World Journal of Engineering
SYNTHESIS AND CHARACTERIZATION OF MESOPOROUS CAO-B2O3-SIO2
BIOACTIVE GLASS
Lay Gaik Teoh*, Yu-Ren Wu, Pei-Hsing Huang and Yi Lin Huang
Department of Mechanical Engineering, National Pingtung University of Science and Technology, Neipu, Pingtung
91201, Taiwan.
structure or the wormhole-like structure. TEM analysis
also shows that mesoporous bioactive glass powder
possess the uniform distribution of wormhole-like
mesopores with average size of 6 nm. The ordering of
mesoporous channel structures may greatly influence
hydroxyapatite forming ability, the protein adsorption
and nutrient-delivery behavior for better in vivo
bioactivity [6], together with presenting the option of
filling the pores with drugs or biological molecules [7].
The corresponding selected area electron diffraction
(SAED) pattern shows the non-crystalline nature of the
mesoporous bioactive glass framework, with only an
amorphous phase present [Fig. 1 inset]. This is in good
agreement with the XRD result.
Introduction
Bioactive glasses, ceramics and glass-ceramics have
attracted much attention as biomaterials since the
pioneering work by Hench et al. in 1971 [1]. These
bioactive materials are biodegradable and have
generally good biocompatibility, and when they are
implanted in the human body a biologically active
apatite layer is formed at the implant-tissue interface.
Subsequently, they spontaneously bond to and
integrate with bone without inducing toxic,
inflammatory, or immune responses [2-4].
It has been reported that increasing the specific surface
area and pore volume of bioactive materials can
influence the formation of the apatite layer [5]. In this
study, we have reported a novel kind of mesoporous
CaO-B2O3-SiO2 bioactive glass prepared by a
combination of surfactant templating and sol-gel
method. This synthesis strategy produces bioactive
glass with uniform and controllable pore size, and
relatively large pore volume.
Experimental
Block copolymer F108 was used as a template material.
Ca(NO3)2·4H2O, (C4H9)3BO3 and Si(OC2H5)4 were
dissolved in ethanol and stirred at room temperature.
The resulting sol solution was gelled at 70 ºC. The
sample was calcined at 600 ºC for 3 hr to remove the
block
copolymer.
The
mesostructure
of
CaO-B2O3-SiO2 obtained was then investigated by
transmission electron microscopy (FEGTEM; FEI E.O
Tecnai F20 G2 Field-Emission TEM, 200 keV), N2
adsorption-desorption
isotherm
measurements
(Micromeritics, ASAP 2010), powder X-ray diffraction
(Rigaku, D/max- Ⅳ , using Cu-Kα radiation), and
scanning electron microscopy (SEM, Hitachi 3000N).
The assessment of in vitro bioactivity was carried out
in a simulated body fluid (SBF) solution (pH 7.4) at 37
°C. The SBF solution has a composition and
concentration similar to that of human plasma. After
soaking for 4, 8 and 48 hr, the samples were removed
from the SBF, washed with deionized water, and dried
at room temperature.
Fig. 1. TEM image of mesoporous CaO-B2O3-SiO2
calcined for 3 hr at 600 ºC.
Table 1 collects the specific surface area, pore size,
and mesopore volume of the pore structure data, which
shows the pore texture features of the prepared sample.
The calculated from the desorption branch of the
nitrogen isotherm using the BJH method, the average
pore size is 63 Å. The surface area is 231.52 m2/g, and
the pore volume is 0.382 cm3/g, which are obviously
higher than those of bioactive glass (57 m2/g for
surface area, 0.09 cm3/g for pore volume).
Results and Discussion
The powder X-ray diffraction pattern of mesoporous
CaO-B2O3-SiO2 calcined at 600 °C for 3 hr is shown in
Fig. 2 (0 hr). A broad band at 22o associated with
Fig. 1 shows the TEM image of the mesoporous
bioactive glass, which reveals disordered mesoporous
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World Journal of Engineering
(c)
amorphous silicate can be noted in XRD pattern of
CaO-B2O3-SiO2 bioactive glass and no other diffraction
peaks are present, as shown in Fig. 2. It is clear to see
that the mesoporous CaO-B2O3-SiO2 sample was still
amorphous when calcined at 600 °C.
The XRD patterns can be used to evaluate the changes
on the mesoporous CaO-B2O3-SiO2 surfaces. The XRD
patterns of mesoporous CaO-B2O3-SiO2 after soaking
in SBF are shown in Fig. 2. After soaking in SBF for 4,
8 and 48 hr, mesoporous CaO-B2O3-SiO2 revealed
several marked peaks, which could be assigned to the
(111), (002), (211), (311), (213) and (004) reflection of
a hydroxyapatite phase (JCPDS card no. 09-0432). In
addition, the broad peaks of hydroxyapatite imply that
the deposited hydroxyapatite had a low crystallinity
structure.
The present study suggests that, mesoporous
CaO-B2O3-SiO2
could
induce
the
bonelike
hydroxyapatite deposition in SBF, at a preparation
temperature that is much lower than that of other
CaO-SiO2-based bioactive ceramic powders. Therefore,
mesoporous CaO-B2O3-SiO2 might be a more
economic reinforcement material for the preparation of
bioactive composites.
H
H
(004)
(311)
H
(213)
(211)
(111)
(002)
H hydroxyapatite
H
H
48 hr
intensity (arb. units)
H
Fig. 3. SEM micrographs of mesoporous
CaO-B2O3-SiO2 after soaking in SBF for (a) 4, (b) 8,
and (c) 48 hr.
8 hr
Conclusion
Mesoporous CaO-B2O3-SiO2 with high surface area
was synthesized using block copolymer as a synthetic
template. The high surface area of 231.52 m2/g and the
average pore size of 63 Å were derived from a sample
prepared under a calcination temperature of 600 °C,
which have much higher textural properties than the
conventional ones. It can be observed that a layer
composed of hydroxyapatite crystallites covered the
surface after soaking for 4 hr. These results imply that
there are potential applications for this high surface
area CaO-B2O3-SiO2 as biomaterial.
References
4 hr
0 hr
20
30
40
50
60
70
80
2degrees
Fig. 2. XRD patterns of mesoporous CaO-B2O3-SiO2
before and after being soaked in SBF for 4, 8 and 48
hr.
The formation of hydroxyapatite deposition was
further proved by SEM analysis. Fig. 3 showed that the
growth of hydroxyapatite particles was observed after
soaking in SBF and the surface of mesoporous
CaO-B2O3-SiO2 was covered with hydroxyapatite
crystals after soaking for 4, 8 and 48 hr in SBF. The
results indicated that mesoporous CaO-B2O3-SiO2 had
superior ability to induce hydroxyapatite formation.
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(a)
(b)
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