Biomedical Engineering Reference
In-Depth Information
are always nanodimensional and nanocrystalline, which have been
formed
under mild conditions. According to many reports,
dimensions of biological apatite in the calcified tissues always
possess a range of a few to hundreds of nanometers with the smallest
building blocks on the nanometer size scale [2, 4, 5, 10, 11]. For
example, tens to hundreds of nanometer-sized apatite crystals in a
collagen matrix are combined into self-assembled structures during
bone and teeth formation [2, 4, 5]. Recent advances suggest that this
is a natural selection, since the nanostructured materials provide a
better capability for the specific interactions with proteins [12].
Due to the aforementioned, nanodimensional and nanocrystalline
forms of calcium orthophosphates are able to mimic both the
composition and dimensions of constituent components of the
calcified tissues. Thus, they can be utilized in biomineralization and
as biomaterials due to the excellent biocompatibility [13, 14]. Further
development of calcium orthophosphate-based biomaterials obviously
will stand to benefit mostly from nanotechnology [15], which offers
unique approaches to overcome shortcomings of many conventional
materials. For example, nano-sized ceramics can exhibit significant
ductilitybeforefailurecontributedbythegrain-boundaryphase.Namely,
already in 1987, Karch et al
in vivo
reported that, with nanodimensional
grains, a brittle ceramic could permit a large plastic strain up to
100% [16]. In addition, nanostructured ceramics can be sintered at
lower temperatures; thereby major problems associated with a high
temperature sintering are also decreased. Thus, nanodimensional and
nanocrystalline forms of bioceramics clearly represent a promising
class of orthopedic and dental implant formulations with improved
biological and biomechanical properties [17].
Many other advances have been made in biomaterial field due to
a rapid growth of nanotechnology [18]. For example, a recent theory
of “aggregation-based crystal growth” [19] and a new concept of
“mesocrystals” [20, 21] highlighted the roles of nano-sized particles
in biological crystal engineering. In this aspect, the study of calcium
orthophosphates is a specific area in nanotechnology, because they
might be applied readily to repair hard skeletal tissues of mammals
[22-24].
Herein, an overview of nanodimensional and nanocrystalline
apatites and other calcium orthophosphates in studies on
biomineralization and biomaterials is given. The available calcium
orthophosphates are listed in Table 1.1. To narrow the subject of
.
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