Surface-treated 3D printed Ti-6Al-4V scaffolds with enhanced bone regeneration performance: an in vivo study

Abstract

Background: Given their highly adjustable and predictable properties, three-dimensional(3D) printed geometrically ordered porous biomaterials offer unique opportunities as orthopedic implants. The performance of such biomaterials is, however, as much a result of the surface properties of the struts as it is of the 3D porous structure. In our previous study, we have investigated the in vitro performances of selective laser melted (SLM) Ti-6Al-4V scaffolds which are surface modified by the bioactive glass (BG) and mesoporous bioactive glass (MBG), respectively. The results demonstrated that such modification enhanced the attachment, proliferation, and differentiation of human bone marrow stromal cells (hBMSC). Here, we take the next step by assessing the therapeutic potential of 3D printed Ti-6Al-4V scaffolds with BG and MBG surface modifications for bone regeneration in a rabbit bone defect model.

Methods: 3D printed Ti-6Al-4V scaffolds with BG and MBG surface modifications were implanted into the femoral condyle of the rabbits, the Ti-6Al-4V scaffolds without surface modification were used as the control. At week 3, 6, and 9 after the implantation, micro-computed tomography (micro-CT) imaging, fluorescence double-labeling to determine the mineral apposition rate (MAR), and histological analysis of non-decalcified sections were performed.

Results: We found significantly higher volumes of regenerated bone, significantly higher values of the relevant bone morphometric parameters, clear signs of bone matrix apposition and maturation, and the evidence of progressed angiogenesis and blood vessel formation in the groups where the bioactive glass was added as a coating, particularly the MGB group.

Conclusions: The MBG coating resulted in enhanced osteoconduction and vascularization in bone defect healing, which was attributed to the release of silicon and calcium ions and the presence of a nano-mesoporous structure on the surface of the MBG specimens.

Keywords: 3D printing; Bone regeneration; bioactive glass; in vivo; mesoporous bioactive glass.

Figure 1

The characteristics of the BG- and MBG-coated Ti-6Al-4Vporous scaffolds. Overview and SEM images of BG-coated Ti-6Al-4Vporous scaffolds (upper row); Overview and SEM images of MBG-coated Ti-6Al-4V porous scaffolds (lower row). BG, bioactive glass; MBG, mesoporous bioactive glass; SEM, scanning electron microscope.

Figure 2

Images of porous scaffolds implantation. The holes drilled in the femoral condyles of rabbits with a diameter of 5.5 mm and a depth of 10 mm (A). The holes were subsequently filled with porous scaffolds with a diameter of 5 mm and a length of 10 mm (scale bars: 5 mm) (B).

Figure 3

Micro-CT images and 3D reconstruction. A cylindrical volume (with a diameter of 5.5 mm and a height of 10 mm) with the titanium alloy porous scaffold in its center was selected as the region of interest (ROI). The volumes of the de novo bone formed in the central part and around the periphery of the porous scaffold are shown in yellow and red, respectively. The porous titanium alloy scaffold is depicted in white. Micro-CT, micro-computed tomography; 3D, three-dimensional.

Figure 4

3D reconstructions of the de novo bone at week 3, 6, and 9. The same color code as in Figure 3 is used here.

Figure 5

The different parameters describing the quantity and quality of centrally formed de novo bone in all experimental groups at week 3, 6, and 9. BV/TV, bone volume/total volume; Tb.Th, trabecular thickness; Tb.N, trabecular number; Tb.Sp, trabecular separation (*indicates P<0.05).

Figure 6

The different parameters describing the quantity and quality of peripherally formed de novo bone in all experimental groups at week 3, 6, and 9. BV/TV, bone volume/total volume; Tb.Th, trabecular thickness; Tb.N, trabecular number; Tb.Sp, trabecular separation (*indicates P<0.05).

Figure 7

The representative merged images of fluorescent double labeling of calcein (green color) and xylenol orange (red color), showing bone formation in the three groups of the porous scaffolds at week 3, 6, and 9 (white scale bar =200 µm).

Figure 8

The mineral apposition rates (MAR = distance of fluorescence double labeling/time) of the three groups at week 3, week 6, and week 9 (* indicates P<0.05).

Figure 9

The representative histological images of non-decalcified sections obtained using methylene blue acid fuchsin staining. The blue arrows indicate neovascularization, while the white arrows indicate the Haversian system. WB, woven bone; LB, lamellar bone (green scale bar =200 µm).