Biomedical Engineering Reference
In-Depth Information
Calcium Alkoxide
Masuda et al. (1990) studied nanohydroxyapatite powder production using the alkoxide-based
system containing calcium diethoxide, triethyl phosphite, ethanediol, and ethanol, modified
with water and acetic acid. Within this system, they synthesized powders and found that the
determining factor for the composition of the resultant powder was the solution's pH. This
was the first systematic approach on controlling the chemistry for pure nanohydroxyapatite
production. No attempts were made to produce monolithic materials or coatings.
Based on the basic chemistry of Matsuda et al. (1990), Ben-Nissan et al. (Ben-Nissan and
Chai 1995; Chai et al. 1998; Gross et al. 1998; Ben-Nissan et al. 2001), and Green et al. (2001)
employed a modified alkoxide process to synthesize HAp powders and coatings via the
sol-gel technique. In a further modified technique, Milev et al. (Milev et al. 2002, 2003; Ben-
Nissan et al. 2001) used multinuclear NMR spectroscopy to monitor the synthesis of carbon-
ate-containing HAp for powder, nanoplatelets and nanocoating productions (Figure 2.9).
Layrolle and Lebugle (1994) developed a synthesis route of different calcium phosphates,
using anhydrous ethanol as solvent and calcium diethoxide (Ca(OEt)
2
) and orthophos-
phoric acid (H
3
PO
4
) as reagents. In a systematic approach using a simple variance of the
ratio of reagents, calcium phosphates of various chemical compositions Ca
x
(HPO
4
)
y
(PO
4
)
z
were precipitated in the ethanol. The solids that formed were characterized by different
physicochemical and thermal analyses. The results revealed that the different solid cal-
cium phosphates are amorphous and of the nanoscale and have large specific surface areas
and high reactivities.
Layrolle et al. (1998) also described the production of a nanosized, amorphous, and
carbonate-containing calcium phosphate powder synthesized from calcium diethoxide
and phosphoric acid in ethanol via a sol-gel method. They concluded that after sintering,
the decomposition of carbonated HAp generated a microporous ceramic with an average
pore size of 0.2 μm and an open porosity of 15.5% and that this microporous bioceramic
can be used as bone filler.
Roest et al. (Roest et al. 2001, 2004; Roest 2010) developed carbonate nanohydroxyapatite
coatings on anodized titanium and titanium alloy (Ti-6Al-4V) by dip and spin coating
methods successfully. Similar methods were used to coat a range of substrates with zirco-
nia nanocoatings.
Zreiqat et al. (2005) compared the effect of surface chemistry modification of titanium
alloy (Ti-6Al-4V) with zinc, magnesium, and alkoxide-derived hydroxy carbonate apatite
(a)
(b)
(Å)
1967
4
984
0
3
2
(µm)
3
1
2
(µm)
1
0
0
FIGURE 2.9
(a) SEM of nanohydroxyapatite coating (scale 100 nm), (b) AFM image of the same nanohydroxyapatite
coating.
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