Interactions Between Organism And The Iron-Based Stent Material Deposited With Thin Film On Its Surface

In order to improve the degradation, mechanical properties and biocompatibility of the iron-based stent material, many research methods and evaluation means in vitro or in vivo have been done, such as by adding other metal elements to form the alloy, by changing forging method to modify mirostructure, by adding other ingredients to change iron-based material, by changing chemical composition or by the surface modification to change pure iron surface structure state. No matter which way the researcher adopts, endothelial cell layer forming on the surface of iron-based stent is the most ideal way to improve the blood compatibility, biocompatibility and maintain the long-term efficacy. In this paper, the surface of the iron-based stent material was modified in order to achieve endothelialization of blood vessel.First of all, pure iron film and iron oxide film are deposited on the monocrystalline silicon surface by unbalanced magnetron sputtering in order to obtain the modification surface of iron materials. The surface roughness, material characteristics of water properties, chemical composition and crystal type of the two types of films were studied systematically. Hemocompatibility and cytocompatibility of the two kinds of films were also studied.1. Pure iron film deposited by unbalanced magnetron sputtering method prepared on the surface of monocrystalline silicon is smooth, compact. The nanoscale grains on the pure iron film are cubic crystal. Pure iron film has good hydrophilicity. Iron oxide film deposited on the surface of monocrystalline silicon by the same method has nanometer grain size, and has no significant protrusions. Iron oxide film is orthorhombic type to Fe2O3 phase, and has better hydrophilic properties of the surface than pure iron film.2. Two detection methods of the blood compatibility were done by scanning electron microscopy and clotting time. After scanning electron microscopy results analysis, the anhydrous ethanol fixed methods of platelet is more suitable for degradable iron-based stent materials to study blood compatibility compared with the glutaraldehyde fixed methods. After comprehensive analysis, two kinds of film have good hemocompatibility.3. The Cytocompatibility of thin films were detected by CCK-8 kit, rhodamine staining, acridine orange/propidium iodide staining and flow cytometry methods. Comprehensive analysis shows that acridine orange/propidium iodide staining method combined with flow cytometric analysis are the more suitable for the biodegradable iron-based materials. Experimental results show that the surfaces of pure iron film and iron oxide film are good for endothelial cells and smooth muscle cells adhesion, growth and proliferation. Compared with on the stainless steel material, cells can adhere rapidly and spread very well on the surfaces of pure iron film and iron oxide film. Compared with the two kinds of thin film, pure iron film has better endothelial cell compatibility, and iron oxide film has better smooth muscle cell compatibility.Secondly, in order to research the interaction between pure iron film deposited on iron-based stent and organism, iron film was deposited on the pure iron stent by unbalanced magnetron sputtering method. This kind vascular stents were implanted in atherosclerotic model vessels and cultured by stress in vitro bioreactor.1. A blood vessel bioreactor was designed and constructed for simulating in vivo environment. Parameters analysis of the bioreactor for quantification including shearing stress, the state of laminar flow and pulse pressure were performed by hydrodynamics methods of theoretical derivation and orthogonal experiment rage analysis. The system can provide a flow range of 0.33-4.67 cm3/s condition. And it was deduced that to the blood vessel with different diameter, the shearing stress can be applied is from 0.08 Pa to 70.51 Pa. In order to maintain lamina conditions of the perfusate, as the length the input tube of the culture chamber is 18 cm, the maximal flow rate for supplied tube should not exceed 4.36 cm3/s, based on the determined perfusate viscosity coefficient and fluid density. The most important influencing factor to affect the blood pressure difference between systolic blood pressure and diastolic blood pressure is the operating distance of pulsation generator. The factors in secondary level are flow and frequency, and the effect of pressure is the lowest. The silicone rubbers were used instead of rabbit common carotid arteries and cultured in the bioreactor dynamically for 15 days. The experimental results show that the performance differences between the four channels was not significant. The results prove that four vessels can be cultivated in the bioreactor at the same time. New Zealand rabbit common carotid arteries were cultured in the bioreactor for 3 days by simulating its blood pressure and heartbeat. The results of scanning electron microscopy and HE staining observation display that endothelial cells still exist, and the vessel structure is not changed. Those results suggest that the bioreactor can simulate biological environment in vivo well.2. Pure iron material stents whose diameter is 1.65 mm were cutted by laser micro cutting mechanism. And pure iron film was deposited on stents surface by unbalanced magnetron sputtering method. The results of optical microscopy and scanning electron microscopy show that the film surface is smooth and flat, except that there are some small pits on the bracket bending position of the stents caused by excessive polishing corrosion. The peeling phenomenon is not found between basis iron material and pure iron film whose the thickness is about 14～16 nm through scanning electron microscopy observation when the stent be distracted by balloon.3. In order to study the interactions between organism and the iron-based stent material deposited with thin film on its surface at organ level, the atherosclerotic rabbit common carotid artery implanted vessel stent in it were cultured dynamically in vascular bioreactor. The daverage optical density of the slices made of the atherosclerotic rabbit common carotid artery which implanted vessel stent in was analyzed statistically through seven immunohistochemical indicators, such as VEGFR-2, VE-cadherin, a-SMA, TNF-a, IL-1, TGF-P and IL-6 etc. Those result show that the vessel implanted the pure iron stent with deposited iron thin film has good endothelial cell proliferation and endothelial cell regeneration trends, and the smooth muscle cell growth of this kind vessel is inhibited, and the inflammatory response of this kind vessel is slight. So, there can be included that the pure iron stent deposited with pure iron thin film has good ability to inhibit inflammation.The results of this paper can provide basis with optimizing the cytocompatibility research methods, and with the application in vivo safely of the biodegradable iron-based stent materials.