Laser Preparation Of Microstructured Surfaces Of Pyrolytic Carbon Mechanical Valves

Replacement of artificial heart valves was a common method to treat heart valve diseases,the artificial mechanical valves have become the most clinically used artificial valve due to its excellent durability.Pyrolytic carbon was currently the material of choice for mechanical valve leaflets,but after being implanted in the human body and for a long time contacted with blood,patients will have complications such as blood clotting and thrombosis.Therefore,how to improve the anticoagulant performance of pyrolytic carbon and reduce the incidence of thrombosis was a hot research topic.In this paper,nanosecond lasers are used to prepare parallel gratings and micropillar array structures on the pyrolytic carbon surface.The superhydrophobic pyrolytic carbon surface was obtained by optimized the laser parameters and combined with silanization.The influence of microstructure and superhydrophobicity on blood compatibility were studied by platelet adhesion,dynamic coagulation,and hemolysis rate experiments.The main research work and results are as follows:(1)The method of nanosecond laser combined with HDTMS modification has fabricated superhydrophobic parallel grating structure on the surface of pyrolytic carbon.When the laser power in the X direction is 27.5 W,the scanning times is 6,and the scanning spacing is 90 ?m,the contact angle can reach 153.21°.Keep the laser power and scanning times in the X direction unchanged,when only the scanning spacing was changed,the contact angle of the pyrolytic carbon surface first increases and then decreases as the scanning spacing increases.The results showed that reducing the scanning spacing as much as possible without destroying the overall morphology of the microstructure can keep the droplets in the Cassie state on the surface of the pyrolytic carbon,increased the contact angle of the sample to over 150°.(2)When the laser power in the X direction is 27.5 W,the scanning times is 6,the scanning spacing is 90 ?m,the scanning spacing of the laser in the Y direction remains unchanged,the contact angle of the prepared micropillar array structure sample surface first increases and then decreases as the laser power and the scanning times increase.When the laser power in the X direction is 27.5 W,the scanning times is 6,the scanning spacing is 90 ?m;the laser power in the Y direction is 15 W,the scanning times is 4,and the scanning spacing is 100 ?m,the contact angle can reach 152.26°.(3)Through the research on the hydrophobic durability of the superhydrophobic pyrolytic carbon surface,it was found that the contact angles of the superhydrophobic parallel grating structure and the micropillar array structure were 152.27° and 150.69°.After being placed in the air for 8 months,sample still have superhydrophobic performance,easy to store after preparation.Through friction and wear experiments,it is found that the average friction coefficient of the smooth pyrolytic carbon surface is 0.096,the average friction coefficient of the parallel grating structure and the micropillar array structure pyrolytic carbon surface are0.042 and 0.040,respectively,indicating that the microstructure can improve the wear resistance of the pyrolytic carbon surface.(4)The experimental results of platelet adhesion,dynamic coagulation and hemolysis rate show that the micro-nano composite structure can effectively reduce the available adhesion area of a single platelet.When the sample reached superhydrophobicity,the contact between blood and sample will be in the Cassie state,which can effectively reduce the actual contact area between blood and sample.At the same time,the higher the contact angle of the sample,the less the number of platelets adhered and the better the anticoagulant effect,the lower the hemolysis rate,the better the blood compatibility.When the contact angle of the pyrolytic carbon surface of the parallel grating structure and the micropillar array structure was close,the anticoagulant performance of the micropillar array structure was better than that of the parallel grating structure.