Construction Of Biomimetic Composite Interface Based On Medical Nitinol And Its Biological Function Study

Cardiovascular disease is the world’s leading cause of death,with atherosclerosis being one of the most common causes of cardiovascular disease.Stent implantation has the advantages of small trauma and significant therapeutic effect and is widely used in the treatment of atherosclerosis.Vascular stents have undergone development from bare metal stents to drug-release stents to degradable stents,effectively improving short-term restenosis.However,complications such as late thrombus formation and restenosis after stent implantation still present significant challenges.Because the vascular stent implantation process inevitably causes endothelial cell damage,resulting in dysfunction of endothelial cell.The excessive proliferation of vascular smooth muscle cells leads to restenosis,and incomplete endothelialization of the stent surface is the main cause of late thrombosis.It is currently believed that increasing endothelial cell function confers rapid re-endothelialization on the surface of the stent to effectively reduce restenosis and advanced thrombosis.In order to achieve rapid endothelial regeneration on the surface after stent implantation,the researchers mainly used three surface modification strategies.In the early stage,endothelial cells were promoted by implanting endothelial cells directly on the surface of the stent.However,due to blood flow,it is difficult for cells to maintain adhesion,so the effect of re-endothelialization is not as good as expected.Then,it promotes endothelial cell migration to immobilize biofunctional molecules on the surface of the stent.The process of re-endothelialization,however,relies heavily on the migration process of endothelial cells at the site of stent implantation.Later,the spontaneous induction of re-endothelialization by stents draws attention.The endothelial progenitor cells are captured by special molecules on the surface of the stents.However,due to the difficulty in controlling the differentiation process of endothelial progenitor cells,the experimental results are not satisfactory.In the natural vascular structure,the endothelial basement membrane attached to the endothelial cells has a micron-scale groove topology,and the surface has nano-scale protrusions,forming a multi-scale micro-nano composite interface between the blood and the endothelium.Based on this,the researchers constructed some complex three-dimensional topological structures of the endothelial basement membrane of different size micro-nanotopography in different vascular stent materials in order to promote the endothelialization process of the stents surface.However,the topography of stents can only partially simulate the growth environment of endothelial cell in vivo.The substrate stiffness is often neglected which is another important mechanical factor of interface.The normal stiffness of vascular endothelial basement membrane is about 30 kPa,and the elastic modulus of the metal vascular stent reaches the order of magnitude of GPa.It has been reported in the literature that substrate stiffness can regulate the secretory process of important functional factors in endothelial cells.Therefore,in order to ensure the normal function of endothelial cells after vascular stent implantation,the substrate stiffness is also one of the most important factors in the design of stents.Based on the above,this study proposes a surface modification method with two important bio-interface factors: the substrate topography and stiffness.The micro-groove topography is performed on the surface of the medical nitinol by ion beam etching.On the surface of groove topography,a layer of hydrogel is constructed by photopolymerization technology.The purpose of this study is combining the substrate topography and stiffness on the surface of the vascular stent to promote endothelial cell function,and to resist platelet adhesion and activation,resulting in decrease of restenosis and late thrombosis.The main contents of the paper are as follows: At the beginning,micro-groove topography was constructed on the surface of medical nitinol by photolithography and ion beam etching,and further photopolymerization technology was used to construct polyvinylphosphonic acid-N,N’-methylenebisacrylamide(P(VPA-coMBAA))on the surface of the groove topography.The groove topography and copolymer hydrogel coating formed a biomimetic composite interface.The characterization by scanning electron microscopy and atomic force microscopy revealed that the groove topography was prismatic,with a top width of about 2 μm,a bottom width of about 6 μm,and a height of about 800 nm.The chemical structure of the copolymer hydrogel was characterized by attenuated total internal reflectance fourier transform infrared spectroscopy.The results showed that the hydrogel coating was successfully constructed.The results of atomic force microscopy showed that the groove topography remained after the hydrogel coating was constructed.The elastic modulus of biomimetic composite interface decreased from GPa to MPa compared with the smooth nitinol.The interface is closer to the real topography and stiffness of endothelial basement membrane.On the basis of the above,the proliferation of endothelial cells and smooth muscle cells on the biomimetic composite interface was evaluated.The results of CCK-8 experiments showed that the groove topography of biomimetic composite interface selectively inhibited the proliferation of smooth muscle cells and did not affect the normal proliferation ability of endothelial cells.The total RNA of endothelial cells was extracted which were cultured on the biomimetic composite interface.The effect of the biomimetic composite interface on the expression of important functional genes and the secretion of functional factors in endothelial cells was investigated.The results of qPCR experiments showed that the hydrogel coating of the biomimetic composite interface promoted the expression of PGIS gene and PGI2 secretion in endothelial cells and inhibited the expression of ET-1 gene and ET-1 secretion.The biomimetic composite interface did not significantly affect expression of eNOS gene and NO secretion.The results of cell migration experiments showed that the biomimetic composite interface promoted the migration of endothelial cells,and the effect on migration of endothelial cells was stronger than that of smooth muscle cells.In summary,the biomimetic composite interface promoted the function of endothelial cells and promoted the migration process of endothelial cells compared with smooth nitinol,which contributed to the rapid reendothelialization on the vascular stent surface.The evaluation of blood compatibility showed that the biomimetic composite interface had anti-platelet adhesion and activation ability,which helped to prevent thrombosis.As an implantable medical device,the hemolysis rate of the biomimetic composite interface was 0.51%,which was far less than 5% of the international standard,and had excellent blood compatibility.In summary,this study is aimed at the nitinol which is widely used as medical vascular stent material.The groove topography and copolymer hydrogel coating were performed respectively forming a biomimetic composite interface on the surface of medical nitinol.In vitro,compared with smooth nitinol,the biomimetic composite interface can promote the secretion of PGI2 and inhibit the secretion of ET-1 in endothelial cells.Therefore,the biomimetic composite interface can improve the function of endothelial cells to some extent.At the same time,the biomimetic composite interface can promote endothelial cell migration and facilitate the rapidly re-endothelialization on the surface of the stents.The results of blood compatibility experiments in vitro indicate that the biomimetic composite interface can effectively resist platelet adhesion and activation,and contribute to prevent thrombosis.Taken together,this study can provide a new strategy for biomimetic modification of implantable medical device such as vascular stents.