Electron Beam Powder Bed Fusion of Ti-48Al-2Cr-2Nb Open Porous Scaffold for Biomedical Applications: Process Parameters, Adhesion, and Proliferation of NIH-3T3 Cells

Abstract

Titanium aluminide (TiAl)-based intermetallics, especially Ti-48Al-2Cr-2Nb, are a well-established class of materials for producing bulky components using the electron beam powder bed fusion (EB-PBF) process. The biological properties of Ti-48Al-2Cr-2Nb alloy have been rarely investigated, specifically using complex cellular structures. This work investigates the viability and proliferation of NIH-3T3 fibroblasts on Ti-48Al-2Cr-2Nb dodecahedral open scaffolds manufactured by the EB-PBF process. A process parameter optimization is carried out to produce a fully dense part. Then scaffolds are produced and characterized using different techniques, including scanning electron microscopy and X-ray tomography. In vitro viability tests are performed with NIH-3T3 cells after incubation for 1, 4, and 7 days. The results show that Ti-48Al-2Cr-2Nb represents a promising new entry in the biomaterial field.

Keywords: 3D printing; X-ray analysis; additive manufacturing; biocompatibility; titanium aluminide.

FIG. 1.

Dodecahedral elementary cell.

FIG. 2.

SEM micrograph of Ti-48-2-2 powder with satellite particles and surface holes, indicated by arrow. Inset of cross-sectional particles reveals holes as spherical pores. SEM, scanning electron microscope.

FIG. 3.

XRD pattern of Ti-48-2-2 powder and scaffold. α₂-Ti₃Al—full dot, γ-TiAl—empty square. TiAl, titanium aluminide; XRD, X-ray diffraction;.

FIG. 4.

Cross-sections at different magnifications of a sample produced using the process parameters set named NET1. Pores are grouped according to their dimension using colored circles. Blue circles identify a pore dimension smaller than 0.025 mm. Green circle highlights pores with dimension between 0.026 and 0.050 mm. Yellow circles were used for pores with a size between 0.050 and 0.099 mm, whereas orange for pores larger than 0.100 mm.

FIG. 5.

SEM micrograph of Ti-48-2-2 scaffold top surface. Inset shows a scaffold node, cut in correspondence of half scaffold height (∼5 mm).

FIG. 6.

Ti-48-2-2 scaffold biocompatibility was analyzed after 1, 4, and 7 from NIH-3T3 cell seeding by cell viability assay (a) and DNA content (b). For viability assay (a), the cell proliferation was plotted as the ratio between viable cell number and the adherent cell number at day 1 set as 100%. For DNA quantification (b), results were expressed as the total μg of DNA per sample. For both (a) and (b), cells seeded on TCPS were used as control. Bars represent the mean ± SD (****p < 0.0001, **p < 0.01, and *p < 0.05). SD, standard deviation; TCPS, tissue culture polystyrene plate.

FIG. 7.

Representative FESEM images of NIH-3T3 cells after 7 days of incubation on control plastic dish (a, c) and Ti-48-2-2 scaffold (b, d) at different magnification (350 × and 650 × , respectively). Insert 2000 × magnification. Red arrows indicate cell distribution onto the scaffold. After 7 days, cells formed a widespread cell monolayer throughout the TCPS surfaces owing to the higher initial cell adhesion on TCPS (≈ 100%) than on Ti-48-2-2 (≈ 40%). FESEM, field emission scanning electron microscope.