Biomedical Engineering Reference
In-Depth Information
chemistry of these systems is similar to that of the hard tissue found
in living organisms. These are based on different types of apatites
and carbonates. The bioactivity aspects of CBBCs will be treated
separately in Chapters 3 and 8.
Oneofthefirstceramicstobeproposedasabiomaterialwas
gypsum, CaSO
O.Thefirstcementtobeproposedandusedwas
a Zn-phosphate, which is still used as a dental cement. Examples of
typical phases formed in CBC systems are presented in Table 1.3.
◊
½H
4
2
Table 1.3
CBC systems
Group/name
Basic system
Typical phases formed
OPC
a
CSH
Amorhous CSH, tobermorite
CAC
b
CAH
Katoite and gibbsite
Gypsum plaster
Ca-sulphates
CaSO
2H
O
4
2
Sorel
MgO-H
O (Cl)
MgOCl
2
Bioglasses
CaO-Na
O-SiO
-P
O
Carbohydroxyapatite
2
2
2
5
Phosphates
CPH
Apaties, brushite, monetite
Carbonates
CaO-CO
-H
O
Calcite, aragonite
2
2
Geopolymers
c
Aluminosilicates,
metakaolin
Amorphous phases
a
OPC = ordinary Portland cement
b
CAC = high-alumina cement: C
3
A, C
A
, CA,
etc.
12
7
c
Geopolymers = metakaolin or synthetic aluminosilicates
CBCs constitute ceramics which are being formed due to chemical
reactions. Often the precursor material is a ceramic powder (e.g.,
Ca-silicate or Ca-aluminate), which is 'activated' in a water-based
liquid. A chemical reaction takes place, in which the initial powder
is partly or completely dissolved and new phases precipitate. The
precipitated phases are composed of species from both the liquid
and the precursor powder. The precipitates can be formed in situ, in
vivo, often in the nanoscale due to low solubility of the phases formed
(see Chapter 6 for details). The nanostructural CBBCs are especially
found within the Ca-phosphate, Ca-aluminate, and Ca-silicate
systems. The large pores between the original dissolving precursor
powdersarefilled,andthematerialhardens.Thedissolutionspeed
and solubility products of the formed hydrate phases determine the
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