Biomedical Engineering Reference
In-Depth Information
Figure 9.2
Surface morphology of Ti after 15 A/cm
2
anodization (a) and
15 A/cm
2
anodization with 5 A/cm
2
cathodic pretreatment (b)
[79].
Figure 9.2a presents the microporous surface morphology of
the Ti after anodization at a current density of 15 A/cm
2
. The
nanoporous structures were obtained on the surface, when the
current density of cathodic pretreatment was between 0.1 and
5 A/cm
2
(10 min in 1M H
2
SO
4
solution at 25°C). A nanoporous
Ti surface was obtained after anodization at 15 A/cm
2
(10 min
in 5M NaOH solution) with cathodic pretreatment at 5 A/cm
2
(Fig. 9.2b). The multi-stage treatment results in thicker titanium
oxide layer. The higher porous oxide thickness results in the
biocompatibility implant improvement. Shih
et al
. [79] found that
TiO
2
/Ti after anodization with cathodic pretreatment is thicker
and more porous than as-machined Ti, cathodic and, anodic Ti
sheets. The TiH
2
is important in forming multi-nanoporous TiO
2
layers. Cathodization involved the hydrogen evolution on titanium.
Anodization dissolves nano-TiH
2
and forms a thicker nanoporous
TiO
2
layer. They suggest that the presence of the TiH
2
phase on
titanium is critical in preparing a multi-nanoporous TiO
2
layer [79].
It should be mentioned that TiH
2
(in powders form) also plays
a crucial role in the metal foaming process [24, 117], resulting in
uniform pore distribution (Fig. 9.3) in whole volume of the implant
(foam), which is assured by Ti-hydrides decomposition. The main
advantage of that structure is the lowest density, higher porosity
(pores in whole volume of the material), and larger pores (in
micrometer range) with respect to only porous surface formed
during anodization of the bulk materials.
