Only a few studies have examined how pore geometry affects the mechanical characteristics, biological behavior, and degradation of additively manufactured biodegradable porous magnesium. In this work, the effects of pore geometry on mechanical qualities, degradation, and biological behavior were investigated using three typical porous architectures with the same porosity. The porous structures were found to satisfy bone tissue engineering requirements because they had sufficient degradation resistance and tunable compressive characteristics. All three types of magnesium alloy scaffolds exhibited good biocompatibility. Additionally, the magnesium alloy porous structures influenced the magnesium scaffold material degradation rate and the surrounding environment, impacting the osteogenic differentiation of bone mesenchymal stem cells and bone tissue regeneration. This work offers conceptual support for optimizing pore geometry to alter the mechanical and degradable characteristics of additively manufactured porous magnesium to meet therapeutic demands.

Laser powder bed fusion (L-PBF) of Mg alloys has provided tremendous opportunities for customized production of aeronautical and medical parts. Layer thickness (LT) is of great significance to the L-PBF process but has not been studied for Mg alloys. In this study, WE43 Mg alloy bulk cubes, porous scaffolds, and thin walls with layer thicknesses of 10, 20, 30, and 40 µm were fabricated. The required laser energy input increased with increasing layer thickness and was different for the bulk cubes and porous scaffolds. Porosity tended to occur at the connection joints in porous scaffolds for LT40 and could be eliminated by reducing the laser energy input. For thin wall parts, a large overhang angle or a small wall thickness resulted in porosity when a large layer thicknesses was used, and the porosity disappeared by reducing the layer thickness or laser energy input. A deeper keyhole penetration was found in all occasions with porosity, explaining the influence of layer thickness, geometrical structure, and laser energy input on the porosity. All the samples achieved a high fusion quality with a relative density of over 99.5% using the optimized laser energy input. The increased layer thickness resulted to more precipitation phases, finer grain sizes and decreased grain texture. With the similar high fusion quality, the tensile strength and elongation of bulk samples were significantly improved from 257 MPa and 1.41% with the 10 µm layer to 287 MPa and 15.12% with the 40 µm layer, in accordance with the microstructural change. The effect of layer thickness on the compressive properties of porous scaffolds was limited. However, the corrosion rate of bulk samples accelerated with increasing the layer thickness, mainly attributed to the increased number of precipitation phases.

Laser powder bed fusion (L-PBF) has been employed to additively manufacture WE43 magnesium (Mg) alloy biodegradable implants, but WE43 L-PBF samples exhibit excessively rapid corrosion. In this work, dense WE43 L-PBF samples were built with the relativity density reaching 99.9%. High temperature oxidation was performed on the L-PBF samples in circulating air via various heating temperatures and holding durations. The oxidation and diffusion at the elevated temperature generated a gradient structure composed of an oxide layer at the surface, a transition layer in the middle and the matrix. The oxide layer consisted of rare earth (RE) oxides, and became dense and thick with increasing the holding duration. The matrix was composed of α-Mg, RE oxides and Mg₂₄RE₅ precipitates. The precipitates almost disappeared in the transition layer. Enhanced passivation effect was observed in the samples treated by a suitable high temperature oxidation. The original L-PBF samples lost 40% weight after 3-day immersion in Hank's solution, and broke into fragments after 7-day immersion. The casted and solution treated samples lost roughly half of the weight after 28-day immersion. The high temperature oxidation samples, which were heated at 525 ℃ for 8 h, kept the structural integrity, and lost only 6.88% weight after 28-day immersion. The substantially improved corrosion resistance was contributed to the gradient structure at the surface. On one hand, the outmost dense layer of RE oxides isolated the corrosive medium; on the other hand, the transition layer considerably inhibited the corrosion owing to the lack of precipitates. Overall, high temperature oxidation provides an efficient, economic and safe approach to inhibit the corrosion of WE43 L-PBF samples, and has promising prospects for future clinical applications.