Histologic and genetic features of remodeling of tissue-engineered small-diameter vascular grafts: outcomes of six-month implantation in a sheep model

Abstract

Surface modification of polymeric scaffolds with drugs to avoid thrombus formation and infection is a promising area in tissue engineering, which also makes it possible to accelerate the remodeling of such scaffolds and improve long-term patency.The objective of this paper is to study the histologic and genetic features of remodeling of tissue-engineered small-diameter vascular grafts (SDVGs) with antithrombogenic drug-coated and reinforced external scaffolds, implanted into a sheep carotid artery.Materials and methods. Poly(ε-caprolactone) (PCL) matrices, ∅4 mm in diameter, were fabricated via electrospinning, followed by creation of a reinforcing spiral PCL scaffold on their outer surface by extrusion. To prevent thrombus formation and infection, the fabricated grafts were modified with iloprost and cationic amphiphile by complexation through polyvinylpyrrolidone (PVP). The work was carried out to evaluate, by infrared spectroscopy, the formation of PVP-based coating, to study the physical and mechanical properties of the grafts in longitudinal and transverse directions, and to implant the vascular grafts (VGs) into a sheep carotid artery. To assess and control the patency of the implanted grafts, Doppler ultrasound was performed at days 1 and 5, then at 1, 3 and 6 months. The explanted samples were studied via histological and immunofluorescent analyses; gene expression profile was evaluated.Results. Ultrasound on days 1 and 5 after implantation showed the patency of vascular grafts to be 100%. At 1 month, the patency decreased to 83.3%; patency was 50% by the end of the implantation period (6 months), without aneurysm formation and detachment of the reinforcing scaffold. Histological and immunofluorescence studies of patent grafts showed the formation of a newly formed three-layer vascular tissue structure on their basis, without signs of inflammation and calcification. However, despite the structural similarity between the newly formed vascular tissue and the native tissue of a sheep carotid artery, analysis of the gene expression profile revealed some differences in terms of genetic profile: CNN and SNA12 expression levels in the neotissue decreased, and those of CTSB, TNFa, and TGFb increased.Conclusion. Modified polymeric vascular scaffolds showed good remodeling of the prosthetic wall, without aneurysm formation. The identified genetic differences between newly formed tissue and native tissue are logical in view of formation on the basis of the artificial polymeric scaffold. Further research on reinforced polymeric scaffolds will be aimed at improving the inner surface in order to improve their thromboresistance.

Keywords

• vascular grafts
• antithrombogenic treatment
• antimicrobial treatment
• iloprost
• cationic amphiphiles