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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.

Oxide coatings were formed on AZ91D Mg alloy by microarc oxidation ͑MAO͒ in a sodium aluminate ͑NaAlO 2 ͒-based electrolyte, and the effects of additive electrolytes, KF, NaOH, and KOH, on the physical and chemical properties of the MAO coatings were investigated, particularly focusing on their corrosion resistance determined by potentiodynamic and potentiostatic tests. The anodizing characteristics ͑breakdown voltage and ignition time͒ and the phase, surface morphology, and thickness of the MAO coatings were strongly dependent on the additive electrolytes. The intense and continuous sparking in the KF-NaAlO 2 electrolyte resulted in a thick MgAl 2 O 4 coating containing F − ions, whereas the MAO coating obtained in either NaOH or KOH-NaAlO 2 electrolyte was thin and poorly crystalline, resulting from the unstable and discontinuous sparking. The MAO coating obtained in the KF-NaAlO 2 electrolyte exhibited the highest corrosion potential, the lowest corrosion current density, and the highest polarization resistance, which were closely related to the crystalline MgAl 2 O 4 phase and the relatively thick dense inner barrier layer. The pitting corrosion occurred in AZ91D Mg alloy, and the pitting was significantly protected by the MAO coating obtained in the KF-NaAlO 2 electrolyte. The pitting potentials for the MAO coatings have been determined by potentiostatic tests.Magnesium ͑Mg͒ and its alloys have been used in a wide range of applications such as construction, automotive, aerospace, and computer parts due to their excellent physical and mechanical properties including low density, high specific strength, high dimensional stability, and good machining and recycling ability. 1,2 However, poor corrosion and wear resistance, particularly when exposed to aggressive electrolyte species such as Cl − ions, severely limits their widespread uses in many applications. 3 The most effective way to improve the corrosion performance is surface modification by protective coatings. 4 Several coating technologies have been explored for Mg and its alloys including anodizing, 5-8 conversion coatings, 9 electrochemical plating, 10 physical vapor deposition coatings, 11,12 and organic coatings. 13,14 Among them, microarc oxidation ͑MAO͒ based on the traditional anodic oxidation is highly attractive because it can produce a thick, hard, and well-adherent ceramic-like coating that has the potential to significantly enhance the corrosion and wear resistance. [15][16][17][18] The nature and microstructure of the MAO coatings depend on numerous parameters, 19-28 but the chemical composition of the electrolyte is known to play a decisive role to determine the properties of the MAO coatings. [19][20][21][22][23] The presence of forsterite ͑Mg 2 SiO 4 ͒, spinel ͑MgAl 2 O 4 ͒, Mg 3 ͑PO 4 ͒ 2 , and MgF 2 in addition to MgO and Mg͑OH͒ 2 is beneficial for the improvement of corrosion resistance of the MAO coatings. 8,17,[22][23][24][25][26][29][30][31][32][33][34][35] Thus, in many studies, alkaline phosphate, silicate, and aluminate-based elec...

Silver-containing oxide coatings on AZ31 Mg alloys were fabricated by microarc oxidation (MAO) in AgNO3 -containing sodium silicate (Na2SiO3) -based electrolyte, and their physical and chemical properties were investigated, particularly focusing on corrosion resistance and antibacterial activity. The porous oxide coatings consisting of Mg2SiO4 and MgO formed in both AgNO3 -containing and AgNO3 -free electrolytes and the MAO coatings were composed of a porous outer layer and a dense inner layer. MAO in AgNO3 -containing electrolyte resulted in a thicker oxide coating, especially a thicker fluorine (F)-rich inner layer. Fluorine (F) was rich in the dense inner layer, and Ag was preferentially located close to the coating surface. The potentiodynamic test indicated that Ag-containing MAO coating had a more positive corrosion potential (−1.42 V), lower corrosion current density (0.02μA/cm2) , and thus higher corrosion resistance (1824kΩcm2) compared to Ag-free MAO coatings (−1.53 V, 0.32μA/cm2 , and 131kΩcm2 , respectively). The electrochemical impedance spectroscopy results revealed that the higher corrosion resistance of Ag-containing MAO coating was due to an order of magnitude higher resistance of the dense inner layer. Ag-containing MAO coating showed an excellent antibacterial activity over 99.9% against two strains of bacteria, Staphylococcus aureus and Escherichia coli.