Biomedical Engineering Reference
In-Depth Information
(Chapter 5); however, no cement formulation is known, which
results in ACP formation, as the major end product [270, 271]. More
to the point, ACPs are present as components of various calcium
orthophosphate coatings; however, just a few studies are known, in
which ACP coatings have been fabricated [272-275].
Not many examples of the biomedical applications of ACPs
are currently available. First of all, the majority of cases of plasma
sprayed calcium orthophosphate coatings should be excluded
because the coatings consist of a complicated mixture of various
phases, where ACP is just one of them [9, 162-174]. Besides, both
the amount and the composition of these amorphous phases cannot
be well controlled. Even in the case, when ACP was plasma sprayed,
the coating was found to be a mixture of a crystalline carbonate-
containing apatite phase with considerable amounts of TTCP and
trace amounts of α-TCP [276]. Thus, these cases may hardly be
mentioned as the biomedical applications of ACPs.
There is another type of calcium orthophosphate coatings,
obtained by a biomimetic route. Some of them contain ACP as
the major component [277-280]. For example, an ACP coating on
polyethersulphone plates was prepared by precipitation from a
simulated body fluid (SBF) at 35°C. It took authors 12 days to obtain
a ~20 μm thick ACP coating and 28 days for a ~50 μm thick one
[277]. Similar results were obtained in other studies [278, 279].
One should stress, that in the vast majority cases, the biomimetic
approach presumes application of SBF, which contains ions of
sodium, magnesium, potassium, sulfate, and hydrogencarbonate;
thus, ion-substituted ACPs are always formed as a result.
Furthermore, ACP coatings can be deposited on titanium using
an electrochemical technique at 36°C and solution pH 6.4 [280]. The
obtained ACP coatings appeared to be unstable and transformed into
those of CDHA. By choice of different electrochemical parameters, a
homogeneous coating of ACP, CDHA or some intermediate phases
could be achieved, thus allowing formation of the coatings with
different morphology and solubility [280].
Among the self-setting calcium orthophosphate formulations
(Chapter 5), there is only one ACP-based composition currently
on the market, namely Biobon
®
®
) [281, 282]. This cement
comprises a mixture of ACP (50 wt. %) and DCPD (50 wt. %) which
is mixed with an appropriate amount of aqueous medium (de-
ionized water or saline) with a liquid to solid ratio of 0.8 ml/g at
(α-BSM
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