Study On Surface Modification And Biocompatibility Of NiTi Alloy Intravascular Stents

Since the vascular stents came out, it has replaced the significant status of the interventional cardiology that PTCA had upbuilt and opened a new way, which can cure the cardio-vascular disease. The technology of conventional stents becomes maturer and maturer in the past thirty years, its biocompatibility has been improving and the area of application also has been broading. At the same time, the inside limitations emerge gradually. Many researchers improved intravascular stent and great achievement was obtained on the surface modification. on the other hand, there had some progress in the fields of Drug-eluting stent and Endothelialized stent . The Drug-eluting stent had been applied in clinic. However,no matter Drug-eluting stent or Endothelialized stent , it is important and difficult to adhere substrate on the surface of NiTi alloy. It is beneficial to the drug-coating and the adhesion of endothelial cells to modify surface of the stent for roughness by ways of chemical erosion and plasma deposition technology. The stent which had been granulated with chemical erosion was treated with TiO₂ film prepared by use of Gel-sol. The surface modification and biocompatibility of NiTi alloy intravascular stents were studied in this text. At first, the chemical erosion was used to increase the roughness of the Ni-Ti alloy intravascular stent surface. The stent was immerged the mixed solutions of the acetic acid and nitric acid with the proportion of 3:7,5:5,7:3 for 3,5,7 min, respectively. The roughness was checked by surface figure machine(SuFcom750A). A TiO₂ film was coated on stent's surface by the way of Sol-Gel in order to restrain release of Ni²⁺. During plasma deposition trials, all samples were pretreated with Argon for 90 seconds (DC 5W, 1 sccm, 25 mtorr), then put in plasma reactor system and treated with different experimental conditions. In two modification methods the blank stents were as the control and each sample had 3 replications. Secondly, the biocompatibility including corrosion resistance , anticoagulation and hydrophilicity. The surface figure, structure and thickness of films were investigated by optical microscope and SEM. Corrosion resistance was measured by Potentiostat/Galvanostat (model 273) in simulated fluid, and anticoagulation was estimated by O.D/time curve according to dynamic cruor time experiment and blood platelet adhere experim in vitro. The hydrophilicity was investigated by observing and assaying the contact angle which was formed by distilled water sprayed on the stent surface. Finally, the effects of two modification ways were estimated by observing the adhesion of endothelial cells on the stent surface. Both chemical erosion and plasma deposition were effective ways for enhancing the surface roughness of stents. Plasma deposition improve the anticoagulation and hydrophilicity of stent, and blood compatibility is enhanced. However, the increase of stent's corrosion resistance is not notable. TiO2 film modification improve blood compatibility of stent,as the same time,its corrosion resistance is not as good as NiTi alloy because of surface films is uneven。Two surface modification ways can improved adherence of endothelial cell。Comparing with TiO2 films way,The plasma deposition is more simple and convenient way.