The Effect Of VEGF Functionalized NiTi On The Behaviors Of Endothelial Cells

NiTi alloys have been widely used in biomedical fields because of their excellentproperties of unique shape memory effect, super-elastic property, high corrosionresistance and good biocompatibility. Despite the good performance of theseNiTi-based implants, material surface induced thrombosis remains one of the keychallenges in clinic applications. In addition, the Ni ion release of NiTi alloy implantsurrounding tissues after implantation may induce allergic and toxic effects. Thus, thedesirable surface engineering NiTi alloy substrate to improve the behaviors of bloodvessel endothelial cells (endothelialiazation) and reduce Ni ion release is essentiallyimportant for the development NiTi-based implants.Previous studies demonatrated that the fabrication of a protective coating on NiTialloy substrates was an efficient approach for reducing the release of Ni ions. Moreover,the coating could improve the biocompatibility of NiTi implants, in turn mediating thebiological functions of the endothelial cells. It is well known that cellularmicroenvironments play an important role in the regulation of cells behaviors. Cellbehaviors (e.g, adhesion, migration, proliferation, and differentiation, etc.) to a materialare highly regulated by material’s surface chemistry and topography. Immobilization ofextracellular matrix components or growth factors on biomaterial substrates can changelocal surface chemistry and regulate the interactions between cell and biomaterials, andthus enhance cell functions. Vascular endothelial growth factor (VEGF) is known toinduce endothelial cells in surrounding tissues to migrate, proliferate and form tubularstructures, and formation of new vessel.In this study, we initially used magnetron sputtering and water thermal oxidationmethods to construct a nano-structured alumina (Al2O3) coating on the surface of NiTialloy, and then vascular endothelial growth factor (VEGF) was immobilized onto itssurface via polydopamine (PDOP) as a intermediate layer. X-ray diffraction (XRD),scanning electron microscopy (SEM), atomic force microscope (AFM), inductivelycoupled plasma mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the samples. The results demonstrated that thenano-structured Al2O3coating was amorphous with porous and needle-like morphology.The root mean square (rms) roughness of the Al2O3coating on NiTi was about22±4nm with thickness of about200nm. The coating significantly decreased the release amount of Ni ions from the substrates. Meanwhile, we evaluated the biologicalbehaviors of endothelial cells adhered to modified NiTi alloy substrates, including cellproliferation, cell spreading and production of prostacyclin (PGI2) and nitric oxide (NO)in vitro. The results demonstrated that human umbilical vein endothelial cells (HUVECs)grown on NiTi-Al2O3-PDOP-VEGF substrate showed statistically higher cell viability(p <0.05or p <0.01), more cell number and larger cell spreading area than thoseadhered to native NiTi substrates. Moreover, the secrection contents of PGI2and NO byHUVECs gorwn onto NiTi-Al2O3-PDOP-VEGF substrates were significantly higherthan those of corresponding native and Al2O3nanocoating modified NiTi alloys (p<0.05). The study accumulated valuable experimental data for the broad application ofNiTi alloy in biomedical fields.