The structure of Nafion 117 membranes was studied through SAXS experiments and 2D pattern simulations. Measurements were taken for different moisture conditions by synchrotron radiation, and for different temperatures through X-ray tube irradiation. The experimental profiles were fitted through simulations based on a new structural model including: the amorphous polymer matrix, polymer crystallites, and inverse core-shell type channels conformed by water cylinders and sulfonic chains. The geometrical parameters intervening in the simulation of the SAXS patterns were optimized for each experimental condition. This approach allowed the proper description of the experimental SAXS profiles for the various moisture conditions studied. In addition, a recent lamelar model was also included in the assessments, and the corresponding performances were discussed.

Ceramides constitute a group of lipids with usually high melting temperature that also favor negative curvature in membranes when mixed with other lipids. The short chain C10:0 ceramide is an asymmetric lipid which consists of an 18 carbon sphingosine base N-acylated with decanoic acid. According to high sensitivity differential scanning calorimetry, it shows a minor exothermic peak at 61°C and a main endothermic transition at 75°C. By small angle X-ray scattering and polarized light microscopy we found that, at temperatures below the main transition, the fully hydrated lipid dispersions are arranged in a tridimensional structure corresponding to an inverted hexagonal phase. Infrared spectroscopy and wide angle X-ray diffraction indicated that the acyl chains of ceramides exhibit a relatively high order in the hexagonal phase. As far as we know, this is the first report of a lipid hexagonal phase having highly ordered acyl chains. Molecular asymmetry due to the different length of the sphingosine and the N-acyl chains of C10:0 ceramide may explain why this novel phase is formed.

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Hydroxyapatite (HA), beta-tricalcium phosphate and bioactive glasses are commonly used as reabsorbable biomaterials, mainly in orthopaedics and dentistry. The performance of each material depends on many factors, in particular, on their chemical and phase composition, microstructure, granule size and pore volume. For this reason, it is important to have a full characterization that allows correlating these properties with the material biological behaviour.In this work, three commercial samples of materials currently used in dentistry as bone substitutes were characterized. Granules corresponding to bovine and synthetic HA and bioactive glass 45S5 type were studied by scanning electron microscopy, conventional and synchrotron radiation X-ray diffraction and X-ray fluorescence. The specific surface area was also obtained by the Brunauer, Emmett and Teller method.We observed that Ca/P molar ratios for both HAs are higher than the value corresponding to the stoichiometric HA. The coherent domain obtained for the bovine HA is larger along the c axis crystal direction, and it is around 15 times lower than the value corresponding to the synthetic HA. The specific surface area for the bovine HA is one of the highest values reported in literature. Low amounts of crystalline CaO were observed only for the synthetic HA sample. Crystalline combeite and wollastonite were detected for the bioactive glass sample and quantified by using rutile as internal standard. The relation between the physicochemical characterization performed in this work and the potential biological response of the materials is discussed in terms of the information available in literature.

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In past decades, the combination of polymers to obtain blends in film shapes has been a very effective strategy to meet the needs of the increasingly demanding market. In this sense, pH- and thermo-sensitive (PHT) polymers have recently drawn the attention of researchers for their countless applications. However, binary mixtures of typical PHTs like polyacrylic acid (p-AAc) and poly-N-isopropylacrylamide (p-NIPAm) were unable to form films. In this sense, it was hypothesized that NIPAm copolymerized with AAc monomers can yield blends with virtually the same functional group composition of binary mixtures of p-NIPAm and p-AAc homopolymers but with different properties of film formation. For this, a copolymeric radical synthesis and the subsequent analytical studies were complemented to get a broad description of these materials. P-NIPAm and p-AAc homopolymers and different proportions of copolymers p-NIPAm-co-AAc were obtained and thoroughly characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Size Exclusion Chromatography (SEC), acid-basic titration, and rotational rheology. Among the samples, the solutions of p-AAc with p-NIPAm and p-NIPAm-co-AAc copolymers with a higher proportion of NIPAm units (0.8 and 0.6 NIPAm/AAc) precipitated as interpolymer complexes. Since it was expected, the combination with p-NIPAm-co-AAc 40/60 copolymer, which has a higher proportion of AAc groups and pH sensitivity, allowed obtaining blends suitable for the preparation of films. Furthermore, despite the fact that the combinations of p-NIPAm-co-AAc 40/60 with p-NIPAm-co-AAc 80/20 or p-NIPAm were successful, the mechanical properties of the films are worse compared to the other blends, leaving this issue open for subsequent studies.

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