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Plasma electrolytic oxidation (PEO) is normally carried out under conditions with electrolyte cooling. However, the effect of the temperature of the electrolytes on the PEO behavior and properties of the resulting coatings is seldom investigated. In this study, PEO of pure Al was carried out in a dilute aluminate electrolyte with the electrolyte temperature being controlled under low (~10–30 °C), medium (~40–50 °C) and high (~70–80 °C) temperature ranges, respectively. The morphology, microstructure, composition and phase component of the coatings fabricated under the different temperature ranges were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The corrosion resistances of the coatings were evaluated by electrochemical methods. The hardness of the coatings and substrate following the PEO treatment in the different electrolyte temperature ranges were also tested. It was found that a higher electrolyte temperature resulted in a higher growth rate and rougher coatings. Moreover, the α-Al2O3 content was reduced as the electrolyte temperature increased. The highest corrosion resistance was registered for the coating obtained under the lowest temperature range, whereas the corrosion resistance of the coating obtained under the highest temperature range was the worst. The higher growth rate under high electrolyte temperatures was associated with the increased kinetics of the PEO reactions. However, the temperature of the electrolyte should be controlled under a suitable range to ensure reasonable coating properties. [ABSTRACT FROM AUTHOR]

Ti and its alloys have received wide attention in marine engineering. However, the limited anti-biofouling capability may hinder their wide application. In the present work, micro-arc oxidation (MAO) with and without the introduction of ultrasonic vibration (UV) has been conducted on metallic Ti substrate in an aqueous solution containing Na2Cu-EDTA to produce a Cu-modified TiO2 coating. Microstructural characterization reveals that the introduction of UV increased the thickness of the coating (ranging from ~13.5 μm to ~26.2 μm) compared to the coating (ranging from ~8.1 μm to ~12.8 μm) without UV. A relatively higher Cu content (~2.13 wt.%) of the coating with UV relative to the coating (~1.39 wt.%) without UV indicates that UV enhances the incorporation of Cu into TiO2. Further, both electrochemical properties and the response to sulfate-reducing bacteria (SRB) were evaluated, revealing that UV introduction endows Cu-modified TiO2 coating with enhanced corrosion resistance and antifouling capability. The present results suggest that ultrasound-auxiliary micro-arc oxidation (UMAO) obviously enhances the surface performance of Ti alloys for promising applications in marine engineering. [ABSTRACT FROM AUTHOR]

Endowing magnesium alloys with both durable antibacterial ability and reliable corrosion resistance is an urgent task for the development of magnesium-based implants. In this work, Mg–Mn layered double hydroxide (LDH) intercalated with organic salicylic acid (SA) anion was synthesized on a PEO-coated Mg–Ag–Mn alloy via the combination of co-precipitation and hydrothermal treatments. The PEO layer endows Mg–Ag–Mn alloy with a moderate corrosion barrier and the Mg–Mn LDH layer not only seals the PEO defects, but also acts as a reservoir for antibacterial agents (namely SA). The PEO/Mg–Mn LDH composite coating on Mg–Ag–Mn alloy dramatically increases its corrosion resistance by up to 3 orders of magnitudes, which also tailors the ionic release kinetics for a desired antibacterial potential to prevent bacterial infection. • Mg–Mn LDH intercalated with organic salicylic acid anion was successfully prepared by co-precipitation method. • PEO/Mg–Mn LDH composite coating exhibits outstanding corrosion resistance. • Ionic release kinetics were successfully tailored by LDH layer for a desired antibacterial potential. [ABSTRACT FROM AUTHOR]

In the present study, the distribution of Ag in the coating formed on Mg-Ag alloy by plasma electrolytic oxidation (PEO) and its ionic release kinetics when exposed to a 0.9 wt.% NaCl solution at 37 °C have been investigated. Both metallic Ag and Ag oxide particles with ∼5 to ∼40 nm in diameters were observed in the PEO coating. Further, an Ag-enriched layer of ∼20 nm in thickness at the substrate/coating interface was also observed. The PEO coating on the Mg-Ag alloy not only increases its corrosion resistance with the corrosion current density decreasing by up to 3 orders of magnitude from 8.04 × 10−3 to 4.03 × 10−6 A/cm2, but also controls the release of Ag+ to the level that is sufficient for anti-infective efficacy without causing cytotoxicity to mammal cells. [ABSTRACT FROM AUTHOR]

The limited antifouling capability of Ti-based components could jeopardize their applications in petroleum engineering. In this work, a Cu-enriched TiO2 coating has been fabricated using an ultrasound-auxiliary micro-arc oxidation (UMAO) method. The Cu enrichment of TiO2 affects its morphology, phase component and chemical configuration, leading to the slightly enhanced corrosion resistance of the Cu-enriched TiO2 coating relative to that free of Cu. Finally, the antifouling capability against sulphate-reducing bacteria (SRB) is significantly improved by preventing the formation of biofilm after the Cu enrichment of TiO2, which potentially widens its application in petroleum engineering. [ABSTRACT FROM AUTHOR]

Bio-medical materials with sufficient antibacterial performance and osteogenic activity are desirable for orthopaedic implantable devices. In the present work, titanium (Ti) surface was modified through micro-arc oxidation in an electrolyte containing Ag nanoparticles (NPs) and disodium zinc ethylenediaminetetraacetate tetrahydrate (Na 2 Zn-EDTA) to fabricate Ag, Zn co-doped titania coating, with the influence of Na 2 Zn-EDTA content on its microstructure, corrosion behaviour and biological performances investigated systematically. By increasing the amount of Na 2 Zn-EDTA from 5 g/L to 50 g/L, the coating exhibits a significantly reduced average pore size along with a decreased coating thickness. Further, unlike micro-sized dicalcium phosphate dehydrate (DCPD) crystals and Ag NP clusters for the coating produced by 5 g/L Na 2 Zn-EDTA, both Ag NPs of a reduced amount and nano-sized amorphous Ca and P-rich components were observed on the coating surface when the electrolyte containing 50 g/L Na 2 Zn-EDTA was used. The microstructural variation inevitably leads to the modification of its performances. The high amount of Na 2 Zn-EDTA results in a bio-ceramic characterized by higher corrosion resistance, enhanced antibacterial capability and improved osteogenic activity relative to that fabricated with the addition of a low amount of Na 2 Zn-EDTA. Therefore, this work provides a new strategy for the fabrication of bio-ceramics on Ti-based implants. [ABSTRACT FROM AUTHOR]

In order to improve antibacterial capability and cell biocompatibility of titanium (Ti), Ag nanoparticles (NPs) and a novel Zn source Na 2 Zn-EDTA (disodium zinc ethylenediaminetetraacetate tetrahydrate) were added in the electrolyte to fabricate Ag, Zn co-incorporated titania through micro-arc oxidation (MAO) method on metallic Ti substrate. Microstructural characterization reveals that the presence of both Ag NP clusters and micro-sized dicalcium phosphate dehydrate (DCPD) flakes on the surface of Ag, Zn co-incorporated TiO 2 coating. Ag species are mainly present as metallic Ag whereas Zn species tend to exist as Zn2+ within titania. Further, corrosion resistance, antibacterial property and cell biocompatibility of the resultant coatings were assessed. It is revealed that the Ag, Zn co-incorporated TiO 2 coating possesses favourable corrosion resistance, desirable in vitro antibacterial capability and cell biocompatibility without cytotoxicity, which is a promising candidate as a bio-ceramics for Ti-based implant. • Ag, Zn co-incorporated TiO 2 coating has been successfully produced using micro-arc oxidation method with Na 2 Zn-EDTA and Ag nanoparticles as Zn and Ag sources. • During the oxidation, dicalcium phosphate dehydrate flakes of micrometre scales were formed on the surface of Ag, Zn co-incorporated TiO 2 coating. • Ag, Zn co-incorporated TiO 2 coating exhibits excellent antibacterial capability and desirable bone formability. [ABSTRACT FROM AUTHOR]

The application of Mg Ag alloy for the fabrication of orthopedic implant requires its enhanced corrosion resistance, desired biocompatibility and bactericidal capability without cytotoxicity. Herein, to achieve those purposes, a novel plasma electrolytic oxidation (PEO) treatment was proposed. The PEO coating with a bimodal pore size distribution could form on Mg Ag alloy surface to enhance its corrosion resistance. Further, the incorporation of magnesium phosphate in the PEO coating may also benefit its biocompatibility. Finally, Ag within the alloy could be gradually oxidized to form incorporated Ag+ and nano-sized Ag 2 O particles in the coating, which potentially optimize the ionic release kinetics of Ag for a desired antibacterial capability without cytotoxicity. Hence, the present work offers a novel PEO method to improve the corrosion resistance and biological response of Mg Ag alloy, which enlightens the application of antibacterial Mg alloy in the field of biomedical devices. • An untraditional voltage response during the PEO process is reported. • Nano-sized magnesium phosphate is incorporated into the PEO coating. • Ag oxide nanoparticle is present in the PEO coating. • PEO coating with bimodal pore size distribution is produced. [ABSTRACT FROM AUTHOR]

Surfaces with desirable cytocompatibility and bactericidal ability are favoured for orthopaedic implants to stimulate osteogenic activity and to prevent implant-associated infection. In this work, we creatively introduce ultrasonic vibration (UV) to micro-arc oxidation (MAO) process and explore its influence on the microstructure, corrosion property and biological responses of Zn-modified TiO 2 coating. With the introduction of UV, a uniform surface layer with homogeneously-distributed clusters could be produced as the outer layer, which possesses a fusion band with the underlying TiO 2. The microstructural modification associated with UV results in the enhanced corrosion resistance, increased adhesive strength and improved biological performances of the resultant coating relative to that with the absence of UV. Hence, the ultrasonic auxiliary micro-arc oxidation (UMAO) is regarded as a promising surface modification method to produce Ti-based orthopaedic implants of high quality. [Display omitted] • A uniform appearance is achieved by ultrasound-auxiliary micro-arc oxidation. • A fusion band enhance the adhesive strength of the coating. • Ultrasonic action benefits corrosion resistance and biological performance. • In vivo biocompatibility of Zn-modified TiO 2 coating is demonstrated. [ABSTRACT FROM AUTHOR]

Surface coatings with the improved antibacterial capability and osteogenic activity are highly favoured for titanium (Ti)-based orthopaedic implants. Herein, Ag, Zn co-modified titania was synthesized using the micro-arc oxidation (MAO) technique with Ag nanoparticles (NPs) as Ag sources and ZnO NPs as Zn sources. The synergistic effects of Ag and ZnO additions not only result in the significant modification of their existing forms, but also promote the formation of two different types of Ca P phases, namely Zn-incorporated dicalcium phosphate dihydrate (DCPD) crystal and submicron-sized amorphous Ca P phase deposition of porous appearance. Anti-corrosion, antibacterial and osteogenic experiments prove that the synthesis strategy of Ag, Zn co-modified titania provides a promising way for Ti-based bioceramic coatings for orthopaedic implants. • The Ag, Zn co-modified titania has been successfully fabricated in the electrolyte containing Ag and ZnO nanoparticles. • Zn-incorporated dicalcium phosphate dehydrate crystal and amorphous Ca P phase are formed. • The synergistic effect of Ag and ZnO enhances the corrosion resistance and biological performances of titania. [ABSTRACT FROM AUTHOR]

In the present work, a laser surface desensitization (LSD) method was carried out on sensitized AA5083 alloy with the underlying microstructural evolution examined. The enhanced corrosion resistance after LSD process was confirmed by nitric acid mass loss test (NAMLT), immersion test and electrochemical measurements, which is mainly ascribed to the modification of grain boundary chemistry. Accompanied with the dissolution of grain boundary β (Al 3 Mg 2) phase during LSD process, the grain boundaries could be characterized by Mg segregation or nano-sized Mg-rich clusters, which may also be absent from chemical uniformity depending on grain boundary misorientation. [Display omitted] • LSD successfully achieves a local reversing sensitization of AA5083 alloy. • LSD results in the dissolution of grain boundary β phase. • Grain boundary chemistry after LSD varies depending on grain boundary misorientation and laser power. [ABSTRACT FROM AUTHOR]

In this work, a Mn-incorporated Ca-P/TiO 2 composite coating was produced through the facile one-step micro-arc oxidation (MAO) method. It is revealed that only when the concentration of Na 2 Mn-EDTA reaches 0.02 mol/L, the Ca-P phase could form on Mn-incorporated TiO 2 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 TiO 2 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/TiO 2 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 Na 2 Mn-EDTA. Unlabelled Image • A Mn-incorporated Ca-P/TiO 2 composite coating could be successfully produced through the micro-arc oxidation method. • The outer Ca-P is amorphous whereas the inner TiO 2 contains two layers with different Mn contents. • Ca-P layer forms only when the concentration of Na 2 Mn-EDTA in the electrolyte reaches at least 0.02 mol/L. • The composite coating exhibits desirable corrosion resistance and bone formability with certain antibacterial ability. [ABSTRACT FROM AUTHOR]

• The coating contains a Mn-rich outer layer and a polycrystalline inner layer. • Mn specie mainly exists as Mn 3 O 4. • The antibacterial capability is mainly ascribed to Mn 3 O 4. • Mn incorporation enhances cellular response and corrosion resistance of TiO 2. In the present work, a Mn-incorporated TiO 2 coating has been fabricated through the facile one-step micro-arc oxidation (MAO) treatment in the electrolyte containing Na 2 Mn-EDTA. Microstructural characterization reveals that Mn-incorporated TiO 2 coating exhibits a two-layered structure based on chemical compositions, which includes the inner layer consisting of polycrystalline TiO 2 with P segregated at the grain boundary and the outer layer comprising of nano-sized Mn 3 O 4 particles. Further, both corrosion resistance and biological performance of the Mn-incorporated TiO 2 coating were investigated. It was revealed that the Mn-incorporated TiO 2 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. [ABSTRACT FROM AUTHOR]

As an effective antimicrobial element, the incorporation of Cu into the surface layer of metallic Ti substrate is regarded as a promising method to enhance its antifouling phenomenon. In this work, a micro-arc oxidation (MAO) process was conducted in an aqueous electrolyte containing Na 2 Cu-EDTA to produce a Cu-modified TiO 2 coating on metallic Ti. The influence of Na 2 Cu-EDTA concentrations on microstructural feature, corrosion resistance and antifouling capability of the Cu-modified TiO 2 coatings were examined. The results indicate that an increased amount of Cu could be incorporated into TiO 2 with a higher concentration of Na 2 Cu-EDTA, which also affects the micro-arc discharge events and, consequently, the morphological features of the coating. The content of incorporated Cu determines the antifouling performance of Cu-modified TiO 2 coating, which remains harmless to the corrosion resistance. • Na 2 Cu-EDTA tailors micro-arc discharge events to affect microstructure of Cu-modified TiO 2 coating. • Corrosion resistance of TiO 2 is insensitive to the content of incorporated Cu. • TiO 2 with a higher content of Cu exhibits an enhanced antifouling performance. [ABSTRACT FROM AUTHOR]

• Both metallic Ag and Ag oxide exist in the coating. • A nano-sized Ag-rich layer exists at the substrate/coating interface. • PEO affects corrosion morphology and susceptibility of Mg-Ag alloy. • A sustained Ag+ release is achieved after PEO of Mg-Ag alloy. The application of biodegradable Mg alloys as implanted devices has been hindered by their low corrosion resistance and potential risk associated with microbial infection. In the present work, a rolled Mg-Ag alloy was studied, which was subjected to plasma electrolytic oxidation (PEO) to achieve a favoured balance between corrosion resistance and antimicrobial capability. The Ag distribution, corrosion resistance and Ag ionic release behaviour have been examined in details. It is revealed that PEO process leads to both incorporated Ag+ and Ag-rich nanoparticles in forms of metallic Ag and Ag oxide across the coating. In addition, a nano-sized Ag-enriched layer also exists at the substrate/coating interface. The microstructural modification associated with PEO process results in an increased corrosion resistance and a sustained Ag ionic release, indicating that it is a promising surface modification technique for antibacterial Mg-Ag alloy. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A uniform appearance is achieved by the introduction of ultrasound. • Ultrasound stimulates the formation of an amorphous Ca, P, Cu and O-rich layer. • Ultrasound is beneficial for corrosion and biological properties of the coating. To achieve a uniform surface layer with enhanced corrosion resistance, antibacterial capability and cytocompatibility on the titanium (Ti)-based orthopaedic implant, ultrasound-auxiliary micro-arc oxidation (UMAO) was carried out on Ti substrate to fabricate a Cu-incorporated TiO 2 coating. Instead of the co-existence of central brown area and peripheral black area in the Cu-incorporated TiO 2 coating fabricated by conventional micro-arc oxidation, a uniform brownish appearance could be achieved after the introduction of ultrasonic vibration (UV). The introduction of UV also significantly modifies the elemental composition, phase component and chemical configuration of the coating, which exhibits a bi-layered structure with the porous TiO 2 as the inner layer and the amorphous Ca, P, O and Cu component as the outer layer. Finally, electrochemical measurement and in vitro biological tests indicate that the introduction of UV is conducive to corrosion resistance, antibacterial capability and cytocompatibility of the Cu-incorporated TiO 2 coating. [ABSTRACT FROM AUTHOR]

In the present work, the early-stage growth behaviour of titania on titanium (Ti) substrate during plasma electrolytic oxidation (PEO) process in an aqueous electrolyte rich in Ca and P was investigated. Microstructural characterization reveals the dramatic evolutions of morphology, porosity, phase component and chemical composition of titania during the early stage of PEO process. The PEO coating initially exhibits ultrafine pores with a completely amorphous structure after oxidation for 5 s, which displays a relatively low Ca/P ratio. With the extension of oxidation periods, titania gradually transforms to grooved morphology with an increased Ca/P ratio, which mainly consists of crystalline anatase phase. Finally, with the prolongation of oxidation period to 1 min, titania exhibits porous morphology typical for PEO coating, which comprises of both rutile and anatase crystals. Along with the prolongation of oxidation periods, the surface wettability of titania remains relatively stable whereas the corrosion resistance changes dramatically, which is closely associated with the combined effects of its porosity and thickness. The results of our present work advance the understanding of early-stage growth of titania during the PEO process, which offer theoretical guidance for the controllable synthesis of PEO coating on Ti and its alloys. • The growth behaviour of titania prior to dielectric breakdown was examined. • Titania initially displays ultrafine pores, transforms to grooved morphology and finally stabilizes as porous structure. • The initial titania is amorphous, which transforms to anatase and finally becomes the mixture of rutile and anatase. • The Ca/P ratio gradually increases with the prolongation of oxidation periods and finally reaches ~0.9. • The combined effect of porosity and thickness results in the dramatic modification of corrosion resistance in titania. [ABSTRACT FROM AUTHOR]

The hydroxyapatite (HA)-based/TiO 2 -based composite coating was produced through plasma electrolytic oxidation (PEO) method in the present work. The microstructural evolution of the composite coating was examined as a function of PEO duration. It was observed that Ca P phase initially appears at the cracks of TiO 2 -based layer in form of plates of micrometre scales after PEO duration of 5 min and then transforms to the hybrid of plates and floccules, which finally convert to clusters composed of nano-sized plates by self-assembly. After 15 min oxidation, a two-layered composite coating was revealed, including TiO 2 -based inner layer and HA-based outer layer. It is also noticed that the thickness of HA-based layer continuously increases as the oxidation period extends whereas both the thickness of TiO 2 -based layer beneath the HA-based layer and the coverage rate of Ca P phase on TiO 2 -based layer remain relatively stable at the late stage of PEO process. The microstructural variation inevitably affects the biocompatibilities and corrosion properties of the composition coatings. With the extension of oxidation periods, an increased amount of Ca P phase was produced in the composite coating, which thus results in an improved corrosion resistance due to its insulation property, hydrophobicity and physical barrier effect. Meanwhile, the enhanced biocompatibility of the composite coating could also be achieved with the prolongation of PEO duration, which is associated with the high bioactivity of Ca P phase. • The hydroxyapatite/TiO 2 composite coating has been successfully produced through plasma electrolytic oxidation. • The formation of hydroxyapatite is closely associated with cracks in the TiO 2 -based layer. • The presence of hydroxyapatite retards the growth of underlying TiO 2. • The coverage rate of hydroxyapatite initially increases dramatically and finally remains stable at approximately 80%. • An increased amount of hydroxyapatite results in an improved corrosion resistance and biocompatibility of the coating. [ABSTRACT FROM AUTHOR]