Characterizing the Molecular Architecture of Hydrogels and Crosslinked Polymer Networks beyond Flory–Rehner. II: Experiments

We previously [ Borges, F. T. P. Biomacromolecules 2020, 21­(12), 5104−5118 ] introduced a novel methodology for the characterization of the dimensions and architecture of hydrogel networks that provides more detailed information than the classical Flory–Rehner theory [ Canal, T. ; Peppas, N. A. J. Biomed. Mater. Res. 1989, 23, 1183−1193 ]. In this article, we illustrate our methodology by applying it to the phototerpolymerization of N-vinyl-2-pyrrolidone (NVP), ethylene glycol methyl ether acrylate (EGA), and poly­(ethylene glycol) diacrylate (PEGDA). The experimental design includes 120 formulations using different fractions of the three monomers. Experimental measurements determined the mass swelling ratio and were coupled with theory to compute the internal dimensions of the network. Results demonstrate how the use of a macromeric crosslinker leads to unique network architectures not predicted by classical F–R theory, e.g., the figure shows that the mass between crosslinks predicted by F–R is actually distributed between branches and the backbone. The methodology presented offers a path toward optimizing/customizing hydrogel properties to suit the size and shape of the specific therapeutic targeted for drug delivery.