One-step Micro-arc Oxidation Research Articles

Improved wear and corrosion resistance of MoS2/MgO/MgAl2O4 composite layer in-situ prepared by one-step micro-arc oxidation

In this study, a MoS2/MgO/MgAl2O4 composite layer was prepared on AZ31 magnesium alloy via a one-step in-situ plasma electrolytic oxidation (PEO) method to enhance its wear and corrosion resistance. Results indicated that the addition of Na2MoO4 and Na2S significantly increased the critical and final voltages during the PEO process, and gradually reduced the layer porosity. When 2.5 g/L Na2MoO4 and 5 g/L Na2S were added, the layer exhibited optimal wear resistance, with an average coefficient of friction (COF) of 0.1521±0.007 and a wear volume of 0.0193±0.001 mm³. Additionally, when 1.5 g/L Na2MoO4 and 3 g/L Na2S were added, the layer exhibited optimal corrosion resistance, with a corrosion current density of 1.466×10−9 A/cm² and a corrosion potential of −0.351 V. Compared to the AZ31 substrate and the single PEO layer, the corrosion current density improved by 4 and 2 orders of magnitude, respectively, and the corrosion potential shifted positively by 0.968 V and 0.182 V, respectively. Elemental analysis showed that S and Mo were primarily distributed at the interface between the layer and the substrate, with their concentration decreasing from the inner to the outer layers of the layer, indicating their involvement in the layer formation process. MoS2 was mainly distributed within the interior of the layer.

Preparation of HA-containing coating by one-step MAO on titanium alloys through synergistic effect of calcium gluconate and calcium glycerophosphate

In a base solution composed of calcium gluconate (CaGlu2) and magnesium gluconate (MgGlu2), the influences of calcium glycerophosphate (Ca-GP), sodium phytate (Na12Phy), phosphoric acid (H3PO4) and constant voltage on the amounts of calcium (Ca) and magnesium (Mg) elements in micro-arc oxidation (MAO) coatings were systematically investigated using an orthogonal experiment. The results show that anodic coatings with the Ca/P molar ratio of 1.35 and containing high bioactive hydroxyapatite (HA) phase are successfully fabricated using one-step MAO treatment by adjusting processing parameters. Ca ions enter into MAO coatings by both electromigration and diffusion. H3PO4 is an effective film-forming agent and the increased concentration significantly decreases both the Ca and Mg amounts. Our results show that compared with Ca-GP, CaGlu2 can effectively improve the Ca amount of anodic coatings. Sole Ca-GP or CaGlu2 cannot significantly improve the Ca amount, while Ca-GP and CaGlu2 can synergistically improve the Ca amount in MAO coatings.

Preparation and mechanical and biological performance of the Sr-containing microarc oxidation layer on titanium implants

A Strontium-doped titanium oxide coating was successfully prepared on a TA4 substrate with one-step microarc oxidation (MAO) technology. Then bioactivity of the coating was performed with the inducation test of bone-like apatite formation immersed in simulated body fluid (SBF). The biological activity of the coating was evaluated with cell culture experiments, and its corrosion resistance was characterized with electrochemical tests in the SBF. The composition and morphology of the coatings before and after SBF immersion were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results showed that the coating had a rough porous structure, which was mainly composed of anatase, rutile and Ti phases. The SBF immersion test showed that abundant 3D micro nanopore structures were formed on the surface of the porous titanium oxide coatings, which enabled the coatings to exhibit good apatite nucleation ability. Faster precipitation of bone-like apatite by MAO-Sr coatings in SBF. Finally, in the biological compatibility test, compared with TA4, the contact angle between the MAO-Sr coating and SBF solution was lower, and the proliferation ability of bone marrow stromal cells (BMSCs) in the biological coating was stronger, indicating the good biocompatibility of the coating.

Preparation and antibacterial properties of ZnSr-doped micro-arc oxidation coatings on titanium

Titanium and titanium alloys are biologically inert materials. The lack of rapid osseointegration and resistance to bacterial infection remain unsolved problems for these materials. To overcome these problems, zinc (Zn) and strontium (Sr) at different concentrations were doped into the surface coating of implants by one-step micro-arc oxidation (MAO) technology. The microstructure, elemental content, chemical composition and corrosion resistance of the coating were studied. The antibacterial activity and biocompatibility of the coating were evaluated by antibacterial tests and proliferation tests of bone marrow mesenchymal stem cells (BMSCs). The results show that the coating is mainly composed of the rutile phase and anatase phase. The content of zinc in the coating decreases with increasing strontium concentration. The addition of zinc and strontium in the electrolyte does not significantly change the microstructure and physical and chemical properties of the coating. The ZnSr-TiO2 coating shows good antibacterial activity against Staphylococcus aureus and Porphyromonas gingivalis, which can effectively promote the proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs), and the cells on the coating with a higher strontium content exhibit greater proliferation.

From bio-inertness to osseointegration and antibacterial activity: A one-step micro-arc oxidation approach for multifunctional Ti implants fabricated by additive manufacturing

Infectious bone defects (IBD) remain a major problem in orthopedics in clinical settings. For IBD repair, implants possessing multiple functions such as osseointegration and antibacterial activity are in demand. This study aims to develop a surface-modified titanium (Ti) implant (MTi/Ag/CaP) with osseointegration and antibacterial functions for IBD repair. The pure Ti implant is printed using a selective laser melting technique, and a two-layer hierarchical structure is formed on its surface using a one-step micro-arc oxidation (MAO) approach. The outer layer is an apatite-like material decorated with Ag nanoparticles, whereas the inner layer is porous TiO2. In vitro experiments show that the MTi/Ag/CaP implant can effectively eliminate and inhibit the adhesion and proliferation of bacteria over a long period time while promoting MG-63 cell adhesion, proliferation, and osteogenic differentiation. In vivo experiments further reveal that the MTi/Ag/CaP implant produces more mineralized bone tissue than non-treated samples and interlocks closely with the bone tissue after 8 weeks. The one-step MAO modification developed in this study is simple, efficient, and environment-friendly, which demonstrates great potential as a promising approach for providing advanced biomedical materials in orthopedic applications, including for the prevention and treatment of IBDs.

Microstructure and Properties of Hydroxyapatite-Containing Ceramic Coatings on Magnesium Alloys by One-Step Micro-Arc Oxidation

Microstructure and Properties of Hydroxyapatite-Containing Ceramic Coatings on Magnesium Alloys by One-Step Micro-Arc Oxidation

Preparation and corrosion resistance of a self-sealing hydroxyapatite- MgO coating on magnesium alloy by microarc oxidation

An ideal self-sealing hydroxyapatite (HA)-MgO coating was designed on an AZ31 Mg alloy by one-step microarc oxidation (MAO) with the addition of HA nanoparticles into a base electrolyte. The formation mechanism of the self-sealing HA-MAO coating was discussed. The effect of the nano-HA addition on the corrosion resistance of the MAO coating was evaluated by corrosion tests in Hank's solution. The results show that HA nanoparticles inertly incorporated into the MAO coating during the process of coating growth. HA and MgO were the main constituents of the HA-MAO coating. The HA nanoparticles were absent in the inner barrier layer but concentrated in the outer porous layer. In addition, HA nanoparticles accumulated much more inside coating defects than in the other zones, which resulted in the nearly ideal sealing of micropores on the coating surface. By forming a denser and more stable outer layer, the incorporation of HA nanoparticles greatly enhanced the anti-corrosion properties of the MAO coating.

From Bio-Inertness to Osseointegration and Antibacterial Activity: A One-Step Micro-Arc Oxidation Approach for Multifunctional Ti Implants Fabricated by Additive Manufacturing

From Bio-Inertness to Osseointegration and Antibacterial Activity: A One-Step Micro-Arc Oxidation Approach for Multifunctional Ti Implants Fabricated by Additive Manufacturing

Improvement corrosion resistance of Ni-Ti alloy by TiO2 coating and hydroxyaptite/TiO2 composite coating using micro arc oxidation process

Titanium oxide ceramic coatings were prepared by micro-arc oxidation (MAO) in galvanostatic regime on biomedical NiTi alloy produce via powder metallurgy, also the composite coating of HA/TiO2 was prepared on the surface of nitinol using a one-step micro-arc oxidation (MAO), the process time for each case at 280 V was 30 min. The surface of TiO2 coating exhibited a typical porous and rough structure. In this study, the hydroxyapatite, Ca–P precipitate it assisted to close the porous and the morphology of the surface coating showed a flower-like structure owing to the incidence of self-assembly because of the longtime of precipitate. Surface characterization of the coatings was determined utilizing SEM, XRD, and AFM. The surface morphology, topography and coating thickness were determined as well. In this study, the properties of corrosion were studied utilizing potentiostat test unit in Ringer's solution. Based on the results, the corrosion properties of NiTi alloys considerably improved due to the existence of TiO2 and HA/TiO2 coatings.

Antibacterial Property and Biocompatibility of Silver, Copper, and Zinc in Titanium Dioxide Layers Incorporated by One-Step Micro-Arc Oxidation: A Review.

Titanium (Ti) and its alloys are commonly used in medical devices. However, biomaterial-associated infections such as peri-implantitis and prosthetic joint infections are devastating and threatening complications for patients, dentists, and orthopedists and are easily developed on titanium surfaces. Therefore, this review focuses on the formation of biofilms on implant surfaces, which is the main cause of infections, and one-step micro-arc oxidation (MAO) as a coating technology that can be expected to prevent infections due to the implant. Many researchers have provided sufficient data to prove the efficacy of MAO for preventing the initial stages of biofilm formation on implant surfaces. Silver (Ag), copper (Cu), and zinc (Zn) are well used and are incorporated into the Ti surface by MAO. In this review, the antibacterial properties, cytotoxicity, and durability of these elements on the Ti surface incorporated by one-step MAO will be summarized. This review is aimed at enhancing the importance of the quantitative control of Ag, Cu, and Zn for their use in implant surfaces and the significance of the biodegradation behavior of these elements for the development of antibacterial properties.

Enhancing Antibacterial Performance and Biocompatibility of Pure Titanium by a Two-Step Electrochemical Surface Coating.

A two-step electrochemical surface treatment has been developed to modify the CP Ti surface on commercially pure titanium grade 2 (CP Ti): (1) anodic oxidation to form TiO2 nanotube precoatings loaded with silver (Ag) and (2) microarc oxidation (MAO) to produce a porous Ca-P-Ag coating in an electrolyte containing Ag, Ca, and P. One-step MAO in the same electrolyte has also been used to produce porous Ca-P-Ag coatings without anodic oxidation and preloaded Ag as a control. Surface morphologies and alloying chemistry of the two coatings were characterized by SEM, EDS, and XPS. Biocompatibility and antimicrobial properties have been evaluated by the MTT method and co-culture of Staphylococcus aureus, respectively. It is demonstrated that porous coatings with high Ag content can be achieved on the CP Ti by the two-step treatment. The optimized MAO voltage for excellent comprehensive properties of the coating is 350 V, in which a suitable chemical equilibrium between Ag, Ca, and P contents and a Ca/P ratio of 1.67 similar to HA can be obtained, and the Ag particles are in the size of less than 100 nm and embedded into the underneath of the coating surface. After being contacted with S. aureus for 1 and 7 days, the average bactericidal rates were 99.53 and 89.27% and no cytotoxicity was detected. In comparison, the one-step MAO coatings contained less Ag, had a lower Ca/P ratio, and showed lower antimicrobial ability than the two-step treated samples.

Synthesis, microstructure, anti-corrosion property and biological performances of Mn-incorporated Ca-P/TiO2 composite coating fabricated via micro-arc oxidation.

In this work, a Mn-incorporated Ca-P/TiO2 composite coating was produced through the facile one-step micro-arc oxidation (MAO) method. It is revealed that only when the concentration of Na2Mn-EDTA reaches 0.02mol/L, the Ca-P phase could form on Mn-incorporated TiO2 coating, which is associated with the combined effect of EDTA complex and Mn species. The Ca-P phase is amorphous, which may contain hydroxyapatite phases whereas the underlying Mn-incorporated TiO2 coating contains two separate layers, including the Mn-rich outer layer and Mn-depleted inner layer. The biological investigation of the Mn-incorporated Ca-P/TiO2 composite coating suggests that it exhibits desirable osteogenesis with certain capability to inhibit the growth of S. aureus bacteria. Hence, a promising composite coating with superior bone formability could be produced using the one-step micro-arc oxidation method in the electrolyte containing Na2Mn-EDTA.

Microstructure, corrosion resistance, osteogenic activity and antibacterial capability of Mn-incorporated TiO2 coating

In the present work, a Mn-incorporated TiO2 coating has been fabricated through the facile one-step micro-arc oxidation (MAO) treatment in the electrolyte containing Na2Mn-EDTA. Microstructural characterization reveals that Mn-incorporated TiO2 coating exhibits a two-layered structure based on chemical compositions, which includes the inner layer consisting of polycrystalline TiO2 with P segregated at the grain boundary and the outer layer comprising of nano-sized Mn3O4 particles. Further, both corrosion resistance and biological performance of the Mn-incorporated TiO2 coating were investigated. It was revealed that the Mn-incorporated TiO2 coating exhibits an enhanced corrosion resistance, osteogenic activity and slightly improved antibacterial capability against S. aureus bacteria relative to that with the absence of Mn, which also exhibits negligible cytotoxicity. Hence, Mn specie is a promising candidate for the production of dual-functional biomedical surfaces for Ti implants.

Characterization and cytocompatibility of hierarchical porous TiO2 coatings incorporated with calcium and strontium by one-step micro-arc oxidation.

Calcium (Ca) and strontium (Sr) are beneficial for bone reconstruction. This study incorporated Ca and Sr into the TiO2 coatings by one-step micro-arc oxidation (MAO) treatment with CaO and SrO added in tetraborate electrolytes. The structure, composition, hydrophilicity, ion release, and cytocompatibility of the coatings were studied. The coatings combine layered micron-scale pores in various sizes and nano-scaled pores, forming a hierarchical structure. This hierarchical structure is highly porous and super-hydrophilic. The coatings are composed of Ti, O, and B, as well as Ca or Sr. Ca and Sr mainly distribute in the outer layer of the coatings and exist in the forms of carbonates and oxides. The formation of the coatings was discussed. Ca and Sr incorporated into the coatings are readily released into aqueous solutions. The homogeneous surface structure of the coatings leads to an excellent and approximating performance in hydrophilicity, as well as the adhesion and spreading of the human bone marrow-derived mesenchymal stem cells (hBMSCs). The simultaneous incorporation of Ca and Sr incorporation exhibits superior facilitation in the proliferation of hBMSCs compared with single Ca or Sr incorporation. This study shows a promising method to incorporate bioactive elements into the MAO coatings on titanium surfaces.

Microstructural evolution and biological performance of Cu-incorporated TiO2 coating fabricated through one-step micro-arc oxidation

In the present work, a Cu-incorporated TiO2 coating was successfully fabricated through a one-step micro-arc oxidation (MAO) of Ti in a solution containing 10 g/L ethylene diamine tetraacetic acid cupric disodium (Na2Cu-EDTA). Interestingly, different colour appearances of the resultant Cu-incorporated TiO2 coating were noticed with the presence of black area at the edge and brown area in the centre. Further, microstructural characterization reveals that, unlike the central brown area with high amount of Cu+, the peripheral black area is mainly enriched in Cu2+, which exhibits a two-layered structure consisting of TiO2 inner layer and porous Ca, P-rich outer layer containing nano-sized hydroxyapatite (HA) crystals. Finally, biological examination reveals that the peripheral black area exhibits both improved bone formability and enhanced antibacterial capability in comparison to the central brown area. Based on the observation, the coating formation mechanism is proposed, which provides valuable guidance for the utilization of MAO method in the field of bio-medical materials.

Characteristics of selenium-containing coatings on WE43 magnesium alloy by micro-arc oxidation

Selenium-containing coatings were developed on WE43 magnesium alloy by micro-arc oxidation (MAO). The results show that anodic coatings fabricated by one-step and two-step MAO treatment separately contain 1.95 wt% and 1.39 wt% Se. Se in MAO coatings is present in Se2− and Se0. The developed coatings doped with Se significantly improve the corrosion resistance of coated WE43 alloy substrate. Compared with one-step MAO, two-step MAO can further improve the coating corrosion resistance of coated Mg alloy substrate due to fewer micro-cracks and greater thickness.

Preparation of BMP-2/chitosan/hydroxyapatite antibacterial bio-composite coatings on titanium surfaces for bone tissue engineering.

In this paper, petaling hydroxyapatite (HA)/TiO2 composite coatings were firstly prepared on titanium (Ti) surface by one-step micro-arc oxidation (MAO), and then pure chitosan (CS) and bone morphogenic protein-2 (BMP-2)-encapsulated CS coatings were respectively loaded on the HA/TiO2 surfaces by dip-coating method to endow Ti with good antibacterial and biological properties. The bonding strength between coatings was studied by scratch method. The degradability of CS, BMP-2 release behavior, bioactivity, biocompatibility and antibacterial activity of the obtained (BMP-2)/CS/HA/TiO2 coatings were examined by in vitro tests. The results showed that, the thicker the HA layer, the larger the loaded BMP-2 and CS amount, resulting in better bonding strength between coatings, antibacterial activity and biocompatibility. In addition, with the increase of CS concentration, more CS was loaded on HA coatings, which benefited the increase of CS degrading amount, the prolonged CS degradation time and BMP-2 release time, resulting in improved antibacterial and biological property. All CS/HA/TiO2 coatings accelerated cell adhesion, spreading and proliferation, and promoted HA formation in simulated body fluids (SBF). After loading BMP-2 in CS, the BMP-2 can significantly improve cell adhesion, spreading and proliferation, and the loaded amount can also be controlled by the concentration of BMP-2 solution. The present study indicates that, by controlling the thickness of HA layers and concentrations of CS and BMP-2 solutions, the Ti implant material with excellent biological and antibacterial properties can be achieved.

Cu and Si co-doped microporous TiO2 coating for osseointegration by the coordinated stimulus action

Biocompatible implant materials with enhanced antibacterial activity, osteogenic and angiogenic capacity are beneficial to osseointegration. Based on the outstanding antimicrobial activity of copper (Cu) and bone-related element silicon (Si), the microporous TiO2 coatings (M-Ti) doped with Cu2+ (M-Cu) and different doses of Si2+ (M-CuSi) were directly fabricated via the simple one-step micro-arc oxidation (MAO). M-Cu causes obvious toxicity towards osteoblasts (OBs) and endothelial cells (ECs) while maintaining excellent antimicrobial activity. By doping Si, it is able to compensate the cytotoxicity of Cu and simultaneously further enhance the activity of OBs and ECs by the synergic stimulatory effects with Cu2+, thus forming a balance between the antibacterial property and biocompatibility. In vitro experiments indicated that the M-CuSi5 coating not only shows good antibacterial properties towards Staphylococcus aureus (S. aureus), but also promotes attachment, spreading, proliferation and differentiation of both OBs and ECs. The most suitable release amount of Cu2+ and Si2+ from M-CuSi5 coating can cause distinctly synergistic stimulatory effects on osteogenesis and angiogenesis by facilitating the osteogenic-related genes and angiogenic-related genes expression. In vivo Micro-CT evaluation and histological observations further mirror that the M-CuSi5 coating results in ameliorative osseointegration, thus being attractive candidate as the bone implant material.

Characterization and property of dual-functional Zn-incorporated TiO2 micro-arc oxidation coatings: The influence of current density

In the present work, with the addition of ZnO nanoparticles (NPs) as Zn source, the Zn-incorporated TiO2 coatings were successfully produced by the facile one-step micro-arc oxidation (MAO) method. The influence of current density on the microstructural features and biological properties of Zn-incorporated TiO2 MAO coatings were systematically examined. It is revealed that, at a relatively low current density of 0.1 A/cm2, Zn species either locate on the coating surface as ZnO nano-sheet clusters or entrap within the coating. By contrast, Zn species tend to fuse into the coating at a relatively high current density of 0.5 A/cm2, which exhibits a three-layered structure with significant difference of crystallinity, composition and morphology between different layers. The biological experiments indicate that different current densities result in different osteogenic activities and antibacterial properties of Zn-incorporated TiO2 coatings. The presence of a Zn-depleted amorphous outer-layer on the MAO coating produced at the current density of 0.5 A/cm2 favours the deposition of apatite-like phases, but retards the release of Zn ions, which thus results in its higher osteogenic activity with lower antibacterial capability compared to that produced at the current density of 0.1 A/cm2. In summary, dual-functional Zn-incorporated TiO2 coatings could be successfully produced through the facile one-step MAO method, with both antibacterial property and bone formability significantly affected by the current density of MAO process.

Characterization and property of bifunctional Zn-incorporated TiO2 micro-arc oxidation coatings: The influence of different Zn sources

Abstract In the present work, Zn-incorporated TiO2 coatings are prepared through a one-step micro-arc oxidation (MAO) method on a grade 4 pure titanium with the addition of either Na2Zn-EDTA solution or ZnO nanoparticles (NPs) as Zn sources. The microstructural features of both Zn-incorporated TiO2 coatings were systematically examined. It is revealed that different Zn sources result in significant difference of phase component, chemical state, composition and morphology between the resultant Zn-incorporated MAO coatings. Zn species could be present as ZnO and Zn(OH)2 in the coating when Na2Zn-EDTA was used as Zn source whereas the presence of ZnO nano-clusters is obvious on the coating surface with ZnO NPs as Zn source. The addition of ZnO NPs during the MAO process also leads to a lower Zn content of the resultant coating, which is more defective with increased thickness in comparison to that of Na2Zn-EDTA. Further, antibacterial property and osteogenic activity of both Zn-incorporated coatings were examined. Both Zn-incorporated coatings exhibit favourable bacterial inhibition ability and bone formability, suggesting the successful synthesis of bifunctional coatings through the facile one-step micro-arc oxidation method.