Preparation And Study Of Antithrombotic Plasma Polymeric Allylamine Films

The metallic biomaterials such as stainless steel (AISI 316L), tantalum and the shape memory alloy TiNi have been widely used for coronary stent, the peripheral vascular stent and vena cava filter which are of the cardiovascular interventional device due to their excellent mechanical attributes. However, the haemocompatibility of these biomedical metals is insufficient for the long-term antithrombogenic demand in vivo applications. Immobilization of heparin biomolecules on biomaterials is a widely investigated approach to modify surfaces for improving antithrombotic property. Because the metallic biomaterials used for cardiovascular implants possess a paucity of reactive functional groups, biomolecular immobilization of these materials is challenging.In this paper, 316L stainless steel as a commonly used cardio vascular material is chosen as the materials in our research. Allylamine films with primary amine (-NH₂) were fabricated on medical stainless steel using pulsed plasma polymerization technique. Allylamine films were subsequently covalently immobilized by heparin via their surface primary amine.The component, structure and properties of the plasma polymerized allylamine (PPAa) films are characterized using Raman laser spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and trifluoromethylbenzaldehyde (TFBA) derivatization process as function of radio frequency (RF) power and pulsed duty cycle (Pdc). The results indicate that PPAa films are polymer-like structure; High content of primary amine was retained in the PPAa film, the highest content of primary amine (NH₂/C) was 2.43% and the concentration of immobilized heparin was 4.10μg/cm² which determined by toluidine blue method.While increasing the RF discharge power and pulsed duty cycle, more and more large size of particles appear in the film, film surface became much rougher, and water contact angle was gradually increased. And our nano-scratch results indicate that these films have a good binding strength to the stainless steel. The complicated change of the weight loss of the films indicated that stability of the films was determined significantly by diversified factors. The PPAa film fabricated under lower RF power displayed bad dynamical stability in the phosphate buffer solution (PBS).In this paper, in order to improve the PPAa films dynamical stability in aqueous solution, the PPAa films was further treated under 200°C and 1.5×10^-4Pa vaccum condition. Raman spectra and XPS results indicate that the configuration of the alkene was disappeared, the component of framework vibration increased significantly, and tiny decreasing content of NH₂. However, the dynamical stability of the films was improved remarkably.The evaluation of hemocompatibility was carried out including in vitro hemolysis ratio, Alamar Blue assay, fibrinogen adsorption, platelet adhesion, the lactate dehydrogenase (LDH), the glycoproteins granule membrane protein 140 (GMP140), activated partial thromboplastin time (APTT) tests and in vivo implantation into dog's external iliac arteries. The hemo-evaluations indicate that the heparin-immobilized PPAa films had better hemocompatibility.