The effect of vascular endothelial growth factor (VEGF) presentation within fibrin matrices on endothelial cell branching

► VEGF is covalently immobilized to heparin nanoparticles. ► VEGF is clustered at high and low densities, and then placed in fibrin gels. ► VEGF conjugated to the particles maintains activity and promotes migration signaling. ► In tube formation assay, high density VEGF significantly improves HUVEC branching. ► In CAM assay, high density VEGF recruits functional host vessels into fibrin gel.