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High-resolution analytical methods, including synchrotron infrared microspectroscopy combined with wavelength-dispersive X-ray emission spectroscopy were applied to study the structure and chemical composition of the oxidized layer of pure and Ag-alloyed Mg exposed to cell culture media without and with osteoblasts. Comparative analysis has been done on pure Mg immersed in two different cell culture media: Dulbecco\'s Modified Eagle\'s Medium (DMEM) and Roswell Park Memorial Institute medium (RPMI), whereas Mg-xAg binary alloys (x = 2, 4, 6, 8 wt%) were studied after immersion in DMEM. It is shown that the physicochemical formation of degradation products as well as the activity of the biological component is influenced by the addition of silver. It could be demonstrated that the presence of Ag in the Mg alloy enhances the chemical reaction between Mg and C to form amorphous and/or crystalline MgCO3 on account of CaCO3. As a consequence, the further available P and Ca react easily to form Mg-poor amorphous calcium phosphate phases. Osteoblasts actively adjusted these phases towards hydroxyapatite-like phases.

Biodegradable materials are under investigation due to their promising properties for biomedical applications as implant material. In the present study, two binary magnesium (Mg) alloys (Mg2Ag and Mg10Gd) and pure Mg (99.99%) were used in order to compare the degradation performance of the materials in in vitro to in vivo conditions. In vitro analysis of cell distribution and viability was performed on discs of pure Mg, Mg2Ag and Mg10Gd. The results verified viable pre-osteoblast cells on all three alloys and no obvious toxic effect within the first two weeks. The degradation rates in in vitro and in vivo conditions (Sprague–Dawley® rats) showed that the degradation rates differ especially in the 1st week of the experiments. While in vitro Mg2Ag displayed the fastest degradation rate, in vivo, Mg10Gd revealed the highest degradation rate. After four weeks of in vitro immersion tests, the degradation rate of Mg2Ag was significantly reduced and approached the values of pure Mg and Mg10Gd. Interestingly, after 4 weeks the estimated in vitro degradation rates approximate in vivo values. Our systematic experiment indicates that a correlation between in vitro and in vivo observations still has some limitations that have to be considered in order to perform representative in vitro experiments that display the in vivo situation.

Magnesium and its alloys have considerable potential for orthopedic applications. During the degradation process the interface between material and tissue is continuously changing. Moreover, too fast or uncontrolled degradation is detrimental for the outcome in vivo. Therefore in vitro setups utilizing physiological conditions are promising for the material/degradation analysis prior to animal experiments. The aim of this study is to elucidate the influence of inorganic salts contributing to the blood buffering capacity on degradation. Extruded pure magnesium samples were immersed under cell culture conditions for 3 and 10 days. Hank's balanced salt solution without calcium and magnesium (HBSS) plus 10% of fetal bovine serum (FBS) was used as the basic immersion medium. Additionally, different inorganic salts were added with respect to concentration in Dulbecco's modified Eagle's medium (DMEM, in vitro model) and human plasma (in vivo model) to form 12 different immersion media. Influences on the surrounding environment were observed by measuring pH and osmolality. The degradation interface was analyzed by electron-induced X-ray emission (EIXE) spectroscopy, including chemical-element mappings and electron microprobe analysis, as well as Fourier transform infrared reflection micro-spectroscopy (FTIR).