Preparation And Properties Study Of Laser-induced Gradient Wettability Surface

More than 100,000 valve replacement surgeries are required in worldwide each year.At present,the most commonly used artificial heart valves are biological valves and mechanical valves.The biological valve has good hemodynamic performance,but it is easy to calcify and cannot be used for a long time.Compared with the biological valve,the mechanical valve has good durability and no risk of calcification,which is more favored by the patients,but the hemodynamic performance is poor and can result into hemolysis,requiring long-term anticoagulation.Currently,people mainly focus on how to effectively reduce the protein adhesion to materials to reduce the formation of thrombus,but only achieving limited success.The gradient wettability surface can theoretically regulate the biological adhesion behavior and reduce the flow resistance,which is expected to reduce the formation of valve thrombus.Therefore,in this thesis,a combination of laser etching technology and low surface energy molecular self-assembly approach will be used to accurately build a gradient wettability surface with a gradient microstructure on the surface of the material.The effect of the gradient wettability surface on biological adhesion behavior and flow resistance will be studied.Finally,a gradient wettability surface with anti-bioadhesion,high blood compatibility and low flow resistance will be obtained.In this thesis,Ni Ti alloy with good biocompatibility,blood compatibility,and low cost is first used as the substrate material.The Ni Ti alloy with porous gradient surface is constructed by a combination of laser etching and surface stearic acids self-assembly approach.Scanning electron microscopy(SEM)characterization showed that the gradient wettability surface composed by a smooth Ni Ti region and three porous regions with different pore sizes and pore distances.Laser confocal microscopy images confirmed that the roughness of the material surface increased along the gradient structure direction.The contact angle measurement showed that the wettability of the Ni Ti alloy surface gradually changed with the combined effect of the gradient structure and the low-surface stearic acid molecular layer,which can drive the droplet motion.Compared to pure Ni Ti,the gradient wettability surface exhibited a better anti-bioadhesion performance,lower hemolysis rate,and lower flow resistance.These results indicate that the prepared gradient wettability surface can be used to reduce the formation of valvular thrombus.In order to achieve the implants with long-term service in vivo,a highly durable gradient infiltrating surface is required.In this thesis,low-temperature isotropic pyrolytic carbon(LTIC)with more stable performance,better biocompatibility and blood compatibility was selected as the substrate material,and fluorosilane with stronger surface binding ability was used as the low energy molecule.The gradient wettability surface on LTIC(LS-LTIC)was constructed by the combination of laser etching and fluorosilane molecular self-assembly approach.Scanning electron microscope(SEM)characterization showed that the gradient-wettability surface consisted of a smooth pyrolytic carbon region and four different periodic grating-like regions.Water and blood contact angle measurements showed a gradient wettability change in the surface.The gradient wettability surface displayed high durability in air and PBS solution and under the long term impact of water flow.Further research found that both the gradient microstructure and low surface energy molecular coatings could affect the bioadhesion properties of the materials,among which the gradient microstructure plays a major role.Compared with smooth LTIC,LS-LTIC exhibited better blood compatibility,and thus can be long time used to reduce the formation of thrombus.In summary,this thesis first employed laser etching technology to build a gradient microstructure,and then used a low-surface energy molecular coating to build a gradient wettability surface.This surface has anti-bioadhesion properties and lower flow resistance,which can fundamentally improve hemodynamic properties for the mechanical valve,and thereby solving the problem of thrombosis.