Mônica Calixto de Andrade

Hydrothermal nucleation of hydroxyapatite on titanium surface

Abstract Titanium plates were submitted to nucleation and growth of hydroxyapatite (HAp) under hydrothermal conditions. A group of these plates were submitted to nucleation without any previous treatment and another group was treated with NaOH 1 M at 130°C inside an autoclave followed by heat-treatment at 600°C. The nucleation were performed by soaking all these titanium pieces, in a simulated body fluid (SBF) solution, containing calcium, phosphate and other ions, in order to promote the nucleation and growth of hydroxyapatite under hydrothermal conditions on the titanium surface. The results show that hydrothermal nucleation and growth of HAp occurs even on the non-treated titanium surface at 150°C. However, a better uniformity of the hydroxyapatite layer was observed on the pre-treated titanium surface, at 80°C, with the renewal of the SBF solution.

Bioactive Porous Titanium: An Alternative to Surgical Implants

Porous titanium implants have been used to improve implant-bone attachment by the ingrowth of bone tissue within the porous structure. Despite the efficient bone adhesion of porous titanium implants, chemical bonds are required at bone-implant interface. These implants can become bioactive by a biomimetic precipitation process. The aim of this work was to enhance the bioactivity of pure porous titanium implants by biomimetic process. The samples immersed in a simulated body fluid promoted the nucleation and growth of calcium phosphate (Ca-P) crystals, such as hydroxyapatite (Hap), on the material surface. Scanning electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy analyses revealed that a Ca-P deposition occurred without the need of pretreatments to improve the surface bioactivity. This present study indicates the potential for growing a bone-like Hap layer on porous titanium implants by biomimetic processes.

Cinética de cristalização não-isotérmica de resíduos de polietileno de alta densidade (PEAD)

Nesta investigacao, diversos residuos incolores ou coloridos pos-consumo de polietileno de alta densidade (PEAD) foram caracterizados atraves do indice de fluidez (MFI) e da calorimetria exploratoria diferencial (DSC). A equacao de Avrami modificada por Jeziorny, e os modelos de Kissenger e Friedman foram utilizados para descrever a cinetica de cristalizacao nao-isotermica das amostras. Foi verificado que os pigmentos presentes no PEAD tem diferentes habilidades nucleantes durante o processo de cristalizacao, bem como diferentes efeitos sobre a taxa de cristalizacao e a energia de ativacao necessaria para o transporte de segmentos macromoleculares para a superficie do cristal em crescimento.

Production and characterization of colored feldspathic enamel for dental application

In this work we synthesized pigments capable of developing dental shades when mixed with dental porcelain and fired at appropriate temperatures. TiO2-xCeO2 pigments (x = 2, 6, 10, 13 and 18 mol%) were synthesized by the Pechini method. Characterization by thermal analysis revealed the stability of the material at temperatures up to 1200 °C. X-ray diffraction showed stable crystalline phases (rutile to TiO2 and cerianite to CeO2) for all pigments studied. Color of pigments was characterized by colorimetric coordinates according to the CIELAB method and reflectance measurements in the visible region. Through colorimetric analysis it was possible to verify the potential use of these pigments in dental ceramics.

Thermodynamic simulation of phosphate precipitation based on ion-selective microelectrode measurements

Simulated body fluids (SBFs) are largely used as biocompatibility screening and also as an alternative process to the plasma spray coating. Biomimetic processes occur heterogeneously on metallic surface; therefore, the use of a microelectrode technique is highly advisable to detect surface changes. In this work, the local pH was monitored during the first 44 h of deposition of calcium phosphates on titanium samples with a simplified SBF solution. Three-dimensional data (local pH, x-y coordinates) were used to simulate equilibrium concentrations of all species. Based on these quantities, relative supersaturations and Gibbs energy variations of hydroxyapatite and octacalcium phosphate were evaluated. The conjoint experimental and theoretical approach suggested that neither local alkalinity nor free calcium concentration alone produces an adequate scenario of precipitation conditions, but the use of both procedures results in interesting findings not achieved using only a single approach.

Análise térmica e propriedades mecânicas de resíduos de polietileno de alta densidade (PEAD)

High density polyethylene (HDPE) post-consumption bottles were collected and milled. After processing in a twin screw extruder, material defined as recycled HDPE (mixture of white, ivory and colorless bottles) was injection molded and mechanical properties, such as tensile strength and impact strength, were evaluated and compared with a commercial HDPE sample. Thermal analysis by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and statistical analysis of the experimental results were also carried out. Regarding tensile strength, difference between samples of recycled HDPE and commercial HDPE was so insignificant that, within the adopted experimental conditions, one might say that recycled and commercial materials are equivalent. In turn, kinetic model used in the thermal analysis showed that commercial HDPE presents process of nucleation and growth of crystals more simple and homogeneous, while activation energy is significantly higher than the other samples of HDPE.

Synthesis and Characterization of Barium Titanate by Solid-State Reaction

Solid-state reactions were used to synthesize pure and doped barium titanate powder. Barium titanate formation with tetragonal perovskite structure was detected by X-ray diffraction and occurred at a temperature above 700°C for pure powder and 500°C for doped powder. However, quite crystalline samples were observed only at 800oC and 600°C for pure and doped barium titanate, respectively, what made the refinement of the synthesized powders possible. They were characterized by X-ray diffraction and Fourier transform infrared spectroscopy and scanning electron microscopy. X-ray diffraction data was analyzed by using the Fullprof Rietveld refinement approach, Thompson-Cox-Hastings pseudo-Voigt with function. The refinement method was effective in the study of the temperature influence on the microstructure of the analysis of pure and doped barium titanate.

Influência dos Cátions na Corrosão do Aço UNS S32750 em Meios Cloretados

Os acos inoxidaveis duplex e superduplex sao cada vez mais utilizados por causa de sua combinacao de boas caracteristicas de resistencia a corrosao localizada e de resistencia mecânica. Neste trabalho, amostras de aco superduplex UNS S32750 foram tratadas termicamente por 15 min a 800 °C, resfriadas ao ar e ensaiadas em diversas solucoes de cloreto. Para determinar as condicoes de ensaio, os cations metalicos (Na + , Mg 2+ , Ca 2+ e Cu 2+ ) dos sais empregados foram caracterizados quanto a sua dureza de ligacao e utilizados nas solucoes contendo um molar de cloreto. Os ensaios de polarizacao potenciodinâmica foram realizados nas temperaturas de 20, 30, 40, 50, 60, 70 e 80 °C para as quatro solucoes (1,0 mol/L NaCl; 0,5 mol/L MgCl 2 ; 0,5 mol/L CaCl 2 e 0,5 mol/L de CuCl 2 ). Os resultados foram apresentados em funcao do pH das solucoes e dos valores de dureza de ligacao dos cations utilizados. Observou-se que os cations metalicos utilizados influenciaram na corrosao do aco. Entretanto, este fato esta mais associado ao pH das solucoes e seu efeito no aumento da dissolucao, sendo maior para os cations de maior dureza. Os cations mais duros produziram solucoes mais acidas devido a hidrolise que acidifica o eletrolito. DOI: 10.5935/1984-6835.20130048

Characterization and Dissolution Dynamics of Tricalcium Phosphates in Acidified Solution

Bioceramics used in biomedical applications must exhibit specific behaviors. In scaffolds, for instance, the degradability of bioceramics is important to allow the cell ingrowth. Therefore, the dissolution of calcium phosphates increases the ionic concentrations around the interface implant–bone, favoring a more rapid bone apposition to the graft surface. The dissolution takes place under static or dynamic conditions, but the latter is usually not performed under rigorous hydrodynamic control. In the present work, two bioceramics, β-tricalcium phosphate and β-tricalcium phosphate substituted by magnesium, were produced by pressing and sintering to form disks. They were characterized by XRD, Raman, ICP, SEM, AFM and photometric test. The influence of chemical composition in the dissolution test was conducted through strict control of the hydrodynamic conditions. The disks were rotating in a precise speed, in order to produce a dissolution under the well-controlled mass transfer. Subsequently, the calcium release was evaluated in a simulated infectious environment using pH equals to circa 4. Thus, it was possible to evaluate the fraction of dissolution related to mass transfer or surface reactions for a large rotation speed range. The magnesium added to the bioceramic inhibits the total dissolution when compared to pure tricalcium phosphate, probably related to more dense and less soluble ceramic. Moreover, the mass transfer affects relatively less the magnesium tricalcium phosphate than pure tricalcium phosphate.

Study of Titanium Surface Topography Influence on Biomimetic Coating Deposition

Studies show that calcium phosphate coatings on titanium implants improve osseointegration at the implant-bone interface, due to the mineral biocompatibility. Titanium implants can be coated with calcium phosphates by a biomimetic precipitation method. This work studied a biomimetic method under a simplified solution with calcium and phosphorus ions. As substrates, commercially dense titanium sheet and macroporous titanium samples produced by powder metallurgy were used, both ASTM F67 grade 2. The substrates were submitted to chemical and heat treatment and then immersed in the solution for 10 days. Samples characterization was performed by Optical Microscopy (OM), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), low angle X-ray Diffractometry (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Powder metallurgy successfully produced macroporous titanium substrates. Calcium phosphate coatings were deposited on both substrates, confirmed by FTIR bands. Such results indicated the potential of this methodology for calcium phosphate coatings on titanium substrates.