Nanostructuring biosynthetic hydrogels for tissue engineering: A cellular and structural analysis

The nanostructuring of hydrogel scaffolds used in tissue engineering provides the ability to control cellular fate and tissue morphogenesis through cell-matrix interactions. Here we describe a method to provide nanostructure to a biosynthetic hydrogel scaffold made from crosslinked poly(ethylene glycol)-fibrinogen conjugates (PEG-fibrinogen), by modifying them with the block-copolymer Pluronic® F127. The copolymeric additive self-assembled into micelles at certain concentrations and temperatures, thereby creating nanostructures within the crosslinked hydrogel. Small-angle X-ray scattering (SAXS) and transmission electron microscopy at cryogenic temperature were used to detect Pluronic® F127 micelles embedded within the crosslinked PEG-fibrinogen hydrogels. The density and order of the micelles within the hydrogel matrix increased as the relative Pluronic® F127 concentration was raised. The transient stability of the micelles within the hydrogel network was analyzed using time-dependent swelling and Pluronic® F127 release measurements. These characterizations revealed that most of the Pluronic® F127 molecules diffuse out of the hydrogels after 4 days in aqueous buffer and SAXS analysis confirmed a significant change in the structure and interactions of the micelles during this time. Cell culture experiments evaluating the three-dimensional fibroblast morphology within the matrix indicated a strong correlation between cell spreading and the hydrogel's characteristic mesh size. The present research thereby provides a more quantitative understanding of how structural features in an encapsulating hydrogel environment can affect cell morphogenesis towards tissue regeneration.