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Long time survival of Bartonella bacilliformis in blood stored at 4 ºC. A risk for blood transfusions.

Mon, 29 Oct 2012 16:36:27 GMT

Title: Long time survival of Bartonella bacilliformis in blood stored at 4 ºC. A risk for blood transfusions. Authors: Champin, Denisse; Cornejo, Hernán; Zabaleta, Víctor; Ruiz, Joaquím; Silva, Wilmer; Pons, Maria J.; Valle Mendoza, Luis Javier del; Tinco, Carmen R.; Casabona, Veronica D.; Gomes, Claudia; Bazan, Jorge

Hybrid polythiophene-clay exfoliated nanocomposites for ultracapacitor devices

Mon, 08 Oct 2012 10:17:51 GMT

Title: Hybrid polythiophene-clay exfoliated nanocomposites for ultracapacitor devices Authors: Aradilla Zapata, David; Azambuja, Denise S.; Estrany Coda, Francesc; Casas Becerra, María Teresa; Ferreira, Carlos A.; Alemán Llansó, Carlos Abstract: Exfoliated nanocomposites of poly(3,4-ethylenedioxythiophene) (PEDOT) and montmorillonite (MMT) have been prepared by in situ anodic polymerization, concentrations of clay ranging from 5% w/w to 50% w/w being included in the aqueous polymerization medium. The morphology, electrical conductivity, adherence, thermal stability, charge storage, specific capacitance, electrostability, doping level and band gap have been determined for the different PEDOT–MMT nanocomposites and compared with those of pristine PEDOT. Many of these properties have been found to depend on both the concentration of clay and the thickness (micrometric or nanometric) of the generated films. Types I and II ultracapacitors have been fabricated using nanometric and micrometric films of PEDOT and PEDOT–MMT. The properties of such devices have been characterized and compared with those reported in the literature for ultracapacitors fabricated using nanocomposites of PEDOT and other inorganic materials. Both nanometric and micrometric type II ultracapacitors, which correspond to an asymmetric configuration of PEDOT and PEDOT–MMT films, have been found to present the better properties (e.g. the specific capacitance for nanometric and micrometric devices is 429 and 116 F g 1, respectively), evidencing the favorable effect of the clay. Finally, the effects of the electrochemicaldegradation on the ultracapacitors have been rationalized using electrochemical impedance spectroscopy.

Controlling the morphology of poly(N -cyanoethylpyrrole)

Tue, 02 Oct 2012 11:08:45 GMT

Title: Controlling the morphology of poly(N -cyanoethylpyrrole) Authors: Fabregat Jové, Georgina; Alemán Llansó, Carlos; Casas Becerra, María Teresa; Armelín Diggroc, Elaine Aparecida Abstract: The morphology of poly(N-cyanoethylpyrrole) has been controlled through the polymerization process. This polymer has been prepared by anodic polymerization, chemical oxidative polymerization in emulsion medium, and layer-by-layer templating polymerization. Anodic polymerization using LiClO4 as supporting electrolyte provides compact films, in which the oxidation degree is controlled through the thickness, useful for the microdetection of dopamine. Chemical polymerization using FeCl3 as oxidant agent results in very well-defined microspheres with porous internal structure, which may be useful in molecular loading and transport processes. Finally, the layer-by-layer templating technique produces core−shell particles of controlled size and thickness. Moreover, these core−shell particles can be easily converted in hollow microspheres by removing the template

Thermal degradation studies on homopolymers and copolymers based on trimethylene carbonate and glycolide units

Thu, 20 Sep 2012 07:59:07 GMT

Title: Thermal degradation studies on homopolymers and copolymers based on trimethylene carbonate and glycolide units Authors: Diaz Celorio, Elena; Franco García, María Lourdes; Marquez, Yolanda; Rodríguez Galán, Rafael Alfonso; Puiggalí Bellalta, Jordi Abstract: The non-isothermal degradation kinetics of poly(trimethylene carbonate) (PTMC) and polyglycolide (PGL) was investigated by thermogravimetric (TG and DTG) analysis in the temperature range between 50 and 550 °C at different heating rates (0.5–40 °C/min). Both homopolymers showed a complex multi-step degradation process. Kinetic analysis was successfully performed for the main degradation steps using the isoconversional Kissinger–Akahira–Sunose and Friedman methods. Activation energies of these steps were practically independent of the degree of conversion. The true kinetic triplets (E, A, f(α)) were determined by the Coats–Redfern method. The results clearly indicated that the two homopolymers mainly degraded by quite different mechanisms, i.e. A3 and F1, which may be associated with different depolymerization processes (e.g. decarboxylation or unzipping). Degradation of copolymers of trimethylene carbonate and glycolide with different chemical microstructures (i.e. random, blocky and segmented) and of blends with different percentages of both homopolymers was also studied. Interestingly, a deceleration and an acceleration for the decomposition of trimethylene carbonate and glycolide segments were observed, respectively. Specifically, the two-step degradation process of the blend with 50 wt% of each homopolymer was analyzed by the above methodologies. Kinetic data indicated that the main degradation process involved a different mechanism from that previously determined for PTMC and PGL, and that the activation energy was intermediate (i.e. EPTMC < EBlend < EPGL).

Synthesis of glycolide/trimethylene carbonate copolymers: influence of microstructure on properties

Mon, 06 Feb 2012 10:26:19 GMT

Title: Synthesis of glycolide/trimethylene carbonate copolymers: influence of microstructure on properties Authors: Diaz Celorio, Elena; Franco García, María Lourdes; Rodríguez Galán, Rafael Alfonso; Puiggalí Bellalta, Jordi Abstract: Copolymers of glycolide and trimethylene carbonate with different compositions and microstructures (i.e. random, blocky and segmented) were synthesized by two-step ring opening polymerization. NMR analyses revealed that transesterification reactions took place during the first step, which corresponded to the synthesis of soft segments, and mainly when the trimethylene carbonate content of the reaction medium was high. The transesterification percentage did not significantly change with the addition of hard blocks in the second reaction step. Infrared spectroscopy was a complementary, highly effective tool to evaluate the hard segment length, crystallinity and glycolide percentage incorporated into the crystalline phase for all studied samples. Calorimetric analyses showed dependency of properties on the length of the polyglycolide hard segment and also good miscibility between glycolide and trimethylene carbonate rich phases. Crystalline morphologies attained with segmented and random copolymers were significantly different, although in all cases a positive birefringence was detected. Thermogravimetric analyses indicated that all studied copolymers had a similar degradation behavior, which was intermediate between those observed in the corresponding homopolymers. Samples with a significant glycolide unit content showed a stabilizing effect for the degradation of poly(trimethylene carbonate) blocks.

Aliphatic polyester and Poly(ester amide) Clay nanocomposites by In-situ Polymerization

Tue, 24 Jan 2012 10:42:48 GMT

Title: Aliphatic polyester and Poly(ester amide) Clay nanocomposites by In-situ Polymerization Authors: Morales Gámez, Laura Teresa; Rodríguez Galán, Rafael Alfonso; Franco García, María Lourdes; Puiggalí Bellalta, Jordi

Preparation and release study of ibuprofen-loaded porous matrices of a biodegradable poly(ester amide) derived from L -alanine units

Fri, 23 Sep 2011 10:10:49 GMT

Title: Preparation and release study of ibuprofen-loaded porous matrices of a biodegradable poly(ester amide) derived from L -alanine units Authors: Valle Mendoza, Luis Javier del; Roca, Diana; Franco García, María Lourdes; Puiggalí Bellalta, Jordi; Rodríguez Galán, Rafael Alfonso Abstract: Scaffolds of a biodegradable poly(ester amide)constituted of L-alanine, sebacic acid, and 1,12-dodecanediol units (abbreviated as PADAS) were prepared by the compression-molding/particulate-leaching method. The influence of the type, size, and percentage of salt on the scaffold porosity and morphology was evaluated. The thermal behavior and crystallinity were also studied for samples obtained under different processing conditions. PADAS scaffolds were not cytotoxic because they showed good cell viability and supported cell growth at a similar ratio to that observed for the biocompatible materials used as a reference. The use of PADAS scaffolds as a drug-delivery system was also evaluated by the employment of ibuprofen, a drug with well known anti-inflammatory effects. Different drug-loading methods were considered, and their influence on the release in a so¨rensen’s medium was evaluated as well as the influence of the scaffold morphology. A sustained release of ibuprofen could be attained without the production of a negative effect on the cell viability. The release kinetics of samples loaded before melt processing was well described by the combined Higuchi/first-order model. This allowed the estimation of the diffusion coefficients, which ranged between 3x10‾14 and 5x10‾13 m2/ s. Samples loaded by immersion in ibuprofen solutions showed a rapid release that could be delayed by the addition of polycaprolactone to the immersion medium (i.e., the release rate decreased from 0.027 to 0.015 h‾1).

Biodegradable Poly(Ester Amide)s: Synthesis and Applications

Mon, 25 Jul 2011 11:13:28 GMT

Title: Biodegradable Poly(Ester Amide)s: Synthesis and Applications Authors: Rodríguez Galán, Rafael Alfonso; Franco García, María Lourdes; Puiggalí Bellalta, Jordi

Nanocomposites of new biodegradable poliesters and polyesteramides

Wed, 23 Mar 2011 17:36:39 GMT

Title: Nanocomposites of new biodegradable poliesters and polyesteramides Authors: Puiggalí Bellalta, Jordi; Morales Gámez, Laura Teresa; Franco García, María Lourdes; Casas Becerra, María Teresa; Valle Mendoza, Luis Javier del; Rodríguez Galán, Rafael Alfonso Abstract: Polymers are easily prepared by bulk polycondensation based on metal-halide salt formation, while crystallization is strongly influenced by incorporation and distribution of silicate nanoparticles.

Synchrotron radiation studies on even-odd and odd-even nylons

Tue, 08 Mar 2011 10:18:07 GMT

Title: Synchrotron radiation studies on even-odd and odd-even nylons Authors: Franco García, María Lourdes; Puiggalí Bellalta, Jordi; Ricart López, Albert; Morales Gámez, Laura Teresa; Soto, David Abstract: Aliphatic polyamides derived from odd diamine or odd dicarboxylic acid units cannot adopt a conventional sheet structure when molecular chains have an all trans conformation. However, typical fiber diffraction patterns of this sheet structure were observed in several polyamides derived from odd units such as nylons 65 and 56. Consequently, a new structure based on the establishment of intermolecular hydrogen bonds along two different directions was postulated. Real-time temperature dependence of X-ray diffraction patterns for nylons 65 and 56 was studied by synchrotron radiation to gain understanding of the Brill transition usually occurring in polyamides. Significant differences were found between the temperature dependence of both nylons, although a transition towards a monoclinic structure characterized by a single equatorial reflection around 0.425-0.420 nm was observed to occur at high temperatures. This transition was reversible for nylon 65 only. In this case, a characteristic hysteresis effect was found.

Influence of degradation on the crystallization behaviour of a biodegradable segmented copolymer constituted by glycolide and trimethylene carbonate units

Fri, 04 Mar 2011 11:23:45 GMT

Title: Influence of degradation on the crystallization behaviour of a biodegradable segmented copolymer constituted by glycolide and trimethylene carbonate units Authors: Franco García, María Lourdes; Rodríguez Galán, Rafael Alfonso; Puiggalí Bellalta, Jordi Abstract: The influence of degradation on non-isothermal crystallization from the melt of a segmented copolymer constituted of glycolide and trimethylene carbonate units and used as a bioabsorbable surgical suture was studied by optical microscopy, differential scanning calorimetry and time-resolved X-ray diffraction. Fibrillar positive spherulites were obtained with slightly degraded samples but new axialitic morphologies were detected when samples had a molecular weight, Mw, lower than 29,000 g/mol and the crystallization started at a high temperature. Crystal growth kinetics of samples degraded under different conditions was evaluated over a wide temperature range by a non-isothermal method. Two crystallization regimes (I and II) were determined for the more degraded samples (i.e., those able to crystallize according to axialitic and spherulitic morphologies), whereas only regime II was found for samples of higher molecular weights. Primary nucleation density decreased with the extent of degradation provided no morphological changes occurred, and so did the regularity of lamellar stacking, as shown by synchrotron measurements, although the morphological parameters remained practically constant.

Thermal stability studies on clay nanocomposites prepared from a degradable poly(ester amide) constituted by glycolic acid and 6-aminohexanoic acid

Fri, 04 Mar 2011 11:04:15 GMT

Title: Thermal stability studies on clay nanocomposites prepared from a degradable poly(ester amide) constituted by glycolic acid and 6-aminohexanoic acid Authors: Morales Gámez, Laura Teresa; Franco García, María Lourdes; Puiggalí Bellalta, Jordi Abstract: An intercalated nanocomposite of the organically modified montmorillonite Cloisite C25A and a degradable poly(ester amide) based on glycolic acid and 6-aminohexanoic acid units (poly(glc-alt-amh)) was prepared using a twin-screw co-rotating extruder. The non-isothermal degradation kinetics was investigated by thermogravimetric analysis (TG and DTG) in the temperature range of 50–600 ◦C at five heating rates (2, 5, 10, 20 and 40 ◦C/min) and compared with the neat polymer. Significant differences were found since the nanocomposite showed three degradation steps instead of the two decomposition processes detected in the pristine sample. The onset mass loss temperature decreased in the nanocomposite due to the presence of the organo-modifier compound, but the presence of the silicate layers significantly decreased the degradation rate at the last stages of decomposition. Kinetic analysis was performed using the Kissinger method and the isoconversional (Kissinger–Akahira–Sunose and Friedman) methods. The true kinetic triplets (E, A, f(˛)) were determined for the first two steps of degradation through the Coats–Redfern and the Invariant Kinetic Parameters methods. The results clearly indicated that the presence of the organo-modified clay modified the mechanisms of degradation.

Degradable Poly(ester amide)s for biomedical aplications

Fri, 04 Mar 2011 08:12:29 GMT

Title: Degradable Poly(ester amide)s for biomedical aplications Authors: Rodríguez Galán, Rafael Alfonso; Franco García, María Lourdes; Puiggalí Bellalta, Jordi Abstract: Poly(ester amide)s are an emerging group of biodegradable polymers that may cover both commodity and speciality applications. These polymers have ester and amide groups on their chemical structure which are of a degradable character and provide good thermal and mechanical properties. In this sense, the strong hydrogen‑bonding interactions between amide groups may counter some typical weaknesses of aliphatic polyesters like for example poly(e-caprolactone). Poly(ester amide)s can be prepared from different monomers and following different synthetic methodologies which lead to polymers with random, blocky and ordered microstructures. Properties like hydrophilic/hydrophobic ratio and biodegradability can easily be tuned. During the last decade a great effort has been made to get functionalized poly(ester amide)s by incorporation of a-amino acids with hydroxyl, carboxyl and amine pendant groups and also by incorporation of carbon-carbon double bonds in both the polymer main chain and the side groups. Specific applications of these materials in the biomedical field are just being developed and are reviewed in this work (e.g., controlled drug delivery systems, hydrogels, tissue engineering and other uses like adhesives and smart materials) together with the main families of functionalized poly(ester amide)s that have been developed to date.

Brill transition and melt crystallization of nylon 56 an odd-even polyamide with two hydrogen-bonding directions

Mon, 10 Jan 2011 11:42:02 GMT

Title: Brill transition and melt crystallization of nylon 56 an odd-even polyamide with two hydrogen-bonding directions Authors: Morales Gámez, Laura Teresa; Soto, David X.; Franco García, María Lourdes; Puiggalí Bellalta, Jordi Abstract: Brill transition and crystallization behaviour of nylon 56, a representative polymer of odd–even polyamides, were investigated by simultaneous WAXD and SAXS synchrotron radiation. Nylon 56 crystallized from solution into a peculiar structure where hydrogen bonds were established along the two directions. Nylon 56 experimented on heating a Brill transition that lead to a pseudohexagonal packing and lately to a monoclinic unit cell where neighbouring molecular segments were shifted along the chain axis direction. In disagreement with conventional polyamides, the Brill transition of nylon 56 was not reversible since on cooling the pseudohexagonal arrangement was mainly attained. Optical microscopy studies performed under both isothermal and non-isothermal conditions demonstrated that nylon 56 spherulites had different optical properties than even–even nylons having conventional sheet structures. The birefringence sign changed in the sequence positive–negative–positive when crystallization temperature was decreased.

Isothermal crystallization study on a biodegradable segmented copolymer constituted by glycolide and trimethylene carbonate units

Wed, 21 Jul 2010 10:11:00 GMT

Title: Isothermal crystallization study on a biodegradable segmented copolymer constituted by glycolide and trimethylene carbonate units Authors: Diaz Celorio, Elena; Franco García, María Lourdes; Puiggalí Bellalta, Jordi Abstract: The isothermal crystallization behavior of a segmented copolymer constituted by hard blocks of polyglycolide and soft segments derived from the copolymerization of glycolide and trimethylene carbonate was investigated. This polymer has applied relevance because it is one of the most widely used for bioabsorbable surgical sutures. Calorimetric, optical microscopy, and infrared techniques were combined to understand the thermal properties and the different factors that influence the crystallization process. Basically, only the hard blocks crystallized, although certain processing conditions allowed performing an additional crystallization associated with small lamellar domains of the soft segment. Crystallization from both the melt and the glass state rendered positive spherulites with a fibrillar texture. The observed unusual sign of birefringence was a consequence of the close packing structure of polyglycolide, which was also corroborated by electron diffraction patterns. Crystallization was characterized by an athermal nucleation, which allowed accurate estimation of the secondary nucleation parameter by using the calorimetric data only. Significant differences in the Avrami exponent (from 2.32 to 1.45) were found between the cold and hot isothermal crystallizations. The stronger geometric constraints observed in the crystallization from the glass state were also corroborated by FTIR analyses