Study On Electrochemical Polishing Process And Surface Properties Of Ni-Ti Alloy Cardiovascular Stent

In the world,cardiovascular disease has been a serious threat to human life and health.It has the characteristics of high morbidity,high disability rate and high mortality.In recent years,it ranks first in the death of diseases.At present,interventional therapy has become the main means of cardiovascular disease treatment,with advantages of small injury,high safety and obvious effect.Ni Ti alloy is considered to be an ideal bioengineering material because of its unique shape memory effect and pseudoelasticity,excellent mechanical properties,physical properties and biocompatibility.The nickel titanium alloy cardiovascular stent is formed by laser cutting technology.The surface of the stent after cutting is thermally damaged,and defects such as residual tensile stress,heat affected zone and recast layer are formed.The precision of forming is low and the surface integrity is poor.Therefore,it is necessary to modify the surface of cardiovascular stents,study the mechanism of improving the surface integrity of cardiovascular stents,enhance their corrosion resistance and inhibit the precipitation of nickel ions in Ni Ti alloy,which is of great significance to improve the biocompatibility of stents.Cardiovascular stent is hollow,its structure is complex,and the effect of traditional mechanical polishing method is poor.Electrochemical polishing is not limited by the shape and size of the material.After polishing,the surface roughness of the cardiovascular stent is significantly improved,and the defects such as scratches,dust inclusion and cracks are effectively removed.The surface integrity of the cardiovascular stent is better.According to the test requirements,the electrochemical polishing device is built by ourselves,which mainly includes DC stabilized power supply,cathode,polishing groove,polishing liquid circulation system and temperature control system.It is easy to operate and easy to use.In the polishing process,1 mol/L ethylene glycol sodium chloride solution was used as the base solution,and 3%hydrogen peroxide,triethanolamine and glucose concentrations were 10 ml/L,10 ml/L and 9 g/L respectively as additives.Through orthogonal test and single factor test,the best combination of process parameters was obtained as follows:polishing voltage 17 V,distance between electrodes 20 mm,polishing time 10 min,polishing temperature 25?.The influence of the above four factors on polishing quality decreased in turn.The lowest surface roughness Ra value was 63.5 nm by white light interferometer.The effect of electropolishing process on the surface properties of Ni Ti cardiovascular stents was further revealed through experimental comparative study.After polishing,the surface roughness of the stent was obviously reduced,and the defects such as heat affected area and recast layer were basically removed.The surface of the obtained stent was bright,smooth,even and glossy.After polishing,TiO2 film with a thickness of about 20 nm was formed on the surface.The dense TiO2 film can effectively inhibit the precipitation of nickel products.The electrochemical corrosion test showed that the smaller the corrosion current density(jcorr=2.444×10-6a/cm~2),the higher the polarization resistance of the polished stent,which enhanced its corrosion resistance.The results of hydrophilic and hydrophobic test showed that the polished stent was hydrophilic,which was beneficial to adsorb albumin,enhanced the blood compatibility of the stent,and effectively improved its biocompatibility.