Figure 9.

Schematic representation which indicates the hypothetical manner in which secondary reactive species (SRS) may interact with the PEGDA hydrogel network structure at the nanoscale. (A) A schematic representation of a pure PEGDA hydrogel network, with nanoscale regions of PEGDA densification which include crosslink junctions (adapted from Waters et al., 2010); (B) We hypothesize that the SRS participate in the crosslink junctions in the dense PEGDA regions and perhaps contribute to increased PEGDA densification. In pure PEGDA hydrogels, the acrylate groups (hydrophobic regions of the PEGDA molecules) bend the PEGDA chains, creating micelles. The grouped acrylate moieties then participate in the formation of crosslink junctions. Given the fact that the acrylate groups will have higher affinity for NVP or the dense, tetraacrylated molecule PEGTA than for water molecules, the presence of these SRS molecules can serve as a nucleation points, bringing additional PEGDA chains in close proximity and increasing the density of the polymer within the nanoscale aggregates. The inset in (C) shows a magnified schematic of a nanoscale PEGDA aggregate in a PEGDA control hydrogel and the inset in (D) shows a nanoscale aggregate in which the SRS (red) has increased the density of the PEGDA chains (blue) at the crosslink junctions.