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In recent years, more attention to unique and complex structures, such as nature-inspired and porous structures for medical applications, has been strongly developed. Open-cell porous metal-based ones display more benefits than rigid ones since they facilitate the transformation of load between the bone and the implants and avoid the phenomenon of stress shielding and bone resorption. By being biodegradable and non-toxic, as well as having lower density and mechanical properties close to those of natural bone, Mg and its alloys are considered promising materials for porous scaffolds. However, a high corrosion rate is the main drawback of Mg alloys. The porosity of porous structures can also worsen it as it enhances the surface area exposed to the corrosive solution and negatively impacts the performance of porous structures, that these issues have not been addressed in detail so far. Since fabrication methods of Mg-based scaffolds can significantly affect the porosity-related properties (e.g., porosity percentage, type, size, and geometry) and, consequently, scaffolds' mechanical behavior and corrosion resistance, this paper reviews and compares the fabrication methods of porous structures and how they affect the resultant properties. However, among different methods, due to the expansion of additive manufacturing as a novel and exciting manufacturing technique, the paper's central focus is on using additive manufacturing in biomedical applications, discussing its advantages over other techniques. The effect of geometrical parameters on mechanical properties and corrosion rate, which strongly affects bio-application, are also given. Moreover, different strategies are briefly introduced for tailoring the high corrosion rate of Mg and its alloys, such as alloying elements and coatings. However, there is still less information regarding the additive manufacturing of porous Mg scaffolds and the optimum way of controlling the corrosion rate of Mg-based parts. [ABSTRACT FROM AUTHOR]

The present study aims to collect data, compare results and assess techniques used for improving corrosion resistance and mechanical properties of biodegradable Mg alloys for fixation elements and orthopedic applications. A general description of biomaterials used for orthopedic implants is performed, including non-bioabsorbable materials. Different methods for reducing the corrosion rate in Mg alloys are researched, and the efficiencies are assessed. After evaluating different techniques, surface modification is found to be the most promising technique to reduce the corrosion rate with an efficiency of 85%. Regarding the Mg alloying agents, Zn is considered as the best candidate to improve the corrosion response and biocompatibility of the Mg. [ABSTRACT FROM AUTHOR]

This study investigated the microstructure, mechanical properties, corrosion behavior of as-cast Mg–1.8Zn–0.4Zr–1.74Gd–xY (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) biodegradable magnesium alloys. Microstructures of the alloys were characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that the alloys were mainly composed of α-Mg matrix (Mg, Zn)3(Gd, Y) phase, Mg3Zn3(Gd, Y)2 phase and Mg12Zn(Gd, Y) phase. It was found that 0–1.25 wt% Y addition led to significant grain refinement of the alloys from 111.5 to 57.3 μm. Moderate amount of Y resulted in improved strength. However, the strength and elongation decreased when the Y content exceeded 0.5 wt%. With 0.5 wt% of Y, the corrosion rate and corrosion current density were 0.721 ± 0.042 mm y−1 and 4.76 μA cm−2, respectively, which were lower than the other investigated alloys. Among all the tested samples, Mg–1.8Zn–0.4Zr–1.74Gd–0.5Y alloy has the moderate corrosion rate and mechanical properties, making it promising for the future optimization of the biodegradable Mg–Zn–Zr–Gd–Y alloys. [ABSTRACT FROM AUTHOR]