Temporally regulated delivery of VEGF in vitro and in vivo.

The exposure duration and tissue distribution will likely dictate the success of vascular endothelial growth factor (VEGF) in therapeutic angiogenesis. We hypothesized that these variables can be regulated via the manner in which the VEGF is incorporated into polymer constructs (formed with a gas foaming technique) used for its delivery. VEGF was incorporated directly into poly(lactide-co-glycolide) (PLG) scaffolds or pre-encapsulated in PLG microspheres used to fabricate scaffolds. Protein release kinetics and tissue distribution were determined using iodinated VEGF. VEGF was positioned predominantly adjacent to scaffold pores when incorporated directly and was released rapidly (40-60% in 5 days). Pre-encapsulation led to the VEGF being more deeply embedded and resulted in a delayed release. Alterations in polymer composition, scaffold size, and matrix composition generated minor variations in release kinetics. In vivo, the released VEGF generated local protein concentrations above 10 ng/mL at distances up to 2 cm from the implant site for the 21 days of the experiment, with negligible release into the systemic circulation, and significantly enhanced local angiogenesis. These data indicate that VEGF can be administered in a sustained and localized fashion in vivo, and the timing of VEGF delivery can be altered with the mechanism of incorporation into polymer scaffolds used for its delivery.