New co-processed MCC-based excipient for fast release of low solubility drugs from pellets prepared by extrusion-spheronization

In this study, a new co-processed excipient composed of microcrystalline cellulose (MCC), sorbitol, chitosan and Eudragit® E, easily obtained by wet massing, to increase the dissolution rate of active ingredients of low water solubility from pellets prepared by extrusion–spheronization is evaluated. Indomethacin, nifedipine, furosemide, ibuprofen, prednisolone and hydrochlorothiazide are used as model drugs of different solubility. All pellet formulations evaluated showed adequate morphological, flow and mechanical properties. Pellets prepared with the co-processed excipient show a higher drug dissolution rate than those prepared with MCC and even higher than the pure drug powder. The fast drug dissolution and the complete disintegration (<3?min) of the pellets can be explained by the great porosity of the formulations, the high solubility of the sorbitol, the disintegrant capacity of the chitosan and the distribution of the Eudragit® E polymer particles in-between the other components of the co-processed mixture. In conclusion, this new co-processed excipient is very suitable to increase the dissolution rate of poorly soluble drugs from pellets prepared by extrusion–spheronization. Moreover, the drug release rate can be estimated from the Ln of the drug solubility in acidic medium.     

On the free volume evolution in a deformed epoxy composite. A positron annihilation study

After fabrication of an epoxy system filled with aluminum powder, followed by inelastic deformations under compression of the specimens, Positron Annihilation Lifetime Spectroscopy (PALS) was used to follow the evolution of the free-volume holes in the matrix. In order to describe the micromechanical deformation mechanism that takes place in the matrix around the inclusions, the experimental free-volume holes data were analyzed in terms of a model specifically developed. This model involves a hydrostatic internal stress resulting from the fabrication process of the composites and the deviatoric part of the applied stress during inelastic deformation. The influence of both kinds of stresses on the modification of the free-volume sizes in the matrix is discussed.     

Measuring publication diversity among the most productive scholars: how research trajectories differ in communication,psychology, and political science

Scientometrics - Examining research patterns across scientific fields constitutes a growing research enterprise to understand how global knowledge production unfolds. However, scattered empirical...     

Application of FISH for in situ detection and quantification of DNA breakage

(TTAGGG)n sequence repeats in human telomeres and in Chinese hamster interstitial centromeric areas were digested in situ with exonuclease III (ExoIII) and exonuclease Bal 31. Incubation with AluI was performed beforehand to increase DNA breaks near telomere sequence areas. DNA removal at these specific regions was quantified by digital image analysis of the fluorescence in situ hybridization signal produced by a telomeric probe. Exonuclease III was 2.6 times more active in interstitial than in terminal telomeric sequence areas. Exonuclease Bal 31 was 2.3 times more effective in terminal than in interstitial telomeric sequence regions. These results support the hypothesis that chromatin is differentially organized in both telomeric sequence areas, despite their similar DNA composition.     

An analysis of the influence of the accelerator/sulfur ratio in the cure reaction and the uniaxial stress–strain behavior of SBR

Vulcanized styrene butadiene rubber (SBR) with different cure systems was prepared and analyzed by using the model of rubber elasticity based on the tube concept, applied to the treatment of the stress–strain measurements. Samples with several ratio accelerators to sulfur, Λ, between 0.22 and 3.0 cured at 433 K were studied. The network chain density and the crosslink density of the samples were evaluated. By means of normalized rheometer curves, the kinetics of cure of these samples were evaluated by considering the model of isothermal curing proposed by Kamal and Sourour. In this frame, the parameters of the kinetics model were obtained. A correlation between the order of the kinetic equation, n, and the network chain density of the cure samples was established. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2601–2609, 2004     

About the measurement of dynamic mechanical properties of bi-layer systems

The bi-layer system has been well developed for many engineering structural components in the aircraft, automotive, microelectronics and modern space industries in the last few decades. Consequently, a good determination of its dynamic mechanical properties is important for an appropriate design of its industrial application. These studies are usually performed by a three-point bending test using a dynamic mechanical analyzer (DMA). In this work, we show that the three points bending test on a bi-layer system carried out with the test tool provided in a commercial DMA, for example the dynamic mechanical thermal analyzer (DMTA) Rheometric IV, can lead to erroneous results. Measurements on polymer-hard substrate bi-layer systems around the glass transition temperature of the polymer, T_g, give larger changes in elastic modulus and loss tangent than they are. This problem is not observed at temperatures lower than T_g. The design of new test tool and specimen geometry for the three points bending test is shown together with its application to the measurement of the dynamic elastic properties of a polyvinyl chloride (PVC)–aluminum bi-layer system.     

Nanohole volume dependence on the cure schedule in epoxy thermosetting networks: A PALS study

A systematic study on the dependence of the volumes at nanoscale in epoxy systems cured with two selected aminic hardeners at different pre-cure temperatures is presented. Nanohole volumes were measured by positron annihilation lifetime spectroscopy. Additional information regarding the structure of the thermosets was obtained using dynamic mechanical analysis. Volume results obtained are discussed in terms of the cure schedule applied to the epoxy systems, their characteristic glass transition temperatures and their crosslink density. The pre-cure temperature and the structure of the hardeners govern the packing of the molecular chains of the epoxy network. Using together positron and mechanical experimental techniques allows to conclude that a strong change in the volume and number density of the nanoholes takes place when the pre-cure temperature crosses the glass transition temperature of the systems.     

Ultimate properties of rubber and core-shell modified epoxy matrices with different chain flexibilities

Preformed polystyrene-co-butylacrylate (PScoBu) core-shell particles and polystyrene microspheres as well as amine-terminated butadiene nitrile (ATBN) rubber have been used for modification of both rigid and more flexible crosslinked DGEBA-based epoxy networks having significantly different crosslink densities. Some variations in cure kinetics have been shown by both thermal and rheological measurements. Independently of the crosslink density of the neat epoxy matrix, function of the cycloaliphatic or aliphatic hardener used, the toughening effect via core-shell modification has been found as good as that for rubber modification but with a better retention of thermal properties. Results are investigated as a function of the morphologies obtained by scanning electron microscopy (SEM) but also by atomic force microscopy (AFM). Larger fracture toughness was obtained for every-unmodified and modified- epoxy matrices cured with the aliphatic hardener as a consequence of the lower crosslink density of the corresponding mixtures.     

Asymmetric biphasic hydrophobic/hydrophilic poly(lactic acid)–polyvinyl alcohol meshes with moisture control and noncytotoxic effects for wound dressing applications

A noncytotoxic film was developed in this work with asymmetric biphasic properties (hydrophilic/hydrophobic) that allow for gas exchange. Among its many biomedical applications, it could be applied as a wound dressing material where the absorption of exuded fluids and control of water loss is required simultaneously. Thin meshes were developed modifying one face of poly(lactic acid) (PLA) electrospun mats with polyvinyl alcohol (PVA) using a simple photografting methodology. The contact angle of the modified face of the film was 44° while that of the other face was the original value of 122°. The chemical modification was covalent, as confirmed by X-ray photoelectron spectroscopy, stable over time and resistant to successive washing steps. Cytotoxic assays with fibroblast cells showed that PVA photo-grafted onto PLA meshes present a high cell viability percentage. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47369.