Preparation and Mechanism of Novel Bioceramics with Controllable Morphology and Crystal Growth - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 161

FIGURE 6.4
FESEM images of the flowerlike HAp powders.
surface, and the β-CD molecules will cross-link with each other to form the
spherelike structure through the hydroxyls.
In most of these cases, large amounts of surfactant and soft templates,
and even unhealthy templates or organic solvents were widely used, which
were hazardous to health and environment. Up to now, self-assembly of
nanounits into the 3D architectures in the absence of any surfactants, tem-
plate support, or structure-directing reagents are still a major challenge. In
the absence of any surfactants, template support, and structure-directing
reagents, uniform 3D structured carbonated apatite flowers (Figure 6.4) with
exclusively nanosheet-assembled network morphology were synthesized by
Lin et al. via a low-temperature hydrothermal process, using Ca(NO 3 ) 2 and
NH 4 H 2 PO 4 as Ca and P sources, and urea as the homogeneous precipitation
reagent. The uniformity in size distribution and shape of the apatite flowers
was probably attributed to the homogeneous precipitation effects, and the
high crystallization of the products was attributed to the hydrothermal treat-
ment. A possible self-assembled mechanism was preliminarily proposed for
the formation of the novel 3D architectures. The process of the morphology
evolution for HAp flowers was proposed as the nucleation-dissolution-
recrystallization-self-assembly growth from nanosheets to a flowerlike mor-
phology process (Figure 6.5) based the basis of time-dependent experiments
and the morphology observations.
Furthermore, we also synthesized the biomimetic HAp porous micro-
spheres with cosubstituted essential trace elements (Na, Mg, K, F, Cl,
and CO 3 2- ) of natural bone via a low-temperature hydrothermal method
(Figure 6.6), in absence of any surfactants, organic solvent, or template-
directing reagents. Comprehensive studies have confirmed that these sub-
stitutions play critical roles in biological performances of the materials in
comparison to stoichiometric HAp. In our synthesis process, the Ca(NO 3 ) 2
and NH 4 H 2 PO 4 were used as Ca and P sources, respectively; NaNO 3 ,