Ana Candida M. Rodrigues - Academia.edu (original) (raw)
Papers by Ana Candida M. Rodrigues
Journal of the American Ceramic Society
Photo-thermo-refractive (PTR) glass is an optical Na–Al–Zn–K–O–F–Br silicate glass doped with Ag,... more Photo-thermo-refractive (PTR) glass is an optical Na–Al–Zn–K–O–F–Br silicate glass doped with Ag, Ce, Sb, and Sn that undergoes photo-thermo-induced volume crystallization of nanosized NaF responsible for localized refractive index changes. PTR glass has found numerous commercial applications, but the intricate mechanism of photo-thermo crystallization is far from being understood. In this paper, we demonstrate that, additional to crystalline phase precipitation, liquid–liquid phase separation (LLPS), i.e. amorphous droplets embedded in the matrix glass, appears concurrently over a wide range of temperatures. The immiscibility temperature is 925°C. The droplet phase is richer in SiO2, rendering the alkali-rich remaining matrix glass a lower glass transition temperature and a higher electrical conductivity than the original glass. The droplet's surface does not catalyze NaF nucleation. Although the effects of LLPS on optical properties of PTR glass are still to be explored, it co...
Science and Technology of Advanced Materials, 2013
The development of bioactive glass-ceramic materials has been a topic of great interest aiming at... more The development of bioactive glass-ceramic materials has been a topic of great interest aiming at enhancing the mechanical strength of traditional bioactive scaffolds. In the present study, we test and demonstrate the use of Biosilicate R glass-ceramic powder to fabricate bone scaffolds by the foam replica method. Scaffolds possessing the main requirements for use in bone tissue engineering (95% porosity, 200-500 µm pore size) were successfully produced. Gelatine coating was investigated as a simple approach to increase the mechanical competence of the scaffolds. The gelatine coating did not affect the interconnectivity of the pores and did not significantly affect the bioactivity of the Biosilicate R scaffold. The gelatine coating significantly improved the compressive strength (i.e. 0.80 ± 0.05 MPa of coated versus 0.06 ± 0.01 MPa of uncoated scaffolds) of the Biosilicate R scaffold. The combination of Biosilicate R glass-ceramic and gelatine is attractive for producing novel scaffolds for bone tissue engineering.
Journal of Materials Science: Materials in Medicine, 2015
The aim of this study was to evaluate the effects of highly porous Biosilicate Ò scaffolds on bon... more The aim of this study was to evaluate the effects of highly porous Biosilicate Ò scaffolds on bone healing in a tibial bone defect model in rats by means of histological evaluation (histopathological and immunohistochemistry analysis) of the bone callus and the systemic inflammatory response (immunoenzymatic assay). Eighty Wistar rats (12 weeks-old, weighing ±300 g) were randomly divided into 2 groups (n = 10 per experimental group, per time point): control group and Biosilicate Ò group (BG). Each group was euthanized 3, 7, 14 and 21 days post-surgery. Histological findings revealed a similar inflammatory response in both experimental groups, 3 and 7 days post-surgery. During the experimental periods (3-21 days post-surgery), it was observed that the biomaterial degradation, mainly in the periphery region, provided the development of the newly formed bone into the scaffolds. Immunohistochemistry analysis demonstrated that the Biosilicate Ò scaffolds stimulated cyclooxygenase-2, vascular endothelial growth factor and runtrelated transcription factor 2 expression. Furthermore, in the immunoenzymatic assay, BG presented no difference in the level of tumor necrosis factor alpha in all experimental periods. Still, BG showed a higher level of interleukin 4 after 14 days post-implantation and a lower level of interleukin 10 in 21 days post-surgery. Our results demonstrated that Biosilicate Ò scaffolds can contribute for bone formation through a suitable architecture and by stimulating the synthesis of markers related to the bone repair.
BioMed Research International, 2013
After an introduction showing the growing interest in glasses and glass-ceramics as biomaterials ... more After an introduction showing the growing interest in glasses and glass-ceramics as biomaterials used for bone healing, we describe a new biomaterial named Biosilicate. Biosilicate is the designation of a group of fully crystallized glass-ceramics of the Na 2 O-CaO-SiO 2 -P 2 O 5 system. Several in vitro tests have shown that Biosilicate is a very active biomaterial and that the HCA layer is formed in less than 24 hours of exposure to "simulated body fluid" (SBF) solution. Also, in vitro studies with osteoblastic cells have shown that Biosilicate disks supported significantly larger areas of calcified matrix compared to 45S5 Bioglass, indicating that this bioactive glass-ceramic may promote enhancement of in vitro bone-like tissue formation in osteogenic cell cultures. Finally, due to its special characteristics, Biosilicate has also been successfully tested in several in vivo studies. These studies revealed that the material is biocompatible, presents excellent bioactive properties, and is effective to stimulate the deposition of newly formed bone in animal models. All these data highlight the huge potential of Biosilicate to be used in bone regeneration applications.
Journal of Non-Crystalline Solids, 2003
We followed the first stages of liquid-liquid phase separation in an alkali-borosilicate glass by... more We followed the first stages of liquid-liquid phase separation in an alkali-borosilicate glass by complex impedance spectroscopy at constant temperatures below and above the glass transition temperature, T g . We found a new feature of the electrical conductivity behavior: at temperatures below T g , the electrical conductivity, r, diminished with time, while above T g , the electrical conductivity increased. The activation energy, E a , for electrical conductivity was largest for samples heat-treated below T g . Other techniques, such as simultaneous small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), and transmission electron microscopy (TEM) were also used. After annealing the glass inside the immiscibility gap, TEM shows a structure with a few Angstroms in size. Above and below the glass transition temperature, in situ SAXS isothermal experiments show an increase of the scattered intensity with time, while WAXS confirms that no crystallization occurred. These facts suggest that glass heat treated below T g develops a SiO 2 rich matrix with lower electrical conductivity and isolated sodium-rich regions. Annealing above T g (of the quenched glass) seems to produce an interconnected Na-rich phase, which dominates the electrical conductivity.
The respective contributions of the charge carrier concentration and mobility to the ionic conduc... more The respective contributions of the charge carrier concentration and mobility to the ionic
conductivity in glasses remain an open question. In the present work we calculate these two
parameters from conductivity data as a function of temperature below and above the glass transition
temperature, Tg. The basic hypothesis assumes that ionic displacement results from the migration of
cationic pairs formed by a partial dissociation, which is a temperature-activated process. Below Tg
their migration would follow a temperature-activated mechanism, while a free volume mechanism
prevails above this temperature, leading to a deviation from the Arrhenius behavior. Expressions are
formulated for the variation in ionic conductivity as a function of temperature in the supercooled and
glassy states. Fitting the experimental data with the proposed expressions allows for the
determination of characteristic parameters such as the charge carrier formation and migration
enthalpies. Based on these values, it is then possible to calculate the charge carrier concentration and
mobility in the entire temperature range. At room temperature, the mobility of effective charge
carriers is estimated close to 10−4 cm2 s−1 V−1 for alkali disilicates glasses under study, while the
ratio between the number of effective charge carriers and the total number of alkali cations is
estimated to be from 10−8 to 10−10, comparable to the concentration of intrinsic defects in an ionic
crystal or dissociated species from a weak electrolyte solution
Conductivity data of the xAgI(1 − x)AgPO3 system (0 ≤ x ≤ 0.5) were collected in the liquid and g... more Conductivity data of the xAgI(1 − x)AgPO3 system (0 ≤ x ≤ 0.5) were collected in the liquid and
glassy states. The difference in the dependence of ionic conductivity on temperature below and above
their glass transition temperatures (Tg) is interpreted by a discontinuity in the charge carrier’s mobility
mechanisms. Charge carrier displacement occurs through an activated mechanism below Tg and
through a Vogel-Fulcher-Tammann-Hesse mechanism above this temperature. Fitting conductivity
data with the proposed model allows one to determine separately the enthalpies of charge carrier formation
and migration. For the five investigated compositions, the enthalpy of charge carrier formation
is found to decrease, with x, from 0.86 to 0.2 eV, while the migration enthalpy remains constant at
≈0.14 eV. Based on these values, the charge carrier mobility and concentration in the glassy state
can then be calculated. Mobility values at room temperature (≈10−4 cm2 V−1 s−1) do not vary significantly
with the AgI content and are in good agreement with those previously measured by the
Hall-effect technique. The observed increase in ionic conductivity with x would thus only be due to
an increase in the effective charge carrier concentration. Considering AgI as a weak electrolyte, the
change in the effective charge carrier concentration is justified and is correlated to the partial free energy
of silver iodide forming a regular solution with AgPO3
A microscopic interpretation is developed of the temperature dependence of viscosity above the gl... more A microscopic interpretation is developed of the temperature dependence of viscosity above the glass transition range,
validating the representation of experimental data by a “hybrid” equation, which is a product of Arrhenius and Vogel–
Fulcher–Tamman–Hesse (VFTH) exponential terms. By employing this hybrid equation to fit experimental viscosity
data for lithium, sodium, and potassium disilicates, we found an activation energy of Eη
A≈1·2 eV for the Arrhenius term.
We propose that this energy is representative of the exchange of nonbridging oxygen atoms between adjacent SiO4 tetrahedra,
allowing for consecutive relaxations of macromolecular silicate chains. Based on a free volume interpretation
of the VFTH term, we also calculated the free volume required for chain movement, which, according to our results, is
about 30% of the intrinsic volume of chain segments. This relatively low free volume may indicate the occurrence of
limited rotational or translational displacements during viscous flow. These results are discussed and compared with the
activation enthalpies and free volumes determined for ionic transport in the same alkali disilicate glasses considering a
similar “hybrid” equation for electrical conductivity
![Research paper thumbnail of Erratum to “Crystallization kinetics of 1Na2O·2CaO·3SiO2 glass monitored by electrical conductivity measurements” [J. Non-Cryst. Solids 353 (2007) 2237–2243]](https://attachments.academia-assets.com/44673838/thumbnails/1.jpg)
](Journal of Non-Crystalline Solids, 2008
Erratum to ''Crystallization kinetics of 1Na 2 O Á 2CaO Á 3SiO 2 glass monitored by electrical co... more Erratum to ''Crystallization kinetics of 1Na 2 O Á 2CaO Á 3SiO 2 glass monitored by electrical conductivity measurements" [J. Non-Cryst. Solids 353 (2007) 2237-2243
Journal of Non-Crystalline Solids, 2007
We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glas... more We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glass with composition close to the stoichiometric 1Na 2 O AE 2CaO AE 3SiO 2 . The nucleation and subsequent growth of sodium-rich crystals in this glass decreases the sodium content in the glassy matrix, drastically hindering further nucleation and growth. Compositional changes of the crystals and glassy matrix at different stages of the crystallization process were determined by EDS. These compositional variations were also monitored by electrical conductivity measurements, carried out by impedance spectroscopy, in glassy, partially, and fully crystallized samples. The electrical conductivity of both crystalline and glassy phases decreases with the increase of the crystallized volume fraction. Starting at a crystallized volume fraction of about 0.5, the crystalline phase dominates the electrical conductivity of the sample. This behavior was corroborated by an analysis of the activation energy for conduction. We show that electrical conductivity is highly sensitive and can indicate compositional shifts, changes in the spatial distribution of mobile ions in the glassy matrix. Conductivity measurements are thus a powerful tool for the investigation of complex heterogeneous systems, such as partially crystallized glasses and glass-ceramics.
Journal of the American Ceramic Society
Photo-thermo-refractive (PTR) glass is an optical Na–Al–Zn–K–O–F–Br silicate glass doped with Ag,... more Photo-thermo-refractive (PTR) glass is an optical Na–Al–Zn–K–O–F–Br silicate glass doped with Ag, Ce, Sb, and Sn that undergoes photo-thermo-induced volume crystallization of nanosized NaF responsible for localized refractive index changes. PTR glass has found numerous commercial applications, but the intricate mechanism of photo-thermo crystallization is far from being understood. In this paper, we demonstrate that, additional to crystalline phase precipitation, liquid–liquid phase separation (LLPS), i.e. amorphous droplets embedded in the matrix glass, appears concurrently over a wide range of temperatures. The immiscibility temperature is 925°C. The droplet phase is richer in SiO2, rendering the alkali-rich remaining matrix glass a lower glass transition temperature and a higher electrical conductivity than the original glass. The droplet's surface does not catalyze NaF nucleation. Although the effects of LLPS on optical properties of PTR glass are still to be explored, it co...
Science and Technology of Advanced Materials, 2013
The development of bioactive glass-ceramic materials has been a topic of great interest aiming at... more The development of bioactive glass-ceramic materials has been a topic of great interest aiming at enhancing the mechanical strength of traditional bioactive scaffolds. In the present study, we test and demonstrate the use of Biosilicate R glass-ceramic powder to fabricate bone scaffolds by the foam replica method. Scaffolds possessing the main requirements for use in bone tissue engineering (95% porosity, 200-500 µm pore size) were successfully produced. Gelatine coating was investigated as a simple approach to increase the mechanical competence of the scaffolds. The gelatine coating did not affect the interconnectivity of the pores and did not significantly affect the bioactivity of the Biosilicate R scaffold. The gelatine coating significantly improved the compressive strength (i.e. 0.80 ± 0.05 MPa of coated versus 0.06 ± 0.01 MPa of uncoated scaffolds) of the Biosilicate R scaffold. The combination of Biosilicate R glass-ceramic and gelatine is attractive for producing novel scaffolds for bone tissue engineering.
Journal of Materials Science: Materials in Medicine, 2015
The aim of this study was to evaluate the effects of highly porous Biosilicate Ò scaffolds on bon... more The aim of this study was to evaluate the effects of highly porous Biosilicate Ò scaffolds on bone healing in a tibial bone defect model in rats by means of histological evaluation (histopathological and immunohistochemistry analysis) of the bone callus and the systemic inflammatory response (immunoenzymatic assay). Eighty Wistar rats (12 weeks-old, weighing ±300 g) were randomly divided into 2 groups (n = 10 per experimental group, per time point): control group and Biosilicate Ò group (BG). Each group was euthanized 3, 7, 14 and 21 days post-surgery. Histological findings revealed a similar inflammatory response in both experimental groups, 3 and 7 days post-surgery. During the experimental periods (3-21 days post-surgery), it was observed that the biomaterial degradation, mainly in the periphery region, provided the development of the newly formed bone into the scaffolds. Immunohistochemistry analysis demonstrated that the Biosilicate Ò scaffolds stimulated cyclooxygenase-2, vascular endothelial growth factor and runtrelated transcription factor 2 expression. Furthermore, in the immunoenzymatic assay, BG presented no difference in the level of tumor necrosis factor alpha in all experimental periods. Still, BG showed a higher level of interleukin 4 after 14 days post-implantation and a lower level of interleukin 10 in 21 days post-surgery. Our results demonstrated that Biosilicate Ò scaffolds can contribute for bone formation through a suitable architecture and by stimulating the synthesis of markers related to the bone repair.
BioMed Research International, 2013
After an introduction showing the growing interest in glasses and glass-ceramics as biomaterials ... more After an introduction showing the growing interest in glasses and glass-ceramics as biomaterials used for bone healing, we describe a new biomaterial named Biosilicate. Biosilicate is the designation of a group of fully crystallized glass-ceramics of the Na 2 O-CaO-SiO 2 -P 2 O 5 system. Several in vitro tests have shown that Biosilicate is a very active biomaterial and that the HCA layer is formed in less than 24 hours of exposure to "simulated body fluid" (SBF) solution. Also, in vitro studies with osteoblastic cells have shown that Biosilicate disks supported significantly larger areas of calcified matrix compared to 45S5 Bioglass, indicating that this bioactive glass-ceramic may promote enhancement of in vitro bone-like tissue formation in osteogenic cell cultures. Finally, due to its special characteristics, Biosilicate has also been successfully tested in several in vivo studies. These studies revealed that the material is biocompatible, presents excellent bioactive properties, and is effective to stimulate the deposition of newly formed bone in animal models. All these data highlight the huge potential of Biosilicate to be used in bone regeneration applications.
Journal of Non-Crystalline Solids, 2003
We followed the first stages of liquid-liquid phase separation in an alkali-borosilicate glass by... more We followed the first stages of liquid-liquid phase separation in an alkali-borosilicate glass by complex impedance spectroscopy at constant temperatures below and above the glass transition temperature, T g . We found a new feature of the electrical conductivity behavior: at temperatures below T g , the electrical conductivity, r, diminished with time, while above T g , the electrical conductivity increased. The activation energy, E a , for electrical conductivity was largest for samples heat-treated below T g . Other techniques, such as simultaneous small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), and transmission electron microscopy (TEM) were also used. After annealing the glass inside the immiscibility gap, TEM shows a structure with a few Angstroms in size. Above and below the glass transition temperature, in situ SAXS isothermal experiments show an increase of the scattered intensity with time, while WAXS confirms that no crystallization occurred. These facts suggest that glass heat treated below T g develops a SiO 2 rich matrix with lower electrical conductivity and isolated sodium-rich regions. Annealing above T g (of the quenched glass) seems to produce an interconnected Na-rich phase, which dominates the electrical conductivity.
The respective contributions of the charge carrier concentration and mobility to the ionic conduc... more The respective contributions of the charge carrier concentration and mobility to the ionic
conductivity in glasses remain an open question. In the present work we calculate these two
parameters from conductivity data as a function of temperature below and above the glass transition
temperature, Tg. The basic hypothesis assumes that ionic displacement results from the migration of
cationic pairs formed by a partial dissociation, which is a temperature-activated process. Below Tg
their migration would follow a temperature-activated mechanism, while a free volume mechanism
prevails above this temperature, leading to a deviation from the Arrhenius behavior. Expressions are
formulated for the variation in ionic conductivity as a function of temperature in the supercooled and
glassy states. Fitting the experimental data with the proposed expressions allows for the
determination of characteristic parameters such as the charge carrier formation and migration
enthalpies. Based on these values, it is then possible to calculate the charge carrier concentration and
mobility in the entire temperature range. At room temperature, the mobility of effective charge
carriers is estimated close to 10−4 cm2 s−1 V−1 for alkali disilicates glasses under study, while the
ratio between the number of effective charge carriers and the total number of alkali cations is
estimated to be from 10−8 to 10−10, comparable to the concentration of intrinsic defects in an ionic
crystal or dissociated species from a weak electrolyte solution
Conductivity data of the xAgI(1 − x)AgPO3 system (0 ≤ x ≤ 0.5) were collected in the liquid and g... more Conductivity data of the xAgI(1 − x)AgPO3 system (0 ≤ x ≤ 0.5) were collected in the liquid and
glassy states. The difference in the dependence of ionic conductivity on temperature below and above
their glass transition temperatures (Tg) is interpreted by a discontinuity in the charge carrier’s mobility
mechanisms. Charge carrier displacement occurs through an activated mechanism below Tg and
through a Vogel-Fulcher-Tammann-Hesse mechanism above this temperature. Fitting conductivity
data with the proposed model allows one to determine separately the enthalpies of charge carrier formation
and migration. For the five investigated compositions, the enthalpy of charge carrier formation
is found to decrease, with x, from 0.86 to 0.2 eV, while the migration enthalpy remains constant at
≈0.14 eV. Based on these values, the charge carrier mobility and concentration in the glassy state
can then be calculated. Mobility values at room temperature (≈10−4 cm2 V−1 s−1) do not vary significantly
with the AgI content and are in good agreement with those previously measured by the
Hall-effect technique. The observed increase in ionic conductivity with x would thus only be due to
an increase in the effective charge carrier concentration. Considering AgI as a weak electrolyte, the
change in the effective charge carrier concentration is justified and is correlated to the partial free energy
of silver iodide forming a regular solution with AgPO3
A microscopic interpretation is developed of the temperature dependence of viscosity above the gl... more A microscopic interpretation is developed of the temperature dependence of viscosity above the glass transition range,
validating the representation of experimental data by a “hybrid” equation, which is a product of Arrhenius and Vogel–
Fulcher–Tamman–Hesse (VFTH) exponential terms. By employing this hybrid equation to fit experimental viscosity
data for lithium, sodium, and potassium disilicates, we found an activation energy of Eη
A≈1·2 eV for the Arrhenius term.
We propose that this energy is representative of the exchange of nonbridging oxygen atoms between adjacent SiO4 tetrahedra,
allowing for consecutive relaxations of macromolecular silicate chains. Based on a free volume interpretation
of the VFTH term, we also calculated the free volume required for chain movement, which, according to our results, is
about 30% of the intrinsic volume of chain segments. This relatively low free volume may indicate the occurrence of
limited rotational or translational displacements during viscous flow. These results are discussed and compared with the
activation enthalpies and free volumes determined for ionic transport in the same alkali disilicate glasses considering a
similar “hybrid” equation for electrical conductivity
Journal of Non-Crystalline Solids, 2008
Erratum to ''Crystallization kinetics of 1Na 2 O Á 2CaO Á 3SiO 2 glass monitored by electrical co... more Erratum to ''Crystallization kinetics of 1Na 2 O Á 2CaO Á 3SiO 2 glass monitored by electrical conductivity measurements" [J. Non-Cryst. Solids 353 (2007) 2237-2243
Journal of Non-Crystalline Solids, 2007
We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glas... more We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glass with composition close to the stoichiometric 1Na 2 O AE 2CaO AE 3SiO 2 . The nucleation and subsequent growth of sodium-rich crystals in this glass decreases the sodium content in the glassy matrix, drastically hindering further nucleation and growth. Compositional changes of the crystals and glassy matrix at different stages of the crystallization process were determined by EDS. These compositional variations were also monitored by electrical conductivity measurements, carried out by impedance spectroscopy, in glassy, partially, and fully crystallized samples. The electrical conductivity of both crystalline and glassy phases decreases with the increase of the crystallized volume fraction. Starting at a crystallized volume fraction of about 0.5, the crystalline phase dominates the electrical conductivity of the sample. This behavior was corroborated by an analysis of the activation energy for conduction. We show that electrical conductivity is highly sensitive and can indicate compositional shifts, changes in the spatial distribution of mobile ions in the glassy matrix. Conductivity measurements are thus a powerful tool for the investigation of complex heterogeneous systems, such as partially crystallized glasses and glass-ceramics.