Conception and validation of a collagen-based Pleiotrophin controlled release system for vascular applications

Post-implantation vascular graft failure is mainly caused by in-graft thrombosis and intimal hyperplasia. A fast endothelialisation has the benefit of reducing these adverse events. Grafts enrichment with pro-endothelialisation molecule has been proposed in recent years to improve endothelialisation. One such molecule is pleiotrophin (PIN), a secreted cytokine known for its beneficial effects on blood vessels and endothelial cells (ECS). Affinity delivery systems based on Type I collagen gels have been developed to better control the release of the loaded proteins. In these systems, specific non-covalent interactions are mediated by molecule, such as heparin, due to its ability to sequester, stabilize and protect growth factors and cytokine. The objective of this work is to develop a controlled release system for PTN. The effects of PTN on ECs have been analysed 10:17 and compared to the one exerted by Stromal Derived Factor ! (SDF-1), a known pro endothelialisatiori molecule. Type I collagen gels have been used as a scaffold for the release system. To increase the binding of PTN to the gel and to prolong its release over time, heparin have been added to the standard gel formulation. Structural analysis (mechanical tests and immunofluorescence analysis of the collagen fibers) have been perforined to evaluate the effects on structural and mechanical properties of the gels after the addition of heparin. PTN-specific ELISA assay has been used to analyse the ability of the heparin-modified collagen gels to bind and released PTN over time in a controlled way. The eftects of the released PTN on the viability and migration of ECs and SMCs has been evaluated and henocompatibility tests have been performed to analyse the effects of the addition of both heparin and PTN on the hemocompatibility properties of the gels. "The modification of Type I collagen gels with PIN and heparin demonstrated a clear added value in. vascular medicine, mainly because the enhanced biological performances