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      Obtenção de titânio metálico com porosidade controlada por metalurgia do pó Translated title: Porous titanium production and porosity control by powder metallurgy (P/M)

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          Translated abstract

          Titanium is an attractive material for structural and biomedical applications because of its excellent corrosion resistance, biocompatibility and high strength-to-weight ratio. The high reactivity of titanium in the liquid phase makes it difficult to produce it by fusion. Powder metallurgy has been shown to be an adequate technique to obtain titanium samples at low temperatures and solid-phase consolidation. The production of compacts with different porosities obtained by uniaxial pressing and vacuum sintering is briefly reviewed. Powder particle size control has been shown to be very important for porosity control. Sample characterization was made using scanning electron microscopy (SEM) images.

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          Biomaterials

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            Preparation, properties and controlled release behaviors of pH-induced thermosensitive amphiphilic gels.

            Two pH-induced thermosensitive amphiphilic gels for controlled drug release were constructed with thermosensitive poly(N-isopropylacrylamide) (PNIPAm) and hydrophobic poly(ethyl acrylate) (PEA) by interpenetrating polymer network (IPN) technology. To obtain pH-induced thermosensitive functionality at physiological temperature, 5 mol % of acrylic acid (AAc) and N, N-dimethyl aminoethyl methacrylate (DMA) were incorporated into PNIPAm chain by their copolymerization. It is found that the IPN hydrogels show pH-induced thermosensitivity at physiological temperature. When the amphiphilic gels with IPN structure were immersed in water, the hydrophobic moieties formed by PEA have the potential to act as reservoirs for hydrophobic drugs, from which drug may be released slowly. Using drug daidzein (DAI) as a model molecule, controlled release behaviors of the IPNs were investigated. It is found that the presence of permanently hydrophobic PEA network can indeed slow the release rate of DAI and to some extent overcome disadvantageous burst effect of PNIPAm-based networks in hydration state. The release kinetics of DAI from the IPNs seems to follow pseudo-zero-order release character, regardless of the hydrogels in swollen or shrunken state.
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              Comparing a photoinduced pericyclic ring opening and closure: differences in the excited state pathways.

              The photochromicity of fulgimides rests on the existence of open (E) and closed ring (C) isomers. As predicted by the Woodward-Hoffmann rules both isomers can photochemically be interconverted. This interconversion has been studied by femtosecond fluorescence and transient absorption spectroscopy. For either direction (E --> C cyclization and C --> E cycloreversion) a biphasic fluorescence decay on the 0.1-1 ps time scale is observed. The longer time constants of the decays equal the formation times of the photoproducts. The time constants retrieved (0.06 and 0.4 ps for E --> C, 0.09 and 2.4 ps for C --> E) and the associated spectral signatures differ substantially. This indicates that no common excited-state pathway for the two directions exists, as one would infer from a simple Woodward-Hoffmann consideration. These findings support recent quantum dynamic calculations on the excited-state topology of fulgimides.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                qn
                Química Nova
                Quím. Nova
                Sociedade Brasileira de Química (São Paulo )
                1678-7064
                April 2007
                : 30
                : 2
                : 450-457
                Affiliations
                [1 ] Instituto Nacional de Pesquisas Espaciais Brazil
                [2 ] Instituto Nacional de Pesquisas Espaciais Brazil
                Article
                S0100-40422007000200037
                10.1590/S0100-40422007000200037
                17ecaa51-749e-4f98-a072-24d24c225613

                http://creativecommons.org/licenses/by/4.0/

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                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0100-4042&lng=en
                Categories
                CHEMISTRY, MULTIDISCIPLINARY

                General chemistry
                titanium,powder-metallurgy,porous
                General chemistry
                titanium, powder-metallurgy, porous

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