Marta Pozuelo

Processing and properties of magnesium containing a dense uniform dispersion of nanoparticles

Magnesium is a light metal, with a density two-thirds that of aluminium, is abundant on Earth and is biocompatible; it thus has the potential to improve energy efficiency and system performance in aerospace, automobile, defence, mobile electronics and biomedical applications. However, conventional synthesis and processing methods (alloying and thermomechanical processing) have reached certain limits in further improving the properties of magnesium and other metals. Ceramic particles have been introduced into metal matrices to improve the strength of the metals, but unfortunately, ceramic microparticles severely degrade the plasticity and machinability of metals, and nanoparticles, although they have the potential to improve strength while maintaining or even improving the plasticity of metals, are difficult to disperse uniformly in metal matrices. Here we show that a dense uniform dispersion of silicon carbide nanoparticles (14 per cent by volume) in magnesium can be achieved through a nanoparticle self-stabilization mechanism in molten metal. An enhancement of strength, stiffness, plasticity and high-temperature stability is simultaneously achieved, delivering a higher specific yield strength and higher specific modulus than almost all structural metals.

A microbial signature for Crohn's disease

Objective A decade of microbiome studies has linked IBD to an alteration in the gut microbial community of genetically predisposed subjects. However, existing profiles of gut microbiome dysbiosis in adult IBD patients are inconsistent among published studies, and did not allow the identification of microbial signatures for CD and UC. Here, we aimed to compare the faecal microbiome of CD with patients having UC and with non-IBD subjects in a longitudinal study. Design We analysed a cohort of 2045 non-IBD and IBD faecal samples from four countries (Spain, Belgium, the UK and Germany), applied a 16S rRNA sequencing approach and analysed a total dataset of 115 million sequences. Results In the Spanish cohort, dysbiosis was found significantly greater in patients with CD than with UC, as shown by a more reduced diversity, a less stable microbial community and eight microbial groups were proposed as a specific microbial signature for CD. Tested against the whole cohort, the signature achieved an overall sensitivity of 80% and a specificity of 94%, 94%, 89% and 91% for the detection of CD versus healthy controls, patients with anorexia, IBS and UC, respectively. Conclusions Although UC and CD share many epidemiologic, immunologic, therapeutic and clinical features, our results showed that they are two distinct subtypes of IBD at the microbiome level. For the first time, we are proposing microbiomarkers to discriminate between CD and non-CD independently of geographical regions.

Self-Catalyzed Epitaxial Growth of Vertical Indium Phosphide Nanowires on Silicon

Vertical indium phosphide nanowires have been grown epitaxially on silicon (111) by metalorganic vapor-phase epitaxy. Liquid indium droplets were formed in situ and used to catalyze deposition. For growth at 350 degrees C, about 70% of the wires were vertical, while the remaining ones were distributed in the 3 other <111> directions. The vertical fraction, growth rate, and tapering of the wires increased with temperature and V/III ratio. At 370 degrees C and V/III equal to 200, 100% of the wires were vertical with a density of approximately 1.0 x 10(9) cm(-2) and average dimensions of 3.9 mum in length, 45 nm in base width, and 15 nm in tip width. X-ray diffraction and transmission electron microscopy revealed that the wires were single-crystal zinc blende, although they contained a high density of rotational twins perpendicular to the <111> growth direction. The room temperature photoluminescence spectrum exhibited one peak centered at 912 +/- 10 nm with a FWHM of approximately 60 nm.

Reduction of butyrate- and methane-producing microorganisms in patients with Irritable Bowel Syndrome.

The pathophysiology of irritable bowel syndrome (IBS) remains unclear. Here we investigated the microbiome of a large cohort of patients to identify specific signatures for IBS subtypes. We examined the microbiome of 113 patients with IBS and 66 healthy controls. A subset of these participants provided two samples one month apart. We analyzed a total of 273 fecal samples, generating more than 20 million 16S rRNA sequences. In patients with IBS, a significantly lower microbial diversity was associated with a lower relative abundance of butyrate-producing bacteria (P = 0.002; q < 0.06), in particular in patients with IBS-D and IBS-M. IBS patients who did not receive any treatment harboured a lower abundance of Methanobacteria compared to healthy controls (P = 0.005; q = 0.05). Furthermore, significant correlations were observed between several bacterial taxa and sensation of flatulence and abdominal pain (P < 0.05). Altogether, our findings showed that IBS-M and IBS-D patients are characterized by a reduction of butyrate producing bacteria, known to improve intestinal barrier function, and a reduction of methane producing microorganisms a major mechanism of hydrogen disposal in the human colon, which could explain excess of abdominal gas in IBS.

MetaTrans: an open-source pipeline for metatranscriptomics

To date, meta-omic approaches use high-throughput sequencing technologies, which produce a huge amount of data, thus challenging modern computers. Here we present MetaTrans, an efficient open-source pipeline to analyze the structure and functions of active microbial communities using the power of multi-threading computers. The pipeline is designed to perform two types of RNA-Seq analyses: taxonomic and gene expression. It performs quality-control assessment, rRNA removal, maps reads against functional databases and also handles differential gene expression analysis. Its efficacy was validated by analyzing data from synthetic mock communities, data from a previous study and data generated from twelve human fecal samples. Compared to an existing web application server, MetaTrans shows more efficiency in terms of runtime (around 2 hours per million of transcripts) and presents adapted tools to compare gene expression levels. It has been tested with a human gut microbiome database but also proposes an option to use a general database in order to analyze other ecosystems. For the installation and use of the pipeline, we provide a detailed guide at the following website (www.metatrans.org).

Nanotwins in nanocrystalline Mg–Al alloys: an insight from high-resolution TEM and molecular dynamics simulation

Twinning in hexagonal close-packed Mg alloys has been reported to be unfavorable when the grain size is reduced below a couple of microns and suppressed at the nanoscale. Using high-resolution transmission electron microscopy, we present evidence of nanotwins (<1 nm) in nanocrystalline Mg–Al alloys processed by cryomilling. The commonly observed twinning modes for coarse-grained Mg are identified and supported with atomistic molecular dynamics simulations. The specific thermomechanical conditions offered by cryomilling facilitate the generation of deformation twins that are not observed with conventional deformation processing methods.

Controlled Synthesis of Nanoscale Icosahedral Gold Particles at Room Temperature

The shape of nanocrystals determines surface atomic arrangement and coordination, influencing their chemical and physical properties. We present a novel and facile approach to synthesize gold icosahedra by employing glucose as reducing reagent and sodium dodecyl sulfate as directing agent in the environmentally benign medium of water at room temperature. The size of the icosahedra can be controlled in the range of 30–250 nm by altering reaction conditions. High‐resolution microscopy and diffraction studies indicate the icosahedra are composed of rotational twins that owe likely to assemblage of tetrahedral units. The gold icosahedra particles catalytic properties are probed in the borohydride reduction of p‐nitrophenols and exhibit a size‐dependence reaction property. Comparison studies with spherical particles prepared by the Turkevich method, coupled with poisoning experiments, infer that the shape has a strong influence in the abundance of active surface sites as well as their activities. The properties of nanoscale icosahedra particles has promising applications for further catalytic processes, surface enhancement spectroscopic methods, chemical or biological sensing, and the fabrication of nanoscale devices.

Alteration of the serum microbiome composition in cirrhotic patients with ascites

The progression of cirrhosis is associated with alterations in the composition of the gut microbiome. To assess microbial translocation, we compared the serum microbial composition of patients with and without ascites and characterized the ascitic fluid microbiome using 16S rDNA high-throughput sequencing data. A complex and specific microbial community was detected in the serum and ascitic fluid of patients with cirrhosis but barely detectable in the serum of healthy controls. The serum microbiome of patients with ascites presented higher levels of lipopolysaccharide binding protein, a marker of microbial translocation, associated with higher diversity and relative abundance of Clostridiales and an unknown genus belonging to the Cyanobacteria phylum compared to patients without ascites. The composition of the fecal microbiome was also more altered in patients with than without ascites, confirming previous studies on fecal microbiome. We propose that alteration of the serum and fecal microbiome composition be considered indicators of cirrhosis progression.

Size-Induced Strengthening in Nanostructured Mg Alloy Micropillars

Size effects on the compressive strength of nanostructured Mg-micropillars were investigated. Mg–10Al alloy micropillars with diameters ranging from 1.5 to 8 μm were prepared by focused-ion-beam and tested under micro-compression. A significant improvement in strength was found by reducing the pillar diameter<3.5 μm. The deformation mechanisms of the compressed pillars were characterized using transmission electron microscopy. We attribute the size-induced strengthening to a less number of dislocation sources along with a higher activity of non-basal deformation mechanisms.

Self-assembled single-crystalline ZnO nanostructures

We report a template-free, halide-free, efficient wet chemical method to synthesize defect-rich ZnO nanostructures with exposed {101} facets. The self-assembled ZnO nanostructures provide an active playground for catalytic reactions, such as CO2 hydrogenation, and exhibits great potential in alternative energy technologies.