Biomedical Engineering Reference
In-Depth Information
discovered X-ray amorphous component of the initial powder was
located on the surface of nanodimensional HA.
3.6
Synthesis of the Nanodimensional and
Nanocrystalline Calcium Orthophosphates
3.6.1
General Nanotechnological Approaches
The synthesis of nano-scale materials has received considerable
attention and their novel properties can find numerous applications,
for example, in the biomedical field. This has encouraged the invention
of chemical, physical, and biomimetic methods by which such nano-
sized materials can be obtained [109]. Generally, all approaches for
preparation of nanodimensional and nanocrystalline materials can
be categorized as “bottom-up” and “top-down” ones [117, 222]. The
bottom-up approach refers to the build up of a material from the
bottom, i.e., atom by atom, molecule by molecule or cluster by cluster
and then assembles them into the final nanostructured material. An
example is production of a nano-sized powder and its compaction
into the final product (e.g
, hot-pressed or sintered nanostructured
ceramics). The top-down approach starts from a bulk material
and then, via different dimension decreasing techniques, such as
milling, slicing, or successive cutting, leads to the formation of
nanodimensional materials [109]. Using this approach, a novel two-
dimensional carbon material graphene of just 1 atom thick has been
prepared from bulk graphite.
Concerning calcium orthophosphates, presumably, all of them
(see Table 1.1) might be manufactured in a nanodimensional and/
or a nanocrystalline state; however, not all of them (especially those
with low Ca/P ionic ratios) have been prepared yet. The details on
the available preparation techniques are given below:
.
3.6.2
Nanodimensional and Nanocrystalline Apatites
First of all, one should stress that the stoichiometric HA with well
resolved X-ray diffraction patterns might be prepared mostly at
temperatures exceeding ~700°C either by calcining of CDHA with
the Ca/P molar ratio very close to 1.67 or by solid-state reactions
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