Preparation and characterization of polyester resin-layered silicate containing reactive groups

Polymer nanocomposites, specifically nanoclay-reinforced polymers, have attracted great interest as matrix materials for high temperature composite applications. Nanocomposites require relatively low dispersant loads to achieve significant property enhancements. These enhancements are mainly a consequence of the interfacial effects that result from dispersing the silicate nanolayers in the polymer matrix and the high in-plane strength, stiffness and aspect ratio of the lamellar nanoparticles. The montmorillonite (MMT) clay, modified with organic onium ions with long alkyl chains as Cloisites, has been widely used to obtain nanocomposites. The presence of reactive groups in organic onium ions can form chemical bonds with the polymer matrix which favours a very high exfoliation degree of the clay platelets in the nanocomposite (1,2)

Connexin-43 prevents hematopoietic stem cell senescence through transfer of reactive oxygen species to bone marrow stromal cells

Hematopoietic stem cell (HSC) aging has become a concern in chemotherapy of older patients. Humoral and paracrine signals from the bone marrow (BM) hematopoietic microenvironment (HM) control HSC activity during regenerative hematopoiesis. Connexin-43 (Cx43), a connexin constituent of gap junctions (GJs) is expressed in HSCs, down-regulated during differentiation, and postulated to be a self-renewal gene. Our studies, however, reveal that hematopoietic-specific Cx43 deficiency does not result in significant long-term competitive repopulation deficiency. Instead, hematopoietic Cx43 (H-Cx43) deficiency delays hematopoietic recovery after myeloablation with 5-fluorouracil (5-FU). 5-FU-treated H-Cx43-deficient HSC and progenitors (HSC/P) cells display decreased survival and fail to enter the cell cycle to proliferate. Cell cycle quiescence is associated with down-regulation of cyclin D1, up-regulation of the cyclin-dependent kinase inhibitors, p21cip1. and p16INK4a, and Forkhead transcriptional factor 1 (Foxo1), and activation of p38 mitogen-activated protein kinase (MAPK), indicating that H-Cx43-deficient HSCs are prone to senescence. The mechanism of increased senescence in H-Cx43-deficient HSC/P cells depends on their inability to transfer reactive oxygen species (ROS) to the HM, leading to accumulation of ROS within HSCs. In vivo antioxidant administration prevents the defective hematopoietic regeneration, as well as exogenous expression of Cx43 in HSC/P cells. Furthermore, ROS transfer from HSC/P cells to BM stromal cells is also rescued by reexpression of Cx43 in HSC/P. Finally, the deficiency of Cx43 in the HM phenocopies the hematopoietic defect in vivo. These results indicate that Cx43 exerts a protective role and regulates the HSC/P ROS content through ROS transfer to the HM, resulting in HSC protection during stress hematopoietic regeneration.

Dielectric behaviour of Hf-doped CaCu3Ti4O12 ceramics obtained by conventional synthesis and reactive sintering

CaCu3(Ti4xHfx)O12 ceramics (JC = 0.04, 0.1 and 0.2) were prepared by conventional synthesis (CS) and through reactive sintering (RS), in which synthesis and sintering of the material take place in one single step. The microstructure and the dielectric properties of Hf-doped CCTO (CCTOHf) have been studied by XRD, FE-SEM, AFM, Raman and impedance spectroscopy (IS) in order to correlate the structure, microstructure and the electrical properties. Samples prepared by reactive sintering show slightly higher dielectric constant than those prepared by conventional synthesis in the same way than the pure CCTO. Dielectric constant and dielectric losses decrease slightly increasing Hf content. For CCTOHf ceramics with x> 0.04 for CS and x> 0.1 for RS, a secondary phase HfTi04 appears. As expected, the reactive sintering processing method allows a higher incorporation of Hf in the CCTO lattice than the conventional synthesis one.

Caracterización funcional de los genes sgb (suppressors of agb1-2 susceptibility to pathogens): Nuevos reguladores de la respuesta de inmunidad innata de Arabidopsis thaliana

Un porcentaje importante de las pérdidas de la producción agrícola se deben a las enfermedades que causan en los cultivos los hongos necrótrofos y vasculares. Para mejorar la productividad agrícola es necesario tener un conocimiento detallado de las bases genéticas y moleculares que regulan la resistencia de las plantas a este tipo de patógenos. En Arabidopsis thaliana la resistencia frente a patógenos necrótrofos, como el hongo Plectosphaerella cucumerina BMM (PcBMM), es genéticamente compleja y depende de la activación coordinada de distintas rutas de señalización, como las reguladas por las hormonas ácido salicílico (SA), ácido jasmónico (JA), etileno (ET) y ácido abscísico (ABA), así como de la síntesis de compuestos antimicrobianos derivados del Triptófano y de la integridad de la pared celular (Llorente et al., 2005, Hernández-Blanco et al., 2007; Delgado-Cerezo et al., 2012). Uno de los componentes claves en la regulación de la resistencia de las plantas a patógenos (incluidos hongos necrótrofos y biótrofos) es la proteína G heterotrimérica, un complejo proteico formado por tres subunidades (Gα, Gβ y Gγ), que también regula distintos procesos del desarrollo vegetal. En Arabidopsis hay un gen que codifica para la subunidad α (GPA1), otro para la β (AGB1), y tres genes para la subunidad γ (AGG1, AGG2 y AGG3). El complejo GPA1-AGB1-AGG (1-3) se activa y disocia tras la percepción de una señal específica, actuando el dímero AGB1-AGG1/2 como un monómero funcional que regula las respuestas de defensa (Delgado-Cerezo et al., 2012). Estudios transcriptómicos y análisis bioquímicos de la pared celular en los que se comparaban los mutantes agb1-2 y agg1 agg2, y plantas silvestres (Col-0) revelaron que la resistencia mediada por Gβ-Gγ1/2 no es dependiente de rutas de defensa previamente caracterizadas, y sugieren que la proteína G podría modular la composición/estructura (integridad) de la pared celular (Delgado-Cerezo et al., 2012). Recientemente, se ha demostrado que AGB1 es un componente fundamental de la respuesta inmune mediada por Pathogen- Associated Molecular Patterns (PTI), ya que los mutantes agb1-2 son incapaces de activar tras el tratamiento con PAMPs respuestas de inmunidad, como la producción de especies reactivas de oxígeno (ROS; Liu et al., 2013). Dada la importancia de la proteína G heterotrimérica en la regulación de la respuestas de defensa (incluida la PTI) realizamos un escrutinio de mutantes supresores de la susceptibilidad de agb1-2 al hongo necrótrofo, PcBMM, para identificar componentes adicionales de las rutas de señalización reguladas por AGB1. En este escrutinio se aislaron cuatro mutantes sgb (suppressors of agb1-2 susceptibility to pathogens), dos de los cuales, sgb10 y sgb11, se han caracterizado en la presente Tesis Doctoral. El mutante sgb10 es un segundo alelo nulo del gen MKP1 (At3g55270) que codifica la MAP quinasa-fosfatasa 1 (Bartels et al., 2009). Este mutante presenta lesiones espontáneas en plantas adultas y una activación constitutiva de las principales rutas de defensa (SA, JA y ET, y de metabolitos secundarios, como la camalexina), que explicaría su elevada resistencia a PcBMM y Pseudomonas syringae. Estudios epistáticos sugieren que la resistencia mediada por SGB10 no es dependiente, si no complementaria a la regulada por AGB1. El mutante sgb10 es capaz de restablecer en agb1-2 la producción de ROS y otras respuestas PTI (fosforilación de las MAPK6/3/4/11) tras el tratamiento con PAMPs tan diversos como flg22, elf18 y quitina, lo que demuestra el papel relevante de SGB10/MKP1 y de AGB1 en PTI. El mutante sgb11 se caracteriza por presentar un fenotipo similar a los mutantes irregular xylem (e.g. irx1) afectado en pared celular secundaria: irregularidades en las células xilemáticas, reducción en el tamaño de la roseta y altura de planta, y hojas con un mayor contenido de clorofila. La resistencia de sgb11 a PcBMM es independiente de agb1-2, ya que la susceptibilidad del doble mutante sgb11 agb1-2 es intermedia entre la de agb1-2 y sgb11. El mutante sgb11 no revierte la deficiente PTI de agb1-2 tras el tratamiento con flg22, lo que indica que está alterado en una ruta distinta de la regulada por SGB10. sgb11 presenta una sobreactivación de la ruta del ácido abscísico (ABA), lo que podría explicar su resistencia a PcBMM. La mutación sgb11 ha sido cartografiada en el cromosoma III de Arabidopsis entre los marcadores AthFUS6 (81,64cM) y nga6 (86,41cM) en un intervalo de aproximadamente 200 kb, que comprende genes, entre los que no se encuentra ninguno previamente descrito como IRX. El aislamiento y caracterización de SGB11 apoya la relevancia de la proteína G heterotrimérica en la regulación de la interconexión entre integridad de la pared celular e inmunidad. ABSTRACT A significant percentage of agricultural losses are due to diseases caused by necrotrophic and vascular fungi. To enhance crop yields is necessary to have a detailed knowledge of the genetic and molecular bases regulating plant resistance to these pathogens. Arabidopsis thaliana resistance to necrotrophic pathogens, such as Plectosphaerella cucumerina BMM (PcBMM) fungus, is genetically complex and depends on the coordinated activation of various signaling pathways. These include those regulated by salicylic acid (SA), jasmonic acid (JA), ethylene (ET) and abscisic acid (ABA) hormones and the synthesis of tryptophan-derived antimicrobial compounds and cell wall integrity (Llorente et al., 2005, Hernández-Blanco et al., 2007; Delgado-Cerezo et al., 2012). One key component in the regulation of plant resistance to pathogens (including biotrophic and necrotrophic fungi) is the heterotrimeric G-protein. This protein complex is formed by three subunits (Gα, Gβ and Gγ), which also regulates various plant developmental processes. In Arabidopsis only one gene encodes for subunits α (GPA1) and β (AGB1), and three genes for subunit γ (AGG1, AGG2 y AGG3). The complex GPA1- AGB1-AGG(1-3) is activated and dissociates after perception of an specific signal, AGB1- AGG1/2 acts as a functional monomer regulating defense responses (Delgado-Cerezo et al., 2012). Comparative transcriptomic studies and biochemical analyses of the cell wall of agb1-2 and agg1agg2 mutant and wild plants (Col-0), showed that Gβ-Gγ1/2-mediated resistance is not dependent on previously characterized defense pathways. In addition, it suggests that G protein may modulate the composition/structure (integrity) of the plant cell wall (Delgado-Cerezo et al., 2012). Recently, it has been shown that AGB1 is a critical component of the immune response mediated by Pathogen-Associated Molecular Patterns (PTI), as agb1-2 mutants are unable to activate immune responses such as oxygen reactive species (ROS) production after PAMPs treatment (Liu et al., 2013). Considering the importance of the heterotrimeric G protein in regulation of defense responses (including PTI), we performed a screening for suppressors of agb1-2 susceptibility to the necrotrophic fungus PcBMM. This would allow the identification of additional components of the signaling pathways regulated by AGB1. In this search four sgb mutants (suppressors of agb1-2 susceptibility to pathogens) were isolated, two of which, sgb10 and sgb11, have been characterized in this PhD thesis. sgb10 mutant is a second null allele of MKP1 gene (At3g55270), which encodes the MAP kinase-phosphatase 1 (Bartels et al., 2009). This mutant exhibits spontaneous lesions in adult plants and a constitutive activation of the main defense pathways (SA, JA and ET, and secondary metabolites, such as camalexin), which explains its high resistance to Pseudomonas syringae and PcBMM. Epistatic studies suggest that SGB10- mediated resistance is not dependent, but complementary to the regulated by AGB1. The sgb10 mutant is able to restore agb1-2 ROS production and other PTI responses (MAPK6/3/4/11 phosphorylation) upon treatment with PAMPs as diverse as, flg22, elf18 and chitin, demonstrating the relevant role of SGB10/MKP1 and AGB1 in PTI. sgb11 mutant is characterized by showing a similar phenotype to irregular xylem mutants (e.g. irx1), affected in secondary cell wall: irregular xylems cells, rosette size reduction and plant height, and higher chlorophyll content on leaves. The resistance of sgb11 to PcBMM is independent of agb1-2, as susceptibility of the double mutant agb1-2sgb11 is intermediate between agb1-2 and sgb11. The sgb11 mutant does not revert the deficient PTI response in agb1-2 after flg22 treatment, indicating that is altered in a pathway different to the one regulated by SGB10. sgb11 presents an over-activation of the abscisic acid pathway (ABA), which could explain its resistance to PcBMM. The sgb11 mutation has been mapped on chromosome III of Arabidopsis, between AthFUS6 (81.64 cM) and nga6 (86.41 cM) markers, in 200 kb interval, which does not include previously known IRX genes. The isolation and characterization of SGB11 supports the importance of heterotrimeric G protein in the regulation of the interconnection between the cell wall integrity and immunity.

Deep reactive ion etching of auxetic structures: present capabilities and challenges

Auxetic materials (or metamaterials) have negative Poisson ratios (NPR) and display the unexpected properties of lateral expansion when stretched, and equal and opposing densification when compressed. Such auxetic materials are being used more frequently in the development of novel products, especially in the fields of intelligent expandable actuators, shape-morphing structures, and minimally invasive implantable devices. Although several micromanufacturing technologies have already been applied to the development of auxetic materials and devices, additional precision is needed to take full advantage of their special mechanical properties. In this study, we present a very promising approach for the development of auxetic materials and devices based on the use of deep reactive ion etching (DRIE). The process stands out for its precision and its potential applications to mass production. To our knowledge, it represents the first time this technology has been applied to the manufacture of auxetic materials with nanometric details. We take into account the present capabilities and challenges linked to the use of DRIE in the development of auxetic materials and auxetic-based devices.