Magnesium (Mg) alloys are promising materials for the development of biodegradable implants. However, the current in vitro test procedures for cytotoxicity, cell viability and proliferation are not always suitable for this class of materials. In this paper we show that tetrazolium-salt-based assays, which are widely used in practice, are influenced by the corrosion products of Mg-based alloys. Corroded Mg converts tetrazolium salts to formazan, leading to a higher background and falsifying the results of cell viability. Tetrazolium-based assays are therefore not a useful tool for testing the cytotoxicity of Mg in static in vitro assays.

An AM60 magnesium alloy nanocomposite reinforced with 1 wt % of AlN nanoparticles was prepared using an ultrasound (US) assisted permanent-mould indirect-chill casting process. Ultrasonically generated cavitation and acoustic streaming promoted de-agglomeration of particle clusters and distributed the particles throughout the melt. Significant grain refinement due to nucleation on the AlN nanoparticles was accompanied by an exceptional improvement in properties: yield strength increased by 103%, ultimate tensile strength by 115%, and ductility by 140%.Although good grain refinement was observed, the large nucleation undercooling of 14 K limits further refinement because nucleation is prevented by the formation of a nucleation-free zone around each grain. To assess the industrial applicability and recyclability of the nanocomposite material in various casting processes, tests were performed to determine the effect of remelting on the microstructure. With each remelting, a small percentage of effective AlN nanoparticles was lost, and some grain growth was observed. However, even after the third remelting, excellent strength and ductility was retained. According to strengthening models, enhanced yield strength is mainly attributed to Hall-Petch strengthening caused by the refined grain size. A small additional contribution to strengthening is attributed to Orowan strengthening.

Sintering of magnesium powder is strongly inhibited by a stable oxide layer that is formed immediately after exposure to air. In contrast to e.g. titanium, no solubility of oxygen in solid magnesium is reported; therefore, the oxide layer is not dissolved during sintering. In this study, different methods are investigated in order to overcome this problem. It is shown that magnesium can be sintered if the sintered parts are surrounded by magnesium getter material. Calcium additions improve sinterability. The optimum calcium content lies in the range of 0.6 wt%.

Evolution of the crystal structure of ceramics BiFeO3–BaTiO3 across the morphotropic phase boundary was analyzed using the results of macroscopic measuring techniques such as X-ray diffraction, differential scanning calorimetry, and differential thermal analysis, as well as the data obtained by local scale methods of scanning probe microscopy. The obtained results allowed to specify the concentration and temperature regions of the single phase and phase coexistent regions as well as to clarify a modification of the structural parameters across the rhombohedral–cubic phase boundary. The structural data show unexpected strengthening of structural distortion specific for the rhombohedral phase, which occurs upon dopant concentration and temperature-driven phase transitions to the cubic phase. The obtained results point to the non-monotonous character of the phase evolution, which is specific for metastable phases. The compounds with metastable structural state are characterized by enhanced sensitivity to external stimuli, which significantly expands the perspectives of their particular use.

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Magnesium (Mg)-based alloys are investigated for the use as lightweight structural metals, e.g., in the automotive industry, [1] as biodegradable implant materials [2] and for hydrogen storage. [3] The choice of alloying system and subsequent processing of the material is a crucial factor for the degradation profile of the alloy and its mechanical properties. [4][5][6][7] This review focuses on use of Mg alloys as implant material, with some references to its application as a structural metal.The degradation profile of Mg alloys is of particular importance for their application as implant materials, as a controlled degradation is required to ensure cell viability and implant stability in vivo. [8,9] During the development of Mg alloys for the application as a biodegradable implant, alloying systems are carefully selected and manufactured, with their microstructure being tailored according to specifications by selecting the appropriate processing route. The microstructure and the mechanical properties of the alloy will be evaluated and the alloy is then tested for in vitro degradation in an aqueous environment under physiological conditions (pH %7.4, 37 C, 5% CO 2 , 21% O 2 , 95% rel. humidity) with and without cells to assess its general degradation properties and cell viability. [10] The mechanical properties and degradation profile need to be tailored depending on the application of the implant. Mg alloys for bone support, for example, require mechanical properties close to that of bone. For bone, the average Young's modulus is between 7 and 31 GPa, depending on the type of bone and its hydration state. [11,12] In longitudinal direction, the bone's tensile and compressive ultimate strength have been reported to be between 93 and 135 MPa, and 154 and 205 MPa, respectively. [13,14] Finally, the elongation to failure of the clinically approved MAGNEZIX screw by Syntellix AG (Hanover, Germany) was determined to be 8%. [15] By contrast, Mg alloys designed for the use as stents must possess a minimum ultimate tensile strength of 300 MPa, low yield strength of 200-300 MPa, and higher ductility (min. 15%-18% elongation to failure, preferably 30%) for their successful deployment. [16,17] Finally, in vivo animal experiments are conducted to evaluate the alloy suitability for the translation into the clinic.

Currently, commercial biodegradable implants are mainly made from degradable polymers, such as polyglycolic acid or polylactide acid (PLA). These polymer implants, produced by injection moulding technique, suffer from long degradation times between 18 and 36 months, poor mechanical properties and acidic degradation behaviour. On the other hand, magnesium alloys are drawing increasing interest as biodegradable medical implant material for orthopaedic applications in bone tissue; thus, a replacement of polymers by Mg would be attractive. The production of biomedical and biodegradable Mg alloy parts and implants by powder metallurgy and metal injection moulding (MIM) respectively offers the opportunity for economic manufacturing of parts with mechanical properties matching those of cortical bone tissue, as well as the provision of porous surface structures beneficial for cell ingrowth and vascularisation. Furthermore, the technique guarantees a homogenous microstructure being crucial for a predictable degradation process. This study shows how magnesium powder can be processed successfully by MIM. Recent magnesium alloy implant prototypes and tensile test specimen, produced by MIM technique, provide strength and stiffness twice as high compared to modern polymer based implants. Ultimate tensile strength (UTS) of 131 MPa, yield strength of 64 MPa, residual porosity of 2-6% and elastic modulus of 46 GPa, measured by dynamic method, were achieved under application of special sintering technique and sintering atmosphere control. The paper is focussing on sintering methods and porosity control and measurement.

Current research has highlighted that magnesium and its alloys as biodegradable material are highly suitable for biomedical applications. The new material fully degrades into nontoxic elements and offers material properties matching those of human bone tissue. As biomedical implants are rather small and complex in shape, the metal injection molding (MIM) technique seems to be well suited for the near net shape mass production of such parts. Furthermore, MIM of Mg-alloys is of high interest in further technical fields. This study focusses on the performance of MIM-processing of magnesium alloy powders. It includes Mg-specific development of powder blending, feedstock preparation, injection molding, solvent and thermal debinding and final sintering. Even though Mg is a highly oxygen-affine material forming a stable oxide layer on each particle surface, the material can be sintered to nearly dense parts, providing mechanical properties matching those of as cast material. An ultimate tensile strength of 142 MPa, yield strength of 67 MPa, elastic modulus of 40 GPa and 8% elongation at fracture could be achieved using novel organic polymer binders for the feedstock preparation. Thus, first implant demonstrator parts could be successfully produced by the MIM technique.