Hierarchical Structure and Crystal Orientation in Poly(ethylene oxide)/Clay Nanocomposite Films

Water-cast nanocomposite films formed by poly­(ethylene oxide) (PEO) and Laponite clay were found to display three characteristic levels of structure with large-scale orientation. The first level with the length scale of ca. 30–50 nm was the clay lamellar bundles, which tended to stack perpendicularly to the film surface. The second level with the characteristic length of 1.8 nm was associated with the alternating stacking of the silicate layers and the PEO chains sandwiched between them. The preferred orientations of these two levels of structure were independent of clay content, solvent removal rate for the film preparation, and the crystallization temperature of the PEO chains situating outside the clay bundles. The third level of structure was characterized by the preferred orientation of the PEO crystalline stems with respect to the surface of the silicate layers. Perpendicular orientation always dominated in the nanocomposite films prepared by slow solvent removal irrespective of crystallization temperature. In the films prepared by fast solvent removal, however, parallel crystal orientation set in as the clay concentration exceeded ca. 33 wt %. The preferred crystal orientation was ascribed to the confinement effect imposed by the clay bundles to the crystallization of the PEO chains situating in the interbundle region. In the films cast by slow solvent removal, the weaker confinement associated with the larger interbundle distance led to perpendicular crystal orientation. When the interbundle distance was reduced to ca. 30 nm in the films prepared by rapid solvent evaporation, the strong confinement directed the crystals to form parallel orientation

Immune-modulatory genomic properties differentiate gut microbiota of infants with and without eczema

<div><p>Gut microbiota play an important role in human immunological processes, potentially affecting allergic diseases such as eczema. The diversity and structure of gut microbiota in infants with eczema have been previously documented. This study aims to evaluate by comparative metagenomics differences in genetic content in gut microbiota of infants with eczema and their matched controls. Stools were collected at the age of one month old from twelve infants from an at risk birth cohort in a case control manner. Clinical follow up for atopic outcomes were carried out at the age of 12 and 24 months. Microbial genomic DNA were extracted from stool samples and used for shotgun sequencing. Comparative metagenomic analysis showed that immune-regulatory TCAAGCTTGA motifs were significantly enriched in the six healthy controls (C) communities compared to the six eczema subjects (E), with many encoded by <i>Bifidobacterium</i> (38% of the total motifs in the C communities). Draft genomes of five <i>Bifidobacterium</i> species populations (<i>B</i>. <i>longum</i>, <i>B</i>. <i>bifidum</i>, <i>B</i>. <i>breve</i>, <i>B</i>. <i>dentium</i>, and <i>B</i>. <i>pseudocatenulatum</i>) were recovered from metagenomic datasets. The <i>B</i>. <i>longum</i> BFN-121-2 genome encoded more TCAAGCTTGA motifs (4.2 copies per one million genome sequence) than other <i>Bifidobacterium</i> genomes. Additionally, the communities in the stool of controls (C) were also significantly enriched in functions associated with tetrapyrrole biosynthesis compared to those of eczema (E). Our results show distinct immune-modulatory genomic properties of gut microbiota in infants associated with eczema and provide new insights into potential role of gut microbiota in affecting human immune homeostasis.</p></div

Immunosuppressive motif occurrence and relative abundance of <i>Bifidobacterium</i> sp. draft genomes.

<p>(A) Occurrence of TCAAGCTTGA motifs per 10⁶ bases. (B) Fold changes of average relative abundance of individual populations. The genome coverage was estimated for the relative abundance of a population. The bar represents the mean fold change (logarithmic scale) and the error bar represents one standard deviation from the mean. *<i>P</i> < 0.05 by Metastats.</p

Phylogenetic composition of microbial communities.

<p>Average relative abundance of major phyla (Avg. > 5% of the total community) <b>(A)</b> and genera (Avg. > 1%) <b>(B)</b> of C (outer circle) and E (inner circles) communities. ‘Others’ represents the combined fraction of the remaining minor taxa.</p

Immunosuppressive motifs differentiate C communities from E communities.

<p>(A) Frequencies of two immunosuppressive motifs (TTAGGG and TCAAGCTTGA) in C and E communities. The asterisk denotes <i>P</i> < 0.05 by Metastats. (B) Phylogenetic affiliation of the metagenomic reads encoding the TCAGCTTGA motifs in C and E communities, respectively. (C) Phylogenetic affiliation of the <i>Bifidobacterium</i> TCAGCTTGA motifs observed in C communities to available <i>Bifidobacterium</i> species genomes (GenBank).</p