Biomedical Engineering Reference
In-Depth Information
adjusted to the physiological value of 7.4 by using organic buffers such as Tris3 or Hepes.
These compounds are not present in human plasma (Kokubo et al. 2000; Kokubo and
Takadama 2006) (Figure 2.4).
SBF has ionic concentrations of 142.0 mM Na
+
, 5.0 mM K
+
, 1.5 mM Mg
2+
, 2.5 mM Ca
2+
,
147.8 mM Cl
−
, 4.2 mM HCO
3−
, 1.0 mM HPO
4
2−
, and 0.5 mM SO
4
2−
and a pH of 7.40, nearly
equal to those in human blood plasma at 36.5ºC. The SBF is usually prepared by dissolv-
ing reagent-grade chemicals of NaCl, NaHCO
3
, KCl, K
2
HPO
4
·3H
2
O, MgCl
2
·6H
2
O, CaCl
2
,
and Na
2
SO
4
into distilled water and buffering at pH 7.40 with tris (hydroxymethyl) amin-
omethane ((CH
2
OH)
3
CNH
3
) and 1.0 M hydrochloric acid at 36.5ºC.
With their ionic compositions more or less similar to that of human blood plasma, HBSS
or SBF formulations have only limited power with regard to the precipitation of apatitic
calcium phosphates. As a direct consequence, nucleation and precipitation of calcium
phosphates from HBSS or SBF solutions are rather slow. To obtain total surface coverage of
a 10 × 10 × 1 mm titanium or titanium alloy substrate immersed into a 1.5 or 2 × SBF solu-
tion, one typically needs to wait for 2 to 3 weeks, with frequent (every 36-48 h) replenish-
ment of the solution (Tas and Bhaduri 2004).
Among the metallic oxide gels prepared using a sol-gel method, those consisting of SiO
2
,
TiO
2
, ZrO
2
, and Ta
2
O
5
were found to have apatite formation on their surfaces in SBF. These
results indicated that Si-OH, Ti-OH, Zr-OH, and Ta-OH groups on the surfaces of these
gels are effective for inducing apatite formation on their surfaces in the body environment
(Kokubo et al. 2000).
Work has been conducted using SBF solutions to deposit apatite on both 2-D and 3-D
scaffolds. Wu et al. (2007) developed a novel bioactive, degradable, and cytocompatible
bredigite (Ca
7
MgSi
4
O
16
) scaffold with a biomimetic apatite layer for bone-tissue engineer-
ing. Porous bredigite scaffolds were prepared using the polymer sponge method. The bre-
digite scaffolds with biomimetic apatite layer were obtained by soaking bredigite scaffolds
in SBF (pH 7.40) at 37°C for 10 days, and the ratio of solution volume to scaffold mass
was 200 ml/g. After soaking, the scaffolds were dried at 120°C for 1 day and the bredig-
ite scaffolds with biomimetic apatite layer (BTAP) were obtained. Their results showed
that the prepared bredigite scaffolds possess a highly porous structure with large pore
size (300-500 μm). Cromme et al. (2007) investigated the activation of regenerated cellu-
lose 2-D model thin films and 3-D fabric templates with calcium hydroxide, Ca(OH)
2
. The
Langmuir-Blodgett (LB) film technique was applied for manufacturing of the model thin
films using a trimethylsilyl derivative of cellulose (TMS cellulose). Regenerated cellulose
films were obtained by treating the TMS cellulose LB films with hydrochloric acid vapors.
For 3-D templates, regenerated cellulose fabrics were used.
Kim et al. (2006) identified that bonelike apatite was more efficiently coated onto the
scaffold surface by using polymer/ceramic composite scaffolds instead of polymer scaf-
folds and by using an accelerated biomimetic process to enhance the osteogenic potential
of the scaffold. The creation of bonelike, apatite-coated polymer scaffold was achieved by
incubating the scaffolds in SBF. The apatite growth on the porous poly(d,l-lactic-
co
-glycolic
acid)/nanohydroxyapatite (PLGA/HAp) composite scaffolds was significantly faster than
on the porous PLGA scaffolds. In addition, the distribution of coated apatite was more uni-
form on the PLGA/HAp scaffolds than on the PLGA scaffolds. It was reported that when
seeded with osteoblasts, the apatite-coated PLGA/HAp scaffolds exhibited significantly
higher cell growth, alkaline phosphatase (ALP) activity, and mineralization in vitro com-
pared to the PLGA scaffolds coated only with hydroxyapatite.
The SBF method was used by Kolos et al. (2006) for fabricating calcium phosphate fibers
for biomedical applications. Natural cotton substrate was pretreated with phosphorylation
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