In vitro evaluation of human osteoblast adhesion to a thermally oxidized gamma-TiAl intermetallic alloy of composition Ti-48Al-2Cr-2Nb (at.%)

Abstract

Ti-48Al-2Cr-2Nb (at.%) (gamma-TiAl), a gamma titanium aluminide alloy originally designed for aerospace applications, appears to have excellent potential as implant material. Thermal treatment of gamma-TiAl renders this alloy extremely corrosion resistant in vitro, which could improve its biocompatibility. In this study, the surface oxides produced by thermal oxidation (at 500 degrees C, and at 800 degrees C for 1 h in air) on gamma-TiAl were characterized by X-ray photoelectron spectroscopy (XPS). hFOB 1.19 cell adhesion on thermally oxidized gamma-TiAl was examined in vitro by a hexosaminidase assay, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) after 1, 7 and 14 days. Ti-6Al-4V surfaces were used for comparison. Hexosaminidase assay data and CLSM analysis of focal contacts and cytoskeleton organization showed no differences in cell attachment on autoclaved and both heat-treated gamma-TiAl surfaces at the different time points. SEM images showed well organized multi-layers of differentiated cells adhered on thermally oxidized gamma-TiAl surfaces at day 14. Unexpectedly, thermally oxidized Ti-6Al-4V surfaces oxidized at 800 degrees C exhibited cytotoxic effects on hFOB 1.19 cells. Our results indicate that thermal oxidation of gamma-TiAl seems to be a promising method to generate highly corrosion resistant and biocompatible surfaces for implant applications.

Fig. 1

Representative wide-scan XPS spectra of thermally oxidized at 500°C (b, d) and at 800°C (a, c) for γ-TiAl (c, d) and Ti–6Al–4V (a, b) surfaces

Fig. 2

Deconvolution of Al 2p_3/2 (a), Ti 2p_3/2,1/2 (b), and O 1s peaks for γ-TiAl alloy (c), O 1s peak for Ti–6Al–4V (d). The results for polished (OA), autoclaved (OB), oxidized at 500°C (I) and at 800°C (II) are displayed. XPS spectra for minor constituents of autoclaved γ-TiAl and thermally oxidized at 500°C Ti–6Al–4V surfaces are shown in (e)

Fig 3

Variability in the metal elemental ratio on γ-TiAl and Ti–6Al–4V surfaces from XPS data according to the temperature of oxidation

Fig. 4

hFOB 1.19 cell attachment on autoclaved and thermally oxidized γ-TiAl and Ti–6Al–4V disks. Cells were cultured on GTi, GTi5, GTi8, TiV, TiV5, and TiV8 surfaces for 1, 7, and 14 days. The data are expressed as the number of cells attached on the different substrates (a), or the number of cells attached on GTi, GTi5, TiV, and TiV5 (not taking into account the data of cells attached on GTi8 and TiV8) (b) determined by the hexosaminidase assay. Each value represents the mean ± SD of three independent experiments, each performed in triplicate (N = 9). *P ≤ 0.05 compared to all others surfaces tested, at the corresponding time point. ^aP ≤ 0.05 compared to day 1

Fig. 5

hFOB 1.19 adhesion after 14-day culture as assessed by SEM on glass coverslips (a, h), GTi (b, i), GTi5 (c, j), GTi8 (d, k), TiV (e, l), TiV5 (f, m), and TiV8 (g, n) disks. Most samples exhibited osteoblasts with cell projections (black arrow), fibrous networks that may correspond to collagen (black arrowhead) and sponge-like structures that may correspond to mineral nodules (white arrowheads). On TiV8 only were observed structures that resemble cell debris (white arrows). Negative control surfaces (incubated with culture media for 14 days but without cells) corresponding to each surface are displayed in (o)–(t) panels. Magnification: a–g = ×1,500, h–t = ×5,000. Scale bar: left = 10 μm, center and right = 1 μm

Fig. 6

Visualization by confocal laser scanning microscopy of focal adhesions and cytoskeleton of hFOB 1.19 cells after 1 day (a, d, g), 7 days (b, e, h), and 14 days (c, f, i) of seeding on autoclaved (a–c), thermally oxidized at 500°C (d–f), and at 800°C (g–i) γ-TiAl surfaces. Cells exhibited stress fibers (arrows), focal contacts at the cell periphery and at the end of the stress fibers (arrowheads). Scale bar: 50 μm

Fig. 7

Visualization by confocal laser scanning microscopy of focal adhesions and cytoskeleton of hFOB 1.19 cells after 1 day (a, d, g), 7 days (b, e, h), and 14 days (c, f, i) of seeding on autoclaved (a–c), thermally oxidized at 500°C (d–f), and at 800°C (g–i) Ti–6Al–4V surfaces. Cells exhibited microspikes (dashed arrows), stress fibers (arrows), focal contacts at the cell periphery or at the end of the stress fibers (arrowheads). Scale bar: 50 μm