Porous tantalum structure integrated on Ti6Al4V base by Laser Powder Bed Fusion for enhanced bony-ingrowth implants: In vitro and in vivo validation

Abstract

Despite the widespread application of Ti6Al4V and tantalum (Ta) in orthopedics, bioinertia and high cost limit their further applicability, respectively, and tremendous efforts have been made on the Ti6Al4V-Ta alloy and Ta coating to address these drawbacks. However, the scaffolds obtained are unsatisfactory. In this study, novel high-interface-strength Ti6Al4V-based porous Ta scaffolds were successfully manufactured using Laser Powder Bed Fusion for the first time, in which porous Ta was directly manufactured on a solid Ti6Al4V substrate. Mechanical testing revealed that the novel scaffolds were biomechanically compatible, and the interfacial bonding strength was as high as 447.5 MPa. In vitro biocompatibility assay, using rat bone marrow mesenchymal stem cells (r-BMSCs), indicated that the novel scaffolds were biocompatible. Alkaline phosphatase and mineralized nodule determination demonstrated that the scaffolds favored the osteogenic differentiation of r-BMSCs. Moreover, scaffolds were implanted into rabbits with femur bone defects, and imaging and histological evaluation identified considerable new bone formation and bone ingrowth, suggesting that the scaffolds were well integrated with the host bone. Overall, these results demonstrated good mechanical compatibility, biocompatibility, and osteointegration performance of the novel Ti6Al4V-based porous Ta scaffold, which possesses great potential for orthopedic clinical applications.

Keywords: Laser powder bed fusion; Orthopedic scaffolds; Osteointegration; Tantalum; Ti6Al4V.

Graphical abstract

Fig. 1

Fabrication and characterization of the novel scaffolds. (a) 3-dimensional view of the diamond unit cell, (b) spherical tantalum and Ti6Al4V powders used for the fabrication of the novel scaffolds, (d) building orientation of the samples, (e) overview of the manufactured samples, (f) scanning electron microscopy (SEM) images of the samples, (g) representative images of Energy-Dispersive Spectrometry (EDS) detection for the samples.

Fig. 2

Mechanical testing of the novel scaffolds. (a) Representative strain-stress curve of the compressive test, (b) distribution images of elements in the interface detected using Energy-Dispersive Spectrometry (EDS), (c) schematic diagram of the flat dog-bone-shaped coupons, (d) tensile test, (e) representative strain-stress curve of the tensile test.

Fig. 3

Biocompatibility of the novel scaffolds. (a) Representative scanning electron microscopy (SEM) images of r-BMSCs on the scaffolds at day 2 and day 12, (b–c) DAPI/phalloidin fluorescence labeling images of r-BMSCs at day 7 and corresponding quantitative analysis of cellular area to nucleus, (d) proliferation of r-BMSCs on the scaffolds. (**P < 0.01).

Fig. 4

In vitro osteogenesis determination. (a) Alkaline phosphatase (ALP) production generated from the r-BMSCs on the scaffolds after culturing for 3 and 7 days, (b) representative images of alizarin red staining of mineralized nodules, (c) quantitative analysis of dissolved mineralized nodules. (*P < 0.05, **P < 0.01). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

Imageology analysis of the in-vivo animal experiment. (a) Representative X-ray images of the femur specimens at sixth week after implantation, (b) representative. 3D reconstructive images of Micro-CT analysis, (c–d) quantitative analysis of the ratio of bone volume to tissue volume (BV/TV) and trabecular number (Tb·N). (*P < 0.05, **P < 0.01).

Fig. 6

Histological analysis of the in-vivo animal experiment. (a–b) Representative images of the van Geison's staing and toluidine blue staining at postoperative six weeks, (c) SEM micrographs of new bone agglomerates and bone microstructure surrounding and inside the scaffolds, (d) EDS images for screening the distribution of elements in the hard tissue sections. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)