Biomedical Engineering Reference
In-Depth Information
2+
4
3-
-
10Ca
OH (mechanism 2)
Body liquid contains hydrogen phosphate ions. In contact with
the basic CA or CS materials during setting and hydration, the
hydrogen phosphates are neutralised and PO
+ 3PO
+ OH
Æ
Ca
(PO
)
10
4
3
4
3-
ions are formed:
4
2-
4
-
-
4
3-
HPO
+ H
PO
+ 3 OH
Æ
2PO
+ 3H
O
(mechanism 3)
2
2
Thereafter the apatite formation reaction occurs as mechanism 2:
10Ca
2+
4
3-
-
OH
Nanosize apatite crystals are precipitated on biological walls and
inside the biomaterial [1]. See Fig. 3.2 below.
+ 3PO
+ OH
Æ
Ca
(PO
)
10
4
3
Figure 3.2
HRTEM image of a precipitated apatite crystal approximately
30 nm in size.
3.1.3
Mechanism 4
In some cases transformation of formed hydrates into apatite occurs
after some time. In the main reaction in the CA system, katoite is
formed as a main phase. However, in contact with body liquid,
the katoite is transformed into the even more stable apatite and
amorphous gibbsite. The overall reaction is as follows:
◊
◊
Æ
2+
4
2-
4
-
Æ
Ca
(Al(OH)
)
(OH)4
2Ca
+ HPO
+ 2H
PO
3
4
2
2
Ca
◊
(PO
)
◊
(OH) + 2Al(OH)
+ 5H
O
5
4
3
3
2
Search WWH ::
Custom Search