Biomedical Engineering Reference
In-Depth Information
the nanotubes were immersed in a 5 mol NaOH solution at 60°C
for up to 60 min. The nanotube samples were then heat-treated
at 500°C/2 h to crystallize the amorphous TiO
2
nanotubes into
the anatase structure (Fig. 9.46). The anatase structure of TiO
2
is
much more eficient in nucleation and growth of hydroxyapatite
than the rutile phase of the TiO
2
, because of the better lattice match
with hydroxyapatite phase [91].
Figure 9.46
Top-view TEM micrograph of the anatase TiO
2
nanotubes
[66].
When exposing the TiO
2
nanotubes to NaOH solution, an
additional, extremely ine, and predominantly nanoiber-like
structure is formed on the top of the TiO
2
nanotubes. These
nanoibers are more sodium titanate compounds, such as Na
2
Ti
5
O
11
or Na
2
Ti
6
O
13
[66]. The preferential occurrence of nanoibers at
the top of nanotubes is explained by surface-tension mechanism,
resulting in dificulties of NaOH solution getting into nanopores
within and in-between TiO
2
nanotubes (Fig. 9.47).
Figure 9.47
Effect of trapped air bubble on NaOH-treated TiO
2
nanotube
array [66].
