Papers by Author: Alexandra A.P. Mansur

Abstract: Chitosan is a polymer from natural source with a wide range of applications, such as in the adsorption of heavy metals. However, it presents limitation in relation to pH, because it is insoluble in neutral and alkaline. Thus, a good alternative has been the use of derivatives of chitosan, as carboxymethyl chitosan (CMC). This chemical modification of chitosan may favor the adsorption process, because it broadens the pH range of solubility and the quantity of chemical groups available for the uptake of ions. This work was carried out the synthesis and characterization of carboxymethyl chitosan. The properties of derivatives synthesized were assessed through the study of solubility at different pHs and using the techniques of potentiometric titration, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) spectroscopy and thermal analysis. The results have demonstrated the effective incorporation of carboxylic groups in the structure of chitosan, as well as the dependence of degree of substitution with the concentration of hydroxide during the synthesis. Hence, the chemical functionalization of chitosan for producing carboxymethyl chitosan offers the possibility of applying this new adsorbent for water treatment.

Abstract: The need for obtaining new materials to replace human body parts that were destroyed or damaged led scientists from different areas of research for developing new biomaterials. Thus, the aim of this work was the synthesis and characterization of niobium-modified apatite bioceramics. Calcium phosphates (CaP) were synthesized with niobium partially replacing calcium sites using aqueous precipitation route at room temperature. The bioceramics, with and without Nb incorporation, were characterized by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) as prepared and after heat treatments The results indicated that Nb was incorporated in the apatite structure promoting morphological and structural changes in the ceramic properties.

Abstract: There is a constant need for bone substitutes. This work was focused on evaluating morphological characteristics of new bioceramic three-dimensional scaffold for bone tissue engineering based on Portland cement with air-voids introduced by outgassing reaction product from lime and aluminum powder. Pores morphology was observed using scanning electron microscopy (SEM). Bulk density, apparent density, and apparent porosity were measured by Archimedes method. Water absorption by total immersion and by capillarity was also investigated. The results have indicated that cement based scaffolds exhibit a hierarchical structure with interconnected macropores and a micropores framework that indicate potential use of the developed porous materials as bone substitutes.

Abstract: Bioactive glasses are materials that have been used for the repair and reconstruction of diseased bone tissues, as they exhibit direct bonding with human bone tissues. However, bioactive glasses have low mechanical properties compared to cortical and cancellous bone. On the other hand, composite materials of biodegradable polymers with inorganic bioactive glasses are of particular interest to engineered scaffolds because they often show an excellent balance between strength and toughness and usually improved characteristics compared to their individual components. Composite bioactive glass-polyvinyl alcohol foams for use as scaffolds in tissue engineering were previously developed using the sol-gel route. The goal of this work was the synthesis of composite foams modified with higher amounts of PVA. Samples were characterized by morphological and chemical analysis. The mechanical behavior of the obtained materials was also investigated. The degree of hydrolysis of PVA, concentration of PVA solution and different PVA-bioactive glass composition ratios affect the synthesis procedure. Foams with up to 80 wt% polymer content were obtained. The hybrid scaffolds obtained exhibited macroporous structure with pore size varying from 50 to 600 µm and improved mechanical properties.

Abstract: Polyvinyl alcohol (PVA) is a unique synthetic biocompatible polymer and it has a large number of hydroxyl groups that can react with many kinds of functional groups. In the present work, nanostructured PVA/TEOS hybrids were characterized by Small-angle X-ray Scattering (SAXS) associated with Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. We have synthesized hybrids based on the reaction of PVA with tetraethoxysilane (TEOS). PVA/TEOS hybrids were also modified in the nanometer-scale by crosslinking with glutaraldehyde (GA) during the synthesis involving hydrolysis and condensation of PVA/TEOS network. FTIR spectra showed major vibration bands associated with organic-inorganic chemical groups present in the hybrid composite PVA/TEOS. XRD coupled to FTIR results have indicated the presence of semi-crystalline domains embedded in amorphous PVA matrix. SAXS results were presented as plots with experimental scattering intensity, I(q), as a function of the modulus of the scattering vector, q. SAXS curves showed quite different trend on vector q with the scattering intensity I(q) corresponding to samples PVA, PVA/GA and PVA/TEOS/GA. Pure PVA sample showed a “knee” type curve, with maximum value q=0.04 Å-1. These results have indicated different nano-ordered disperse phases for PVA, PVA/TEOS hybrid and PVA/TEOS/GA chemically crosslinked hybrid.

Abstract: In the present work, we aimed to investigate the immobilization of Bovine Serum Albumin (BSA) into poly (vinyl alcohol) (PVA) network. PVA hydrogels with BSA were characterized by Synchrotron SAXS radiation associated with Fourier Transform Infrared Spectroscopy (FTIR). We synthesized hydrogels by dissolving PVA in aqueous solution (5.0 wt%) and crosslinked with glutaraldehyde (GA). PVA and PVA/GA hydrogels samples were immersed in BSA aqueous solution for protein immobilization. FTIR spectra showed major vibration bands associated with PVA and GA chemical groups, and BSA protein amides. Regarding to SAXS characterization, the slope of the log I(q), scattering intensity, as a function of log q, the scattering vector, provided important information about the morphology of entities present in the system. Two different scattering patterns were obtained for PVA (slope = 3.5) and PVA/BSA (slope=1.5 and 3.0). These results have given strong evidence of nano-ordered dispersed globular BSA immobilized into chemically crosslinked PVA hydrogel network. SAXS analyses have indicated that the scattering q-vector maximum value was shifted by altering PVA polymer hydrogel with GA crosslinker and also with BSA incorporation into the network.

Abstract: In the present work, a novel biocomposite has been developed based on lignin (Lig) and HA/b-TCP bioceramic materials. The Lig/HA and Lig/b-TCP systems were investigated by Scanning Electron Microscopy coupled to EDX microprobe (SEM/EDX). Lignin is a lignosulfonate natural polymer with complex random coupling and the exact chemical structure is yet unknown. FTIR spectroscopy is an important tool for lignin characterization based on several major vibration bands associated with generally found chemical groups. Consequently, FTIR spectroscopy was used to evaluate the chemical functionalities and major components present in the material. SEM photomicrographs of biocomposites Lig/HA and Lig/b-TCP have shown uniform dispersion of the natural polymer binder in the bioceramic matrix. Also, chemical composition obtained by EDX spectra have indicated lignin evenly distributed in the HA and b-TCP compounds. Novel biocomposites based on lignin/HA and lignin/b-TCP were developed with porosity ranging from 50 to 100 µm. These results have confirmed the high potential application of lignin as a non-toxic natural polymer binder to be used as 3D scaffold template for biomedical applications.

Abstract: In the present work, natural coral from Brazilian reefs were studied according to their crystallography by X-ray diffraction and microstructure by Scanning Electron Microscopy (SEM/EDX). FTIR spectroscopy was also used to evaluate the chemical functionalities and major components present in the material. The SEM morphology results have shown a tri-dimensional coral structure with porous ranging from 50 to 200 µm. Aragonite was identified as the major crystalline phase through XRD analysis and FTIR spectroscopy. Strontium calcium carbonate, (Sr,Ca)CO3, was also identified by XRD analysis. After sintering at 900º/1h, the conversion from aragonite to CaO and calcite was observed. These results have endorsed the high potential application of natural coral materials as 3D scaffolds for biomedical application, because of calcium carbonate compounds can be converted to HA by hydrothermal and biomimetic coating processes.