Biomedical Engineering Reference
In-Depth Information
Fig. 6.18
Typical scanning electron microscopy (SEM) images of the fracture surface of the
crystalline tablet obtained after mineralization reaction (
a
) low magnification view, (
b
)high
magnification image, (
c
) view of higher local magnification of the Mg-calcite. The compact tablet
of Mg-ACC powder is put into 500 mL double-distilled water at 25
ı
C for 2 days. (Reproduced
from [
117
], Copyright © 2011, Royal Society of Chemistry)
found to be incorporated into the calcite lattice. Moreover, according to the ICP-
AES, the Mg/Ca molar ratio of the crystalline flake is 1:4.3. Therefore, the mass
fractions of the obtained Mg-calcite and aragonite are 89.88 wt% and 10.12 wt%,
respectively. It has been demonstrated that the confined crystallization plays a key
role in preventing the escape of Mg
2C
and incorporation of magnesium in the
calcite lattice, which may suggest that similar roles of confined environment in
the formation of biological magnesian calcite [
117
]. In addition, some intermediate
states can be captured in this special confined crystallization process of the compact
tablet of magnesian ACC nanoparticles.
Furthermore, peanut-shaped CaCO
3
aggregates consisting of two dandelion-like
heads have been obtained via a facile precipitation reaction between Na
2
CO
3
and
CaCl
2
at room temperature in the presence of ethanol solvent and magnesium ions
[
118
]. The polymorph transformation of ACC to calcite and aragonite was observed
in the growth process. In this experiment, a high concentration of ethanol solvent
and magnesium ions played key roles in the formation of the unusual peanut-like
CaCO
3
aggregates. The ethanol solvent increases the influence of magnesium ions
on the morphology of CaCO
3
due to dehydrated magnesium ions are more readily
adsorbed on the certain surfaces of calcite and thus affect the morphology [
119
]. On
the other hand, the adsorption of Mg ions onto the specific growing crystal surfaces
leaded to the morphological change of calcium carbonate.
Tang et al. found that the poly(4-sodium styrene sulfonate)-stabilized amorphous
calcium carbonate (PSS-ACC) particles use themselves as the templates to form
the new crystallized shells. It is a simple and new way for preparation of hollow
calcium carbonate nanospheres under mild conditions [
120
]. The hollow-structured
CaCO
3
can be utilized as drug deliverers and diagnostic markers since it provides
an excellent biocompatibility. The hydrolysis of carbonate source method is used
to obtain the PSS-ACC precursors. Fifteen milligram of PSS-ACC was dispersed in
10 mL of anhydrous ethanol in the presence of an ultrasonic treatment for 1 h. Then,
water was added into the slurry to induce crystallization of ACC. The solids were
separated by centrifugation and were washed using anhydrous ethanol. It has been
demonstrated that the hollow vaterite nanospheres can be obtained by water-induced
