| Cardiovascular disease is well recognized as a major cause of morbidity and mortality, currently accountable for30%of globle deaths. Angioplasty and stenting procedures, as well as bypass surgery, are used in the treatment of occluded vessels. However, angioplasty and stenting procedures may cause intima hyperplasia, leading to the stenosis again. And the inadequate autologous vessels limited their availability. Nowadays, with the development of tissue engineering, the research of vascular prosthesis has become a hot spot. Some vascular prostheses made from synthetic polymers, such as expanded polytetrafluoroethylene (ePTFE) and polyethylene terephthalate (PET, Dacron), have been widely used in clinic as large-diameter vascular grafts. However, when used as small-diameter vascular grafts (<6mm), these polymers have been proven unsatisfactory due to occlusion and restenosis. In this thesis, we adopted the strategy of in situ inducing rapid endothelialization to improve the long-term patency of small diameter vascular grafts. Combined with the structure design of the grafts, the tissue remodeling process in vivo was also facilitated. These researches became the foundation of development of the ideal small-diameter vascular grafts.In the last few decades, the arginine-glycine-aspartic acid (RGD), a tripeptide derived from the cell adhesion sequence of fibronectin, was demonstrated to improve the migration, adhesion and proliferation of endothelial cells. Due to the relatively slow degradation rate and bio-inert property, functional modification of the PCL grafts is still urgent. Thus, we developed different strategies to immobilize RGD on PCL grafts. First, we focused on developing a new and convenient method based on the condensation reaction of CBT groups and peptides containing D-cysteine. It belongs to the chemoselective ligation, a novel approach that usually proceeded under mild conditions without any catalysts and results in good yields with excellent biocompatibility. Our results proved that this method was safe, facile, and effective in improving surface performances of PCL, including hydrophilicity and cytocompatibility. Second, we innovatively developed a safe and mild surface coating technique which was carried out under physiological conditions. Nap-FFGRGD peptides could be coated on the PCL grafts through "surface-induced self-assembly". The amphiphilic peptide could self-assemble on the hydrophobic surface of PCL fibers and form a stable bioactive layer. The RGD modification inhibited platelet aggregation and improved the adhesion, spread and proliferation of endothelial cells in vitro. After implanted into rabbit carotid artery, RGD modified PCL grafts exhibited improved patency, reduced thrombosis deposition and accelerated endothelialization and smooth muscle regeneration. In addition, through the study of the mechanism of the inhibitive effect of Nap-FFGRGD to platelet aggregation, we demonstrated that Nap-FFG could selectively bind to the surface of platelet through unknown ligand-receptor interactions, initiating the self-assembly of Nap-FFG and hydrogelation around the surface of platelet, thus preventing the human platelet aggregation by negative charge repulsion and steric hindrance effect. Based on the above studies, the Nap-FFGRGD modified PCL grafts could realize in situ induction of rapid endothelialization and anticoagulation at the same time.However, RGD modified PCL grafts still had limited cell infiltration and capillaries formation due to the small pore size related to the common electrospining technique, which is not suitable for the long-term tissue remodeling. Therefore, a three-layered porogenic PCL graft (tPCL) was prepared by electrospinning of PCL and co-electrospraying of PEO. It consisted of a thin dense inner layer, a loose middle layer with average pore size of40-50μm and a dense outer layer. The micro porosity and nano-fiber structure of the tPCL graft allowed rapid infiltration of cells, thus accelerating the degradation process and extracellular matrix secretion. Moreover, the rate of endothelialization, capillary formation and smooth muscle regeneration within tPCL grafts were largely improved, partly owing to the large amount of monocyte/macrophage (Mφ) and secreted various cytokines in different stage of graft remodeling. These results should allow for better structural design of small-diameter vascular graft in the future.In clinic, patients who need artificial vascular graft usually are complicated. They might suffer from other diseases at the same time, for example, type2diabetes. Herein, we investigated the performances of PCL and PCL-RGD vascular grafts in diabetic rats and healthy rats. Compared with healthy rats, increased platelet adhesion, slow endothelization, early calcification and chronic inflammation were observed in our study, showed that diabetic rats have higher major adverse events than healthy rats, indicating that RGD modification could not improve the regeneration of vascular grafts in diabetic rats. Thus, the development of a promising vascular graft for diabetic patients is necessary and urgent. Type2diabetes should become an important disease model for follow-up evaluation in vivo performance of vascular grafts.Besides, we have reported on the first example of a molecular hydrogelator with the enzyme-controllable NO release functionality. The release rate of NO was constant and could be adjusted via changing the concentration of β-galactosidase added to the hydrogel. The hydrogel could be applied for the topical treatment of wound. We believed that this hydrogel system had great potential for locally controllable delivery of NO in the field of regenerative medicine and tissue engineering.In summary, this thesis deeply studied the construction of small diameter vascular grafts with the ability of in situ inducing tissue remodeling and anticoagulation from two aspects of peptide modification and structure design. |
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