World Journal of Engineering
SYNTHESIS, CHARACTERIZATION AND IN VITRO BIOACTIVITY OF
SOL-GEL DERIVED MESOPOROUS BIOACTIVE GLASS
Yu-Ren Wu, Lay Gaik Teoh*, Pei-Hsing Huang and Wei Haw Wu
Department of Mechanical Engineering, National Pingtung University of Science and Technology, Neipu, Pingtung
91201, Taiwan.
Introduction
temperature.
Mesoporous bioactive materials are characterized as
having high specific surface areas and pore volume,
and uniform channel diameters [1-4] have received
much interest for applications in bone tissue
regeneration and drug delivery [3]. Meanwhile,
mesoporous bioactive materials exhibit better in vitro
bone-forming bioactivity compared to conventional
sol-gel derived bioactive glasses [3, 5]. Therefore, it is
speculated that the pore size, pore volume and pore
structure of the bioactive materials play important roles
in their properties.
In this work we demonstrate the synthesis of
mesoporous SiO2-CaO-P2O5 bioactive glass with a
high specific surface area and pore volume produced
by a sol-gel process with Ca, P and Si sources, and
with a combination of surfactant templating by using a
triblock copolymer as the template. The in vitro
bioactivity of the mesoporous SiO2-CaO-P2O5 was also
investigated, demonstrated by formation of apatite
nanocrystals
after
soaking
the
mesoporous
SiO2-CaO-P2O5 in SBF.
Results and Discussion
The TGA curve at the heating rate of 5 °C/min for the
as-synthesized bioactive glass sample synthesized with
a triblock copolymer as the template is depicted in Fig.
1. The TGA result suggests a two-step process: the
desorption of ethanol solution at about 80 °C, the
subsequent loss of the triblock copolymer between 100
and 210 °C. However, the residual triblock copolymer
is incompletely removed from the as-synthesized
bioactive glass upon calcination at 210 °C. Therefore,
the calcination temperature was fixed at 600 °C in the
later experimental design to completely remove this.
Experimental
In a typical synthesis, 2 g of F108 (Aldrich) was
dissolved in 25 ml of ethanol. Afterward tetraethyl
orthosilicate (TEOS, Acros), calcium nitrate
(Ca(NO3)2.4H2O, Aldrich), and triethyl phosphate
(TEP, Aldrich) were used as SiO2, CaO, and P2O5
sources, respectively, and were added under vigorous
stirring for 1 h. The sol was introduced into a petri dish
at room temperature. The gel was aged for 2 days, and
then the dried gel was calcined at 600 °C for 3 h to
obtain the final calcined mesoporous bioactive glass.
The mesostructure of SiO2-CaO-P2O5 obtained was
then investigated by thermogravimetric analysis
(SETSYS Evolution TGA), N2 adsorption-desorption
isotherm measurements (Micromeritics, ASAP 2010),
powder X-ray diffraction (Rigaku, D/max-Ⅳ, using
Cu-Kα radiation), and transmission electron
microscopy (FEGTEM; FEI E.O Tecnai F20 G2
Field-Emission TEM, 200 keV). The assessment of in
vitro bioactivity was carried out in a 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 10 h, the sample was removed from the
SBF, washed with deionized water, and dried at room
Fig. 1. TGA curve of the as-synthesized
SiO2-CaO-P2O5 produced with a triblock copolymer as
the template.
The N2 adsorption-desorption isotherm plot of the
prepared mesoporous bioactive glass was measured
and is shown in Fig. 2, together with the corresponding
pore size distribution. The curve can be identified as a
type IV isotherm with a well-defined P/P0 step between
0.4 and 0.8, which indicates that the mesoporous
bioactive glass has a mesoporous structure. The sample
shows type H1 hysteresis loop between adsorption and
desorption modes, according to BDDT classification,
which is indicative of mesoporous materials with the
characteristic of cylindrical pores open at both ends.
Due to the mesoporous texture, the material exhibits a
high specific surface area, which enhances ion release
from the surface and therefore the bioactivity of the
sample [6]. The pore size distribution is shown in inset
of Fig. 2. The sample presents a single-modal pore size
distribution centered around 5.28 nm. The ordering of
mesoporous channel structures may greatly influence
hydroxyapatite forming ability, the protein adsorption
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World Journal of Engineering
and nutrient-delivery behavior for better in vivo
bioactivity [7], together with presenting the option of
filling the pores with drugs or biological molecules [8].
nm. The electron diffraction pattern (inset in Fig. 4)
indicates clearly visible diffraction rings, whose
interplanar spacings are in good agreement with the
characteristic spacings of an apatite structure. This
supports the result of the XRD result.
Fig. 2. N2 adsorption-desorption isotherm and BJH
pore size distribution curves for mesoporous
SiO2-CaO-P2O5 calcined at 600 °C for 3 h.
Fig. 4. TEM images of mesoporous SiO2-CaO-P2O5
after soaking in SBF for 10 h.
Conclusion
Fig. 3(a) illustrates the wide angle XRD diffraction
pattern of the mesoporous SiO2-CaO-P2O5 bioactive
glass. A broad band between 20 and 30o can be clearly
noted in XRD pattern of mesoporous bioactive glass. It
can be seen that after being calcined at 600 °C for 3 h
the sample almost has an amorphous state, which is
indicative of the internal disorder and glassy nature of
this material.
Highly ordered mesoporous SiO2-CaO-P2O5 bioactive
glass has been obtained by the sol-gel method, using a
nonionic triblock copolymer as the organic template.
The mesostructured SiO2-CaO-P2O5 calcined at 600 °C
has an amorphous form, a specific surface area and
pore volume of 317.24 m2/g and 0.474 cm3/g,
respectively, and with a narrow pore size distribution.
In vitro bioactivity test of the mesoporous
SiO2-CaO-P2O5 shows that it could develop an apatite
layer on the surface after soaking in SBF for 10 h. This
material is an excellent candidate for use in grafts for
bone tissue regeneration.
References
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ordered mesoporous bioactive glasses with superior in vitro
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mesoporous molecular sieves. Science, 267 (1995) 865-867.
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Fig. 3. XRD patterns of mesoporous SiO2-CaO-P2O5
before (a) and after being soaked in SBF for 10 h (b).
The
bone-forming
activity
of
mesoporous
SiO2-CaO-P2O5 in vitro was then tested in SBF to
monitor the formation of apatite on the surface of the
mesoporous SiO2-CaO-P2O5. XRD pattern of the
bioactive glass after soaking in SBF for 10 h is shown
in Fig. 3(b), a diffraction peak at 31.7° emerge,
corresponding to the (211) reflection of hydroxide
apatite. The result indicates that the bioactive glass can
induce the formation of an apatite layer on their
surface in SBF even for short soaking period. This is
consistent with the known superiority of bioactive
glass in their in vitro bone-forming bioactivity.
The bright field (Fig. 4) TEM image reveals that the
surface of the mesoporous SiO2-CaO-P2O5 undergoes
important changes during the reaction with SBF. The
growth of apatite nanocrystals on the surface of the
mesoporous SiO2-CaO-P2O5 can be observed after
soaking for 10 h, and the crystallite size is about 6-8
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