Biocompatibility and osteogenic properties of porous tantalum

Abstract

Porous tantalum has been reported to be a promising material for use in bone tissue engineering. In the present study, the biocompatibility and osteogenic properties of porous tantalum were studied in vitro and in vivo. The morphology of porous tantalum was observed using scanning electron microscopy (SEM). Osteoblasts were cultured with porous tantalum, and cell morphology, adhesion and proliferation were investigated using optical microscopy and SEM. In addition, porous tantalum rods were implanted in rabbits, and osteogenesis was observed using laser scanning confocal microscopy and hard tissue slice examination. The osteoblasts were observed to proliferate over time and adhere to the tantalum surface and pore walls, exhibiting a variety of shapes and intercellular connections. The porous tantalum rod connected tightly with the host bone. At weeks 2 and 4 following implantation, new bone and small blood vessels were observed at the tantalum-host bone interface and pores. At week 10 after the porous tantalum implantation, new bone tissue was observed at the tantalum-host bone interface and pores. By week 12, the tantalum-host bone interface and pores were covered with new bone tissue and the bone trabeculae had matured and connected directly with the materials. Therefore, the results of the present study indicate that porous tantalum is non-toxic, biocompatible and a promising material for use in bone tissue engineering applications.

Keywords: biocompatibility; bone tissue engineering; cell toxicity; osteogenesis; porous tantalum.

Figure 1

Model and physical properties of porous tantalum. (A) Intraoperative photograph of the bone defect experiment showing the porous tantalum implantation model in the rabbit femoral condyles. The bone defect was filled with porous tantalum (arrow). (B) Appearance of porous tantalum. (C-E) Pore morphology of the porous tantalum specimen, with a rough and irregular surface and interconnected pores with diameters of 400–600 μm. (C) Material surface and cross-section show interconnected pore distribution, with a pore diameter size of 200–400 μm (scale bar, 200 μm). (D) Trabecular pillar exhibits a micropore structure, with the diameter of the interval of the trabecular pillar ~100 μm (scale bar, 100 μm). (E) Micropore structure of the trabecular pillar, where the diameter of the micropores was ~10 μm. (Scale bar, 50 μm).

Figure 2

3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay results demonstrating the effect of tantalum extract on osteoblast proliferation. Osteoblast cell proliferation efficiency of the groups treated with (experimental) or without (control) porous tantalum extract between days 1 and 8 of cell culture. Proliferation of experimental group cells changed from slow to rapid, and then to slow again, ultimately entering the stable phase, between days 1 and 8 of osteoblast culture. Cell proliferation did not statistically differ between the groups with extended cultivation time. Independent sample t-tests: P>0.05, vs. control group. OD, optical density.

Figure 3

Scanning electron microscopy images of osteoblasts cultured on tantalum. (A-C) By day 5, adjacent cells connected with each other across the pores, creating a flake with burr-like projections extending out to the surroundings (scale bars for A-C are 200, 100 and 50 μm, respectively). (D-F) By day 10, cells on the surface and in the pores grew into multiple layers, secreting matrix and covering the surface completely (scale bars for D-F are 200, 100 and 50 μm, respectively).

Figure 4

Histological observation of hard tissue slices prepared from porous tantalum implants at weeks (A) 2, (B) 4, (C) 8 and (D) 12 after implantation (methylene blue staining; magnification, ×100).

Figure 5

Osteogenesis assessment via laser scanning confocal microscopy revealed a (A) 488-nm calcein fluorescence band and (B) 543-nm alizarin red fluorescence band. (C) Overlaid image of A and B.