Preparation And Mechanism Investigation Of Gallium Or Selenium-containing Coatings On Medical Titanium Alloys

Titanium alloys are widely used in the medical field due to their excellent mechanical properties,corrosion resistance and biocompatibility.However,titanium alloys belong to bio-inert materials with poor wear resistance and do not possess any antibacterial properties.During the implantation process,patients are susceptible to bacterial infections,which leads the surgical failure.Micro-arc oxidation（MAO）is an effective surface treatment technology that can grow coatings in situ on the surface of titanium alloys.The used electrolyte compositions and concentrations,and electrical parameters play an important role on the coating property.Gallium（Ga）element has clinical efficacy in promoting osteogenesis,inhibiting bone resorption and malignant tissue proliferation,anti-infection and immunomodulation.Selenium（Se）is an essential trace element with antibacterial and anticancer properties.Copper（Cu）has antibacterial,osteogenic and vascularizing biomedical functions.In this paper,gallium nitrate（Ga（NO₃）₃）and sodium selenite（Na₂Se O₃）were separately selected as Ga-and Se-containing electrolytes,while phytic acid,sodium phosphate（Na₃PO₄）,sodium silicate（Na₂SiO₃）and sodium sulfate（Na₂SO₄）were used as film-forming agents.Ga-or Se-containing coatings were prepared on the surface of titanium alloys by MAO technique and the influences of electrolyte compositions and concentrations on coating property were investigated.This main work of the paper is followings:（1）The influences of Ga（NO₃）₃ concentration,Na₂SiO₃ concentration,Na₂SO₄concentration and treatment time on coating properties were studied by using an orthogonal experiment.The results show that the Ga ions enter into MAO coatings by both diffusion and electromigration.The Si content is negatively related to the P content resulted from the competition between Na₂SiO₃ and Na₃PO₄ to take part in the coating formation,while the P content is positively related to the Ga content.The main existence form of Ga ions in MAO coatings is amorphous Ga₂O₃ and Ga PO₄.Na₂SO₄,Na₂SiO₃ and Na₃PO₄ act as film-forming agents,while Ga（NO₃）₃ is harmful for coating formation.（2）In a base solution of 2 g/L Na₂SO₄,2 g/L Na₂SiO₃ and 3 g/L Na₃PO₄,the influences of 1,2,3 and 4 g/L Ga（NO₃）₃ on the Ga amounts and surface morphology were investigated.The results show that with the increase of Ga（NO₃）₃ concentration,the fabricated coatings contain high Ga amounts.In addition,the higher Ga（NO₃）₃concentration results in thicker and rougher anodic coatings.（3）In a solution composed of Na₂Se O₃ and ethylene diamine tetraacetic acid copper disodium salt（（Na OOCCH₂）₂-N=CH₂CH₂=N（CH₂COO）₂Cu）,anodic coatings containing Se and Cu elements were fabricated by MAO treatment.The results show that Na₂Se O₃ concentration considerably influence the surface morphology,chemical compositions and coating thickness.With the increase of Na₂Se O₃ concentration,the Se content and coating thickness increase with rough surface characteristics and some cracks.The highest Se amount in MAO coatings is2.06 at.%.Se element in the coating exists in the form of elemental Se and Se O₂,while Cu element is in the form of CuO and Cu₂O.