Construction Of Biomimicking Vascular Stent Based On Active Heparin Conjugation And In-Situ Nitric Oxide Generation

The stent intervention is one of the most common means for treating cardiovascular diseases(CVDs) in clinic owing to the advantages of minimal invasion, immediately massive effectiveness and positive effect of maintaining vascular patency. In the past several decades,multiple techniques have been used to improve the therapeutic effect of vascular stent,especially for drug eluting stent (DES) with their abilities of significantly reducing the incidence of in-stent restenosis. However, in-stent restenosis and late-stage thrombosis (LST)are still two main complications of vascular stents limiting their clinical applications. Thus, it still needs exploration and a long way from the goal of designing an ideal vascular stent according to clinical requirement.Healthy endothelium is the natural barrier to prevent thrombosis and thus enable the vascular stent surface normal endothelium function represents the most effective way to inhibit above complications. Heparin is a structural mimic of the proteoglycan heparan sulfate, which is also a major anticoagulant on the endothelial surface in all tissues. Another important job of the endothelium is to create the signaling molecule nitric oxide (NO), a crucial molecule in the cardiovascular system. Thus, we tried to construct endothelium function mimicking vascular stents based on active heparin conjugation and in-situ NO generation.Due to the limitation of insufficient of reactive groups on metallic stent surface and difficulty to immobilize biomolecules, this thesis developed a facile method to create controllable amine group densities adhesive polymer coatings for f’urther optimization immobilization of target biomolecules by the novel cross-linking of dopamine and hexamethylendiamine (HD). In addition to demonstrate the feasibility of this coating for multifunctional stent platform by coupling bioactive molecules, the investigations of required compatibility evaluations were carried out. The performances of strong adhesion strength and excellent stability as well as good endothelial cytocompatibility were found in PDAM/HD coating, indicating potential application as a stent coating.Based on the PDAM/HD platform, heparin was conjugated (Hep-PDAM/HD) by chemical coupling technique with a grafting density of ～900 ng/cm2. The well retained bioactivity of the immobilized heparin was confirmed by a remarkable prolongation of the activated partial thromboplastin time (APTT), suppression of platelet adhesion and prevention of the denaturation of adsorbed fibrinogen. The Hep-PDAM/HD also presented a favorable microenvironment for selectively enhancing EC adhesion, proliferation and migration, and at the same time inhibiting SMC adhesion and proliferation. Upon subcutaneous implantation,the Hep-PDAM/HD exhibited mitigated tissue response, with reduced inflammatory cell infiltration and less granulation formation compared to the control 316L SS.Two approaches were reported to develop NO generating coatings based on previous studies.One is to immobilize NO-generating agent of 3,3-diselenodipropionic acid (Se-Se) and 3,3-disulfodipropionic acid (S-S) on PDAM/HD coatings. Another is to synthesize NO-catalytic adherent polymer coating through simple one-step surface dip-coating of objects into a mixed aqueous solution by introducing Cu(Ⅱ) during the polymerization of dopamine (PDAM@Cu).All the NO catalytic coatings showed the ability to continuously catalyze RSNO to generate NO in the presence of proper thiol reducing agent. A wide and high controllable range of NO generation rates from LV to 12 n1ol/cm1/min were obtained. We demonstrated that all NO catalytic coatings exhibited outstanding inhibition effect on platelet adhesion, aggregation and activation via the cyclic guanylate monophosphate (cGMP) signal pathway. Moreover, the PDAM@Cu coatings could promote the adhesion and growth of ECs but inhibit proliferation of SMCs via the cGMP signal pathway, suggesting the great potential in endothelium repair ability’.All in all, this thesis was aimed to to construct endothelium function mimetic coating based on PDAM/HD. In addition to demonstrate the feasibility of strategy for ideal vascular stent by coupling through introducing bioactive molecules with multiple functions including heparin and NO, the results of this work help to further deciphering the biological responses to blood,ECs, SMCs and inflammation related cells, and will likely serve as a guide for the design of the new generation of vascular stents.