The purpose of this study was to compare short term in vitro and in vivo biodegradation studies with low purity Mg (> 99.94 %), Mg-10Gd and Mg-2Ag designed for biodegradable implant applications. Three in vitro testing conditions were applied, using (i) phosphate buffered saline (PBS), (ii) Hank's balanced salt solution (HBSS) and (iii) Dulbecco's modified eagle medium (DMEM) in 5 % CO 2 under sterile conditions. Gas evolution and mass loss (ML) were assessed, as well as the degradation layer, by elemental mapping and scanning electron microscopy (SEM). In vivo, implantations were performed on male Sprague-Dawley rats evaluating both, gas cavity volume and implant volume reduction by micro-computed tomography (µCT), 7 d after implantation. Samples were produced by casting, solution heat treatment and extrusion in disc and pin shape for the in vitro and in vivo experiments, respectively. Results showed that when the processing of the Mg sample varied, differences were found not only in the alloy impurity content and the grain size, but also in the corrosion behaviour. An increase of Fe and Ni or a large grain size seemed to play a major role in the degradation process, while the influence of alloying elements, such as Gd and Ag, played a secondary role. Results also indicated that cell culture conditions induced degradation rates and degradation layer elemental composition comparable to in vivo conditions. These in vitro and in vivo degradation layers consisted of Mg hydroxide, Mg-Ca carbonate and Ca phosphate.

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Magnesium and its alloys are currently considered to be a promising metallic biomaterial. The interest in magnesium alloys arises from their biocompatibility, bioabsorbility, and especially from their mechanical properties, which are more compatible to those of human bone than the mechanical properties of other metallic biomaterials, such as stainless steel and titanium. A medical application in which magnesium is gaining interest is regenerative medicine where scaffolds are used to create tissues from cells. For its application in regenerative medicine, the scaffolds have to present a 3D open-cell structure. The main purpose of the present research is to set up the fabrication procedure necessary to manufacture porous magnesium scaffolds; for this the replication (infiltration) process has been used and adapted to process magnesium alloys, processing five different biodegradable magnesium alloys (AZ91E, WE43, ZM20, ZWM200, and ZXM200).

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In this work the microstructure and degradation behavior of several as-cast alloy compositions belonging to the Mg rich corner of the Mg-Si-Sr system are presented and related. The intermetallic phases are identified and analyzed describing the microstructure evolution during solidification. It is intended in this work to obtain insight in the behavior of the ternary alloys in in vitro tests and to analyze the degradation behavior of the alloys under physiologically relevant conditions. The as-cast specimens have been exposed to immersion tests, both mass loss (ML) and potentiodynamic polarization (PDP). The degradation rate (DR) have been assessed and correlated to microstructure features, impurity levels and alloy composition. The initial reactions resulted to be more severe while the degradation stabilizes with time. A higher DR is related with a high content of the MgSr phase and with the presence of coarse particles of the intermetallics MgSi, MgSiSr and MgSiSr. Specimens with a higher DR typically have higher levels of impurities and alloy contents.