Biomedical Engineering Reference
In-Depth Information
Table 2.1
Examples of solid solutions of HA as minerals and biological
apatites
Type of
apatite
Major sub-
stituent(s)
Main formula
Comments
HA
Ca
(PO
)
(OH)
-
Basic
structure
5
4
3
F-aptite
Ca
(PO
)
(OH,F)
F
Mineral
5
4
3
Mineral
OH-apatite
Ca
(PO
)
(OH)
-
Mineral
5
4
3
Dahllite
Ca
(PO
, CO
)
(OH)
CO
Mineral
5
4
3
x
y
3
Staffelite
Ca
(PO
,CO
)
(OH, F)
CO
, F
Mineral
5
4
3
x
y
3
Human
enamel
apatite
(Ca,Mg)
(PO
,HPO
,CO
)
(OH,Cl)
Mg, HPO
,
Biological
apatite
x
4
4
3
y
4
CO
, Cl
3
Shark
enameloid
Ca
(PO
,CO
, HPO
)
(OH, F)
F, C O
,
and
Biological
apatite
x
4
3
4
y
3
HPO
4
, which is why solid
solutions in Table 2.1 can be described as (Ca, Mg)
The united cell of apatite is Ca
(PO
)
(OH)
10
4
6
2
(PO
, CO
,
10
4
3
. Other substituents in low concentrations are also
possible, especially other metals such as Sr, Ba, Na, Li, Mn, and Zn.
Thus three main positions—one for cations and two for anions—
are found within the apatite structure. In many chemically bonded
bioceramics (CBBCs) apatite structures are formed. In several other
CBBCs two of these three positions are the same as in apatite. As an
example for hydrated Ca-aluminate the phase Ca
HPO
)
(OH, Cl, F)
4
6
2
[Al(OH)
]
(OH)
is
3
4
2
4
shown.
The amount of apatite in enamel is very high, approximately 96
wt.%. In dentine and bone tissues the apatite content is approxi-
mately 60% and 35%, respectively. The soft tissue part in hard struc-
tures is different types of collagen, intracellular matrix, and water.
The structures of apatite in hard tissue are designed to meet
requirements on the macro-, micro-, and nanosize levels with
regard to the formation and mechanical properties developed. All
structures are based on nanosize crystals and nanosize inter- and
intralayers [1, 3]. See Table 2.2.
Search WWH ::
Custom Search