RESUMEN
Hydroxyapatite coating on commercially pure titanium has been produced by a biomimetic method in order to improve osteointegration for medical implant purposes. A specific chemical treatment by etching titanium substrate with different concentrations of NaOH aqueous solution at 130 degrees C in an autoclave, followed by heat treatment at 600 degrees C was selected to obtain an activated titanium substrate. The microporous surface obtained has allowed the nucleation and growth of a calcium phosphate layer by soaking the substrate in a simulated body fluid (SBF). Scanning electron microscopy (SEM) together with energy dispersive analyzer for X-ray (EDS), X-ray diffraction (XRD) as well as Fourier transform infrared spectroscopy (FT-IR) were employed to evaluate the hydroxyapatite coating. A homogeneous structure coating without cracks defined the chemical treatment condition of the substrate.
RESUMEN
Titanium was submitted to chemical attack with sodium hydroxide solution under hydrothermal (SBF) conditions and then kept for 4 weeks in simulated body fluid after heat treatment. The resultant coating titanium samples were characterized regarding nucleation and growth of hydroxyapatite on their surfaces using scanning electron microscopy and energy dispersive spectroscopy, as well as low angle X-ray diffraction. In order to obtain a thermodynamic explanation of same results, Eh-pH diagrams of Na-Ti-H2O and Ca-Ti-H2O systems at 25, 100, 200, and 300 degrees C were built for selected activities of the species in aqueous solutions. Values of pairs corresponding to the predominance limit of the species in solution at equilibrium with 0.21 atm of oxygen pressure were taken from these Eh-pH diagrams for subsequent building of the pNa-pH and pCa-pH diagrams of the same systems at each referred temperature (pi = -log10ai). In addition, the titanate-apatite free energy of formation was estimated and then a pCa-pH diagram of the Ca-P-Ti-H2O system at 25 degrees C was built. Examination of the resultant diagrams could elucidate the thermodynamic viability of the process.
Asunto(s)
Materiales Biocompatibles Revestidos/química , Durapatita/química , Hidróxido de Sodio/farmacología , Titanio/química , Microscopía Electrónica de Rastreo , Modelos Químicos , Termodinámica , Difracción de Rayos XRESUMEN
Chemical formation of a glucose-cyanide complex was necessary for metabolic degradation of cyanide at concentrations up to 50.0 mg/L by a strain of Escherichia coli isolated from gold extraction circuit liquids. Ammonia accumulating during the culture log phase as the sole nitrogen by-product was further utilized for bacterial growth. Washed (intact) cells, harvested at different periods of bacterial growth on cyanide, consumed oxygen in presence of cyanide. These findings suggest that metabolism of cyanide involved a dioxygenase enzyme that converted cyanide directly to ammonia, without the formation of cyanate.
Asunto(s)
Cianuros/metabolismo , Escherichia coli/metabolismo , Contaminantes Químicos del Agua/metabolismo , Amoníaco/metabolismo , Biodegradación Ambiental , Industria Química , Escherichia coli/crecimiento & desarrollo , Glucosa/metabolismo , Oro , Concentración de Iones de Hidrógeno , Consumo de OxígenoRESUMEN
Eight cases of subcutaneous phaeohyphomycosis are presented. A lack or scarcity of fungal pigmentation was seen in six of these cases. The simple act of lowering the microscope condenser makes these uncolored fungi easily visible. The thick hyaline capsule becomes refringent, presenting single oval or round cells and septated hyphae, which can be short or elongated, branched or unbranched, and irregularly swollen. The dematiacious character of the fungi is confirmed by using the Fontana-Masson stain. The fungi are not visible under polarized light. Our studies point to the probability of subcutaneous phaeohyphomycosis being a widespread tropical disease in Brazil. However, it is rarely diagnosed because of the common practice of fixing tissue specimens without prior culturing and the difficulties of detecting the fungal forms using customary microscopic procedures, especially when the fungi have a lack of pigment and are hard to detect by hematoxylin and eosin stain.