Papers by Author: Euler Araujo dos Santos

Abstract: In this current study it was investigated the influence of positively and negatively charged surfaces on apatite nucleation process from a supersaturate solution containing calcium and phosphorus (SBF solution). Glass slides were coated with polyelectrolytes thin films using a standard method to produce self-assembled monolayers (SAMs). Slides without treatment were used as control. Positive and negative glass slides were soaking in simulated body fluid (1.5 SBF) for 2, 8, 24 and 96 hours. The surfaces were characterized by scanning electron microscopy (SEM). Accordingly, the apatite mineralization was observed on all surfaces, no matter the surface charge. No remarkable morphological changes were verified between the precipitate in both positive and negative surfaces. It suggests that the crystal growth is not influenced by the initial attraction between either a negative surface and Ca²⁺ ions or a positive one and PO₄^3- ions.

Abstract: In this work, nanocomposites of hydroxyapatite and Pluronic F127 were prepared by a wet chemical method, using acid-basic reaction with Ca/P ratio of 1.67 in 10% (m/V) Pluronic F127 at 0, 37 and 90°C. The final concentration of Pluronic F127 was adjusted to 37% (m/V) at 4°C. Afterwards, the samples were lyophilized. Characterization was performed in purified samples (after Pluronic F127 removal), samples with 10% (m/V) of Pluronic F127 and calcined samples at 1000°C by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Analyses by XRD of non-calcined samples showed that hydroxyapatite was obtained, in which the samples prepared at 0°C exhibited larger peaks attributed to lower crystallite sizes. For the calcined samples, both Raman spectroscopy and XRD exhibited hydroxyapatite for the syntheses at 37 and 90°C whereas the one prepared 90°C were identified as β-tricalcium phosphate (β-TCP). Morphological analysis by SEM indicated that the hydroxyapatite was sphere or rod agglomerates in mesoporous morphology for the nanocomposites prepared at 0 and 37°C, while the sample prepared at 90°C was nanospheres agglomerated into a smother matrix. After Pluronic F127 removal, samples fabricated at 0 and 37 °C exhibited coalescence of the nanostructures, whereas the sample synthesized at 90°C kept mesoporous. Calcined samples showed sintering and some rods structures.

Abstract: The current trends in bioactive ceramics point out the ionic substitution in hydroxyapatite (HA) as a concrete way to create new active ceramics with a high developed biomimetic character. Accordingly, our objective in this work was investigating the effects of the simultaneous replacement of Ca²⁺ ions for Mg²⁺, Sr²⁺ and Mn²⁺ into the crystalline structure of HA.

Abstract: It has been reported that there is a slight equilibrium between calcite and apatite precipitation from SBF solution during typical bioactivity assays, once it is supersaturating in both ionic precursors. In order to better understand this mechanism, we have proposed here to evaluate the role of three different aqueous medium (water, SBF and McCoy), under equilibrium (agitation) and out of equilibrium (no agitation).