Papers by Author: S. Bertazzo

Abstract: The surface of alumina discs (γ phase) was modified by the reaction between the Al-OH groups on the surface of alumina and oxalic acid, resulting in carboxylatoaluminoxanes. The alumina discs with modified surface were soaked in SBF for 6 hours, promoting an intense precipitation of calcium phosphate. The formation of evenly distributed calcium phosphate crystals controlled by the alumina surface, achieved in this work, has the potential to significantly modify the bioinert behavior presented by this material.

Abstract: The surface charge of calcium phosphates in Simulated Body Fluid (SBF) may be one of the factors associated with the adhesion of cells and proteins, processes that are related with osteogenesis. For calcium phosphates in SBF, surface charge varies with solution pH due to the adsorption of positive ions and to the reactions that occur at the solid/biological fluid interface. In this work, the variation of the density of protons adsorbed and the surface charge as a function of pH were determined for Hydroxyapatite, CaHPO4, and Bone Mineral.

Abstract: In this work, the dissolution of calcium phosphates was studied through the calcium ion concentration, determined during the dissolution process in SBF (Simulated Body Fluid) at pH 6.35, 7.00 and 7.40, at 37oC. The results allowed the determination of the number of adsorption sites (ns) on the surface of the phosphates. Regardless of previous knowledge of the Ca/P ratio and crystallinity of the studied phosphates, the ns values provide the evidence that at the end of the dissolution process, the surfaces of the phosphates are similar.

Abstract: In this work, calcium phosphate particles were obtained from systems composed of Renex-100, hexanol, cyclohexane and Ca2+, PO4 3- and OH- aqueous solutions. Particles of chemical composition, crystalline structure, morphology and size similar to those of bone mineral were obtained by varying the composition of the components of the system. For comparison, the mineral phase of bone was obtained from parietal bone and femur of 15-day, 1-month and 1-year-old Wistar rats. Synthetic calcium phosphates and bone samples were analyzed by XRD, ICP/OES and electronic microscopy. The results show that, by controlling the composition of the surfactant system, it is possible to obtain particles of different morphologies and sizes, which are more similar to the particles that compose bone mineral. This similarity might indicate that the body makes use of systems to synthesize bone mineral. These systems might present properties similar to those of the systems studied in this work.

Abstract: Some microscopy studies on the mineral phase of bone have been carried out either utilizing Optical or Scanning Electron Microscopy (SEM), generally around 1000x magnification, to observe the interaction between cells and bone mineral. Other studies have been utilizing Transmission Electron Microscopy (TEM), generally around 1000000x magnification, to observe the fundamental particles that form bone mineral. The literature lacks works that utilize Scanning Electron Microscopy around 10000x magnification, particularly suitable for the study of structures composed by the aggregation of fundamental particles. The objective of this work was to study the morphologic differences between the mineral phase of femur and parietal bone of Wistar rats. Observation of the micrographs showed that the microscopic morphology of the mineral phase of femur was very similar to that of the parietal bone. It was also possible to notice that the morphology of the mineral phases varied with age, yet this variation was practically the same for the material obtained from the two types of bones.

Abstract: In this work, some modifications that occur in crystallites that compose the mineral phase of bone throughout the lives of animals were studied by X-ray diffractometry. The Debye-Scherrer equation was applied to the diffractograms, allowing the determination of the mean crystallite size and the changes in the mean crystallite size with relation to the diffraction planes 002 and 310. Likewise, the intensity of peaks in the diffractograms corresponding to the same diffraction planes was correlated with the number of crystallographic planes or of unit cells present in the crystallites.

Abstract: In this work, Scanning Electron Microscopy (SEM) has been used to determine the size and morphology of bone mineral crystals obtained from hydrazine-deproteinated parietal bone and femur of Wistar rats aged 15 days, 1 month and 1 year. Apart from the Scanning Electron Microscopy study, crystal size was also determined by X-ray diffractometry, using the Debye- Scherrer equation. Analyzing the results obtained and those reported in the literature for isolated crystals, it is possible to evaluate the influence of age and type of bone on the nanostructure of bone mineral and also propose the existence of a fundamental morphological unit that repeats itself in bone mineral formation.