Induction of angiogenesis using VEGF releasing genipin-crosslinked electrospun gelatin mats

Rapid and controlled vascularization of engineered tissues remains one of the key limitations in tissue engineering applications. This study investigates the possible use of natural extracellular matrix-like scaffolds made of gelatin loaded with human vascular endothelial growth factor (VEGF), as a bioresorbable platform for long-term release and consequent angiogenic boosting. For this aim, gelatin was firstly electrospun and then cross-linked at two different concentrations (0.1% and 0.5% w/v) by using genipin, a low toxic agent, in order to fabricate a suitable substrate to be loaded with VEGF. Collected fibers were homogeneous and free of beads, the fibrous structure was retained after cross-linking. Mechanical properties were deeply affected by the chemical treatment showing a different behavior, depending on the testing conditions (i.e., dry or wet state). VEGF release was assessed by means of ELISA assay: a cumulative release of about 90% (0.1% w/v) and 60% (0.5% w/v) at 28 days was measured. Both VEGF loaded mats induced cell viability, endothelial differentiation and showed chemoattractive properties when tested on human mesenchymal stromal cells (hMSCs). In vitro and in vivo angiogenic assays demonstrated that the VEGF loaded mats induced an angiogenic potential in stimulating new vessel formation similar, if not superior, to fresh VEGF. VEGF retains bioactive and pro-angiogenic potential for up to 14 days. The results demonstrated that genipin cross-linked electrospun gelatin mats loaded with VEGF could be part of a useful strategy to stimulate and induce angiogenesis in tissue engineered applications.