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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]

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]

In the present work, plasma electrolytic oxidation (PEO) is creatively introduced as a novel method to fabricate multi-layered nanospheres. Titanium (Ti) was oxidized in a phosphate-based electrolyte containing ZnO nanoparticles (NPs), which results in the formation of nanospheres on the ceramic coating. The as-fabricated nanosphere is amorphous with a three-layered architecture. The inner layer of the nanosphere contains Zn, Ca and P whereas Cu and P were detected in the medium layer with the outer layer enriched in Cu, O and Ti, which is promising in the field of bio-medical implanted devices. Herein, a novel one-pot synthesis strategy is proposed to fabricate multi-layered nanospheres, which could enlighten the preparation of hierarchical structures in various fields. [Display omitted] [ABSTRACT FROM AUTHOR]

Currently, biodegradable Mg-based implants used in clinical practice barely degrade after more than ten months of use. To achieve controlled degradation, we prepare a novel surface system on a Mg Mn Ag alloy composed of a ceramic layer produced by plasma electrolytic oxidation (PEO) and a polypyrrole (PPy)-loaded polycaprolactone (PCL) composite coating. The surface system exhibits superior corrosion resistance to prevent premature failure of the Mg alloy. After near-infrared (NIR) irradiation, the photothermal conversion effect of PPy promotes the transformation of PCL from a rubbery state to a viscous state, thereby facilitating the infiltration of external electrolytes for a dramatically increased degradation rate. As a result, the reduction of i corr and | Z | 0.01Hz by 4 orders of magnitude after NIR irradiation could be achieved. Hence, this work provides a new strategy for remotely regulating the degradation rate of Mg-based implants. [Display omitted] • A novel surface layer composed of a PEO ceramic layer and a PCL-PPy composite coating was fabricated on Mg Ag Mn alloy. • PEO/PCL-PPy layer exhibits desired corrosion resistance. • NIR irradiation dramatically decreases the corrosion resistance of the surface layer. [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]

• 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]