Biomedical Engineering Reference
In-Depth Information
The annual consumption of a phosphate rock has approached ~150
million tons and about 95 percent of this production is utilized in
fertilizer industry [80, 81].
In biological systems, many organisms, ranging from bacteria and
isolated cells to invertebrates and vertebrates, synthesize calcium
orthophosphates [41]. Formation of calcium orthophosphates in
primitive organisms is believed to enable the storage and regulation
of essential elements such as calcium, phosphorus and, possibly,
magnesium. The morphology of precipitates in these organisms
(small intracellular nodules of ACP often located in mitochondria)
complies with the necessities for rapid mobilization and intracellular
control of the concentration of these elements [82]. In vertebrates
calcium orthophosphates occur as the principal inorganic constituent
of normal (bones, teeth, fish enameloid, deer antlers and some
species of shells) and pathological (dental and urinary calculus and
stones, atherosclerotic lesions, etc.) calcifications [27, 83-88]. Except
for small portions of the inner ear, all hard tissues of the human
body are formed of calcium orthophosphates. Structurally, they
occur mainly in the form of poorly crystalline, non-stoichiometric,
calcium-deficient, Na-, mg- and carbonate-containing HA (often
called “biological apatite” [89-93] (which might be abbreviated
as BAp [94, 95]), bioapatite [96-99] or dahllite [100]). The main
constituents of human bones are calcium orthophosphates (~60-70
wt.%), collagen [104] (~20-30 wt.%) and water (up to 10 wt.%) [87,
96-98, 105-107]. Detailed information on the chemical composition
of the most important human normal calcified tissues is comprised
in Table 1.2. One should note that the values mentioned in Table 1.2
are approximate; the main constituents can vary by a percent or
more [108].
1.3
The Members of Calcium Orthophosphate
Family
In the ternary aqueous system Ca(OH)
-H
PO
-H
O (or CaO-
2
3
4
2
P
O) [109-111] there are twelve known non-ion-substituted
calcium orthophosphates with the Ca/P molar ratio within 0.5
and 2.0 (Table 1.1). An anhydrous phase diagram of CaO-P
O
-H
2
5
2
O
at
2
5
∞
temperatures within 200-2200
C is shown in Fig. 1.3 [112, 113].
Table 1.3 comprises crystallographic data of the existing calcium
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