Biomedical Engineering Reference
In-Depth Information
Body Fluid
Cl -
Mg 2+
Cl -
Mg 2+
Cl -
Na +
Na +
Na +
Ca 2+
Ca 2+
Ca 2+
HPO 4 2-
HCO 3 -
HPO 4 2-
HCO 3 -
HPO 4 2-
K +
HCO 3 -
K +
K +
1
2
3
Si 4+
Si 4+
OH - + H 3 O +
OH
HO
OH
O
O
Na +
O
HO
OH
HO
OH
HO
Na +
Si
Si
Si
Si
Si
Si
O
O
O
O
O
O
O
O
O
O
O
O
O
Ca 2+
Na +
Ca 2+
Ca 2+
Ca 2+
Si
Si
Si
Si
Si
Si
O
O
O
O
O
O
O
O
O
Silicate-Based Ceramic
1. Rapid diffusion-controlled ion exchange of network modifying Ca 2+ and/or Na + ions from
the ceramic with H 3 O + ions from the body fluid and silanol groups (Si-OH) at the surface
form.
2. HPO 4 2- and Ca 2+ ions from the body fluid are incorporated into the silicate layer from
an amorphous calcium phosphate layer (nucleation).
3. Crystallization and growth into biological hydroxyapatite.
FIGURE 5.3
( See color insert. ) Schematic of the mechanism of formation of calcium phosphate on the sur-
face of silicate based ceramics.
Arcos et al. (2011) also reported that the biomineralization of MBGs could
enhance their mechanical strength. The increase of the mechanical strength
is due to their internal mesoporous structure, which facilitates the ionic
transport through the bulk pieces. The newly crystallized apatite phase rein-
forces the grain boundary interaction, resulting in a biomimetic nanocom-
posite within the whole implant volume.
The mechanism of precipitation of apatite on the family of calcium silicates
ceramics is similar to silicate-based bioactive glasses. The release of high
content of Ca ion and the formation of Si-OH on their surfaces stimulate the
nucleation of apatite crystals. Chang and colleagues have proved the good in
vitro bioactivity of calcium silicate, dicalcium silicate, tricalcium silicate, and
other calcium silicate-based ceramics (Gou and Chang 2004; Gou et al. 2004,
2005; Wu and Chang 2004; Zhao and Chang 2004, 2005; Lin et al. 2005). Li et
al. (2007) reported that mesoporous amorphous calcium silicate had a fast
precipitation of apatite within 4 hours on its surface.
Ca-aluminate (CA)-based bioceramics have been studied as a biomate-
rial in odontology, orthopedics, and as a carrier material for drug delivery
(Hermansson 2011). CA-based materials exhibit unique curing and harden-
ing characteristics. The hydrate layer forms when CA meets with the fluid.
After a long time soaking, the katoite would transform into apatite and
gibbsite phases (Hermansson et al. 2008).
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