Biomedical Engineering Reference
In-Depth Information
commercially available powder of HA was dissolved in 0.1M HCl
solution. The second electrolyte consist 0.042M Ca(NO
3
)
2
+ 0.025M
(NH
4
)
2
HPO
4
+ 0.1M HCl, which is often reported in the literature
[60, 116] (but they did not reports using of HCl). The molar ratio of
Ca/P is 1.68 which corresponds to HA. In the second electrolyte, the
addition of HCl dissolve the reaction product (calcium-phosphates
particles) of the Ca(NO
3
)
2
+ (NH
4
)
2
HPO
4
and make the electrolyte
homogenous for cathodic deposition at -1.5 V for 60 min, for
example, in both electrolytes. In these depositing conditions, the
formed layers have good mechanical strength and adhere strictly to
the porous surface.
Anodic etching of titanium results in surface roughening [33]
attractive in osseointegration. During 30 min of anodization in 1M
H
3
PO
4
+ 10% NH
4
F at relatively low 10 V potential, the Ti atoms
are effectively removed from the surface, resulting in pits formation
with diameter in the range of 7-12 μm [33]. Additionally, etching
in H
3
PO
4
electrolyte results in some phosphorous deposition on the
etched surface, useful for the osseointegration [31].
The surface after calcium phosphate deposition, with using
the 0.1M HCl + 0.005M HA electrolyte, is shown on Fig. 9.72. For
the lat and porous surface, the Ca-P layer has comparable spongy
morphology. In the case of lat surface (a), a lot of cracks or grain
boundaries in the layer are visible in spite of porous sample, where
the layer strictly covers the titanium background (b). The positions
of pores are still visible as the darker circular spots. Deposition
of calcium-phosphate with using the 0.042M Ca(NO
3
)
2
+ 0.025M
(NH
4
)
2
HPO
4
+ 0.1M HCl electrolyte, results in signiicantly different
morphology (Fig. 9.73) than presented on Fig. 9.72. The deposited
HA layer is rough with large lamellas features. When comparing
the small spongy structure from Fig. 9.72 to large lamellas on
Fig. 9.73, the former one could be an initial stage of grow of the
thick HA layer and the spongy structure (Fig. 9.72) is also com-
posed from the lamellas, but in different (smaller) scale than on
Fig. 9.73. The initial porous surface is not visible, and both porous
and lat samples after HA deposition looks comparable, but with
expected stronger adhesion of the HA layer to the porous surface.
The HA morphology presented on Fig. 9.73 is in good agreement
with structures obtained by Yen and Lin [116].
