Figure 1.

VEGF modified particle synthesis. (A) Heparin coated polystyrene particles are fabricated by first oxidizing heparin to generate aldehyde groups. These groups are used to bind the photoactive crosslinker (ABH) and facilitate attachment to the amine-functionalized polystyrene particles. Once the particle is coated with heparin, the bind-and-lock strategy is employed. First VEGF interacts with heparin and forms its specific electrostatic interaction. Then, UV light activates the crosslinker, which non-specifically binds to the closest amine. The heparin-binding domain of VEGF has many available amines on the lysine groups that interact with the sulfate groups on heparin. (B) For the heparin nanoparticle, the heparin polymer chain is modified with the photoactive crosslinker and a dihydrazide through EDC chemistry. The dihydrazide is reacted in a large enough molar ratio to saturate binding and avoid unwanted crosslinking. Once the modified polymer is purified, it is combined with surfactants into a hexane solution for sonication. During the inverse emulsion sonication process, radical initiators are added to the solution to generate radical polymerization. The formed nanoparticles are purified in a liquid-liquid extraction process and then bound to VEGF in a similar fashion as the heparin coated polystyrene particles. (C) High density and low density binding are utilized, where distribution of VEGF in the gel is varied by maintaining constant growth factor concentration with different number of particles. (D) With VEGF bound, the particles are introduced to a fibrin gel and analyzed for induction of branching (arrow heads) and sprouts (arrows) from endothelial cell-coated cytodex beads. Tube length (line) and tube thickness (double-headed arrow) are also quantified. Tube lengths are summed to give total network length.