Papers by Author: Maria Helena F.V. Fernandes

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Authors: A.G. Dias, M.A. Costa, M.A. Lopes, José D. Santos, Maria Helena F.V. Fernandes
Authors: Carlos M. Queiroz, Maria Helena F.V. Fernandes, Jorge R. Frade
Authors: Nuno A.F. Almeida, Maria Helena F.V. Fernandes
Abstract: In silicate glasses the kinetics of apatite layer formation is usually rapid but the adhesion to the base glass is poor. Glass ceramics promote a stronger bonding between layer and substrate but decrease the rate of the apatite layer formation. In this work a glass of composition (wt%) 54,89%C3P-24,81%SiO2-20,30%MgO has been studied. This glass was heat treated at four temperatures (840 °C, 870 °C, 890 °C and 910 °C) to obtain glass ceramics with different contents of the same crystalline phase. A calcium magnesium phosphate phase was formed in all glass ceramics in a volume percent increasing with temperature. The apatite layer precipitated after immersion in simulated body fluid (SBF) formed faster on the glass than on the glass ceramics and a decrease in the amount of apatite formed was observed with the increase in crystallinity. It was generally concluded that heat treatment can turn a reactive glass into glass ceramics of different surface behaviors, from bioactive to quasi bio inert materials.
Authors: Claudinei dos Santos, R.C. Souza, Maria Helena F.V. Fernandes, Nuno A.F. Almeida, Flávia A. Almeida, Rui F. Silva
Abstract: In this study, the influence of La-rich glass addition and sintering conditions on the densification and mechanical properties of 3 mol.%Y2O3-stabilized tetragonal zirconia polycrystals (3Y-TZP) ceramics were evaluated. High-purity tetragonal ZrO2 powder stabilized with 3 mol.% Y2O3 and La2O3-Rich glass were used as starting powders. Two compositions, ZrO2 containing 5 and 10 wt.% of a La2O3-rich glass were studied in this work. The starting powders were mixed/milled by planetary milling, dried at 90°C for 24 hours, sieved through a 60 mesh screen and uniaxially cold pressed under 80 MPa. The samples were sintered in air at 1200, 1300 and 1400°C for 60min, and at 1450°C for 120min, with heating and cooling rates of 10°C/min. Sintered samples were characterized by relative density, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The mechanical properties, hardness and fracture toughness, were obtained by Vickers indentation method. Dense sintered samples were obtained for all conditions. Samples sintered at 1300°C for 60 min presented the optimal mechanical properties with hardness of 1170 and fracture toughness of 8.3 MPam1/2.
Authors: A.M.B. Silva, Rui N. Correia, J.M. Oliveira, Maria Helena F.V. Fernandes
Abstract: This study compares the in vitro behaviour in SBF of glasses from two different systems, TiO2-CaO-P2O5 and SiO2-CaO-P2O5 with the same TiO2 and SiO2 molar content, in order to evaluate the effect of TiO2 and SiO2 on the surface reactivity of those glasses. The glass formation regions in both systems were observed for compositions with less than 40 mol% TiO2 and 40 mol% SiO2, respectively. Four glasses with similar TiO2 and SiO2 molar contents have been selected for comparison. These glasses are equimolar in CaO and P2O5 with TiO2 or SiO2 varying from 4 to 33 mol %. Powder glasses were immersed in Simulated Body Fluid (SBF) and kept at 37°C for different times, up to 14 days. Surfaces were observed by Scanning Electron Microscopy (SEM) and specimen ion leaching to SBF was studied by Inductively Coupled Plasma (ICP) spectroscopy. Preliminary spectroscopic studies by Raman were performed to identify the structure of the glasses. For glasses of the SiO2-CaO-P2O5 system a significant dissolution of all ions was observed together with the formation of phosphoric acid. In opposition, the immersion of TiO2-CaO-P2O5 glasses produced a small Ca consumption and stable Ti and P concentrations, indicating the formation of a Ca-P rich layer on these glasses. The observed differences in the dissolution behaviour are tentatively explained in terms of the glass structures obtained by spectroscopy.
Authors: M.C. Ferro, Maria Helena F.V. Fernandes, C.F.M.L. Figueiredo, M.S.J.G. Alendouro, Regina da Conceição Corredeira Monteiro
Authors: M.C. Ferro, Christian Leroy, Regina da Conceição Corredeira Monteiro, Maria Helena F.V. Fernandes
Authors: J.K.M.F. Daguano, Claudinei dos Santos, Paulo Atsushi Suzuki, Luiz A. Bicalho, Maria Helena F.V. Fernandes
Abstract: Glasses based on the 3CaO.P2O5-SiO2-MgO system present high bioactivity aiming the use as bone restorations. On the other hand, the low mechanical properties reduce the importance of this glass aiming the use as restoration bulk specimens. In this work, glass-ceramics were obtained by devitrification of this glass using different temperatures. CaCO3, SiO2, MgO and Ca(H2PO4).H2O were used as starting-powders. Powder mixture was milled/homogenized and melted at 1600°C, for 2h and annealed at 700°C for 4h with cooling rate of 3°C/min. Glass specimens of 151550mm3 were characterized by DTA and XRD analysis. Specimens were heat-treated in different temperatures between 7000C and 1050°C, for 4 hours, obtaining glass-ceramics with different crystallized phase content. Hardness and fracture toughness were determined and correlated with crystalline phase content. The results indicated that crystallization-degree increase with the temperature, and the mechanical properties are improved: Hardness values present increases lower than 20% as function of the crystallization. Fracture toughness may increase 100% as function of temperature (crystallization degree).
Authors: Kanji Tsuru, Yuki Shirosaki, Satoshi Hayakawa, Akiyoshi Osaka, M.A. Lopes, José D. Santos, Maria Helena F.V. Fernandes
Abstract: Chitosan-silicate hybrid membranes were prepared using g-glycidoxy-propyltrimethoxysilane (GPSM) through a sol-gel process. The amino groups of chitosan chains were reacted with the epoxy groups of GPSM and GPSM have a function as the agent to cross-link the chitosan chains. The cross-linking degree of the hybrid membranes was determined by ninhydrin assay. Fourier-transform infrared (FT-IR) spectroscopy and 29Si cross-polarization (CP) magic-angle spinning (MAS)-NMR spectroscopy were used to assess the structure of the hybrid membranes. The biodegradability of the hybrid membranes in phosphate-buffered saline solution or lysozyme solution was investigated as a function of the GPSM concentration.
Authors: Yuki Shirosaki, Kanji Tsuru, Satoshi Hayakawa, Akiyoshi Osaka, M.A. Lopes, José D. Santos, Maria Helena F.V. Fernandes
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