Porous tantalum structures for bone implants: fabrication, mechanical and in vitro biological properties

Abstract

The relatively high cost of manufacturing and the inability to produce modular implants have limited the acceptance of tantalum, in spite of its excellent in vitro and in vivo biocompatibility. In this article, we report how to process Ta to create net-shape porous structures with varying porosity using Laser Engineered Net Shaping (LENS) for the first time. Porous Ta samples with relative densities between 45% and 73% have been successfully fabricated and characterized for their mechanical properties. In vitro cell materials interactions, using a human fetal osteoblast cell line, have been assessed on these porous Ta structures and compared with porous Ti control samples. The results show that the Young's modulus of porous Ta can be tailored between 1.5 and 20 GPa by changing the pore volume fraction between 27% and 55%. In vitro biocompatibility in terms of MTT assay and immunochemistry study showed excellent cellular adherence, growth and differentiation with abundant extracellular matrix formation on porous Ta structures compared to porous Ti control. These results indicate that porous Ta structures can promote enhanced/early biological fixation. The enhanced in vitro cell-material interactions on the porous Ta surface are attributed to its chemistry, its high wettability and its greater surface energy relative to porous Ti. Our results show that these laser-processed porous Ta structures can find numerous applications, particularly among older patients, for metallic implants because of their excellent bioactivity.

Figure 1

Influence of specific energy on (a) relative density and (b) total, open and closed porosity of LENS™ processed Ta samples.

Figure 2

FESEM microstructures of porous Ta structures (a), (b) porosity characteristics in 55 % and 73% dense samples, respectively, (c) grain size of LENS™ processed porous Ta.

Figure 3

Mechanical properties of porous Ta structures as a function of sample’s relative density (a) 0.2% proof strength, (b) Young’s modulus.

Figure 4

SEM micrographs illustrating hFOB cell morphology after 3 days of culture period on (a) 27 % porous Ta (Ta-27), (b, c) 45 % porous Ta (Ta-45), and (d) 27 % porous Ti (Ti-27) sample surfaces.

Figure 5

SEM micrographs illustrating hFOB cell morphology after 7 days of culture period on (a) Ta-27, (b) Ta-45, and (d) Ti-27 sample surfaces.

Figure 6

SEM micrographs illustrating hFOB cell morphology after 11 days of culture period on (a) Ta-27, (b, c) Ta-45, and (d) Ti-27sample surfaces.

Figure 7

MTT assay of cells on 27% porous Ta (Ta-45), 45% porous Ta (Ta-45) and 27% porous control Ti samples after 11days of incubation time. There were significant differences in optical density (* = P < 0.05, n = 5) between porous Ti and Ta samples for all time period. However, after 11 days culture period the difference was not significant between Ta-27 and Ta-45 samples (** = P > 0.05, n = 5).

Figure 8

Confocal micrographs of vinculin protein expression in hFOB cells on (a) 27 % porous Ta (Ta-27), (b, c) 45 % porous Ta (Ta-45), and (d) 27 % porous Ti (Ti-27) after 3 days of culture period. Green fluorescence indicating antibody bound to vinculin and cell nuclei were contrast-labeled in red by adding propidium iodide (PI).

Figure 9

Confocal micrographs of ALP protein expression in hFOB cells on (a) 27 % porous Ta (Ta-27), (b, c) 45 % porous Ta (Ta-45), and (d) 27 % porous Ti (Ti-27) after 11 days of culture period. Green fluorescence indicating antibody bound to ALP and cell nuclei were contrast-labeled in red by adding propidium iodide (PI).