Biocompatibility of micro-arc oxidation coatings developed on Ti6Al4V alloy in a solution containing organic phosphate
Introduction
Due to low density and elastic modulus, good corrosion resistance and biocompatibility, titanium alloys have been one of the most widely used hard-tissue implant materials [1], [2], [3]. However, titanium alloys belong to bio-inert materials. Micro-arc oxidation (MAO) can effectively improve the bioactivity of titanium alloys and the used electrolytes play an important role in determining the coating property [1], [2], [3]. As a source of bioactive phosphorus element, inorganic phosphates are widely used as the main MAO electrolytes [1], [2], [4], [5]. Because bone is a typical inorganic–organic composite, in recent years, researchers are more and more focusing on the development of composites by mimicking the unique composition and structure of bone tissue [6]. In order to further improve the bioactivity of titanium alloys, selecting environmentally friendly organic electrolytes especially organic phosphates is very important.
Phytates are found in abundance in beans, cereals, oilseeds, nuts, spores, tubers, pollen and organic soil [7]. Phytates especially phytic acid and sodium phytate (Na12C6H6O24P6, abbreviated as Na12Phy) have a variety of benefits on human health and can be used as anti-cancer agent, inhibitor for renal stone development and anti-oxidant agent [7]. As a simple ringed carbohydrate with six phosphate groups attached to each carbon, Na12Phy has powerful chelating capability with di- and multi-valent cations. In view of the peculiar structure and property, Na12Phy may be used as an electrolyte of MAO on titanium alloys. However, to the best of the authors׳s knowledge, there is no report on this area. In the paper, the properties of anodic coatings formed on Ti6Al4V alloy were characterized by using SEM, XRD, XPS and MTT assay.
Section snippets
Materials and methods
Ti6Al4V was used as the substrate and the experimental samples were anodized after they were ground successively with SiC paper, degreased by acetone, washed with distilled water and dried in a warm air stream. The used MAO solution contained 3 g/L NaOH and 15 g/L high quality Na12Phy (purity≥98%, Zigong Jin Sui Industrial Co., Ltd.). A homemade MAOI-50C power supply was used under a constant current control mode. The used electric parameters were current density 50 mA/cm2, frequency 2000 Hz, duty
Results and discussion
Fig. 1 shows surface and cross morphologies of anodic coatings. The coatings exhibit the typical porous structure and the pore size is about 3 μm in diameter (Fig. 1a). The coatings are composed of 1.93% C (in wt%, the same below), 45.02% O, 6.23% P, 45.92% Ti and 0.85% Na. The P element in the coatings comes from the electrolyte, showing that Na12Phy takes part in the coating formation. From Fig. 1b, anodic coatings are closely developed on the substrate and about 5 μm thick.
Fig. 2 shows the
Conclusions
Anodic coatings which mainly contain anatase TiO2 are successfully fabricated on Ti6Al4V alloy by MAO in a solution containing sodium phytate. Sodium phytate takes part in the coating formation and phytates are developed in anodic coatings. MTT tests indicate that both Ti6Al4V and the MAO treated Ti6Al4V achieve good biocompatibility.
Acknowledgments
The authors thank the supports of the National Natural Science Foundation of China (Nos. 51061007 and 51361011).
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