Biomedical Engineering Reference
In-Depth Information
Table 10.4
List of the different calcium orthophosphates
Compound
Abbreviation Formula
Ca/P
Compounds which can precipitate at room temperature in aqueous systems
Monocalcium phosphate
MCPM
Ca(H
2
PO
4
)
2
·H
2
O
0.50
monohydrate
Dicalcium phosphate
DCPD
CaHPO
4
·2H
2
O
1.00
dihydrate (brushite)
Octocalcium phosphate
OCP
Ca
8
H
2
(PO
4
)
6
·5H
2
O
1.33
Precipitated hydroxyapatite PHA
Ca
10
(PO
4
)
6
(OH)
2
1.67
Calcium deficient
CDHA
Ca
10-
x
(HPO
4
)
x
(PO
4
)
6-
x
(OH)
2-
x
1.50-1.67
hydroxyapatite
Amorphous calcium
ACP
-
1.35-1.5
phosphate
Compounds obtained at high temperature
Monocalcium phosphate
MCPA
Ca(H
2
PO
4
)
2
0.50
anhydrous
Dicalcium phosphate
DCP
CaHPO
4
1.00
(monetite)
a
-Tricalcium phosphate
a
-TCP
a
-Ca
3
(PO
4
)
2
1.50
b
-Tricalcium phosphate
b
-TCP
b
-Ca
3
(PO
4
)
2
1.50
Sintered hydroxyapatite
SHA
Ca
10
(PO
4
)
6
(OH)
2
1.67
Oxyapatite
OHA
Ca
10
(PO
4
)
6
O
1.67
Tetracalcium phosphate
TTCP
Ca
4
(PO
4
)
2
O
2.00
the thermodynamic solubility product and, therefore, the thermodynamics of
calcium phosphate salts in an aqueous solution at room or body temperature
is the basis for understanding the manufacturing technology involved in CPCs
for clinical applications.
14, 115, 116
Moreover, it has to be considered that in
addition to thermodynamic factors, kinetic factors can also control both phase
dissolution and the precipitation of new phases and can determine the final
products obtained in a CPC setting reaction.
117, 118
Therefore, the conclusions
that can be derived from the solubility and relative stability diagrams of the
different calcium phosphates must be taken as a first approximation, but not
as an exhaustive explanation of what is actually happening during the setting
reaction.
Apatite calcium phosphate bone cements
The mineral phase of bone has an apatitic structure, which can exist in a
range of compositions. Non-stoichiometric or calcium deficient hydroxyapatite
(CDHA) can be obtained at low temperatures, with a composition which
can be expressed as Ca
10-
x
(HPO
4
)(PO
4
)
6-
x
(OH)
2-
x
, where
x
ranges from 0
to 1, being 0 for stoichiometric hydroxyapatite (HA) and 1 for fully calcium
deficient hydroxyapatite. In fact, biological apatite is a carbonate containing
calcium deficient hydroxyapatite, which in addition contains several other
ionic substitutions such as na
+
, K
+
, Mg
2+
, F
-
and Cl
-
.
