Publications by authors named "Edgar D Zanotto"

26 Publications

  • Page 1 of 1

Direct determination of Lennard-Jones crystal surface free energy by a computational cleavage method.

J Chem Phys 2021 Sep;155(9):094101

Department of Materials Engineering, Federal University of São Carlos, Via Washington Luiz, km. 235, 13.565-905 São Carlos, SP, Brazil.

The surface free energy of solids, γ, plays a crucial role in all physical and chemical processes involving material surfaces. For the first time, we obtained γ directly from molecular dynamics simulations using a crystal cleavage method. The approach was successfully realized in a Lennard-Jones system by inserting two movable external walls, each consisting of a single crystal layer, into a bulk crystal to create flat, defect-free surfaces. The cleavage technique designed allowed us to calculate the surface free energy according to its definition and avoid surface premelting. The temperature dependence of γ was determined for the (100) and (110) crystal planes along the whole sublimation line and its metastable extension, up to T = 1.02 · T, where T is the melting point. Good agreement with indirect values of γ(T) was found. The proposed computational cleavage method can be applied to other solids of interest, providing valuable insight into the understanding of chemical and physical surface processes, and demonstrates the successful import of the cleavage method, traditionally used in technical preparation and study of crystal surfaces, into a modern atomistic simulation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/5.0059882DOI Listing
September 2021

Optimizing the microstructure of a new machinable bioactive glass-ceramic.

J Mech Behav Biomed Mater 2021 10 13;122:104695. Epub 2021 Jul 13.

Vitreous Materials Laboratory, Materials Engineering Department, Federal University of São Carlos, São Carlos, SP, Brazil.

Objectives: This study aimed to optimize the crystallization process and the microstructure of a new bioactive glass-ceramic (GC) previously developed by our research group to obtain machinable glass-ceramics.

Methods: Differential scanning calorimetry (DSC) analyses were conducted to explore the characteristic temperatures and construct a semi-quantitative nucleation curve. The GC specimens were characterized by X-ray diffraction (XRD) and Rietveld refinement. Their brittleness index (B) and machinability were characterized and compared with IPS e.max-CAD®. Their Young's modulus, fracture toughness, and hardness were assessed.

Results: We found that the maximum crystal nucleation rate temperature of this GC is ~470 °C. Treatments were designed based on the 1st DSC peak onset (570 °C), 1st peak offset (650 °C), and 2nd peak offset (705 °C) crystallization temperatures of lithium metasilicate (LS, LiSiO) and lithium disilicate (LS2, LiSiO). Rietveld refinement indicated an increase in LS2 and a reduction in LS and amorphous phase for increased temperatures and longer treatment times. Their B values indicate good machinability compared with that of the control group based on statistical analyses. As expected, lower levels of LS2 increase the machinability regardless of the rotation speed adopted, leading to a greater depth of cut and reduced Edge Chipping Damage Depth (ECDD).

Conclusion: This bioactive GC with optimized microstructure presents high machinability. For treatment temperatures above 570 °C, the number of elongated LS2 crystals increases and decreases the amorphous phase content, which reduce the machinability of the GC, and should therefore be avoided. The best results were obtained using heat treatment at 570 °C, which produces LS crystals embedded in a glassy matrix (67%) with small contents of secondary phases.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jmbbm.2021.104695DOI Listing
October 2021

Effects of Glass Transition and Structural Relaxation on Crystal Nucleation: Theoretical Description and Model Analysis.

Entropy (Basel) 2020 Sep 29;22(10). Epub 2020 Sep 29.

Vitreous Materials Laboratory, Department of Materials Engineering, Federal University of São Carlos, UFSCar, São Carlos 13565-905, SP, Brazil.

In the application of classical nucleation theory (CNT) and all other theoretical models of crystallization of liquids and glasses it is always assumed that nucleation proceeds only after the supercooled liquid or the glass have completed structural relaxation processes towards the metastable equilibrium state. Only employing such an assumption, the thermodynamic driving force of crystallization and the surface tension can be determined in the way it is commonly performed. The present paper is devoted to the theoretical treatment of a different situation, when nucleation proceeds concomitantly with structural relaxation. To treat the nucleation kinetics theoretically for such cases, we need adequate expressions for the thermodynamic driving force and the surface tension accounting for the contributions caused by the deviation of the supercooled liquid from metastable equilibrium. In the present paper, such relations are derived. They are expressed via deviations of structural order parameters from their equilibrium values. Relaxation processes result in changes of the structural order parameters with time. As a consequence, the thermodynamic driving force and surface tension, and basic characteristics of crystal nucleation, such as the work of critical cluster formation and the steady-state nucleation rate, also become time-dependent. We show that this scenario may be realized in the vicinity and below the glass transition temperature, and it may occur only if diffusion (controlling nucleation) and viscosity (controlling the alpha-relaxation process) in the liquid decouple. Analytical estimates are illustrated and confirmed by numerical computations for a model system. The theory is successfully applied to the interpretation of experimental data. Several further consequences of this newly developed theoretical treatment are discussed in detail. In line with our previous investigations, we reconfirm that only when the characteristic times of structural relaxation are of similar order of magnitude or longer than the characteristic times of crystal nucleation, elastic stresses evolving in nucleation may significantly affect this process. Advancing the methods of theoretical analysis of elastic stress effects on nucleation, for the first time expressions are derived for the dependence of the surface tension of critical crystallites on elastic stresses. As the result, a comprehensive theoretical description of crystal nucleation accounting appropriately for the effects of deviations of the liquid from the metastable states and of relaxation on crystal nucleation of glass-forming liquids, including the effect of simultaneous stress evolution and stress relaxation on nucleation, is now available. As one of its applications, this theoretical treatment provides a new tool for the explanation of the low-temperature anomaly in nucleation in silicate and polymer glasses (the so-called "breakdown" of CNT at temperatures below the temperature of the maximum steady-state nucleation rate). We show that this anomaly results from much more complex features of crystal nucleation in glasses caused by deviations from metastable equilibrium (resulting in changes of the thermodynamic driving force, the surface tension, and the work of critical cluster formation, in the necessity to account of structural relaxation and stress effects) than assumed so far. If these effects are properly accounted for, then CNT appropriately describes both the initial, the intermediate, and the final states of crystal nucleation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/e22101098DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7597199PMC
September 2020

Crystallization of Supercooled Liquids: Self-Consistency Correction of the Steady-State Nucleation Rate.

Entropy (Basel) 2020 May 16;22(5). Epub 2020 May 16.

Vitreous Materials Laboratory, Department of Materials Engineering, Federal University of São Carlos, UFSCar, 13565-905 São Carlos-SP, Brazil.

Crystal nucleation can be described by a set of kinetic equations that appropriately account for both the thermodynamic and kinetic factors governing this process. The mathematical analysis of this set of equations allows one to formulate analytical expressions for the basic characteristics of nucleation, i.e., the steady-state nucleation rate and the steady-state cluster-size distribution. These two quantities depend on the work of formation, Δ G ( n ) = - n Δ μ + γ n 2 / 3 , of crystal clusters of size and, in particular, on the work of critical cluster formation, Δ G ( n c ) . The first term in the expression for Δ G ( n ) describes changes in the bulk contributions (expressed by the chemical potential difference, Δ μ ) to the Gibbs free energy caused by cluster formation, whereas the second one reflects surface contributions (expressed by the surface tension, σ : γ = Ω d 0 2 σ , Ω = 4 π ( 3 / 4 π ) 2 / 3 , where d 0 is a parameter describing the size of the particles in the liquid undergoing crystallization), is the number of particles (atoms or molecules) in a crystallite, and n = n c defines the size of the critical crystallite, corresponding to the maximum (in general, a saddle point) of the Gibbs free energy, . The work of cluster formation is commonly identified with the difference between the Gibbs free energy of a system containing a cluster with particles and the homogeneous initial state. For the formation of a "cluster" of size n = 1 , no work is required. However, the commonly used relation for Δ G ( n ) given above leads to a finite value for n = 1 . By this reason, for a correct determination of the work of cluster formation, a self-consistency correction should be introduced employing instead of Δ G ( n ) an expression of the form Δ G ˜ ( n ) = Δ G ( n ) - Δ G ( 1 ) . Such self-consistency correction is usually omitted assuming that the inequality Δ G ( n ) ≫ Δ G ( 1 ) holds. In the present paper, we show that: (i) This inequality is frequently not fulfilled in crystal nucleation processes. (ii) The form and the results of the numerical solution of the set of kinetic equations are not affected by self-consistency corrections. However, (iii) the predictions of the analytical relations for the steady-state nucleation rate and the steady-state cluster-size distribution differ considerably in dependence of whether such correction is introduced or not. In particular, neglecting the self-consistency correction overestimates the work of critical cluster formation and leads, consequently, to far too low theoretical values for the steady-state nucleation rates. For the system studied here as a typical example (lithium disilicate, Li 2 O · 2 SiO 2 ), the resulting deviations from the correct values may reach 20 orders of magnitude. Consequently, neglecting self-consistency corrections may result in severe errors in the interpretation of experimental data if, as it is usually done, the analytical relations for the steady-state nucleation rate or the steady-state cluster-size distribution are employed for their determination.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/e22050558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7517078PMC
May 2020

Effect of bioactive Biosilicate /F18 glass scaffolds on osteogenic differentiation of human adipose stem cells.

J Biomed Mater Res A 2021 08 11;109(8):1293-1308. Epub 2020 Nov 11.

CeRTEV-Center for Research, Technology, and Education in Vitreous Materials, Vitreous Materials Laboratory (LaMaV), Department of Materials Engineering (DEMA), Graduate Program in Materials Science and Engineering, Federal University of São Carlos (UFSCar), São Carlos, Brazil.

This study evaluated the gene expression profile of the human adipose-derived stem cells (hASCs) grown on the Biosilicate /F18 glass (BioS-2P/F18) scaffolds. hASCs were cultured using the osteogenic medium (control), the scaffolds, and their ionic extract. We observed that ALP activity was higher in hASCs grown on the BioS-2P/F18 scaffolds than in hASCs cultured with the ionic extract or the osteogenic medium on day 14. Moreover, the dissolution product group and the control exhibited deposited calcium, which peaked on day 21. Gene expression profiles of cell cultured using the BioS-2P/F18 scaffolds and their extract were evaluated in vitro using the RT Profiler polymerase chain reaction (PCR) microarray on day 21. Mineralizing tissue-associated proteins, differentiation factors, and extracellular matrix enzyme expressions were measured using quantitative PCR. The gene expression of different proteins involved in osteoblast differentiation was significantly up-regulated in hASCs grown on the scaffolds, especially BMP1, BMP2, SPP1, BMPR1B, ITGA1, ITGA2, ITGB1, SMAD1, and SMAD2, showing that both the composition and topographic features of the biomaterial could stimulate osteogenesis. This study demonstrated that gene expression of hASCs grown on the scaffold surface showed significantly increased gene expression related to hASCs cultured with the ionic extract or the osteogenic medium, evidencing that the BioS-2P/F18 scaffolds have a substantial effect on cellular behavior of hASCs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jbm.a.37122DOI Listing
August 2021

Development and evaluation of reparative tricalcium silicate-ZrO -Biosilicate composites.

J Biomed Mater Res B Appl Biomater 2021 04 28;109(4):468-476. Epub 2020 Aug 28.

Department of Restorative Dentistry, School of Dentistry, São Paulo State University (UNESP), Araraquara, Sao Paulo, Brazil.

Biosilicate is a bioactive glass-ceramic used in medical and dental applications. This study evaluated novel reparative materials composed of pure tricalcium silicate (TCS), 30% zirconium oxide (ZrO ) and 10 or 20% biosilicate, in comparison with Biodentine. Setting time was evaluated based on ISO 6876 standard, radiopacity by radiographic analysis, solubility by mass loss, and pH by using a pH meter. Cytotoxicity was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and NR assays. Alkaline phosphatase (ALP) activity and alizarin red were used to evaluate cell bioactivity. Antimicrobial activity was assessed on Enterococcus faecalis by the direct contact test. The data were submitted to analysis of variance (ANOVA)/Tukey; Bonferroni and Kruskal-Wallis, and Dunn tests (α = 0.05). The association of Biosilicate with TCS + ZrO had appropriate setting time, radiopacity, and solubility, alkaline pH, and antimicrobial activity. TCS and Biodentine showed higher ALP activity in 14 days than the control (serum-free medium). All cements produced mineralized nodules. In conclusion, Biosilicate + TCS ZrO decreased the setting time and increased the radiopacity in comparison to TCS. Biosilicate + TCS ZrO2 presented lower solubility and higher radiopacity than Biodentine. In addition, these experimental cements promoted antimicrobial activity and mineralization nodules formation, suggesting their potential for clinical use.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jbm.b.34714DOI Listing
April 2021

Crystal Nucleation Kinetics in Supercooled Germanium: MD Simulations versus Experimental Data.

J Phys Chem B 2020 Sep 31;124(36):7979-7988. Epub 2020 Aug 31.

Department of Physics, Federal University of São Carlos, via Washington Luiz, km. 235, 13565-905 São Carlos, São Paulo, Brazil.

The validity of the classical nucleation theory (CNT), the most important tool to describe and predict nucleation kinetics in supercooled liquids, has been at stake for almost a century. Here, we carried out comprehensive molecular dynamics simulations of the nucleation kinetics of a fast quenched supercooled germanium using the Stillinger-Weber potential at six temperatures, covering a supercooling range of / = 0.70-0.86, where is the equilibrium melting temperature. We used the seeding method to determine the number of particles in the critical crystal nuclei at each supercooling, which yielded = 150-1300 atoms. The transport coefficient at the liquid/nucleus interface and the melting point were also obtained from the simulations. Using the parameters resulting directly from the simulations, the CNT embraces the experimental nucleation rates, (), with the following fitted (average) values of the nucleus/liquid interfacial free energy: γ = 0.244 and 0.201 J/m, for the experimental and calculated values of thermodynamic driving force, Δμ(), respectively, which are close to the value obtained from (). Without using any fit parameter, the calculated nucleation rates for the experimental and calculated values of Δμ() embrace the experimental () curve. Therefore, this finding favors the validity of the CNT.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.jpcb.0c05480DOI Listing
September 2020

Understanding Glass through Differential Scanning Calorimetry.

Chem Rev 2019 Jul 23;119(13):7848-7939. Epub 2019 May 23.

School of Materials Science and Engineering , Qilu University of Technology (Shandong Academy of Sciences) , Jinan 250353 , China.

Differential scanning calorimetry (DSC) is a powerful tool to address some of the most challenging issues in glass science and technology, such as the nonequilibrium nature of the glassy state and the detailed thermodynamics and kinetics of glass-forming systems during glass transition, relaxation, rejuvenation, polyamorphic transition, and crystallization. The utility of the DSC technique spans across all glass-forming chemistries, including oxide, chalcogenide, metallic, and organic systems, as well as recently discovered metal-organic framework glass-forming systems. Here we present a comprehensive review of the many applications of DSC in glass science with focus on glass transition, relaxation, polyamorphism, and crystallization phenomena. We also emphasize recent advances in DSC characterization technology, including flash DSC and temperature-modulated DSC. This review demonstrates how DSC studies have led to a multitude of relevant advances in the understanding of glass physics, chemistry, and even technology.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.chemrev.8b00510DOI Listing
July 2019

In vitro biocompatibility of new bioactive lithia-silica glass-ceramics.

Mater Sci Eng C Mater Biol Appl 2019 Jan 5;94:117-125. Epub 2018 Sep 5.

Laboratório de Materiais Vítreos, Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, São Carlos, SP, Brazil.

Glass-ceramics based on the LiO-SiO system have been extensively used as restorative dental materials due to their excellent chemical durability, aesthetics, inertness in the buccal environment, and high fracture strength; but they are not bioactive. On the other hand, all known bioactive glasses show ability to bond to bone, teeth and cartilage coupled to osteoconduction and osteoinduction, but their fracture strength and toughness are rather low. The aim of this study is to develop and evaluate the in vitro biocompatibility of a new type of (bioactive and strong) lithia-silica glass-ceramic. For these purposes, two types of glass-ceramics based on a multicomponent lithia-silica system were studied: lithium metasilicate (LM) and lithium disilicate (LD). The in vitro bioactivity study was conducted in a SBF solution, before and after different times of immersion; the new materials were analyzed by XRD, FTIR, and SEM. Some samples were subjected to in vitro biodegradation tests to quantify the release of lithium and the weight loss. Cytotoxicity, adhesion, and cell proliferation on different samples were examined by using the Methyl Tetrazolium salt (MTS) and Alizarin Red. For ~40 vol% crystallinity, lithium metasilicate was detected as the major phase, whereas for ~80 vol% crystallinity, lithium disilicate was the major phase. The LD proved to be strong (3p-bending strength of 233 ± 12 MPa) and bioactive after 14 days of immersion in SBF. In terms of lithium ion release, the LD was outside the toxic range (>8.3 ppm). The LM and LD are not cytotoxic. The LD shows the best cellular adhesion and proliferation, leading to the formation of a mineralized matrix after 21 days. These results clearly suggest that the new LD brand is strong and highly biocompatible and warrants further study.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.msec.2018.09.006DOI Listing
January 2019

Comment on "Glass Transition, Crystallization of Glass-Forming Melts, and Entropy" 2018, , 103.

Entropy (Basel) 2018 Sep 13;20(9). Epub 2018 Sep 13.

Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.

In a recent article, Schmelzer and Tropin [ , , 103] presented a critique of several aspects of modern glass science, including various features of glass transition and relaxation, crystallization, and the definition of glass itself. We argue that these criticisms are at odds with well-accepted knowledge in the field from both theory and experiments. The objective of this short comment is to clarify several of these issues.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/e20090703DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7513222PMC
September 2018

The race within supercooled liquids-Relaxation versus crystallization.

J Chem Phys 2018 Jul;149(2):024503

Vitreous Materials Laboratory, Department of Materials Engineering, Federal University of São Carlos, São Carlos, SP, Brazil.

Can any liquid be cooled down below its melting point to an isentropic (Kauzmann) temperature without vitrifying or crystallizing? This long-standing question concerning the ultimate fate of supercooled liquids is one of the key problems in condensed matter physics and materials science. In this article, we used a plethora of thermodynamic and kinetic data and well established theoretical models to estimate the kinetic spinodal temperature, T (the temperature where the average time for the first critical crystalline nucleus to appear becomes equal to the average relaxation time of a supercooled liquid), and the Kauzmann temperature, T, for two substances. We focused our attention on selected compositions of the two most important oxide glass-forming systems: a borate and a silicate-which show measurable homogeneous crystal nucleation in laboratory time scales-as proxies of these families of glass-formers. For both materials, we found that the T are significantly higher than the predicted T. Therefore, at ambient pressure, at deep supercoolings before approaching T, crystallization wins the race over structural relaxation. Hence, the temperature of entropy catastrophe predicted by Kauzmann cannot be reached for the studied substances; it is averted by incipient crystal nucleation. Our finding that T > T for two real glasses corroborate the results of computer simulations for a pressurized silica glass.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.5034091DOI Listing
July 2018

Role of dynamic heterogeneities in crystal nucleation kinetics in an oxide supercooled liquid.

J Chem Phys 2016 Dec;145(21):211920

Vitreous Materials Laboratory (LaMaV), Department of Materials Engineering (DEMa), Federal University of São Carlos (UFSCar), São Carlos 13.565-905, Brazil.

The temperature at which the classical critical nucleus size is equal to the average size of the cooperatively rearranging regions (CRR) in a supercooled liquid has been referred to as a "cross-over" temperature. We show, for the first time, using published nucleation rate, viscosity, and thermo-physical data, that the cross-over temperature for the lithium disilicate melt is significantly larger than the temperature of the kinetic spinodal and is equal or close to the temperature corresponding to the maximum in the experimentally observed nucleation rates. We suggest that the abnormal decrease in nucleation rates below the cross-over temperature is most likely because, in this regime, the CRR size controls the critical nucleus size and the nucleation rate. This finding links, for the first time, measured nucleation kinetics to the dynamic heterogeneities in a supercooled liquid.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4964674DOI Listing
December 2016

Elemental and cooperative diffusion in a liquid, supercooled liquid and glass resolved.

J Chem Phys 2017 Jul;147(1):014501

CeRTEV-Center for Research, Technology and Education in Vitreous Materials, Department of Materials Engineering, Federal University of São Carlos, 13565-905 São Carlos, SP, Brazil.

The diffusion mechanisms controlling viscous flow, structural relaxation, liquid-liquid phase separation, crystal nucleation, and crystal growth in multicomponent glass-forming liquids are of great interest and relevance in physics, chemistry, materials, and glass science. However, the diffusing entities that control each of these important dynamic processes are still unknown. The main objective of this work is to shed some light on this mystery, advancing the knowledge on this phenomenon. For that matter, we measured the crystal growth rates, the viscosity, and lead diffusivities in PbSiO liquid and glass in a wide temperature range. We compared our measured values with published data covering 16 orders of magnitude. We suggest that above a certain temperature range T (1.2T-1.3T), crystal growth and viscous flow are controlled by the diffusion of silicon and lead. Below this temperature, crystal growth and viscous flow are more sluggish than the diffusion of silicon and lead. Therefore, T marks the temperature where decoupling between the (measured) cationic diffusivity and the effective diffusivities calculated from viscosity and crystal growth rates occurs. We reasonably propose that the nature or size of the diffusional entities controlling viscous flow and crystal growth below T is quite different; the slowest is the one controlling viscous flow, but both processes require cooperative movements of some larger structural units rather than jumps of only one or a few isolated atoms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4986507DOI Listing
July 2017

Putty-like bone fillers based on CaP ceramics or Biosilicate® combined with carboxymethylcellulose: Characterization, optimization, and evaluation.

J Biomater Appl 2017 08 14;32(2):276-288. Epub 2017 Jun 14.

2 Department of Biomaterials (309), Radboudumc, Nijmegen, The Netherlands.

Calcium phosphates and bioactive glass ceramics have been considered promising biomaterials for use in surgeries. However, their moldability should be further enhanced. We here thereby report the handling, physicochemical features, and morphological characteristics of formulations consisting of carboxymethylcellulose-glycerol and hydroxyapatite-tricalcium phosphate or Biosilicate® particles. We hypothesized that combining either material with carboxymethylcellulose-glycerol would improve handling properties, retaining their bioactivity. In addition to scanning electron microscopy, cohesion, mineralization, pH, and viscoelastic properties of the novel formulations, cell culture experiments were performed to evaluate the cytotoxicity and cell proliferation. Putty-like formulations were obtained with improved cohesion and moldability. Remarkably, mineralization in simulated body fluid of hydroxyapatite-tricalcium phosphate/carboxymethylcellulose-glycerol formulations was enhanced compared to pure hydroxyapatite-tricalcium phosphate. Cell experiments showed that all formulations were noncytotoxic and that HA-TCP60 and BGC50 extracts led to an increased cell proliferation. We conclude that combining carboxymethylcellulose-glycerol with either hydroxyapatite-tricalcium phosphate or Biosilicate® allows for the generation of moldable putties, improves handling properties, and retains the ceramic bioactivity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1177/0885328217713354DOI Listing
August 2017

Bioactive gel-glasses with distinctly different compositions: Bioactivity, viability of stem cells and antibiofilm effect against Streptococcus mutans.

Mater Sci Eng C Mater Biol Appl 2017 Jul 9;76:233-241. Epub 2017 Mar 9.

Laboratório de Materiais Vítreos, Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, São Carlos, SP, Brazil.

In this study, an evaluation was performed to determine the in vitro bioactivity, viability of stem cells, and antibiofilm effect against Streptococcus mutans of two bioactive gel-glass 60SiO-36CaO-4PO (BG-A) and 80SiO-15CaO-5PO (BG-B) compositions. Both materials were bioactive and undergo the formation of hydroxycarbonate apatite (HCA) on their surfaces when immersed in simulated body fluid (SBF) after 12h, but the BG-A composition showed a more significant formation rate. The pH variation of the samples during the test in SBF indicated that an abrupt change had occurred for the BG-A composition within the first few hours, and the pH was subsequently maintained over time, supporting its stronger antibacterial effects against S. mutans. For the in vitro viability test using mesenchymal stem cells (MSCs), the BG-B showed significantly higher cell viability compared to the BG-A composition at concentrations of 0.125, 1.25 and 12.50mg/mL for 2days. These results indicated that the higher solubility of the BG-A glass favors bioactivity and antibacterial effects. However, as a result of rapid degradation, the increase in the concentration of ions in the cell culture medium was not favorable for cell proliferation. Thus, by varying the composition of glasses, and consequently their dissolution rate, it is possible to favor bioactivity, antimicrobial activity or stem cell proliferation for a particular application of interest.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.msec.2017.03.056DOI Listing
July 2017

The microscopic origin of the extreme glass-forming ability of Albite and BO.

Sci Rep 2017 02 27;7:43022. Epub 2017 Feb 27.

Department of Materials Engineering, Center for Research, Technology and Education in Vitreous Materials, Federal University of São Carlos, São Carlos, SP, Brazil.

Understanding the conditions that favour crystallisation and vitrification has been a longstanding scientific endeavour. Here we demonstrate that the extremely high glass-forming ability of unseeded supercooled NaO·AlO·6SiO (Albite) and BO-known for decades as "crystallisation anomaly"-is caused by insufficient crystal nucleation. The predicted temperatures of the maximum homogeneous nucleation rates are located well below their glass transition temperatures (T), in a region of very high viscosity, which leads to extremely long nucleation time-lags and low nucleation rates. This behaviour is due to the remarkably small supercoolings where the glass transition occurs for these liquids, which correspond to a very small driving force for crystallisation at and above the T, where crystallisation is normally observed. This meagre nucleation ability is caused by the significant difference in the structures of the supercooled liquids and their isochemical crystals. These findings elucidate the cause behind the crystallisation anomaly, and could be used for the design of other oxide glasses that are extremely stable against crystallisation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep43022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5327395PMC
February 2017

Bone regeneration and gene expression in bone defects under healthy and osteoporotic bone conditions using two commercially available bone graft substitutes.

Biomed Mater 2015 May 8;10(3):035003. Epub 2015 May 8.

Department of Biomaterials, Radboudumc, 6500 HB Nijmegen, The Netherlands.

Biosilicate(®) and Bio-Oss(®) are two commercially available bone substitutes, however, little is known regarding their efficacy in osteoporotic conditions. The purpose of this study was to evaluate the osteogenic properties of both materials, at tissue and molecular level. Thirty-six Wistar rats were submitted to ovariectomy (OVX) for inducing osteoporotic conditions and sham surgery (SHAM) as a control. Bone defects were created in both femurs, which were filled with Biosilicate(®) or Bio-Oss(®), and empty defects were used as control. For the healthy condition both Biosilicate(®) and Bio-Oss(®) did not improve bone formation after 4 weeks. Histomorphometric evaluation of osteoporotic bone defects with bone substitutes showed more bone formation, significant for Bio-Oss(®). Molecular biological evaluation was performed by gene-expression analysis (Runx-2, ALP, OC, OPG, RANKL). The relative gene expression was increased with Biosilicate(®) for all genes in OVX rats and for Runx-2, ALP, OC and RANKL in SHAM rats. In contrast, with Bio-Oss(®), the relative gene expression of OVX rats was similar for all three groups. For SHAM rats it was increased for Runx-2, ALP, OC and RANKL. Since both materials improved bone regeneration in osteoporotic conditions, our results suggest that bone defects in osteoporotic conditions can be efficiently treated with these two bone substitutes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1748-6041/10/3/035003DOI Listing
May 2015

Biosilicate-gelatine bone scaffolds by the foam replica technique: development and characterization.

Sci Technol Adv Mater 2013 Aug 13;14(4):045008. Epub 2013 Aug 13.

Institute of Biomaterials, Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Cauerstrasse 6, D-91058 Erlangen, Germany.

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 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 m 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 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 scaffold. The combination of Biosilicate glass-ceramic and gelatine is attractive for producing novel scaffolds for bone tissue engineering.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1468-6996/14/4/045008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090327PMC
August 2013

Histopathological, cytotoxicity and genotoxicity evaluation of Biosilicate® glass-ceramic scaffolds.

J Biomed Mater Res A 2013 Mar 31;101(3):667-73. Epub 2012 Aug 31.

Department of Physiotherapy, Post-Graduate Program of Biotechnology, Federal University of São Carlos (UFSCar), São Carlos, SP, Brazil.

This study evaluated the biocompatibility of Biosilicate® scaffolds by means of histopathological, cytotoxicity, and genotoxicity analysis. The histopathologic analysis of the biomaterial was performed using 65 male rats, distributed into the groups: control and Biosilicate®, evaluated at 7, 15, 30, 45, and 60 days after implantation. The cytotoxicity analysis was performed by the methyl thiazolyl tetrazolium (MTT) assay, with various concentrations of extracts from the biomaterial in culture of osteoblasts and fibroblasts after 24, 72, and 120 h. The genotoxicity analysis (comet assay) was performed in osteoblasts and fibroblasts after contact with the biomaterial during 24, 72, and 96 h. In the histopathology analysis, we observed a foreign body reaction, characterized by the presence of granulation tissue after 7 days of implantation of the biomaterial, and fibrosis connective tissue and multinucleated giant cells for longer periods. In the cytotoxicity analysis, extracts from the biomaterial did not inhibit the proliferation of osteoblasts and fibroblasts, and relatively low concentrations (12.5% and 25%) stimulated the proliferation of both cell types after 72 and 120 h. The analysis of genotoxicity showed that Biosilicate® did not induce DNA damage in both lineages tested in all periods. The results showed that the Biosilicate® scaffolds present in vivo and in vitro biocompatibility.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jbm.a.34360DOI Listing
March 2013

Biocompatibility analysis of bioglass® 45S5 and biosilicate® implants in the rabbit eviscerated socket.

Orbit 2012 Jun;31(3):143-9

Department of Ophthalmology, Otolaryngology and Head and Neck Surgery, Faculdade de Medicina de Botucatu, Universidade Estadual Paulista (UNESP), São Paulo, SP, Brazil.

Purpose: Bioactive glass and bioactive glass-ceramic cone implants were placed in the rabbit eviscerated socket to assess their biocompatibility.

Methods: Fifty-one Norfolk albino rabbits underwent evisceration of the right eye followed by implantation of cones made from Bioglass(®) 45S5 (control group) and two types of bioactive glass-ceramic (Biosilicate(®)), a single- and a two-phase bioactive glass-ceramic implants into the scleral cavity. Postoperative reactions, animal behavior and socket conditions were monitored daily. Clinical exam, biochemical evaluations, and orbit computed tomographic scan were done at 7, 90, and 180 days post-procedure. After that, the animals were euthanized, and the orbital content was removed and prepared to light microscopy with morphometric evaluation and scanning electron microscopy examination. Statistical analysis was done by parametric and non-parametric analysis of variance, complemented by Dunn's and Tukey's tests (p < 0.05).

Results: All animals did not develop systemic toxicity throughout the experimental period and also did not have orbit infection, implant migration or extrusion. Morphological analysis demonstrated pseudocapsule around all implants. Bioglass(®) and single-phase Biosilicate(®) implants induced less inflammation and pseudocapsule formation than two-phase Biosilicate(®) cones. Seven days post-procedure, the inflammatory reaction was intense and gradually decreased throughout the experiment. Tissue reaction was least intense in animals receiving Bioglass(®) implants.

Conclusions: We observe discrete differences among the studied materials, with best responses obtained with use of Bioglass(®) 45S5 and single-phase Biosilicate(®). The authors agree these implants might be useful in the management of the anophthalmic socket.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3109/01676830.2011.648798DOI Listing
June 2012

Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics.

Acta Biomater 2012 Jan 17;8(1):321-32. Epub 2011 Oct 17.

Department of Materials Engineering, Federal University of São Carlos, São Carlos, SP, Brazil.

Bioactive glasses having chemical compositions between 1Na(2)O-2CaO-3SiO(2) (1N2C3S) and 1.5Na(2)O-1.5CaO-3SiO(2) (1N1C2S) containing 0, 4 and 6 wt.% P(2)O(5) were crystallized through two stage thermal treatments. By carefully controlling these treatments we separately studied the effects on the mechanical properties of two important microstructural features not studied before, crystallized volume fraction and crystal size. Fracture strength, elastic modulus and indentation fracture toughness were measured as a function of crystallized volume fraction for a constant crystal size. Glass-ceramics with a crystalline volume fraction between 34% and 60% exhibited a three-fold improvement in fracture strength and an increase of 40% in indentation fracture toughness compared with the parent glass. For the optimal crystalline concentration (34% and 60%) these mechanical properties were then measured for different grain sizes, from 5 to 21 μm. The glass-ceramic with the highest fracture strength and indentation fracture toughness was that with 34% crystallized volume fracture and 13 μm crystals. Compared with the parent glass, the average fracture strength of this glass-ceramic was increased from 80 to 210 MPa, and the fracture toughness from 0.60 to 0.95 MPa.m(1/2). The increase in indentation fracture toughness was analyzed using different theoretical models, which demonstrated that it is due to crack deflection. Fortunately, the elastic modulus E increased only slightly; from 60 to 70 GPa (the elastic modulus of biomaterials should be as close as possible to that of cortical bone). In summary, the flexural strength of our best material (215 MPa) is significantly greater than that of cortical bone and comparable with that of apatite-wollastonite (A/W) bioglass ceramics, with the advantage that it shows a much lower elastic modulus. These results thus provide a relevant guide for the design of bioactive glass-ceramics with improved microstructure.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.actbio.2011.10.014DOI Listing
January 2012

In vivo biological performance of a novel highly bioactive glass-ceramic (Biosilicate®): A biomechanical and histomorphometric study in rat tibial defects.

J Biomed Mater Res B Appl Biomater 2011 Apr 2;97(1):139-47. Epub 2011 Feb 2.

Department of Physiotherapy, Post-Graduate Program of Physiotherapy, Federal University of São Carlos (UFSCar), São Carlos, SP, Brazil.

This study aimed to investigate bone responses to a novel bioactive fully crystallized glass-ceramic of the quaternary system P(2)O(5)-Na(2)O-CaO-SiO(2) (Biosilicate®). Although a previous study demonstrated positive effects of Biosilicate® on in vitro bone-like matrix formation, its in vivo effect was not studied yet. Male Wistar rats (n = 40) with tibial defects were used. Four experimental groups were designed to compare this novel biomaterial with a gold standard bioactive material (Bioglass® 45S5), unfilled defects and intact controls. A three-point bending test was performed 20 days after the surgical procedure, as well as the histomorphometric analysis in two regions of interest: cortical bone and medullary canal where the particulate biomaterial was implanted. The biomechanical test revealed a significant increase in the maximum load at failure and stiffness in the Biosilicate® group (vs. control defects), whose values were similar to uninjured bones. There were no differences in the cortical bone parameters in groups with bone defects, but a great deal of woven bone was present surrounding Biosilicate® and Bioglass® 45S5 particulate. Although both bioactive materials supported significant higher bone formation; Biosilicate® was superior to Bioglass® 45S5 in some histomorphometric parameters (bone volume and number of osteoblasts). Regarding bone resorption, Biosilicate® group showed significant higher number of osteoclasts per unit of tissue area than defect and intact controls, despite of the non-significant difference in the osteoclastic surface as percentage of bone surface. This study reveals that the fully crystallized Biosilicate® has good bone-forming and bone-bonding properties.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jbm.b.31795DOI Listing
April 2011

Efficacy of a bioactive glass-ceramic (Biosilicate) in the maintenance of alveolar ridges and in osseointegration of titanium implants.

Clin Oral Implants Res 2010 Feb 13;21(2):148-55. Epub 2009 Nov 13.

Faculty of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.

Objectives: The aims of this research were to evaluate the efficacy of a bioactive glass-ceramic (Biosilicate) and a bioactive glass (Biogran) placed in dental sockets in the maintenance of alveolar ridge and in the osseointegration of Ti implants.

Material And Methods: Six dogs had their low premolars extracted and the sockets were implanted with Biosilicate, Biogran particles, or left untreated. After the extractions, measurements of width and height on the alveolar ridge were taken. After 12 weeks a new surgery was performed to take the final ridge measurements and to insert bilaterally three Ti implants in biomaterial-implanted and control sites. Eight weeks post-Ti implant placement block biopsies were processed for histological and histomorphometric analysis. The percentages of bone-implant contact (BIC), of mineralized bone area between threads (BABT), and of mineralized bone area within the mirror area (BAMA) were determined.

Results: The presence of Biosilicate or Biogran particles preserved alveolar ridge height without affecting its width. No significant differences in terms of BIC, BAMA, and BABT values were detected among Biosilicate, Biogran, and the non-implanted group.

Conclusions: The results of the present study indicate that filling of sockets with either Biosilicate or Biogran particles preserves alveolar bone ridge height and allows osseointegration of Ti implants.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1600-0501.2009.01812.xDOI Listing
February 2010

Effects of biosilicate and bioglass 45S5 on tibial bone consolidation on rats: a biomechanical and a histological study.

J Mater Sci Mater Med 2009 Dec;20(12):2521-6

Department of Physiotherapy, Federal University of São Carlos (UFSCar), Sao Carlos, SP, Brazil.

The purpose of this study was to investigate the effects of Bioglass 45S5 and Biosilicate, on bone defects inflicted on the tibia of rats. Fifty male Wistar rats were used in this study, and divided into five groups, including a control group, to test Biosilicate and Bioglass materials of two different particle sizes (180-212 microm or 300-355 microm). All animals were sacrificed 15 days after surgery. No significant differences (P > 0.05) were found when values for Maximal load, Energy Absorption and Structural Stiffness were compared among the groups. Histopathological evaluation revealed osteogenic activity in the bone defect for the control group. Nevertheless, it seems that the amount of fully formed bone was higher in specimens treated with Biosilicate (granulometry 300-355 microm) when compared to the control group. The same picture occurred regarding Biosilicate with granulometry 180-212 microm. Morphometric findings for bone area results (%) showed no statistically significant differences (P > 0.05) among the groups. Taken together, such findings suggest that, Biosilicate exerts more osteogenic activity when compared to Bioglass under subjective histopathological analysis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s10856-009-3824-zDOI Listing
December 2009

Diffusion coefficients for crystal nucleation and growth in deeply undercooled glass-forming liquids.

J Chem Phys 2007 Jun;126(23):234507

S. I. Vavilov State Optical Institute, Ulitsa Babushkina 36-1, 193171 St. Petersburg, Russia.

We calculate, employing the classical theory of nucleation and growth, the effective diffusion coefficients controlling crystal nucleation of nanosize clusters and the subsequent growth of micron-size crystals at very deep undercoolings, below and above Tg, using experimental nucleation and growth data obtained for stoichiometric Li2O.2SiO2 and Na2O.2CaO.3SiO2 glasses. The results show significant differences in the magnitude and temperature dependence of these kinetic coefficients. We explain this difference showing that the composition and/or structure of the nucleating critical clusters deviate from those of the stable crystalline phase. These results for diffusion coefficients corroborate our previous conclusion for the same glasses, based on different experiments, and support the view that, even for the so-called case of stoichiometric (polymorphic) crystallization, the nucleating phase may have a different composition and/or structure as compared to the parent glass and the evolving macroscopic crystalline phase. This finding gives a key to explain the discrepancies between calculated (by classical nucleation theory) and experimentally observed nucleation rates in these systems, in particular, and in deeply undercooled glass-forming liquids, in general.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.2746502DOI Listing
June 2007

Pressure dependence of viscosity.

J Chem Phys 2005 Feb;122(7):074511

Institut für Physik der Universität Rostock, Universitätsplatz, 18051 Rostock, Germany.

We reanalyze the pressure dependence of viscosity of liquids of constant composition under isothermal conditions. Based exclusively on very general considerations concerning the relationship between viscosity and "free volume," we show that, at moderate values of pressure, viscosity increases, as a rule, with increasing pressure, provided the liquid is in stable or metastable (undercooled) equilibrium states. However, even if the behavior of the viscosity is governed by free volume effects, deviations from a positive pressure dependence are possible, when the liquid's thermal expansion coefficient is negative. We derive an equation that allows one to quantitatively determine the pressure dependence of viscosity, which requires, in the simplest case, only the knowledge of the temperature dependence of viscosity at constant pressure, the thermal expansion coefficient, and the isothermal compressibility of the liquid. As an example, the negative pressure dependence of water in the range of temperatures 0-4 degrees C and of several silicate liquids, such as albite, jadeite, dacite, basalts, etc., could be explained in such a way. Other glass-forming liquids initially (for moderate pressures) show a positive pressure dependence of viscosity that changes to a negative one when subjected to high (approximately GPa) isostatic pressure. A detailed analysis of water and already mentioned silicate melts at GPa pressures shows that, in addition to free volume effects, other pressure induced structural transformations may have to be accounted for in a variety of cases. By this reason, the theoretical analysis is extended (i) in order to describe the pressure dependence of viscosity for systems that are in frozen-in thermodynamic nonequilibrium states (glasses, i.e., undercooled liquids below the glass transition temperature Tg) and (ii) to systems which undergo, in addition to variations of the free volume, pressure induced changes of other structural parameters. In such cases a decrease of viscosity with increasing pressure may occur, in principle, even if the thermal expansion coefficient is positive. In this way, the present analysis grants a general tool to estimate the pressure dependence of viscosity and supposedly settles the controversy in the current literature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.1851510DOI Listing
February 2005
-->