Laser powder bed fusion of magnesium alloys for orthopaedic implants

In an initial literature review of existing implants, the design requirements and material properties of potential bioresorbable orthopaedic implants were set forth and the three main design categories were identified, namely, a platebased (patient-specific) design, macro-porous trabecular bone mimicking structure, and combination of both. Based on the observations of maximum achievable relative densities, a hypothetical model for the powder fusion process was formulated, where the breakdown of the outer oxide layer of the powder particles plays the pivotal role and dictates the energy input of the L-PBF process.

Furthermore, the importance of adapting the process to the geometry of the desired part was shown by the variation of scanning strategy. It was also found that an effective post-processing strategy is essential for macro-porous parts. Finally, it was demonstrated that mechanical properties close to those of the conventional routes were achievable for the L-PBF parts, although the part orientation with respect to the building direction and the scanning strategy had a significant influence.

The introduction of residual stress or deformation revealed the current limitations. The manufacturing of different macro-porous-sized sheet-based gyroids demonstrated the possibility of fabricating trabecular bone mimicking structures and parts with a pore diameter of 400 μm exhibited twofold higher compressive loads than the human cortical bone. The possibility to vary pore sizes illustrated the tuneability of mechanical and degradation properties to the need of an potential implant.<br><br>