Biomedical Engineering Reference
In-Depth Information
adhesion, differentiation and proliferation, osteointegration and
deposition of calcium containing minerals on its surface better than
microcrystalline HA; thus enhancing formation of a new bone tissue
within a short period [574-576]. More to the point, nanodimensional
HA was found to cause apoptosis of the leukemia P388 cells [577].
Natural bones and teeth are hierarchical biocomposites of
biological origin based on nanodimensional compounds because
they consists of nano-sized blade-like crystals of biological apatite
grown in intimate contact with the organic matrix rich in bioorganic
fibers and organized in complicated hierarchical structures (see
section
for details). Given the fact that the major bioorganic phase
of bones is collagen, i.e
1.4
a natural polymer (Table 6.1), it is obvious
that a composite of a nanodimensional calcium orthophosphate
with a biodegradable polymer should be advantageous as bone-
substitution material. The inorganic nanodimensional phase
would be responsible for the mechanical strength (hardness) and
bioactivity, while the polymeric phase would provide the elasticity.
In addition, the solubility of calcium orthophosphates depends on
their crystallite size (smaller crystals have a higher solubility) and
on their carbonate content (higher carbonate content increases
the solubility) [578]. To the author's best knowledge, among
calcium orthophosphates listed in Table 1.1, before very recently
only apatites (CDHA, HA and, perhaps, FA) have been available in
nanodimensional state. However, recently, nano-sized DCPA [503-
505] and nano-sized MCPM [579] have been synthesized and applied
to prepare biocomposites with strong ionic release to combat tooth
caries. Presumably, all calcium orthophosphates from Table 1.1
might be manufactured in nanodimensional and/or nanocrystalline
state; however not all of them have been prepared yet (see Chapter
3 for details).
A number of investigations have been conducted recently to
determine the mineralization, biocompatibility, and mechanical
properties of the biocomposites based on various (bio)polymers
and nanodimensional HA. Unfortunately, in the majority of the
already published papers it often remained unclear whether
“nanodimensional HA”, in fact, represented the nanodimensional
stoichiometric HA or a nanodimensional non-stoichiometric CDHA.
These studies covered biocomposites with PLA [332, 580-589] and
its copolymer with PGA [590-593], collagen [594-607], collagen +
PLA [607-615], collagen + PVA [616], collagen + alginate [617, 618],
.
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