Biomedical Engineering Reference
In-Depth Information
(a)
(b)
100 nm
100 nm
FIGURE 6.1
FETEM images of the HAp nanoparticles obtained via (a) hydrothermal treatment and (b)
hydrothermal-microemulsion process at 180°C for 18 h.
with a low chemical driving force at low pH condition promoting the formation
of two-dimensional (2D) nanostructures in the case of apatite presented in the
bones. The similar phenomenon was observed in the formation of HAp at low
temperatures by decomposition of a Ca-EDTA complex (Arce et al. 2004).
Though the hydrothermal technique usually gives HAp powders with a
high degree of crystallinity and with a Ca/P ratio close to the stoichiomet-
ric value (Byrappa 2001), the obtained powders are usual in agglomeration
and the size distribution is wide (Figure  6.1a). Therefore, the size distribu-
tion of the products cannot be well controlled using a normal hydrothermal
method. To overcome these limitations, microemulsion and hydrothermal-
microemulsion methods have been developed to synthesize inorganic mate-
rials with uniform particle morphology, size, and size distribution. Especially
for the newly developed hydrothermal-microemulsion technique, which is
considered as an effective, convenient, and mild synthetic methodology for
the synthesis of nanopowders, nanoneedles, and nanowires (Chen et al. 2003;
Zhang and Gao 2003; Lin et al. 2006). The microemulsion not only can serve as
nanoreactors to control the particle size and size distribution in the reaction
process but also inhibit the excess agglomeration of particles, since the surfac-
tants can absorb on the particle surface when the particle size approaches that
of the water (or oil) pool. In addition, the surfactants in the microemulsion can
also serve as a versatile “soft template” for the synthesis of 1D nanostructural
materials. Furthermore, the hydrothermal treatment can effectively increase
the crystallinity of the product. We synthesized the stoichiometric single
crystal HAp nanorods with monodispersion and narrow size distribution in
diameter via reversed microemulsion (water dispersed in oil, W/O) of CTAB-
n-pentanol-n-hexane-water under hydrothermal condition (Figure 6.1b) (Lin,
Chang, Cheng et al. 2007). The homogeneity in size distribution and shape
 
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