RESUMO
Porous silica gels with high surface areas were prepared from tetraethylothosilicate and polyacrylic acid (PAA) of high molecular weight in acidic media by a sol-gel method. PAA content and ageing temperatures were varied in order to obtain different microstructures. Samples were sintered at temperatures up to 400 degrees C, and subjected to in vitro evaluation by soaking them in acellular inorganic solutions at 37 degrees C and pH 7.3. Surface precipitation of carbonate-apatite on some of the gels was observed by FTIR spectroscopy, scanning electron microscopy and EPMA. Silica dissolution and re-precipitation phenomena were also observed. The relationship between both phenomena during the in vitro test is discussed mainly in terms of structural and microstructural features of the gel.
Assuntos
Resinas Acrílicas/química , Silanos/química , Dióxido de Silício/química , Apatitas/química , Líquidos Corporais/química , Teste de Materiais , Microscopia Eletrônica de Varredura , Porosidade , Sílica Gel , Espectroscopia de Infravermelho com Transformada de Fourier , Propriedades de Superfície , TemperaturaRESUMO
A commercial acrylic bone cement was modified by the incorporation of different weight fractions of polycrystalline hydroxyapatite (HA), and the modified formulation was investigated. The influence of the filler proportion on the flow characteristics and the mechanical behavior of the resultant composite was evaluated. The residual monomer present in the cured materials was measured by gas chromatography. The comparison of the residual monomer present in the cements with and without reinforcement demonstrated that the degree of polymerization was not affected by the addition of HA. Porosity morphology was analyzed by optical and scanning electron microscopy. Image examination revealed that the porosity and the pore size of the hardened cement increased with an increasing amount of particulate filler. Flexural, compressive, and fracture properties of the cement with varying amounts of HA reinforcement were measured. It was found that up to 15 wt% HA could be added for increases in flexural modulus and fracture toughness. HA acts as a rigid filler that enhances fracture resistance and flexural modulus. Our results show that the workability of the modified formulation limited the incorporation of the ceramic filler to a maximum value of 15 wt%.
Assuntos
Materiais Biocompatíveis/química , Cimentos Ósseos/química , Hidroxiapatitas/química , Polimetil Metacrilato/química , Microscopia Eletrônica de Varredura , PorosidadeRESUMO
Sintering of two hydroxyapatite (HA) samples with different Ca/P ratios was studied as a function of thermal pretreatments, sintering temperature and additives (0-0.6 ion % Li+ or 0-5 ion % Mg2+). The samples were sintered in air and characterized by density measurements, scanning electron microscopy, differential thermal analysis, X-ray diffraction and dilatometry. Upon sintering, samples with Ca/P ratio of 1.51 (HA C) transformed to beta-Ca3(PO4)2 and Ca10(PO4)6(OH)2, resulting in materials with low densities and containing agglomerated beta-Ca3(PO4)2 when sintered above 1200 degrees C. Samples with a Ca/P ratio of 1.77 (HA S), without beta-Ca3(PO4)2, showed better sinterability and homogeneous microstructures. Li+ additions favoured liquied-phase sintering and reduced the beta-Ca3(PO4)2 content in sintered materials. Mg2+ additions did not result in higher densities, but inhibited the hydroxyapatite grain growth rate. A significant percentage of the added Mg2+ was incorporated into the beta-Ca3(PO4)2 structure.