Biomedical Engineering Reference
In-Depth Information
For example, to improve cell adhesion, hydrophilic array of ACP was
fabricated on a surface of hydrophobic polystyrene [301]. A similar
effect was found when coatings composed of ACP and hyaluronic acid
were used [302]. Furthermore, in the acidic oral environment the
ACP-containing biocomposites take advantage of the ability of ACPs to
release calcium and orthophosphate ions, which potentially can take
part in enamel remineralization [51-66, 188, 288, 289, 303-324].
Such ACP-containing biocomposites and hybrid biomaterials might
be coatings [292] and cements [155, 286, 287]. In dentistry, the ACP-
containing formulations are used mainly as anti-cariogenic and/or
remineralizing agents [303-324], e.g., in chewing gums [306-308],
sugar confections [74], various tooth mousses [309-311], bleaching
gels [314, 315], various drinks [316, 317] or even in milk [321, 322].
Furthermore, ACP-containing formulations are used in orthodontics
[291-298].
2.6
Conclusions
ACPs can be both found in living organisms (especially invertebrates)
and synthesized in a laboratory. Due to their chemical variability, they
should be recognized as a special class of calcium orthophosphates
offering a wide variety of compositions. Presumably, all known
calcium orthophosphates (see Table 1.1) might be prepared in an
amorphous state; however, not all of them (especially, those with
Ca/P ratio < 1.1) have been prepared. Furthermore, in the available
literature nothing has been found on existence of amorphous TTCP.
The vast majority of the available publications on ACPs in fact
describe wet-precipitated compounds with Ca/P ratio close to ~1.5,
i.e. amorphous TCP. As Poster's cluster has a chemical composition
of TCP, it might be located in the atomic structures of HA (Fig. 2.11),
TCPs, and OCP. Since TTCP and all acidic calcium orthophosphates
have the Ca/P ionic ratios far away from 1.5, presumably, at SRO
and MRO scales, all of them in an amorphous state should contain
structural units, which will be quite different from Posner's clusters.
Nothing on this point has been found in the available literature.
Obviously, this topic needs to be investigates in future.
In aqueous solutions, all currently known ACPs are easily
converted into crystalline phases of calcium orthophosphates,
especially into poorly crystalline CDHA. Therefore, advantages
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