Biomedical Engineering Reference
In-Depth Information
Li et al. (2007) showed that F ion played a marked effect on the composi-
tion and morphology of deposited HAp crystals. In the absence of F ions,
spherical morphology HAp containing CO 3 2− was formed on the sulfonic-ter-
minated self-assembled monolayer (SAM). When F was added, HAp crys-
tals containing both CO 3 2− and F were formed on the SAM. Needle-shaped
crystals of high aspect ratio and 1 to 2 µm in length grew elongated along the
c-axial direction in bundles, mimicking HAp crystals in tooth enamel. The
formation of enamel-like HAp can be attributed to the substitute of F for
OH by disturbing the normal progress of HAp formation on the SAM.
Yuan et al. (2008), using porous anodic aluminum oxide (AAO) as a tem-
plate, fabricated a highly ordered array of HAp nanotubes with uniform
length and diameter using the sol-gel autocombustion method. A potential
mechanism of “an autocombustion from dried gel to nanoparticles and a
subsequent in situ reaction from nanoparticles to nanotubes” was proposed
based on the electron diffraction, x-ray diffraction (XRD), and x-ray photo-
electron spectroscopy survey.
Other than the polymers and proteins, the small molecules with special
structures and functional groups can also be used as the template to direct
the crystal growth and their aggregations. Compared with the traditional
proteins, the small molecules process has more robust physicochemical
properties, such as tolerance of temperature and resistance to acid or base,
which would allow it to be better applied in wider and more severe reac-
tion conditions. Recently, Liu et al. (2012) synthesized the highly oriented
HAp arrays (Figure  6.9b) with the aid of small quercetin (C 15 H 10 O 7 , QUE;
Figure  6.9a) molecule via hydrothermal treatment of α-TCP precursors in
a QUE-containing ethanol-distilled water solution. Furthermore, the mor-
phologies of HAp nanocrystals varied from wide-angle branching to small-
angle branching, and finally parallel-packed arrays could be well modulated
by simply regulating the concentration of QUE. The HAp morphology regu-
lating might be attributed to the physicochemical properties of QUE. The
(a)
(b)
OH
Quercetin
OH
3'
4'
5'
2'
C
1'
HO
O
6'
8
9
2
7
6
A
B
10
3
5
4
OH
O
OH
FIGURE 6.9
(a) Molecular structure of QUE and (b) FESEM image of samples obtained under 180°C for 24 h
with QUE concentration of 50.00 mg/20 mL, top-right insert: higher resolution image.
 
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