title: Protective layer formation on magnesium in cell culture medium.
abstract: In the past, different studies showed that hydroxyapatite (HA) or similar calcium phosphates can be precipitated on Mg during immersion in simulated body fluids. However, at the same time, in most cases a dark grey or black layer is built under the white HA crystals. This layer seems to consist as well of calcium phosphates. Until now, neither the morphology nor its influence on Mg corrosion have been investigated in detail. In this work commercially pure magnesium (cp) was immersed in cell culture medium for one, three and five days at room temperature and in the incubator (37 °C, 5% CO2). In addition, the influence of proteins on the formation of a corrosion layer was investigated by adding 20% of fetal calf serum (FCS) to the cell culture medium in the incubator. In order to analyze the formed layers, SEM images of cross sections, X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX) and Fourier Transformed Infrared Spectroscopy (FTIR) measurements were carried out. Characterization of the corrosion behavior was achieved by electrochemical impedance spectroscopy (EIS) and by potentio-dynamic polarization in Dulbecco's Modified Eagle's Medium (DMEM) at 37°C. Surface analysis showed that all formed layers consist mainly of amorphous calcium phosphate compounds. For the immersion at room temperature the Ca/P ratio indicates the formation of HA, while in the incubator probably pre-stages to HA are formed. The different immersion conditions lead to a variation in layer thicknesses. However, electrochemical characterization shows that the layer thickness does not influence the corrosion resistance of magnesium. The main influencing factor for the corrosion behavior is the layer morphology. Thus, immersion at room temperature leads to the highest corrosion protection due to the formation of a compact outer layer. Layers formed in the incubator show much worse performances due to completely porous structures. The existence of proteins in DMEM seems to hinder the formation of a corrosion layer. However, protein adsorption leads to similar results as concerns corrosion protection as the formed calcium phosphate layer.
authors.affiliation: Chair for Surface Science and Corrosion, Department Materials Science, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Wagener
authors.affiliation: Chair for Surface Science and Corrosion, Department Materials Science, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen, Germany. Electronic address: virtanen@ww.uni-erlangen.de.
authors.forename: S
authors.initials: S
authors.lastname: Virtanen
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry; D003470:Culture Media / Q000737:chemistry*; D058266:Dielectric Spectroscopy; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D056951:Photoelectron Spectroscopy; D013052:Spectrometry, X-Ray Emission; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D002130:Calcium Phosphates; D003470:Culture Media; C519480:amorphous calcium phosphate; D008274:Magnesium
keywords: Calcium phosphate coating; Corrosion protection electrochemical impedance spectroscopy; Magnesium; Protein influence