Absorption capacity, kinetics and mechanical behaviour in dry and wet states of hydrophobic DEDMS/TEOS-based silica aerogels

This work is a new approach to the study of the structural, mechanical and absorption properties of hybrid organic/inorganic silica-based aerogels. Diethoxydimethylsilane and tetraethoxysilane have been used as precursors. Changes in properties such as specific surface area, porous volume, pore radius, and surface texture and chemistry were researched as a function of the relative organic content. In addition, the absorption properties were tested for different organic liquids. The discrepancy in the absorption mechanisms and the kinetics of pure inorganic and hybrid samples were discussed. It was confirmed that swelling occurs in samples with high organic content, which, in turn, governs the absorption process. Finally, the mechanical behaviour was studied by uniaxial compression. A significant rise of the rupture strain up to 0.45 and a 10-fold decrease in the Young’s modulus to 7.8 MPa were measured in the dry samples by increasing the organic content. The mechanical response of the samples after saturation by the absorption of two reference oily liquids, namely, common motor oil and liquid polydimethylsiloxane, was also compared with the behaviour of dry samples. The presence of liquid within the sample reduced the value of the mechanical parameters in almost all cases. Moreover, the inclusion of organic chains also made the wet aerogels highly deformable. In summary, these first results suggest that tuning the organic ratio of the hybrid aerogels allows the control of not only the structural and mechanical properties but also the absorption properties.Junta de Andalucía P09-TEP-546

Reinforced silica-carbon nanotube monolithic aerogels synthesised by rapid controlled gelation

This work introduces a new synthesis procedure for obtaining homogeneous silica hybrid aerogels with carbon nanotube contents up to 2.50 wt.%. The inclusion of nanotubes in the highly porous silica matrix was performed by a two-step sol–gel process, resulting in samples with densities below 80 mg/cm3. The structural analyses (N2 physisorption and SEM) revealed the hierarchical structure of the porous matrix formed by nanoparticles arranged in clusters of 100 and 300 nm in size, specific surface areas around 600 m2/g and porous volumes above 4.0 cm3/g. In addition, a relevant increase on the mechanical performance was found, and an increment of 50% for the compressive strength and 90% for the maximum deformation were measured by uniaxial compression. This reinforcement was possible thanks to the outstanding dispersion of the CNT within the silica matrix and the formation of Si–O–C bridges between nanotubes and silica matrix, as suggested by FTIR. Therefore, the original synthesis procedure introduced in this work allows the fabrication of highly porous hybrid materials loaded with carbon nanotubes homogeneously distributed in the space, which remain available for a variety of technological applications

Effect of the drying procedure on hybrid sono-aereogels for organic solvent remediation

Hybrid organic–inorganic aerogels are highly hydrophobic porous solids that avoid the brittleness and moisture adsorption of the standard silica aerogels. Superhydrophobic porous materials have attracted great interest because of their ability for selective absorption of organic solvents while repelling water, as excellent candidates for remediation techniques. This work shows a comparative of three drying procedures of DEDMS/TEOS (diethoxydimethylsilane/tetraethylorthosilicate) gels, namely, by supercritical CO2, by supercritical ethanol, and dried at ambient conditions. Supercritical CO2 and ambient drying produced superhydrophobic aerogels (θ > 150°), while supercritical ethanol drying produces denser aerogels with smaller both porous volume and specific surface area. Regarding the absorption of organic liquids, swelling is observed in all cases. Hexane had faster diffusion that obeyed Fick's law (∝t0.5) whereas liquid polydimethylsiloxane exhibited slower non-Fickian diffusion process (∝tn, n < 0.5

Chitosan-GPTMS-Silica Hybrid Mesoporous Aerogels for Bone Tissue Engineering

This study introduces a new synthesis route for obtaining homogeneous chitosan (CS)-silica hybrid aerogels with CS contents up to 10 wt%, using 3-glycidoxypropyl trimethoxysilane (GPTMS) as coupling agent, for tissue engineering applications. Aerogels were obtained using the sol-gel process followed by CO2 supercritical drying, resulting in samples with bulk densities ranging from 0.17 g/cm(3) to 0.38 g/cm(3). The textural analysis by N-2-physisorption revealed an interconnected mesopore network with decreasing specific surface areas (1230-700 m(2)/g) and pore sizes (11.1-8.7 nm) by increasing GPTMS content (2-4 molar ratio GPTMS:CS monomer). In addition, samples exhibited extremely fast swelling by spontaneous capillary imbibition in PBS solution, presenting swelling capacities from 1.75 to 3.75. The formation of a covalent crosslinked hybrid structure was suggested by FTIR and confirmed by an increase of four hundred fold or more in the compressive strength up to 96 MPa. Instead, samples synthesized without GPTMS fractured at only 0.10-0.26 MPa, revealing a week structure consisted in interpenetrated polymer networks. The aerogels presented bioactivity in simulated body fluid (SBF), as confirmed by the in vitro formation of hydroxyapatite (HAp) layer with crystal size of approximately 2 mu m size in diameter. In vitro studies revealed also non cytotoxic effect on HOB(R) osteoblasts and also a mechanosensitive response. Additionally, control cells grown on glass developed scarce or no stress fibers, while cells grown on hybrid samples showed a significant (p < 0.05) increase in well-developed stress fibers and mature focal adhesion complexes

Innovación en las enseñanzas universitarias: experiencias presentadas en las III Jornadas de Innovación Educativa de la ULL

En este libro se recoge un conjunto de experiencias de innovación educativa desarrolladas en la ULL en el curso 2011-12. Se abordan distintos ámbitos y ramas del conocimiento, y ocupan temáticas variadas que han sido desarrolladas con rigor, y con un claro potencial para su extrapolación a efectos de la mejora educativa en el ámbito universitario. Esta publicación constituye una primera edición de una serie que irá recogiendo las experiencias de innovación educativa de la ULL. Este es un paso relevante para su impulso en nuestra institución, como lo es el de su vinculación con la investigación educativa, para potenciar su publicación en las revistas científicas en este ámbito cada vez más pujante y relevante para las universidades. Sobre todo representan el deseo y el compromiso del profesorado de la ULL para la mejora del proceso educativo mediante la investigación, la evaluación y la reflexión compartida de nuestras prácticas y planteamientos docentes

Propuesta metodológica para la adquisición y evaluación de competencias en asignaturas experimentales

En este trabajo se presenta una estrategia metodológica basada en aprendizaje cooperativo para asignaturas prácticas de titulaciones de carácter técnico o científico. La técnica utilizada se basa en la conocida como grupos de investigación, en la que se asigna a cada grupo de alumnos un trabajo de investigación asumiendo el rol de director/coordinador; la parte experimental será asumida por el resto de grupos que tendrán el rol de ejecutor/operario. Se ha ensayado en la asignatura Experimentación en Ingeniería Química del título de Ingeniero Químico y los resultados obtenidos muestran que, los alumnos valoran muy positivamente la adquisición de competencias tales como trabajo en equipo, toma de decisiones y razonamiento crítico, así como las distintas actividades empleadas para su consecució

Structure-Related Mechanical Properties and Bioactivity of Silica–Gelatin Hybrid Aerogels for Bone Regeneration

We report the synthesis of mesoporous silica–gelatin hybrid aerogels with 15, 25, and 30 wt. % gelatin contents, using 3-glycidoxypropyl trimethoxysilane (GPTMS) as a coupling agent, for tissue-engineering applications. Aerogels were obtained using a one-step sol–gel process followed by CO2 supercritical drying, resulting in crack-free monolith samples with bulk densities ranging from 0.41 g cm−3 to 0.66 g cm−3. Nitrogen adsorption measurements revealed an interconnected mesopore network and a general decrease in the textural parameters: specific surface areas (651–361 m2 g−1), pore volume (1.98–0.89 cm3 g−1), and pore sizes (10.8–8.6 nm), by increasing gelatin content. Thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy and uniaxial compression experiments confirmed that the structure, thermal properties and mechanical behavior of these aerogels changed significantly when the concentration of gelatin reached 25 wt.%, suggesting that this composition corresponds to the percolation threshold of the organic phase. In addition, the samples exhibited hydrophilic behavior and extremely fast swelling in phosphate-buffered saline (PBS), with swelling ratios from 2.32 to 3.32. Furthermore, in vitro bioactivity studies revealed a strong relationship between the kinetics of the nucleation and growth processes of hydroxyapatite in simulated body fluid (SBF) and the gelatin content. The live/dead assay revealed no cytotoxicity in HOB® osteoblasts in vitro and a positive influence on cell growth, focal adhesion development, and cytoskeletal arrangement for cell adhesion. Mineralization assays confirmed the positive effects of the samples on osteoblast differentiation. The biomaterials described are versatile, can be easily sterilized and are suitable for a wide range of applications in bone tissue-engineering, either alone or in combination with bioactive-reinforced phases

El abandono escolar temprano en las ciudades de Ceuta y Melilla

Resumen basado en el de la publicaciónSe presenta un estudio que tiene como objetivo ahondar en las causas del abandono escolar temprano en las ciudades de Ceuta y Melilla. Se analizan factores demográficos y de escolarización en ambas ciudades poniendo un especial énfasis en las condiciones del alumnado y en los factores laborales, socioculturales y familiares que influyen de manera decisiva en los procesos de escolarización. Se ha identificado el perfil del estudiante que deja los estudios en función del género y del grupo cultural de pertenencia, a través de diferentes métodos de investigación como encuestas o grupos de discusión. Finalmente se presentan los resultados y las conclusiones junto con algunas propuestas para prevenir y evitar el fracaso y abandono escolar.AndalucíaBiblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín, 5 - 3 planta; 28014 Madrid; Tel. +34917748000; [email protected]

Robocasting and Laser Micromachining of Sol-Gel Derived 3D Silica/Gelatin/&beta;-TCP Scaffolds for Bone Tissue Regeneration

The design and synthesis of sol-gel silica-based hybrid materials and composites offer significant benefits to obtain innovative biomaterials with controlled porosity at the nanostructure level for applications in bone tissue engineering. In this work, the combination of robocasting with sol-gel ink of suitable viscosity prepared by mixing tetraethoxysilane (TEOS), gelatin and &beta;-tricalcium phosphate (&beta;-TCP) allowed for the manufacture of 3D scaffolds consisting of a 3D square mesh of interpenetrating rods, with macropore size of 354.0 &plusmn; 17.0 &mu;m, without the use of chemical additives at room temperature. The silica/gelatin/&beta;-TCP system underwent irreversible gelation, and the resulting gels were also used to fabricate different 3D structures by means of an alternative scaffolding method, involving high-resolution laser micromachining by laser ablation. By this way, 3D scaffolds made of 2 mm thick rectangular prisms presenting a parallel macropore system drilled through the whole thickness and consisting of laser micromachined holes of 350.8 &plusmn; 16.6-micrometer diameter, whose centers were spaced 1312.0 &plusmn; 23.0 &mu;m, were created. Both sol-gel based 3D scaffold configurations combined compressive strength in the range of 2&ndash;3 MPa and the biocompatibility of the hybrid material. In addition, the observed Si, Ca and P biodegradation provided a suitable microenvironment with significant focal adhesion development, maturation and also enhanced in vitro cell growth. In conclusion, this work successfully confirmed the feasibility of both strategies for the fabrication of new sol-gel-based hybrid scaffolds with osteoconductive properties

Las responsabilidad de los profesores noveles en la adaptación de la docencia al nuevo crédito ECTS

Los autores exponen los cambios metodológicos que implica la nueva definición de crédito establecida por el RD 1125/2003, como consecuencia del proceso de adaptación al EEES. El grupo de noveles expone la experiencia desarrollada en las asignaturas "Derecho Financiero I" y "Fiscalidad Internacional", señalando los resultados obtenidos, así como las ventajas y dificultades del nuevo sistema. Las nuevas técnicas se concentraron en el análisis de la jurisprudencia constitucional, la resolución de casos prácticos, el establecimiento de un programa de tutorías que resultara atractivo a los alumnos y la implantación de las nuevas tecnologías (página web del Departamento, lista de distribución de correo electrónico y tutorías online)The authors explain the changes in the teaching methodology that imply the new concept of credit included in the RD 1125/2003, approved to adapt the Spanish regulation to the European Higher Education Area. The lerner lectures group describes its pilot experience in the subjects "Tax Law I" and "International Tax Law", and exposes the results, the advantages and the problems of the new system. The group has tested with the students the analysis os the constitutional jurisprudence and cases, an attractive program of supervision and monitoring, and the use of new technologies (the creation of a site web and a mailing list, and the online tutorship