Additive manufacturing (AM) techniques, owing to their capability to fabricate complex and purposeful geometrical structures, have garnered attentions as a viable option for fabricating metal scaffolds (in the realm of porous implants). This study aimed to eva‎luate the performance of porous Ti-6Al-4V structures fabricated using electron beam powder bed fusion (EB-PBF or EBM) from both mechanical and corrosion behavior perspectives, with the goal of assessing their potential as metal scaffolds. To do so, two different lattice structures, namely Rhombic Dodecahedron (RD) and Diamond (DO), were designed and fabricated. The goal was to assess the effects of cell type and cell size, considered as two key factors in determining scaffold performance, on both mechanical and corrosion performance of the EB-PBF Ti-6Al-4V scaffolds. The findings revealed that the geometrical deviation of the scaffolds from the designed CAD models decreased after post-processing chemical etching. The microstructural eva‎luation of the scaffolds indicated that, regardless of the cell type, different microstructures emerged with changes in the cell size of the scaffolds. This phenomenon can be attributed to alterations in the strut thickness, leading to changes in the molten pool volume and subsequently, differences in cooling rates during the EBM process. However, all scaffolds exhibited a dual α/β phase microstructure, which is desirable from a mechanical standpoint for bone implants. The mechanical behavior of Ti-6Al-4V scaffolds fabricated via EBM demonstrated that both scaffold groups displayed adequate yield strength and elastic modulus compatible with bone, potentially mitigating stress shielding. Results indicated that cell type had no significant effect on dynamic wettability and permeability of scaffolds, as influential factors affecting the scaffold's biological behavior. on biological behavior of scaffold, However, a reduction in cell size, corresponding to a decrease in pore size, resulted in decreased dynamic wettability and permeability. The short and long-term corrosion behavior of the fabricated scaffolds indicated that regardless of cell type, the larger the cell size, the higher the corrosion resistance, possibly stemming from their reduced available surface area. The fabricated Ti-6Al-4V scaffolds showed favorable long-term corrosion behavior and acceptable ion release. In another stage of the present study, plasma electrolytic oxidation (PEO) was employed to surface modification of the fabricated scaffolds. The effects of the resulting oxide layer on the corrosion and biological performance of the EB-PBF Ti-6Al-4V scaffolds were investigated. The findings demonstrated that employing the PEO method enables the attainment of a a uniform distribution of micro-pores with an average diameter of 1-5 μm on both the external and internal surfaces of the scaffolds. The PEO coating consisted of a compact inner layer and a porous outer layer, with thicknesses varying from 4-6 μm in different regions of the scaffolds. The differences in morphology and coating thickness were observed between the external and internal zones of the scaffolds. In the internal zones, an increase in the number of micro-pores with smaller size was observed, accompanied by a decrease in the thickness of the oxide coating. These differences became more pronounced with the reduction of the cell size. Phase eva‎luations revealed that the scaffolds consisted of titanium oxide phases in the forms of rutile and anatase, unaffected by cell type and cell size. The PEO-modified EB-PBF Ti-6Al-4V scaffolds demonstrated improved electrochemical behavior, bioactivity, biocompatibility, adhesion, and cell proliferation compared to non-modified ones. This improvement can be attributed to alterations in the surface topography and morphology of the scaffolds, as well as the formation of dense and porous double-layer coatings through the PEO method.

فخرالدين اشرفي زاده , مسعود عطاپور

عبدالله صبوري

مهران نحوي , عبدالمجيد اسلامي , مهدي ابراهيميان حسين آبادي