Biomedical Engineering Reference
In-Depth Information
prepared by mechanochemical synthesis of a dry mixture of CaO and
DCPD [362, 371] or from coral skeletal carbonate by hydrothermal
exchange [372-374]. relatively large single crystals of HA might be
prepared from those of chlorapatite [375] or by recently developed
controlled homogeneous precipitation method [376]. Lower sized
particles of HA might be prepared by a pyrosol technique, where
an aerosol, containing calcium and orthophosphate ions in the
adequate ratio, is transported to a furnace where the pyrolisis takes
place [377]. Synthesis of nano-sized HA has also been described
[378, 379], while the chronological development of nano-sized HA
synthesis might be found in another paper [380]. Two-dimensional
nanocrystalline HA might be also synthesized [381]. Space-grown
and terrestrial HA crystals were found to differ in size: the former
appeared to be at least 1-1.5 orders of magnitude bigger in length
[382, 383]. Transparent HA ceramics is also known [384-387]. The
detailed information on HA synthesis is available elsewhere [388-
396]. In addition, there are good reviews on HA solubility, crystal
growth and intermediate phases of HA crystallization [397], as well
as on HA dissolution (ref. [398] and Chapter 7 of this topic).
Pure HA never occurs in biological systems. However, due to the
chemical similarities to bone and teeth mineral (Table 1.2), HA is
widely used as a coating on orthopedic (e.g., hip joint prosthesis)
and dental implants [399-406]. HA particles might be implanted as
well [407]. Due to a great similarity to biological apatite, over a long
time HA has been used in liquid chromatography of nucleic acids,
proteins and other biological compounds [408-417] and for drug
delivery purposes [418-421]. Also, HA is added to some brands of
toothpaste as a gentle polishing agent instead of calcium carbonate
[422, 423]. Non-biomedical applications of HA include its using as
an environmentally friendly filler for elastomers [424], a sorbent of
poisonous chemical elements [425, 426] and a carrier for various
catalysts [427-429]. Furthermore, HA by itself might act as a
catalyst for formaldehyde combustion at room temperature [430].
To conclude this topic, one should mention on other reviews devoted
to HA and its biomedical applications [431-435].
1.3.11
FA (or FAp)
Fluorapatite (Ca
(PO
)
F, but is usually written as Ca
(PO
)
F
2
to denote that the crystal unit cell comprises two molecules; the
5
4
3
10
4
6
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