THE PRESENCE OF MgO, MnO, SrO AND ZnO IMPROVING
SURFACE TRANSFORMATIONS ON A STANDARD BIOGLASS
Gilderman S. L., Silmara C. S., Euler A. dos S.
Laboratório de Biomateriais, P²CEM/Universidade Federal de sergipe, São Cristovão (SE), Brasil
E-mail: euler@ufs.br
Abstract. In this study, the synthesis of bioactive glass-based system (SiO2.CaO.Na2O.P2O5) and containing
four different modifiers (SiO2.CaO.Na2O.P2O5.ZnO.MnO.MgO.SrO) were prepared using the method sol-gel.
Tablets were produced from the powder obtained by uniaxial pressing and sintering at 700° C. the bioactivity
was measured by immersion in McCoy's 5A modified medium under sterile conditions at 37° C for 1, 4 and 7
days. TGA / DTA, XRD, DRIFT, and SEM-EDS were used to characterize the changes and the bioglass surface
after immersion. As expected, the introduction of modifiers induced a decrease in crystallization temperature in
comparison with those measured for the standard bioglass. The XRD analysis confirmed the presence of an
amorphous structure as crystalline peaks were not observed. Spectra showed bands DRIFT large vibration
asymmetric and symmetric stretching of Si-O-Si (1090 and 800 cm -1, respectively). After soaking, globular
precipitates appeared gradually coating the entire surface. EDS spectrum also showed a gradual increase of Ca
and P on the surface and a lower Si, suggesting formation of a CaP-rich layer. This behavior was remarkably
pronounced on the bioglass containing modifiers. Spectra showed absorption bands DRIFT additional around
609 cm-1 (v4 O-P-O) and 972 cm-1 (v1 P-O), indicating the formation of a layer of phosphate after immersion.
The XRD, using low angle of incidence have shown no crystalline phase, which would suggest the formation of
an amorphous calcium phosphate or nano crystals. Probably, the breaking of the network caused by the
insertion of glass modifiers facilitated its dissolution and, consequently, the reprecipitation process.
Kenwoods: bioglass, apatite precipitation, sol-gel.
1.
INTRODUCTION
The bioglass biocompatibility has been accessed by its ability in forming an apatite
layer after immersion in biological fluids [KOKUBO and TAKADAMA, 2006]. However, it
is known that not only apatite formation can remarkably affect the cellular metabolism but
also the ionic dissolution products by changing the intracellular ionic concentrations [HOPPE,
GÜLDAL and BOCCACCINI, 2011]. One way of controlling the dissolution and
reprecipitation process is to insert elements called network modifiers into bioglass systems. In
general, these modifiers have a strong ionic character and act disrupting the covalent network
formed by SiO4 and PO4 tetrahedral units, increasing the reactivity of bioglass [ARCOS and
VALLET-REGÍ, 2010]. It is known that some network modifiers are completely involved in
osteogenesis and angiogenesis [HOPPE, GÜLDAL and BOCCACCINI, 2011]. In this sense,
our objective in this work was to evaluate the effect of the insertion of ZnO, MnO, MgO and
SrO in a standard bioglass (SiO2.CaO.Na2O.P2O5) on the dissolution/reprecipitation process
after immersion in a biological fluid.
2.
MATERIALS AND METHODS
A standard bioglass (SiO2.CaO.Na2O.P2O5) and a bioglass containing four different
modifiers (SiO2.CaO.Na2O.P2O5.ZnO.MnO.MgO.SrO), called here of BV and BV4M,
respectively, were prepared using the sol-gel method [SBOORI, RABIEE, et al., 2009]. In
this sense, tetraethyl orthosilicate (TEOS) was hydrolyzed in nitric acid followed by the
addition of triethylphosphate (TEP), under agitation. The other reagents were added
consecutively, under continuous agitation, in amounts shown in table 1. The gel was dried for
10 days and then grounded and sieved. Tablets were produced from the obtained powder by
uni-axial pressing and calcination at 700°C. The samples were immersed in McCoy's 5A
modified medium under sterile conditions at 37°C for 1, 4 and 7 days. TGA/DTA, XRD,
DRIFT and SEM-EDS were used to characterize the bioglass and the surface transformations
after immersion.
Table 1 - Nominal composition of bioglass pattern synthesized by sol-gel.
PRECURSORS
Amount in grams per each 150 mL
of HNO3 0,1 mol L-1
BV
BV4M
(*)
66,646
66,646
4,549
4,549
Ca(NO3)2.4H2O
30,700
29,77
NaNO3
2,125
2,125
Zn(NO3)2
-
1,60 x10-3
Mn(NO3)2.xH2O
-
7,85 x 10-6
Mg(NO3).6H2O
-
0,911
Sr(NO3)2
-
1,71 x 10-2
TEOS
(**)
TEP
3.
RESULTS AND DISCUSSION
From TG/DTA curves was possible to observe three distinct regions of weight loss
(Fig. 1 and 2). The first lost (stage 1) occurred around 60°C at 120oC and was followed by the
appearance of endothermic peaks commonly attributed to the loss of residual water. The
second one (stage 2) was observed around 270°C and corresponded to the chemical
desorption of water, which was accompanied by exothermic peaks. The last one (stage 3)
occurred around 520°C with a large endothermic peak generated by both volatilization of
NO2, CO2 and reactions between remaining alkoxide groups. A small exothermic peak at
924°C and 889°C is observed for BV and BV4M, respectively, corresponding to the
beginning of crystallization [MA, CHEN, et al., 2011; MA, CHEN, et al., 2010].
-0,14
BV
BV4M
-0,12
1
0,3
1
0,2
-0,10
-0,02
0,1
0,0
3
o
3
Weight (%)
Weight (%)
-0,04
2
-0,1
0,00
0
200
400
600
800
-0,2
0,02
1200
1000
Deriv. weight (%/ C)
-0,06
o
Deriv. weight (%/ C)
-0,08
2
0
200
400
600
800
1000
1200
o
Temperature ( C)
o
Temperature ( C)
Figure 1 - TGA curves of the bioglass BV and BV4M after being dried at 120°C, heating rate of 5o min-1.
BV
o
Temperature difference ( C/mg)
*
BV4M
*
0
200
400
600
800
1000
1200
o
Temperature ( C)
Figure 2 – DTA curves of the bioglass BV and BV4M after being
dried at 120°C, heating rate of 5o min-1. Temperature of
crystallization (*).
BV
BV4M
o
900 C
Intensity (u.a.)
Intesity (u.a.)
900oC
800oC
o
800 C
o
10
20
30
2(°)
40
700 C
700 C
600oC
600 C
50
o
o
60
10
20
30
2(°)
Figure 3 - XRD profiles of the bioglasses after sintering in four different temperatures.
40
50
60
Figure 4 - SEM images obtained from bioglasses surface after immersion in culture medium.
The decrease of approximately 35°C seen for the crystallization temperature is
probably related to the presence of the network modifiers in the modified bioglass (BV4M)
[CHIANG, BIRNIEIII and KINGERY, 1997]. According to these results, a sintering
temperature below 800° C would be able to produce a bioglass free of residual synthesis
products and of crystalline phases. Indeed, XRD patterns obtained from samples sintered from
600 to 900° C (fig.3) have confirmed the absence of crystalline phases for the samples
sintered above 800°C.
The SEM images for the bioglasses before and after immersion in McCoy’s 5A
modified medium revealed a gradual deposition of spherical particles on the surfaces along
time (Fig. 4). The precipitated features suggest the formation of apatite layer on the surfaces
[NAYAK, KUMAR and BERA, 2010; AGATHOPOULOS, TULYAGANOVA, et al., 2006].
These precipitates entirely covered the surfaces after 7 days of immersion. This behavior was
markably pronounced on the modified bioglass BV4M, fig.4.
The standard elements from the standard bioglass (Si, Ca, P and Na) were detected by
EDS analysis (Fig.5 and 6). However, the network modifiers were not detected by EDS,
except the Mg (Fig. 6). Probably, the very low quantities added in substitution to the Ca
avoided the detection. The intensities of the Ca and P peaks (Fig. 5 and 6) increased as a
function of immersion time, suggesting the formation of a CaP-rich layer onto bioglasses
surface. At the same time, it was possible to observed a decrease of the Si peak, which lead us
to confirm this gradual CaP precipitation on the surfaces. If we compare the Si peak decrease
in both BV and BV4M along time, it is evident that the precipitation onto BV4M was faster
than onto the BV. It is also observed that Mg signal become more pronounced along time of
immersion indicated that CaP layer can easily incorporate this element from McCoy’s
medium. DRIFT spectra are shown in Fig.7 and 8. The vibrational modes for Si-O-Si can be
observed as a broad absorption band around 500 cm-1 and 1035cm-1 [SBOORI, RABIEE, et
al., 2009; LUCAS-GIROT, MEZAHI, et al., 2011] for all spectra.
Si
O
10000
BV
Ca Control
Ca
P
Si
8000
Intensity (counts.)
Na
O
Ca
P
Na
Ca
1 day
6000
Si
O
4000
2000
Ca
P
Na Mg
Ca
Si
O
0
0
Na Mg
1
Ca
P
2
4 days
Ca
3
4
7 days
5
Binding energy (eV)
Figure 5 –EDS spectra obtained from BV surface before and after immersion
in the McCoy’s 5A modified medium.
Si
10000
BV4M
O
Intensity (counts.)
8000
Ca
P
Na
Ca Control
Si
6000
O
4000
O
Na Mg
Si
Ca
P
Na
Ca
Ca
P
Ca
2000
O
Na Mg
0
0
1
Si
1 day
4 days
Ca
P
Ca
2
3
Binding energy (eV)
7 days
4
5
Transmitânce (%)
1035 870
Si -O-Si
7 days
O -P -O
BV4M
C-O
Si - O- Si
Figure 6 – EDS spectra obtained from BV4M surface before and after
immersion in the McCoy’s 5A modified medium.
609 500
4 days
1 day
Control
2000
1600
1200
-1
Wavernumber (cm )
800
400
Figure 7 – DRIFT spectra of BV4M before (control) and after immersion in
the McCoy’s 5A modified medium.
Tranmitânce (%)
1035 870
4 days
Si - O - Si
O-P-O
7 days
C-O
Si - O - Si
BV
609 500
1day
Control
2000
1600
1200
-1
800
400
Wavernumber (cm )
Figure 8 – DRIFT spectra of BV before (control) and after immersion in the
McCoy’s 5A modified medium.
The main P-O vibration mode rises in the same region of the Si-O-Si one, which can
strongly difficult the identification of the phosphate precipitation onto bioglasses. However,
other phosphate vibration modes around 609 cm-1 (v4 O-P-O) and 972 cm-1 (v1 P-O) can be
observed on the spectra after immersion [LUCAS-GIROT, MEZAHI, et al., 2011; SBOORI,
RABIEE, et al., 2009], confirming the presence of this functional group in the precipitates. A
slight band at 870 cm-1 (related to the C-O vibration mode) indicates the presence of
carbonate in the deposited layer. . This leads us to assume that a carbonated apatite layer was
probably formed on the surfaces during immersion in the culture medium.
4.
CONCLUSIONS
Both standard and modified bioglasses produced in this work have exhibited surface
bioactivity. However, the insertion of the network modifiers in the BV4M seemed to
remarkably improve its surface reactivity relatively to the BV. Probably, the disruption of the
glass network caused by the insertion of the modifiers facilitated its dissolution and,
consequently, the reprecipitation process.
AGRADECIMENTOS
Authors would like to thank the FAPITEC/SE, FAPERJ, CAPES and CNPq for
providing financial support to this project.
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