Antimicrobial activity of poly(ester urea) electrospun fibers loaded with bacteriophages

The capacity to load bacteriophages into electrospun nanofibers of two representative biocompatible polymers has been evaluated, paying special attention to the possibility of preserving their antibacterial activity. Specifically, the work involves the following steps: (a) Evaluation of the effect of the applied electrical field on the phage activity; (b) evaluation of the activity when a lyophilization process could be avoided by using water soluble polymers (e.g., poly(ethylene glycol); (c) evaluation of the activity when dissolution of the polymer requires an organic solvent and lyophilization is theoretically necessary. In this case, a poly(ester urea) (PEU) derived from the natural L-leucine amino acid has been considered. Adsorption of commercial bacteriophage preparations into calcium carbonate particles was demonstrated to be a promising methodology to avoid lyophilization and keep the initial bactericide activity at a maximum. Phagestaph and Fersis bacteriophage commercial preparations have been selected for this study due to their spPeer ReviewedPostprint (published version

Nanostructured amphiphilic systems based on hyaluronic acid ionic complexes

In this communication we wish to report on HyA ionic complexes prepared by coupling with a) choline-based surfactants (nACh·HyA complexes), and b) alkylphosphonium surfactants (nATMP·HyA complexes) with n being the number of carbons of the alkanoyl or alkyl side chain. nACh surfactants are synthesized from choline and fatty acids, and distinguished because they are fully biobased and biocompatible. The nATMP surfactants have been scarcely studied as counterions of polyacids in spite of being more stable to heat and less harmful than their alkylammonium analogs.Postprint (published version

Ultracapacitors made with Hybrid conducting polymer–clay exfoliated nanocomposites

Ultracapacitors form exfoliated nanocomposites of poly(3,4-ethylenedioxythiophene) (PEDOT), and montmorillonite (MMT), have been fabricated, and have been characterized by electrochemical and macroscopic methods, found to present very good electrical properties (e.g. the specific capacitance), evidencing the favorable effect of the clay, and the thinness of the film.Peer Reviewe

Mineralization of DNA into nanoparticles of hydroxyapatite

Encapsulation of DNA into hydroxyapatite (HAp) has been investigated using a rational approach that involves computer simulation and experimental techniques. The temporal evolution of the radial distribution functions derived from atomistic molecular dynamics simulations of Ca2+, PO4 3− and OH−-containing aqueous solutions in the presence and absence of B-DNA has been used to conclude that the backbone of the double helix acts as a template for HAp growth. More specifically, results reveal the formation of calcium phosphate clusters at the first stages of the simulations, which subsequently reorganize to nucleate HAp. This effect is produced in the absence and, especially, presence, of DNA indicating that the biomolecules do not inhibit but even promote mineral growth. Furthermore, computer simulations suggest that the diffusion of the OH− anions through the inorganic solution is the limiting step for the nucleation of the biomineral. Nanocapsules and crystalline nanorods of HAp containing DNA molecules inside have been prepared by mixing solutions containing Ca2+ and PO4 3− ions with fish sperm DNA at high pH. The dimensions and morphology of such nanostructures have been examined by transmission electron microscopy, while the characterization of the biomineral has been focused on the identification of DNA inside HAp using infrared, X-ray photoelectron and UV-vis spectroscopies, as well as gel electrophoresis. The biominerals reported in this work are important for biomedical applications requiring the protection of DNA from aggressive environmental conditionsPostprint (published version

Ensayos sobre crecimiento económico en Colombia

'Ensayos sobre crecimiento económico en Colombia', editado por Adolfo Meisel y Hernando Vargas, es el resultado de una agenda de investigación del Banco de la República sobre el crecimiento económico en Colombia. Su objetivo principal es analizar algunas de las restricciones de carácter estructural que limitan el crecimiento económico en el largo plazo. Así mismo, pretende entender cuáles son las causas del lento crecimiento del país, indispensable para formular políticas públicas tendientes a lograr un mayor crecimiento económico, y analizar la relación entre el desempeño económico regional y el crecimiento de largo plazo para identificar políticas de desarrollo regional adecuadas. La obra analiza en profundidad seis temas de gran relevancia para el país: descentralización fiscal y crecimiento regional; capital humano y físico y crecimiento municipal; innovación y empleo; productividad y participación en el mercado exportador; capital humano y participación laboral, y desempeño de las exportaciones colombianas

Preferential incorporation of azelaic acid units into the crystalline phase of the copoly(alkylene dicarboxylate) derived from 1,9-nonanediol and an equimolar mixture of pimelic and azelaic acids

The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate) (PES 9,7) and poly(nonamethylene azelate) (PES 9,9)) was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio that was strongly depended on the supercooling degree. The crystalline structure of both homopolyesters was defined by an orthorhombic P2(1)ab space group and a large unit cell containing four molecular segments with an all-trans conformation. Nevertheless, the structure in the chain axis projection was equivalent to a simpler cell containing only two segments. Crystalline lamellae were effectively degraded by lipases, starting the enzymatic attack on the lamellar surfaces. The random copolymer constituted by an equimolar amount of pimelate and azelate units (COPES 9,7/9) crystallized according to regular lamellae with a similar molecular arrangement in the chain axis projection. The structure of this copolymer was preferably conditioned by the azelate component as could be deduced from both, diffraction and spectroscopic data. Analysis of small angle X-ray scattering patterns pointed out that less crystalline lamellae with higher amorphous thickness had developed in the copolymer. This feature was interpreted as a consequence of the preferential incorporation of pimelate comonomer units in the folding surface.Peer Reviewe

The preparation of cutback bitumens to ASTM specifications by blending readily available constituents

SIGLEAvailable from British Library Document Supply Centre- DSC:7768.29(TRRL-RR--104) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Preferential incorporation of azelaic acid units into the crystalline phase of the copoly(alkylene dicarboxylate) derived from 1,9-nonanediol and an equimolar mixture of pimelic and azelaic acids

The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate) (PES 9,7) and poly(nonamethylene azelate) (PES 9,9)) was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio that was strongly depended on the supercooling degree. The crystalline structure of both homopolyesters was defined by an orthorhombic P2(1)ab space group and a large unit cell containing four molecular segments with an all-trans conformation. Nevertheless, the structure in the chain axis projection was equivalent to a simpler cell containing only two segments. Crystalline lamellae were effectively degraded by lipases, starting the enzymatic attack on the lamellar surfaces. The random copolymer constituted by an equimolar amount of pimelate and azelate units (COPES 9,7/9) crystallized according to regular lamellae with a similar molecular arrangement in the chain axis projection. The structure of this copolymer was preferably conditioned by the azelate component as could be deduced from both, diffraction and spectroscopic data. Analysis of small angle X-ray scattering patterns pointed out that less crystalline lamellae with higher amorphous thickness had developed in the copolymer. This feature was interpreted as a consequence of the preferential incorporation of pimelate comonomer units in the folding surface.Peer Reviewe

Structural transitions of nylon 47 and clay influence on its crystallization behavior

Basic diffraction data on nylon 47 pointed out a peculiar structure of hydrogen bonds along two directions. Nylon 47 showed reversible polymorphic transitions during heating/cooling processes that were analyzed by real time synchrotron WAXD experiments. Results indicated that nylon 47 had a first structural transition at low temperature, followed by a gradual Brill transition towards a pseudohexagonal packing. Nylon 47 crystallized from the melt giving rise to spherulites with different characteristics than those attained with conventional even-even nylons. Interestingly, spherulites crystallized at low supercooling underwent a reversible change in birefringence with temperature. This was due to the reversible structural changes caused by temperature variations and the flat on lamellar morphology. Intercalated and exfoliated nanocomposites based on nylon 47 were prepared by solution intercalation and melt mixing using Cloisites 25A and 30B. The influence of the final silicate layer morphology on the hot crystallization behavior was investigated. Crystallization rates of the neat polymer and its two nanocomposites were significantly different, mainly due to variations in the primary nucleationPeer Reviewe

Microstructures of group III-nitrides after implantation with gallium

High doses of gallium have been implanted into layers of aluminium nitride (AIN), indium nitride (InN) and amorphous silicon nitride (a-SiN_x) in an attempt to bond gallium with nitrogen and form binary or ternary alloys. The microstructure of the resultant layers have been characterised using, principally, transmission electron microscopy and X-ray photoelectron spectroscopy. The implantation of a high dose of Ga ions into AIN was successful in synthesising a GaN/GaAlN compound. The resultant layers were largely uniform but contained aluminium precipitates near the surface. These precipitates were pure Al and were most common in the region associated with the maximum Ga concentration. Deconvolution of X-ray photoelectron spectroscopy peaks indicated that Ga existed in a number of chemical states, including the nitride. Electron diffraction patterns from the implanted layers were closely indexed to both AIN and GaN. A further N implant was used to reduce the concentration of the aluminium precipitates and increase the concentration of GaN bonds. The yield of Ga-N bonds dramatically increased and a reduction in the concentration of Al precipitates was observed. Laser and thermal annealing was performed on the implanted AIN substrates. The near surface regions of the implanted specimens appeared to free of precipitates and bubbles. Laser annealing did have a noticeable effect on the electrical and optical properties of the layers. After laser annealing the conductivity of the Ga implanted layer was lower, indicating that the quality of the material had improved. PL measurements showed that a new PL peak at 2.6 eV appeared after laser annealing. It has been found that implanting InN with gallium can yield Ga-N bonds. However, Ga implants into InN were not as successful at synthesising GaN compounds as those by implanting Ga into AIN, due to the low thermal stability of InN. The implanted InN layers were very irregular and contained large indium precipitates and bubbles. A capping layer was used in an attempt to control the degradation of the implanted layer mechanically, but this was unsuccessful. The evidence from XPS and electron diffraction complemented one another and suggested that Ga-N bonds were in fact present. Thermal and laser anneals were performed in an attempt to lessen the bubble and precipitate damage caused by the implantation of Ga into InN, however no improvement in microstructure uniformity was observed. Gallium implantations into silicon nitride performed by S. A. Almieda (1998) were also studied using various microstructural characterisation techniques. It was found that the implanted Ga existed in a dispersion of colloids (5 nm in diameter). These colloids were found to be void of N, which is surprising since Ga-N bonds were detected by XPS in these specimens. It is proposed that either a low percentage of N remained undetected in the colloids allowing Ga-N bonds to form, or more likely that Ga-N bonds were present at the boundary formed between the Ga colloid and the a-SiN_x layer. The microstructure of the layer appeared to be unaffected by the nitrogen concentration in the original a-SiN_x layer. Annealing caused a broadening of the Ga colloid depth range and a reduction in the diameter of the colloids. Using CALPHAD, phase diagrams for the Ga-ln-N and Ga-AI-N alloy systems have been proposed. It has been shown that thermodynamic arguments can explain the observations of Al and In precipitation following Ga implantation into AIN and InN, respectively. The coalescence of Ga to form Ga clusters after implantation into a-SiN_x is also explained using thermodynamic arguments. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN043526 / BLDSC - British Library Document Supply CentreGBUnited Kingdo