Fabrication And Evaluation Of Coatings On Titanium By Sol-gel Method

It is already known that the essential requirement for an artificial material to bond to living bone is the formation of a bone-like apatite layer on its surface in the body environment. The bone-like apatite formation on bioactive materials can be reproduced even in an acellular simulated body fluid (SBF).Generally, titanium is covered with a passive oxide layer and is bioinert. But titanium can be modified to be bioactive when previously treated in NaOH. In NaOH solution, the passive oxide layer dissolves and sodium titanate is formed on the surface. When exposed to SBF, the Na⁺ ions are released from the sodium titanate and hydronium ions enter into the surface layer, resulting in the formation of Ti-OH groups in the surface. And Ti-OH groups can induce apatite nucleation on the titanium surface. However, since the composition and thickness of the passive oxide layer on titanium differ and there are several kinds of sodium titanate, the sodium titanate formed by NaOH treatment is hard to be unique. Whether all kinds of sodium titanate are bioactive is still unknown.Among numerous methods used to improve the bioactivity of titanium, sol-gel processing represents an alternative approach for the coating preparation with potential advantages, such as higher purity and chemical homogeneity, finer grain structure, lower processing temperature, easier procedure and controllable thickness. Many researches have been carried out to use sol-gel method to modify the surface of titanium. Most of them focused on HA and TiO₂ coatings.While it is promising to use sol-gel method to provide an exclusive and uniform sodium titanate by controlling the proportion of the components, thus we can use this method to study the properties of sodium titanate more deeply.In this study, an exclusive sodium titanate (Na₂Ti₆P₁₃) was fabricated and coated on commercially pure titanium (c.p Ti) discs by sol-gel method. The characterization and evaluation of the coating in vitro were carried out. Meanwhile, we also prepared HA and TiO₂ coatings on titanium by sol-gel method and evaluated these three kinds of coatings by osteoblast-like cells behavior in vitro.This research is composed of the following 3 parts:Part 1 The development, characterization and evaluation of sodium titanate (Na₂Ti₆O₁₃) coating on titanium by sol-gel method.In this part, an exclusive sodium titanate (Na₂Ti₆O₁₃) coating on titanium was fabricated by sol-gel method. The coating was characterized by SEM and XRD. The bioactivity of the Na₂Ti₆O₁₃ coating was evaluated by the biomimetic growth of apatite on its surface after soaked in an acellular simulated body fluid (SBF) for a period of time. XRD patterns showed that Na₂Ti₆O₁₃ was well crystallized when the coating was heated at 800℃. SEM observation exhibited that the Na₂Ti₆O₁₃ coated titanium had a homogeneous surface without any cracks. The thickness of the coating was about 0.5μm. After immersion in SBF, the apatite layer can be formed on the coating. It can be concluded that Na₂Ti₆O₁₃ coating on titanium obtained by sol-gel method is bioactive.Part 2 The fabrication and characterization of HA and TiO₂ coatings on titanium by sol-gel method.In this part, HA and TiO₂ coatings on titanium were prepared and characterized by SEM and XRD. HA was well crystallized when the coating was heated at 720℃, and anatase was formed when TiO₂ coating was heated at 540℃. The coatings had a homogeneous surface without any cracks. The thickness of HA coating was about 0.8μm while TiO₂ coating was about 1.2μm.Part 3 Evaluation of three kinds of coatings by osteoblast-like cells behaviors in vitro.In this part, osteoblast-like cells were seeded on three kinds of coatings. The adhesion, proliferation and differentiation of the cells were investigated. It can be concluded that the coatings were suitable and favorable for the growth of cells without any cytotoxicity.Based on these findings, sodium titanate coating by sol-gel method used in this paper provided another option to modify titanium. Moreover, in further studies, the bioactivity of different kinds of sodium titanate can be investigated through this method thus to make it clear the effect of the content of sodium in sodium titanate on its bioactivity. Meanwhile, we evaluated the cells behaviors on three coatings to explore the mechanism of their cytocompatability.