics (DPD) framework that captures degradation of hydrogels at the mesoscale. We characterize the average mesh size of the degrading polymer network, the mean square displacements of the polymer junctions and the reactive beads, and the self-part of the van Hove correlation function. Characterizing average mesh size allows one to predict transport properties of a penetrant within the polymer network via a confinement parameter, defined as a ratio of the size of the penetrant to the mesh size. Further, to quantify the effect of structural and dynamics heterogeneities on mechanical properties of the degrading network, we calculate the shear modulus using related network theories. The results of this work allow one to characterize mechanical properties of degrading hydrogel material dependent on the extent of degradation and could provide guidelines for designing degrading materials with dynamically controlled mechanical properties.