Abstract We investigated the Biogran on bone repair and metabolism at several time-intervals upon grafting into rat tibia artificial defects. The biomaterial was thoroughly characterized in vitro, and its dissolution behavior upon immersion was assessed in simulated body fluid (SBF) solution for 1, 3, 7, 14, and 30 days. Biogran was also assessed by in vitro hydroxyapatite formation in SBF solution, which is a marker for bioactive behavior. In vivo, distal and proximal bone defects were performed in the Wistar rat's right tibia and filled according to the experimental groups: I) negative control, no filling; II) positive control, 10 mg of autogenous bone; and III) 10 mg of Biogran. Animals were euthanized at 1, 2, 3, 4, 7, and 10 weeks. Bone neoformation was analyzed using histomorphometry (proximal defect), and local levels of bone morphogenetic protein 2 (BMP-2) were measured using the ELISA assay (distal defect). In vitro, the Biogran sample showed a fast dissolution rate within the first 7 days, parallel to the formation of the hydroxyapatite layer. In vivo, the sample was progressively resorbed at a higher rate within the first month until it became almost absent at week 10th. The sample presented similar or higher bone neoformation concerning the autogenous bone. BMP-2 levels were sustained in the Biogran group (around 200 pg/mg) and detected until the last experimental time with a significant difference compared with the controls. Results suggest Biogran is a candidate for hard tissue engineering even in highly active bone remodeling sites.

RESUMO O conhecimento das transformações de fase e o papel de diferentes parâmetros no desempenho de sistemas ligados a fosfato são de extrema importância para o campo refratário. Os efeitos do agente de endurecimento, da concentração de ácido fosfórico e dos aditivos no tempo de endurecimento, resistência ao impacto a frio, módulo de ruptura a quente, resistência à abrasão e resistência ao choque térmico dos sistemas refratários quimicamente ligados ao fosfato foram avaliados. O tempo de endurecimento foi menor para misturas contendo cimento (CaO) e uma menor concentração de ácido. Misturas com maior concentração de ácido apresentaram melhor resistência mecânica, à abrasão e ao choque térmico. Apesar de aumentar a resistência mecânica a frio e a abrasão dos materiais, o Budit 6H impactou negativamente as propriedades quentes. Para o aditivo Fabutit761, não houve formação de fase líquida em temperaturas intermediárias e esse aditivo aumentou a resistência mecânica a frio, mas também impactou negativamente a resistência mecânica a quente. As composições contendo cimento como agente endurecedor, ácido fosfórico a 40° Be e aditivo Fabutit761 como fonte extra de fosfato apresentaram um melhor conjunto de propriedades.

ABSTRACT The knowledge of the phase transformations and the role of different parameters in the performance of phosphate-bonded systems are of utmost importance for the refractory field. The effect of the setting agent, phosphoric acid concentration and additives on the setting time, cold crush strength, hot modulus of rupture, abrasion resistance, and thermal shock resistance of the phosphate chemically bonded refractory systems was evaluated. The setting time was shorter for mixtures containing cement (CaO) and a lower acid concentration. Mixtures with a higher acid concentration presented better mechanical, abrasion and thermal shock resistance. In spite of increasing the cold mechanical resistance and abrasion of the materials, the Budit 6H negatively impacted the hot properties. For Fabutit761, there was no liquid phase formation at intermediate temperatures and this additive increased the cold mechanical strength, but it also negatively impacted the hot mechanical strength. Compositions containing cement as a setting agent, 40°Be phosphoric acid and Fabutit761 additive as an extra source of phosphate presented a better set of properties.

ABSTRACT Films of lanthanum strontium manganite, LSM (La0.8Sr0.2MnO3) were deposited on yttria stabilized zirconia (YSZ) substrates by different methods aiming to establish the most suitable route to prepare cathodes for solid oxide fuel cells (SOFC). Samples were obtained by using a solution of lanthanum, strontium and manganese nitrates or a dispersion of the LSM powder in this solution. Both commercial and synthetized LSM powders were used, the last one obtained by amorphous citrate method. The films were deposited by spray pyrolysis on YSZ substrates prepared by uniaxial and isostatic pressing. Samples were characterized by scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction and two-probe conductivity measurements. The area specific resistance and relaxation to cathodic activation were measured by electrochemical impedance spectroscopy. The substrate obtained by uniaxial pressing and the commercial LSM produced films with the highest amount of surface cracks. The film obtained from the suspension showed area specific resistance and activation energy lower than the other produced from the solution. For both samples, the cathodic activation process resulted in an initial reduction of the total resistance of around 20%, the sample produced from the suspension being more resistant to relaxation. Therefore, the LSM suspension is more suitable than the salts solution for preparing films by spray pyrolysis on YSZ substrates to obtain efficient cathodes for SOFC.

This paper is focused on a review of the design features and the electrochemistry characterization of anode-supported planar SOFC. Studies and results of metallic alloy interconnectors and recovery for protection against corrosion and for contact layer are showed. Moreover a discussion of examples of measurements of impedance spectrometry, according to the literature and our experimental results are made. For the anode supported fuel cells the power density varies from 0.1 to 0.5 Wcm², according to results in the literature (showed in this paper). For electrolyte supported fuel cell the power density can be 10 Wcm-2 for high temperatures. An English-Portuguese glossary of most used terms in SOFC stack is given for greater clarity and to introduce new terms to the reader.

O grande desafio para se melhorar o desenvolvimento de pilhas a combustível de óxido sólido (PACOS) é diminuir as resistências de polarização ôhmica e de polarização de concentração, sobretudo no catodo. Uma alternativa efetiva é a introdução de uma camada catódica funcional entre o eletrólito e o catodo convencional. Esta camada funcional é um compósito constituído pelos materiais de eletrólito e catodo que neste caso são a zircônia estabilizada com ítria (ZEI) e a manganita de lantânio e estrôncio (MSL). Esta camada melhora o contato entre o catodo e o eletrólito diminuindo a resistência ôhmica de polarização de concentração devido ao aumento do número de pontos de contato triplo (PCT) no volume do material. Neste trabalho, duas meias células foram preparadas: a primeira é constituída por um filme catódico funcional (50% p/p) e a camada coletora de corrente depositados sobre uma pastilha de ZEI. A segunda meia célula é composta apenas pela camada catódica de MSL também depositada sobre a pastilha de ZEI. O estudo elétrico foi realizado por espectroscopia de impedância na faixa de temperatura entre 700 e 900 °C. As resistências das amostras diminuíram com o aumento da temperatura e, foi observado que a meia célula que possuía o catodo funcional apresentou menores resistências elétricas. Após tratamento térmico a 750°C por 3 dias foi verificado que a amostra sem a camada funcional apresentou um semicírculo adicional no diagrama de impedância caracterizado como uma resistência devida a baixa aderência eletrólito/catodo. Este fenômeno foi confirmado por imagens de microscopia eletrônica de varredura (MEV).

The greatest challenge to improve SOCF (Solid Oxide Fuel Cell) development is to decrease polarization and ohmic concentration resistances mainly for the cathode. One effective alternative is the introduction of a functional cathode layer between the electrolyte and the conventional cathode. This functional cathode layer is a composite constituted by the electrolyte and cathode materials, in this case, yttria stabilized zirconia (YSZ) and lanthanum doped strontium (LSM). This layer improves the contact between the cathode and the electrolyte decreasing the ohmic concentration polarization due to the increasing of triple contact points (TPB) in the bulk concentration. In this work, two half cells were prepared: the first one is constituted by a functional cathode film (50% in weight), and a collecting current layer (LSM) both deposited on a YSZ pellet. The second half cell is composed by a LSM cathode layer deposited on the YSZ Tosoh pellet. The electric study has been realized by Impedance Spectroscopy varying the temperature from 700 to 900 ºC. The two half cells resistance decreased with increasing the temperature, and it has noted that the half cell with the functional cathode layer presented the lowest resistance. After annealing at 750 °C for 3 days, the sample without the functional cathode layer presented additional half circles in IS diagrams characterized as resistances due to the bad electrolyte/ electrode adherence. This phenomenon has been confirmed by Scanning Electron Microscopy (SEM).

A modelagem computacional contribui para o projeto, o dimensionamento e, também, para a avaliação do desempenho de pilhas a combustível de óxido sólido. No entanto, essa modelagem é complexa devido a grande quantidade de fenômenos físicos envolvidos. Além dos fenômenos físicos, as dimensões presentes dificultam a validação dos resultados. Neste trabalho, os canais de um interconector adjacente a um anodo foram modelados visando avaliar o escoamento nesse sistema. A validação dos procedimentos e das considerações foi feita de maneira indireta. O escoamento no interconector foi avaliado através das equações de Navier-Stokes e, no anodo, foi utilizada a Lei de Darcy. A técnica de volumes finitos foi empregada para a solução das equações. Foram utilizados valores típicos de permeabilidade, enquanto viscosidade e densidade foram determinadas numericamente, considerando a mistura de hidrogênio e água. Foi considerado regime permanente e isotropia em relação a todas as propriedades físicas determinadas a várias temperaturas. Foram analisadas as influências no escoamento da razão entre porosidade do anodo e viscosidade da mistura H2 e H2O; da densidade e; da temperatura. Um estudo de como a densidade da malha afeta os resultados também foi realizado. Foi possível notar que, quando a mistura hidrogênio/água penetra no meio poroso, o escoamento sofre uma redução de velocidade, em relação ao valor médio aplicado na entrada. Já a pressão, nessa situação, não apresenta redução significativa.

The computational modeling contribute for design, dimensioning and also for performance evaluation of Solid Oxide Fuel Cells. Nevertheless, the modeling is complex due to of large quantity of physics phenomena involved. In addition of physics phenomena, the present dimensions raise difficulties to validate the results. In this work, the interconnect channels adjacent to an anode have modeled aiming evaluate the flowing in this system. The validation of procedures and considerations has done by indirect mode. The flowing at interconnect has been evaluate through the Navier-Stokes equations and at anode it has been used the Darcy's Law. The technique of finite volume has used to solving of equations. It has been used typical values of permeability, while viscosity and density have been numerically determined, considering a mixture of hydrogen and water. It has been considered steady state and isotropy in relation of all physical properties determined at different temperatures. It have been analyzed the influences at the flowing by ratio between the porosity of anode and viscosity of mixture H2O and H2O; density and temperature. A study of how the mesh affects the results also has been done. It has been possible the see that, when the mixtures of hydrogen/water enters at porous media, the flowing suffer a reduction of velocity in relation of medium value applied at entering. The pressure, in this situation, does not show significant reduction.

Bioactive glasses undergo corrosion with leaching of alkaline ions when exposed to body fluids. This results in the spontaneous formation of a layer of hydroxyapatite (HA), the mineral component of natural bone, which in turn can induce bone growth in vivo. This paper describes the different types of bioactive glasses, the characterization methods currently used, and the main factors that influence their bioactivity. Nucleation and crystallization, the main mechanisms involved in the formation of hydroxyapatite, Ca10(PO4)6(OH)2, are discussed as a function of the chemical composition and the reactivity of the surface of the material. Finally, promising applications are considered.

Samples of a commercial glass fiber FM® (Fiber Max) were used to test the efficacy of a chemical sol-gel surface treatment to enhance their bioactivity. After treatment with tetraethoxysilane (TEOS), individual fiber samples were soaked into a simulated body fluid (SBF) solution, from which they were removed at intervals of 5 and 10 days. Micrographs obtained by scanning electron microscopy (SEM) analysis of samples chemically treated with TEOS revealed the formation of a hydroxyapatite (HA) coating layer after 5 days into SBF solution. Fourier transform infrared spectroscopic (FTIR) analyses confirmed that the coating layer has P-O vibration bands characteristic of HA. The in vitro cytotoxicity was evaluated using a direct contact test, minimum essential medium elution test (ISO 10993-5) and MTT assay. Fibers immersed in SBF and their extracts exhibited lower cytotoxicity than the controls not subjected to immersion, suggesting that SBF treatment improves the biocompatibility of the fiber.

The focus of this work is to show the influence of surface charge on the bioactivity of modified collagen fiber surface. Because silica plays an important role on bone mineralization process, silica obtained by a sol-gel process was used as a surface modification agent. Zeta potential (xi) of silica-coated and non-coated samples was measured as a function of pH. It was observed a shift in xi vs. pH. The isoelectric point for silica-coated collagen was 6.8, while that of non-treated sample it was near 10. Pure silica has isoelectric point near 2, and the shift observed indicates that at least part of the silica was incorporated onto the surface during the treatment. The ability of samples exposed to biological simulated fluids (SBF) to form a hydroxyapatite layer has been used to recognize bioactive materials. The pH of these biological solutions is about 7.3. It means that treated samples acquire negative charge when in contact with the biological solution and attract ions like Ca2+, HPO4(2-), and OH- to form HA coatings. Micrographs of chemically treated samples corroborate this assumption. For treated samples, the formation of a coating layer is clear after 5-day immersion in SBF, while pure collagen remains practically unaltered. Fourier Transform Infrared Spectroscopic (FTIR) analyses confirmed that the coating layer has P-O vibration bands near 1060 cm-1 and 600 cm-1 characteristic of hydroxyapatite (HA).