Biomedical Engineering Reference
In-Depth Information
specific gene delivery [643, 644]. Assemblies of block-copolymer/
nano-sized calcium orthophosphate were prepared and used for cell
transfection; a high biocompatibility of this system was emphasized
[645]. Structures that are even more complex are known as well
[646-648]. A schematic drawing of a functionalized nano-sized
particle suitable for both imaging and drug delivery purposes is
shown in Fig. 3.8 [649]. Furthermore, vaccination to protect against
human infectious diseases may be enhanced by using adjuvants that
can selectively stimulate immuno-regulatory responses and nano-
sized particles of calcium orthophosphates were found to be suitable
for such purposes [650, 651].
Figure 3.8
A generalized schematic setup of a nanodimensional particle of
a calcium orthophosphate suitable for both imaging and drug
delivery purposes. Reprinted from Ref. [649] with permission.
In all these new applications of nano-sized calcium
orthophosphates, knowledge of the exact internalization pathway
into the cells represents the first necessary step towards the detailed
investigation and optimization of the functional mechanism. The
main groups of pathways into the cell are diffusion, passive and
active transport, as well as a number of endocytic mechanisms
[612]. Bigger particles of far above 10 nm are internalized by
eukaryotic cells through the endocytic pathways including
phagocytosis, macropinocytosis, clathrin-mediated endocytosis,
and non-clathrin-mediated endocytosis such as internalization via
caveolae. To date, the exact internalization pathway of nano-sized
calcium orthophosphates into cells has not been determined and
there are many questions that remain to be answered, particularly,
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