Preparation And Performance Study Of Cobblestone Pattern On The Surface Of Pyrolytic Carbon Mechanical Valve

More than 15 million people die of sudden cardiac disease every year worldwide,which accounts for 30%of all deaths and ranking the top one among various causes of death.Among all cardiac disease,the valvular heart disease is one of the most common heart diseases.At present,the main method of clinical treatment of valvular heart disease is to replace the diseased valve with artificial heart valve.Artificial heart valves mainly include biological valves and mechanical valves,but biological valves have calcification problems and cannot be used for a long time.Although mechanical valves do not calcify and have a longer service life,their blood compatibility is poorer than that of natural valves,and the anticoagulation effect is not ideal.Pyrolytic carbon（Py C）as a mechanical valve material has been widely used in clinical,but when blood flows through the surface of a Py C based mechanical valve,there is a turbulent flow phenomenon,which activates platelets and eventually forms a thrombus.It is found that the key to solving the problem of mechanical valve thrombosis is to create a turbulence-reducing surface with low flow resistance.Based on this,the bionic cobblestone pattern with low flow resistance was prepared on Py C surface by laser etching and low surface energy modification technology,and the surface adhesion,flow resistance and blood compatibility of the biomimetic pattern were studied.（1）In this thesis,first,Py C with good mechanical properties and biological inertness was used as the substrate,and the low-adhesion superhydrophobic biomimetic cobblestone pattern（C-Py C）was obtained on the Py C surface by laser etching and fluorosilane self-assembly technology.At the same time,a grating pattern（G-Py C）and a mastoiding pattern（M-Py C）were also prepared as the control.Scanning electron microscope（SEM）observation found that C-Py C,G-Py C and M-Py C with regular arrangement were successfully prepared on the Py C surface.All the surface patterns show superhydrophobic properties.The surface adhesion,flow resistance and rolling angle of C-Py C are the smallest among all the patterns.What is more,the blood compatibility results show that C-Py C has the longest clotting time,very low hemolysis rate and poor platelet adhesion capability,which is expected to solve the problem of thrombosis on the surface of mechanical valve.（2）The durability of the superhydrophobic surface obtained by self-assembling fluorosilane molecules is not ideal,and the superhydrophobic effect will be lost under liquid impact and friction environment.In order to improve the stability of the surface to ensure that the mechanical valve can still maintain stable performance in the long-term blood flushing environment,in this paper,fluoride ions were injected into the surface of the bionic cobblestone pattern structure to obtain a mechanical valve surface with a fluorine biomimetic cobblestone pattern（FC-Py C）.SEM results show that the ion implantation does not change the morphology of the cobblestone.The contact angle test results show that when the concentration of implanted fluoride ions is 2.0×10¹⁷ions/cm²（FC-Py C-2）,the static contact angle is the largest（about 140°）,close to the superhydrophobic state.X-ray photoelectron spectroscopy（XPS）analysis found that the reason for the surface hydrophobicity of FC-Py C-2 was the existence of-CF and-CF₂hydrophobic groups on the surface after fluoride ions injection.The abrasion resistance experiment found the friction coefficient of FC-Py C-2reduced by 20.7%when compared to that of before ion implantation,indicating the significantly improvement of the surface wear resistance.After washed with water for a long time,the hydrophobicity of FC-Py C-2 did not change significantly,and it maintained good blood compatibility,indicating that the fluoride ion implanted mechanical valve has excellent durability.In summary,among the three surface patterns prepared on the surface of mechanical valves by laser etching,the C-Py C surface has the lowest adhesion and the smallest surface flow resistance,and is most likely to avoid the coagulation problem caused by turbulent flow on the valve surface.Additionally,fluoride ion implantation further improved the stability of the hydrophobic properties of the mechanical valve.Therefore,ion implantation of fluorine with excellent durability on the surface of bionic cobblestone pattern with low flow resistance will provide a new technical way to completely solve the coagulation problem on the surface of mechanical valve.