Biomedical Engineering Reference
In-Depth Information
determined by dimensions, surface charge, morphology, and surface
chemistry. Furthermore, nano-sized particles penetrate and leave
biological organisms more readily using a number of pathways.
Namely, very small (<10 nm) particles are generally eliminated
from the body via renal clearance, i.e. being filtered through the
kidneys and eliminated through urine, while nano-sized particles
of larger dimensions are phagocytized by tissue macrophages of
the reticuloendothelial system in the liver and spleen [609]. For
example, intravenously administered nanodimensional (~40 nm
and ~200 nm) rod-shaped crystals of apatite showed clearance
from the bloodstream within 2 h, with ~90% of them being cleared
in the first 10 min post injection; those nanodimensional crystals of
apatite were observed primarily in the liver with a minority seen in
the spleen [282]. These results indicate that bloodstream clearance
occurs rapidly for a wide range of nanodimensional sizes. The
accumulation of nanodimensional (50-100 nm in size) apatite in the
liver was also noted in another study [434].
Thus, understanding the biological influence of nano-sized and
nanocrystalline calcium orthophosphates is essential for a future
development of bionanotechnology [670]. This interdisciplinary
approach is very complicated and the effective collaboration of
scientists from different disciplines is the key [13].
3.9
Conclusions
With a high surface area, un-agglomerated nanodimensional and
nanocrystalline bioceramic particles are of interest for many
applications including injectable or controlled setting bone cements,
high strength porous or non-porous synthetic bone grafts, and the
reinforcing phase in biocomposites that attempt to mimic both the
complex structure and superior mechanical properties of bone.
Therefore, nano-sized and nanocrystalline calcium orthophosphates
have already gained much regard in the biomedical field due to their
superior biocompatibility and biomechanical properties. This is easily
seen from a permanent increasing of the amount of publications. At
present, apatites (HA and CDHA) and β-TCP are the major calcium
orthophosphates used in clinics. Currently, nanodimensional apatites
are used primarily as bioactive coatings on bioinert materials like
titanium and its alloys, in bone tissue repairs and implants, as well
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