Resumen: 

This first-year work focuses on the development of bioabsorbable Zn-0.2Mg-0.5Mn (wt.%) scaffolds manufactured by laser powder bed fusion (L-PBF) for bone regeneration applications. The project aims to understand how alloy composition, processing route, surface condition and scaffold architecture affect microstructure, corrosion behaviour, Zn2+ release and early biological response. Zn-based biodegradable metals are promising because they offer an intermediate degradation behaviour between Mg, which often corrodes too rapidly, and Fe, which degrades too slowly. However, pure Zn has limited mechanical performance, and its degradation and biological response must be carefully controlled. Therefore, alloying with Mg and Mn, together with additive manufacturing and surface modification, is explored as a strategy to obtain temporary porous implants with suitable structural integrity and controlled degradation.

The first-year work was organised into two connected stages. The first stage focused on compact samples to separate the effects of alloying, processing route and surface modification. Four conditions were compared: commercially pure cast Zn, cast ZnMgMn, L-PBF ZnMgMn and PEO-treated L-PBF ZnMgMn. These samples were characterised by microscopy, SEM/EDS, EBSD, electrochemical testing, wettability measurements, Zn2+ release analysis and cell tests using L-929 fibroblasts. The second stage transferred the study to three-dimensional porous scaffolds, focusing on BCC architectures manufactured by L-PBF and analysed by micro-computed tomography.

The results show that the behaviour of Zn-0.2Mg-0.5Mn is strongly influenced by the processing route. The cast ZnMgMn alloy showed the most favourable balance among the uncoated compact samples, with a refined microstructure, the lowest Zn2+ release after 24 h and the highest mitochondrial activity. In contrast, the L-PBF ZnMgMn condition exhibited a finer microstructure but also a more reactive surface state, lower surface-film resistance and higher Zn2+ release. This indicates that grain refinement alone is not sufficient to improve degradation behaviour, since L-PBF also changes phase distribution, oxide formation and electrochemical heterogeneity.

PEO treatment clearly improved the electrochemical response of the L-PBF alloy, reducing the apparent corrosion current and increasing the interface resistance. However, this improvement did not result in a clear enhancement of cell adhesion or mitochondrial activity. This suggests that corrosion protection alone is not enough to optimise the biological response, and that coating morphology, wettability and ion transport must also be controlled.

The scaffold study confirmed the feasibility of manufacturing ZnMgMn porous architectures by L-PBF. AE-7 and AE-8 scaffolds reached internal densities above 99.8%, although their defect content and spatial distribution depended on processing parameters and local geometry. Overall, this work establishes the experimental basis for developing Zn-0.2Mg-0.5Mn biodegradable scaffolds. Future work will focus on optimising lattice structures, evaluating compression behaviour, improving surface treatments and studying degradation and biological response under more representative scaffold conditions.