Biomedical Engineering Reference
In-Depth Information
The cross section of the anodic titanium oxide ilm obtained by
Oh et al . [62] formed by electrochemical method at 180 V for 30 min
in 1.5M H 2 SO 4 + 0.3M H 3 PO 4 + 0.3M H 2 O 2 electrolyte is shown in
Fig. 9.23. The variation of pore layer thickness and diameter is
shown, too. The growth of the pore diameter of cell structure with
anodic time increases rapidly in the beginning stage of anodization.
The pore diameter and layer thickness of TiO 2 increases with
anodization time. The anodic ilm thickness is dependent on anodic
time with a rate of 3.15 × 10 -2 μm/min at 180 V [62].
Figure 9.23 Cross-sectional image of TiO 2 ilm (a) and the relationship
between average pore diameter and anodic ilm thickness
with anodizing time at 180 V in 1.5M H 2 SO 4 + 0.3M H 3 PO 4 +
0.3M H 2 O 2 electrolyte (b) [62].
The bioactivity of the as-prepared surface is improved with
the immersion in SBF for 3 days, resulting in the formation of
surface Ca-P compounds. The nucleation of Ca-P compounds is
made convenient by ions introduced to the surface layer during
anodization [47, 63]. The depth proiles of phosphorus concentration
in anodic titania (Fig. 9.24) show that the degree of the residual
phosphate concentration in anodic oxide layer increases with
concentration of H 3 PO 4 in electrolyte [47]. The species containing
phosphate ions iniltrate into the oxide ilm during anodization
[55, 62] and these ions in electrolyte penetrate more easily into the
oxide/electrolyte interface with the phosphoric acid concentration
[47]. In the surface layer, phosphorus is in the forms of mainly
HP O 4 , P O 4 , and P O 3 . Therefore, these negatively charged species on
the anodic titania surface can act as preferential nucleation sites of
calcium phosphate by attractive interaction with Ca 2+ ions in SBF
[47].
 
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