| Stent thrombosis affects the prognosis of percutaneous coronary intervention. The hydrophobicity and hydrophilicity of the surface are closely related to stent thrombosis. The blood compatibility needs good balance of the hydrophobicity and hydrophilicity. At present, the relationship between the restenosis and different hydrophobicity of stent surface has not been reported. The material of coronary stents is mainly 316L stainless steel, and the silane which has different hydrophobic groups can be grafted onto the surface of metal. Therefore, we can get different hydrophobic surface of coronary stent by modifying silane onto the surface of stainless steel stents, and then the relationship can be investigated.The octyltriethoxysilane, 3-(2, 3-epoxypropoxy) propyltrimethoxysilane, methyltriethoxylsilane and propyltriethoxysilane were modified onto the surface of bare 316L stainless steel. The hydrophobic intensity was evaluated by testing contact angle. The contact angles of octyltriethoxysilan, 3-(2, 3-epoxypropoxy) propyltrimethoxysilane, methyltriethoxylsilane, propyltriethoxysilane were separately 95o, 105o, 110o and 115o. Infrared spectra showed that the corresponding silane group vibrated and SEM confirmed that micron and nano-structure formed on the surface, which indicated silane had been grafted successfully. The reason of the different contact angle in each group was the different hydrophobic bulky group of silane and the formation of micron and nano-structure.The dynamic blood clotting, hemolysis, platelet adhesion, anti-clotting time and protein adsorption were carried out to evaluate the haemocompatibility of each group. As time went on, the time of the blood coagulation at the surface of materials didn't have close relationship with the hydrophobicity of stainless steel modified with saline. But the research indicated that the time of the blood coagulation increased as the hydrophobicity enhaced 50 minutes later. The blood compatibility of methyl silane-modified stainless steel surfaces was the best. The prothrombin time and actived partial thromboplastin time extended as the hydrophilicity of different stainless steel enhanced .Hemolytic rate of all materials was less than 5%, which indicated the stainless steel modified with saline matched the standard of medical material. With the hydrophobicity increasing, the platelet adhesive rate on the surface increased. The amount of adsorbed protein increased with the increased hydrophobicity. Compared with the bare stainless steel, the amount of adsorbed protein that of stainless steel modified with saline were less.With hydrophobicity increased, vascular endothelial cell adhesive ability increased. The morphology of vascular endothelial cells was spindle-shaped or round, and they did not grow as single layer. Some cells extend pseudopodia on the material and the cells appear interconnected phenomena. MTT showed that the number of cell of each group increased and they had no difference. The application of flow cytometer make the evaluation of cell proliferation quicker and more exactly by detecting the content of DNA and distribution of each stage of cell cycle. The number of S stage of the group modified with saline was a little less than the control group, but they have no significant difference. The results of MTT and flow cytometry showed silane-modified stainless steel had good cytocompatibility.The stents with different hydrophobic surfaces were implanted into the rabbit's abdominal aorta. Through vivo experiments, the amount of P-selectin and TXB2 were tested to evaluate the platelet activation. The research indicated that the amount of P-selectin and TXB2 increased obviously after stenting than those before stenting. The platelet activation in each group with different hydrophobic properties had no significant difference. Compared with bare stent, there were no significant differences too. The mechanism of activation of platelet may be the mechanical tear of intima and the damage of the vascular wall. The hydrophobicity of the stent surface played little roles.With the methods such as the abdominal aorta angiography, intravascular ultrasound, histological evaluation of biopsy, the author evaluated the effect of the stents thrombosis and intimal hyperplasia in each group which was implanted different hydrophobic stent. Angiography showed one case of octyltriethoxysilane group and one case of propyltriethoxysilane group had approximately 20-30% stenosis, and the others had no significant stenosis. Immediately after stent intravascular ultrasound suggested good adherence, but two stents had poor adherence four weeks later. The intimal hyperplasia could be seen between the stent and vascular wall obviously. The other stents had good adhere four weeks later, and the intimal hyperplasia also could be seen. The intimal hyperplasia of groups modified with saline was stronger than that of the bare stent group. Tissue injury scores of each group had no significant difference. Histopathologic examination showed that one case of bare stent group and one case of KH560 group had new thrombosis, while one case of methyl triethoxysilane group had old thrombosis. Compared with the bare stent group, the incidence of stent thrombosis of hydrophobic stent did not increased. One month later the increased hydrophobic properties of the stent did not increased or reduced the incidence of thrombosis. Around the stent, there was no obvious inflammatory response. HE staining showed that the inflammatory response of the placement around the stent modified with saline, compared with bare metal stent group and sirolimus-eluting stent group , did not enhance. Some small amount of lymphocytes and no foreign body giant cells could be seen in each group, which indicated the material did not cause severe inflammation. The inflammatory response of methyltriethoxysilane group was slightly stronger that that of other groups, which indicates the stents modified with silane had good biocompatibility. The intimal hyperplasia has enhanced with the increasing of stent hydrophobicity.
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