Biomedical Engineering Reference
In-Depth Information
Protein
HPO
2-
Cl
-
Cl
-
Ca
2+
Ca
2+
Cl
-
Cl
-
HPO
2-
Ca
2+
Ca
2+
Mg
2+
HPO
2-
Mg
2+
Mg
2+
M
x+
M
x+
Na
+
Ca
2+
CO
2-
Ca
2+
Ca
2+
Na
+
HPO
2-
CO
2-
Ca
2+
FIGURE 5.2
(
See color insert.
) Schematic process of biomineralization of biological hydroxyapatite in sim-
ulated body fluid containing proteins.
phase that may be nonstoichiometric, hydrated, and susceptible to rapid
phase transformation (Colfen and Mann 2003).
Generally, the biomineralization of bioceramics is always under mild con-
ditions (see Figure 5.2). The temperature is around 37°C, close to the human
body temperature. The compositions of solutions are similar to that of human
body fluid. Proteins are involved or not involved in the crystallization. The
formation consists of apatite with small crystals and low crystallinity. The
biomineralized apatite does not contain calcium and phosphate only. It is a
multi-ion substituted apatite, and can be easily functionalized by proteins
and drugs.
Table 5.2 summarizes most of the popular mineralizing solutions that
mimic the compositions of human body fluid. Simulated body fluid (SBF)
plays a significant role in biomineralization of bioceramics, which is affected
by the composition, concentration, pH, and flowing state of SBF and its addi-
tives, such as trace elements, proteins, and drugs. The most famous SBF is
Kokubo's solution (Kokubo et al. 1990), which has almost the same mineral
concentrations as human blood plasma and is used to evaluate the ability of
the bone bonding in an
in vitro
model. Other modified Kokubo's SBF have
also been used to study the apatite formation on a bioceramic surface. Except
for Kokubo's SBF, other buffer solutions containing calcium and phosphate
ions have been tested, such as ringer's solution, EBSS (Earle's balanced salt
solution), Hank's solution, SCS (supersaturated calcification solution), and
DPBS (Dulbecco's phosphate buffer saline).
Biomineralization of bioceramics is also interesting. Because it mimics
the process of bone mineralization, the newly formed crystal is similar to
the apatite in human bone. Thus, the bone-like apatite precipitated from
the above solutions is expected to show high affinity to the bone tissue. The
mechanism behind the biomineralization of bioceramics would be useful for
the explanation of (1) bone mineralization, (2) bonding between bond and
bioactive ceramics, and (3) how to decrease the failure of bone materials.
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