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Type: TESE
Title: Influencia de alginato e quitosana na precipitação de fosfatos de calcio
Title Alternative: Influence of alginate and chitosan on the precipitation of calcium phosphates
Author: Lima, Daniel Oliveira de
Abstract: Resumo: Não informado

Abstract: Natural systems are able to create organic-inorganic composites of remarkable properties. Bone, for instance, presents properties that are found both in ceramics and polymers. This effect is related to the organic matrix, which controls nucleation and growth of calcium phosphate crystals, besides composite's organization and architecture in nanometric levels, in order to achieve a better understanding of this process, precipitation of calcium phosphate was carried out in a medium which contained small amounts of alginate and chitosan, seeking to emulate the matrix effect. Calcium phosphates precipitates were obtained using two different concentrations of the biopolymer and one control sample. The experiments were divided in two groups, depending on the system's initial pH. In the first group, the starting pH was acid. However, part of the reaction medium was separated and had its pH adjusted to an alkaline range. In the second group, the initial pH was calculated in order to be in the range of hydroxyapatite stability. Characterization was accomplished by scanning electron microscopy, X-Ray diffraction and Fourier-transform infrared spectroscopy. The powders obtained in the first group were compose mainly by brushite (CaHPO4.2H2O) and its anhydrous phase, monetite, CaHP04. In the first group of experiments with alginate, monetite concentration was related mainly to the reaction medium pH, suggesting that alginate-calcium interaction was strongly dependent on the formation of complexes among carboxyl radicals and calcium, which avoided water bonding. Chitosan-doped samples, on the other hand, seemed to be affected mainly by the biopolymer concentration. Chitosan and monetite concentration seemed to be inversely proportional. This is attributed to the ionotropic effect, which reduced auto-diffusion and consequently, calcium phosphate-chitosan interaction. These samples also possessed an apparent degree of orientation, supposedly due to a coherent growth of calcium phosphate crystals over heterogeneous nuclei. Alginate-doped samples obtained in the second group of experiments presented reduced cristal Unity, which was related to reprecipitation of the crystals over biopolymers nuclei. Chitosan-doped samples, however, presented an increase in crista!Iinity. This may be attributed to a process of nucleation inside the gel, implying in crystalline growth controlled by sterical effects
Subject: Quitosana
Fosfato de cálcio
Language: Português
Editor: [s.n.]
Date Issue: 2006
Appears in Collections:FEQ - Dissertação e Tese

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