Preparation And Biological Properties Of Mg-incorporated Ni-Ti-O Nanopore Coatings On NiTi Alloy Surface

Due to its good biocompatibility,shape memory effect,superelasticity and other excellent properties,nearly equiatomic nickel-titanium（NiTi）alloy has been widely used as a biomedical implant material in the fields of cardiovascular surgery,dentistry and orthopedics.However,there are also many problems in clinical application,such as poor corrosion resistance,unsatisfactory antibacterial properties and excessive release of Ni²⁺.Especially,although the alloy has excellent mechanical properties,its biological functions are weak.Construction of suitable nanostructures while loading biological functional elements on NiTi alloy surface is an ideal way to render it biological functions.Based on the previous studies,nickel-titanium-oxygen（Ni-Ti-O）nanopore（NP）coating was prepared on the NiTi alloy surface by anodization,and then biofunctional element magnesium（Mg）was loaded into the NPs coating by hydrothermal treatment to obtain Mg-incorporated Ni-Ti-O nanopores coatings（NP-Mg）.The surface morphology,elemental composition,chemical valence and ion release behavior of the coatings were characterized and analyzed.In addition,in vitro osteogenic activity,angiogenic activity,antibacterial and corrosion resistance were investigated in detail.The research results are as follows:（1）Mg-incorporated Ni-Ti-O NP coatings are prepared on NiTi alloy surface by anodization and hydrothermal treatment.The amount of loaded Mg can be regulated by the NPs length and the hydrothermal duration.Due to the doping of Mg,the surface morphology of the coatings transform from nanosheets to nanopores with the prolongation of hydrothermal duration.The Mg is uniformly distributed in the coatings,which mainly exists in magnesium titanate（MgTiO₃）.（2）The NP-Mg coatings are able to release Ni²⁺and Mg²⁺efficiently and safely.Compared to NiTi substrate,Ni²⁺release in NP-Mg coatings are reduced,and prolonging the hydrothermal duration can reduce the release concentration of Mg²⁺.（3）Biocompatibility experiments show that the surface of NP-Mg coatings have no cytotoxicity and facilitates initial adhesion and cytoskeleton assembly of BMSCs.The Mg²⁺release can promote the proliferation of BMSCs,that is,the coatings show good biocompatibility.Osteogenic differentiation experiments show NP-Mg coatings obtained by long hydrothermal duration（5 h）can significantly promote ALP activity,type I collagen secretion and extracellular matrix mineralization of BMSCs,indicating that the coatings have good osteogenic activity.（4）The results of potentiodynamic polarization show that the corrosion resistance of Ni-Ti-O NP coating is significantly better than that of NiTi substrate.After hydrothermal treatment,the corrosion resistance of the coatings is slightly improved,but there is no significant difference among NP-Mg groups.The antibacterial properties of the coatings against Staphylococcus aureus and Escherichia coli were evaluated by plate counting method.The results show that the bactericidal effects of NPs and NP-Mg coatings against adherent bacteria are significantly better than that of NiTi substrate.（5）The NP-Mg coatings can well support the proliferation of endothelial cells,but there is no significant difference between the groups.The experiments of endothelial cell function expression show that NP-Mg coatings significantly promote NO synthesis and VEGF secretion compared to NiTi substrate,indicating that the coatings have good angiogenic activity.