Construction Of Multifunctional Plasma Polymerized Coatings And Study On Biocompatibility

Cardiovascular diseases (CADs) are major causes of morbidity and mortality worldwide. Intervention treatment is one of the most common methods in clinical treatment of CADs with the advantages of minimal invasion, immediately massive effectiveness and long-term positive effect, compared with drug therapy, surgical treatment. Vascular stent is the most important biomedical device for CADs intervention treatments. Multiple techniques have been used to improve the therapeutic effect of vascular stent during the past few decades, especially for drug eluting stent (DES), with their abilities of dramatically reducing the incidence of in-stent restenosis. However, in-stent restenosis and late-stage thrombosis (LST) are still two main complications of vascular stents limiting their clinical applications. Thus, it still needs exploration and a long way from the goal of designing an ideal vascular stent according to clinical requirement.Immobilizing biomolecules with specific biological functions onto cardiovascular implant materials surface in order to improve the anti-coagulation and accelerate the recovery of endothelium function is research hotspot. However,the lack of sufficient functional group density on metal stent surface limits the conjugation amount of biomolecules. Plasma polymerization technique could deposit coatings onto virtually all types of substrate surfaces (including glass, metal, polymers), with any complex geometry shapes. Plasma polymerized coatings are compact, flexibility, with strong adhesion to substrate and possess ability to resist deformation. More importantly, plasma polymerized coatings with different concentrations and different kinds of functional groups could be prepared through regulating monomers and depositing parameters depending on specific demands. Hence, plasma polymerized coating has great advantages in applications like vascular stent materials with huge deformation during the implantation process.As described, plasma polymerized allylamine (PPAam) coatings rich in amine groups were deposited onto 316L SS surface, which is lack of functional groups. PPAam were prepared by pulse plasma polymerization technique with allylamine (Aam) as precursor.Then, tannins acid(TA) molecule with the functions of anti-oxidation, scavenge free radicals and anti-inflammation was conjugated onto PPAam coating surface to construct TA-PPAam functional coating rich in phenolic hydroxyl groups. Water contact angle, infrared spectroscopy, X-ray photoelectron spectroscopy, quantitative detection of phenolic hydroxyl and amine groups, quartz crystal microbalance assays were used to characterize the chemical composition of the coating and conjugation amount of TA molecule. The hemocompatibility and cytocompatibility of the modified materials were evaluated by platelet adhesion, vascular endothelial cells, vascular smooth muscle cells and macrophages seeding tests. The results indicated that TA was successfully immobilized onto PPAam coating with the amount of 330±12 ng/cm2, showing good hemocompatibility,endothelial cytocompatibility and anti-inflammatory property.Anticoagulation and accelerate endothelium regeneration are essential biological functions and primary demands for cardiovascular implant materials,such as vascular stent materials. In this work, BVLD with specificity of direct thrombin inhibitor and VEFG with specificity to promote vascular endothelial cell growth were conjugated onto TA-PPAam functional coating rich in phenolic hydroxyl groups to construct BVLD @TA-PPAam and VEFG@TA-PPAam under the condition of physiological pH value, respectively. The results indicated that BVLD and VEGF were successfully immobilized onto TA-PPAam coating with the amount of 930±80 ng/cm2 and 158±13 ng/cm2,respectively. BVLD and VEGF modified TA-PPAam retained good biological activities of two biomolecules.VEGF@TA-PPAam coating has significantly promoted the attachment, spreading and proliferation behaviors of vascular endothelial cells. BVLD@TA-PPAam has remarkably inhibited the adhesion and activation of platelets through the specificity of capturing and inhibiting activity of direct thrombin inhibitor. Besides, it's shown that BVLD @TA-PPAam coating could also promoted the adhesion and growth of vascular endothelial cells. These together provided the possibility of designing and constructing multifunctional vascular stents, thus reducing the ratios of in-stent restenosis and late-stage thrombosis complications.Mimicking endothelium just from one or a few aspects couldn't always obtain ideal function similar to cell or extracellular matrix. The modification of various biomolecules could offer cardiovascular implant materials surface multiple biological functions, leading to better mimicking of cell or extracellular matrix functions and obtaining multifunctional stent to meet clinical demands. It's quite difficult to obtain multifunctional vascular stent surface by immobilizing single biomolecule. In our study, plasma copolymerized allylamine/acrylic acid (Aam/Aac) coatings rich in amine and carboxyl groups were deposited onto 316L SS surface by plasma polymerization technique with Aam and Aac as precursors. Water contact angle, infrared spectroscopy, X-ray photoelectron spectroscopy,quantitative detection of phenolic hydroxyl and amine groups assays were used to characterize the chemical composition of the coating. The hemocompatibility,cytocompatibility and tissue-compatibility of the modified materials were evaluated by platelet adhesion, hemolysis test, vascular endothelial cells and smooth muscle cells seeding tests, and in vivo subcutaneous implant test. The results indicated that the amine and carboxyl groups could be successfully introduced onto 316L SS surface through depositing Aam/Aac copolymerized coating, in order to realize the aim of two functional groups and further provide active sites for two biomolecules conjugation. Further conjugations of heparin and BVLD were carried out,with the amount of 210±6 ng/cm2 and 195±8 ng/cm2,respectively. The co-immobilization of heparin and BVLD onto Aam/Aac copolymerized coating rich in both amine and carboxyl groups were constructed by two steps. The conjugation amounts of heparin and BVLD were 210 ng/cm2 and 200 ng/cm2, similar to the alone conjugation amount. Thus, two biomolecules could be co-immobilized onto Aam/Aac(1.5:1.5) copolymerized coating rich in both amine and carboxyl groups to provide platform for constructing multifunctional surface.In conclusion, this study is based on plasma polymerized coating to construct surface with multiple functions. Related functional evaluations of the modified surface were carried out to get a better understanding of the in vitro biocompatibility of various modified coatings. In further to provide technology support to expand the applications of plasma polymerized coatings in biomaterials surface modification fields and new ideas for the designing and constructing of multiple functional vascular stent.