The enhancement of VEGF-mediated angiogenesis by polycaprolactone scaffolds with surface cross-linked heparin

This study investigates the effect of surface cross-linked heparin on vascular endothelial growth factor (VEGF)-mediated angiogenesis in porous polycaprolactone (PCL) scaffolds in vivo. We tested the hypothesis that VEGF delivered by scaffolds coated with a sub-micron thick layer of immobilized heparin would accelerate angiogenesis. The bioactivity of retained VEGF was confirmed by its phosphorylation of VEGF receptor-2. After 7 and 14 days of subcutaneous implantation in mice, the heparin-PCL scaffolds loaded with VEGF displayed significantly higher infiltration of blood vessels which traversed the entire scaffold thickness (2 mm). The stability and function of the newly formed vessels were confirmed by smooth muscle cell coverage and vessel perfusability, respectively. The contribution of individual components was assessed by varying the VEGF dose and heparin thickness. Prolonging the cross-linking reaction on PCL scaffolds resulted in higher heparin content, thicker heparin layer, and higher VEGF retention. While a dose dependent angiogenic response was observed with VEGF, higher amount of cross-linked heparin did not translate into additional improvement in angiogenesis for a given dose of VEGF. The synergism of immobilized heparin and VEGF in stimulating angiogenesis was observed in vivo.