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Abstract: Hydroxyapatite (HAp) coatings were uniformly formed on pure Mg by a hydrothermal treatment using a C10H12N2O8Na2Ca (Ca-EDTA) solution. The growth mechanism of the HAp coating was investigated with XRD, SEM and TEM. At the initial stage, dome-shape HAp precipitates were formed on the Mg. Subsequently, the precipitates grew and the coating became a dual-layer consisting of an inner dense HAp layer and outer course layer consisting of rod-like HAp crystals. The protectiveness of the coatings with different treatment times was investigated by a polarization test in a 3.5wt.% NaCl solution. The corrosion current density decreased with the growth of the HAp coating. [Copyright &y& Elsevier]

Abstract: Hydroxyapatite (HAp) coatings with and without octacalcium phosphate (OCP) were uniformly formed on pure magnesium by a hydrothermal treatment using a Ca-EDTA solution. The crystal structure, crystallographic orientation and lattice images were investigated using transmission electron microscopy (TEM) and high-resolution TEM. It was demonstrated that the crystal phase and microstructure of the calcium phosphate-coatings can vary with the pH of the treatment solution. In a weak acid treatment solution, a dual-layer structure was formed: an outer coarse layer consisting of plate-like OCP crystals and an inner dense layer consisting primarily of HAp crystals. One piece of the OCP plate corresponded to a single OCP crystal growing parallel to the (100)OCP. In a weak alkali treatment solution, a dual-layer structure was also formed: an outer coarse layer consisting of rod-like HAp crystals and an inner dense layer consisting of HAp crystals. One piece of the HAp rod corresponded to a single HAp crystal growing along [002]HAp. In a strong alkali treatment solution, needle-like HAp crystals were formed. No defect was observed in the lattice image of the OCP and HAp. The corrosion current density of pure magnesium in a 3.5wt.% NaCl solution decreased with the HAp coating more significantly than the OCP+HAp coating. It is revealed that the degree of protection afforded by calcium phosphate-coatings varies with their crystal phase and microstructure. [ABSTRACT FROM AUTHOR]

Abstract: The possibility of magnesium and its alloys in medical applications is actively investigated in these days for the realization of biodegradable metallic devices. However, the degradation behavior and mechanisms of magnesium and its alloys in physiological environment such as inside the human body have not been elucidated. In this study, we performed 14-d long immersion tests of pure magnesium (3N) in 4 kinds of physiological solutions simulating the body fluids to examine the effects of the chemical components of the body fluids on the degradation of magnesium. The degradation rate of pure magnesium was strongly influenced by the kinds of the solution used. The highest degradation rate was obtained in NaCl, followed by E-MEM, Earle''s solution, and E-MEM+FBS. The average degradation rate in NaCl for 8–14 d is about 100 times larger than that in E-MEM+FBS, which is the closest solution to human blood plasma. These results show that protein adsorption and insoluble salt formation retarded magnesium degradation, whereas organic compounds such as amino acids encourage the dissolution of magnesium. Buffering the solution also influenced the degradation rate; buffering NaCl with HEPES increased the degradation rate but buffering with NaHCO3 decreased it. Based on these results, the use of appropriate solution such as E-MEM+FBS is important for in vitro evaluation of the magnesium degradation rate under the physiological environment simulating inside the human body. [Copyright &y& Elsevier]

For orthopaedic applications, additive manufactured (AM) porous scaffolds made of absorbable metals such as magnesium, zinc or iron are of particular interest. They do not only offer the potential to design and fabricate bio-mimetic or rather bone-equivalent mechanical properties, they also do not need to be removed in further surgery. Located in a physiological environment, scaffolds made of absorbable metals show a decreasing Young's modulus over time, due to product dissolution. For magnesium-based scaffolds during the first days an increase of the smeared Young's modulus can be observed, which is mainly attributed to a forming substrate layer of degradation products on the strut surfaces. In this study, the influence of degradation products on the stiffness properties of metallic scaffolds is investigated. For this, analytical calculations and finite-element simulations are performed to study the influence of the substrate layer thickness and Young's modulus for single struts and for a new scaffold geometry with adapted polar cubic face-centered unit cells with vertical struts (f2cc,z). The finite-element model is further validated by compression tests on AM scaffolds made from Zn1Mg (1 wt% Mg). The results show that even low thicknesses and Young's moduli of the substrate layer significantly increases the smeared Young's modulus under axial compression. [ABSTRACT FROM AUTHOR]

In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn–0.8Mg–0.2Sr (wt.%) alloy on a rabbit model. An alloy screw was implanted into one of the tibiae of New Zealand White rabbits. After 120 days, the animals were euthanized. Evaluation included clinical assessment, microCT, histological examination of implants, analyses of the adjacent bone, and assessment of zinc, magnesium, and strontium in vital organs (liver, kidneys, brain). The bone sections with the implanted screw were examined via scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). This method showed that the implant was covered by a thin layer of phosphate-based solid corrosion products with a thickness ranging between 4 and 5 µm. Only negligible changes of the implant volume and area were observed. The degradation was not connected with gas evolution. The screws were fibrointegrated, partially osseointegrated histologically. We observed no inflammatory reaction or bone resorption. Periosteal apposition and formation of new bone with a regular structure were frequently observed near the implant surface. The histological evaluation of the liver, kidneys, and brain showed no toxic changes. The levels of Zn, Mg, and Sr after 120 days in the liver, kidneys, and brain did not exceed the reference values for these elements. The alloy was safe, biocompatible, and well-tolerated. [ABSTRACT FROM AUTHOR]

Background: Post-operative severe vascular stenosis and proliferating endothelial tissue lead to severe circulatory disorders and impair organ perfusion. Bioabsorbable magnesium scaffolds may help to overcome these obstructions without leaving obstructing stent material. We analyse their role in the treatment of vascular stenosis in infants., Methods: Since 2016, 15 magnesium scaffolds with a diameter of 3.5 mm were implanted in 9 patients aged 15 days to 7.6 years. Eight scaffolds were implanted in pulmonary venous restenoses, five in pulmonary arterial stenosis including one in-stent stenosis, one into a stenotic brachiocephalic artery, and one in a recurrent innominate vein thrombosis., Results: All patients clinically improved after the implantation of a scaffold. The magnesium scaffolds lost integrity after 30-48 days (mean 42 days). The innominate vein thrombosed early, while all other vessels remained open. Two patients died after 1.3 and 14 weeks not related to the scaffolds. Five patients needed further balloon dilations or stent implantations after the scaffold had fractured. At first recatheterisation after in mean 2.5 months, the mean minimum/maximum diameter in relation to the scaffold's original diameter was 89%/99% in the arterial implantations (n = 6) and 66%/77% in the pulmonary venous implantations., Conclusions: The magnesium scaffolds can be used as a bridging solution to treat severe vascular stenosis in different locations. Restenosis can occur after degradation and make further interventions necessary, but neither vessel growth nor further interventions are hindered by stent material. Larger diameters may improve therapeutic options.