One-step Micro-arc Oxidation Research Articles

Bioceramic Coating Produced on AZ80 Magnesium Alloy by One-Step Microarc Oxidation Process

A self-sealing bioceramic coating was prepared on AZ80 magnesium alloy by one-step microarc oxidation (MAO) in an alkaline silicate solution in the presence of HA nanoparticles and K2TiF6. The influence of oxidation time on the microstructure and corrosion resistance was investigated. The surface and cross-sectional morphologies of the coatings were characterized by scanning electron microscopy, while their phase structure and chemical composition were obtained by x-ray diffraction analysis and energy-dispersive spectroscopy, respectively. The corrosion behavior of the coatings was evaluated by electrochemical measurements in a simulated body fluid. The results show that the self-sealing bioceramic coatings are mainly composed of MgO, MgF2, Ti3O5, Mg2SiO4, and HA phases, which effectively improve the corrosion resistance of the AZ80 magnesium alloy. The added K2TiF6 plays a key role in producing self-sealing coating, while the HA nanoparticles improve the bioactivity of the coating. Thus, the self-sealing bioceramic coating obtained by the one-step MAO process may develop into a suitable surface treatment technology for bone implants in clinical application.

Formation Mechanism and Biological Properties of Different Structured HA/TiO2 Coatings on Titanium Prepared by Micro-Arc Oxidation

In this paper, porous, flocculent and petal-structured hydroxyapatite (HA)/TiO2 composite coatings were prepared on titanium (Ti) surfaces by one-step micro-arc oxidation (MAO) to enhance the biological property, and the formation mechanism of the different coatings was investigated. The results showed that, compared with the porous and flocculent coatings which can be easily formed, the petal-structured HA/TiO2 coating can only be formed when Ca(COOH)2 concentration, current, voltage and time reached certain threshold values. At low current, the HA petals were large, the surface morphology, roughness and hydrophilicity were all affected by voltage and time. At high current, the petals tended to grow small and dense, however the surface morphology and roughness were less affected by voltage and time, only that the hydrophilicity was affected by voltage and time at low values within narrow ranges. All the prepared coatings had good combination with Ti substrate when the applied current was less than 0.8 A. Based on the results, the growth process model of the HA/TiO2 coatings was proposed. Compared with the flocculent and porous coatings, the petal-structured HA/TiO2 coating was more beneficial for MC3T3-E1 cells adhesion, spreading and proliferation, it also showed better bioactivity. The optimal performance can be obtained by controlling the Ca(COOH)2 concentration, current, voltage and time during MAO process. The improved biological property of the petal-structured HA/TiO2 was attributed to the suitable coating thickness, large surface roughness, highly exposed HA area and good hydrophilicity.

Synthesis and characterization of a bi-functional hydroxyapatite/Cu-doped TiO2 composite coating

In the present work, a two-layer hydroxyapatite (HA)/Cu-doped TiO2 composite coating was prepared via one-step micro-arc oxidation in an aqueous electrolyte containing calcium acetate, sodium di-hydrogen phosphate and ethylene diamine tetraacetic acid cupric disodium (CuNa2-EDTA) at a constant current density of 100 mA/cm2. After micro-arc oxidation for 20 min, Cu species incorporate into the TiO2 as CuO and Cu2O, resulting in the formation of Cu-doped TiO2-based coating. In addition, spherical-shaped HA phase of nanometre scale is also present on the Cu-doped TiO2-based coating. With HA phase boosting osseointegration and Cu species killing pathogenic microbes, a bi-functional coating fabricated by one-step micro-arc oxidation is of promising potential application in the bio-medical field.

Influences of Na2SiO3 and EDTA-ZnNa2 concentration on properties of zinc-containing coatings on WE43 magnesium alloys

There exists great interest in the development of coatings that can simultaneously improve corrosion resistance and contain essential trace elements on biomedical magnesium alloys. In an alkaline solution composed of NaF, phytic acid (H12Phy), Na2SiO3 and EDTA-ZnNa2, it was demonstrated that zinc-containing coatings with improved corrosion resistance were successfully fabricated on WE43 magnesium alloys using a one-step micro-arc oxidation (MAO) procedure. The influences of Na2SiO3 and EDTA-ZnNa2 concentrations on MAO coating properties were systematically evaluated using SEM, EDS, XRD, XPS, scratch test and potentiodynamic polarization. These results demonstrate that MAO coatings containing 1.67 wt% Zn exhibit superior corrosion resistance. Na2SiO3 is one type of passive agent of magnesium alloys, and has been shown to be favorable for the formation of coatings as it enhances corrosion resistance by improving surface uniformity, coating thickness and adhesion to the substrate. Raised EDTA-ZnNa2 in the range of 1 to 3 g/L is found to increase zinc content in MAO coatings but decrease their corrosion resistance. As an acidic substance, EDTA-ZnNa2 is a corrosive agent of magnesium alloys and has shown to be harmful for the formation of MAO coatings. Additionally, the corrosion mechanism of MAO coatings was discussed by measuring electrochemical impedance spectroscopy as a function of immersion time.

Characterization and corrosion properties of hydroxyapatite/graphene oxide bio-composite coating on magnesium alloy by one-step micro-arc oxidation method

A biodegradable hydroxyapatite/graphene oxide bio-composite (HA/GO) coating has been fabricated on magnesium (Mg) alloy by a convenient one-step method of micro-arc oxidation (MAO) for biodegradable implants. The microstructure and phase constituents of the obtained powders and coatings were characterized by XRD, SEM, TEM, FT-IR, XPS and the corrosion resistance in vitro has been investigated by electrochemical measurements in simulated body fluid (SBF). The results suggested that HA/GO powder has been successfully prepared and filled into the discharging pores of the coating during MAO process. The electrochemical measurements in SBF indicated that the corrosion current of Mg substrate has been significantly decreased by the HA/GO coating. Furthermore the EIS measurement suggested that the HA/GO coating more effectively inhibited the Mg substrate from corrosion compared to pure MAO coating. These results suggested that HA/GO coating on Mg alloy could be a promising candidate for biomedical application.

Formation mechanism and adhesive strength of a hydroxyapatite/TiO2 composite coating on a titanium surface prepared by micro-arc oxidation

A hydroxyapatite (HA)/TiO2 composite coating was prepared on a titanium surface by one-step micro-arc oxidation (MAO). The formation mechanism of the composite coating was investigated and the adhesion of the coating to the substrate was also measured. The results showed that flocculent structures could be obtained during the early stages of treatment. As the treatment period extended, increasing amounts of Ca–P precipitate appeared on the surface, and the flocculent morphology transformed into a plate-like morphology. Then the plate-like calcium and phosphate salt self-assembled to form flower-like apatite. The Ca/P atomic ratio gradually decreased, indicating that the amounts of Ca2+ ions which diffused into the coating decreased more rapidly than that of PO43− or HPO42−. The adhesive strength between the apatite and TiO2 coating was improved. This improvement is attributed to the interlocking effect between the apatite and TiO2 layer which formed simultaneously during the early stages of the one-step MAO. This study shows that it is a promising method to prepare bioactive coating on a titanium surface.

Antibacterial properties of Ag (or Pt)‐containing calcium phosphate coatings formed by micro‐arc oxidation

Silver (or platinum)-containing calcium phosphate (hydroxyapatite (HA) and tricalcium phosphate (alpha-TCP)) coatings on titanium substrates were formed by micro-arc oxidation (MAO) and their in vitro antibacterial activity and in vitro cytotoxicity were evaluated. MAO was performed in an electrolytic solution containing beta-glycerophosphate disodium salt pentahydrate (beta-GP) and calcium acetate monohydrate (CA), and Ag and Pt were introduced in the form of AgNO(3) (or CH(3)COOAg) and H(2)PtCl(6), respectively. The MG63 and human osteosarcoma (HOS) cell lines were used to investigate the proliferation and differentiation behavior of the cells, respectively, whereas two strains of bacteria, Staphylococcus aureus and Escherichia coli, were used to evaluate the antibacterial activity of the coatings. The phase, morphology, and Ag content of the coatings were strongly dependent on the applied voltage and Ag precursor concentration. HA and alpha-TCP phases were detected in the coatings oxidized above 400 V and the presence of Ag was confirmed by EDS. While the coatings with a high content of Ag were cytotoxic and those obtained in the Pt-containing electrolyte had no apparent antibacterial activity, the calcium phosphate coatings obtained in the low Ag concentration electrolyte exhibited in vitro antibacterial activity but no cytotoxicity. Thus, biocompatible calcium phosphate coatings on Ti implants with antibacterial activity can be achieved by one-step MAO.