Biomedical Engineering Reference
In-Depth Information
from open vessels for rSBF [860, 869-873] by means of
permanent bubbling of gaseous CO
losses of CO
2
through the solutions. Addition
of the most important organic and biological compounds like
glucose [871], albumin [869, 918], lactates [919] and collagen [920]
is another direction to improve biomimetic properties of various
types of SBF. Once a cow milk-based rSBF has been prepared [921].
Further improvements of all biomimetic solutions are to be made in
future. Occasionally, condensed solutions of SBF (e.g.
2
1.5-fold, 2-fold
[920, 922, 923], 5-fold [924, 925], and even 10-fold [926]) are used
to accelerate precipitation and increase the amount of precipitates.
However, whenever possible this should be avoided because the
application of condensed solutions of SBF leads to changes in the
chemical composition of the precipitates; namely, the concentration
of carbonates increases, while the concentration of orthophosphates
decreases [927].
To conclude this part, one should note on difficulties in
mimicking the calcification process that occurs in bones and teeth.
A reasonable mechanism of the induction of CDHA nucleation and
crystallization by carboxylate groups on the bioorganic matrices
looks as this. At first, calcium and orthophosphate ions are combined
with carboxylate groups. By using this as seeds, CDHA crystals then
grow to generate interfaces that contain the most stable structure
of the {100} faces. Such a crystallization mechanism explains why
the
,
-axes of biological apatite are parallel to the organic matrices.
Collagen fibers can be regarded as axis-like organic matrices:
when CDHA is formed on the surface of collagen fibers parallel to
the
c
-axes are oriented parallel to the fiber orientation
[928]. A step further would be to perform the precipitation from
the simulating solutions on templates of biomineralization proteins
for the control of crystal organization and properties. For example,
there are successful attempts to crystallize calcium orthophosphates
on collagen in order to obtain bone-like composites [572, 929-938].
Such collagen/calcium orthophosphate biocomposites are currently
under investigation for clinical use (see section
c
-axes, the
c
6.4.4. Biocomposites
with collagen
for details). Other popular biomimetic matrixes
to perform calcium orthophosphate crystallization comprise
gelatin [436-441, 939-941], chitosan [939, 942, 943], organic
polyelectrolytes [944-947], metals and alloys [948-954], polymers
[955], cellulose [956], self-assembled monolayers [957] and many
other materials (Chapter 6). Such biomimetically prepared calcium
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