11 research outputs found

    Influence of S/B middle block composition on the morphology and the mechanical response of polystyrene-poly(styrene-co-butadiene)-polystyrene triblock copolymers

    No full text
    Polystyrene-poly(styrene-co-butadiene)-polystyrene triblock copolymers (PS-P(S-co-B)-PS) having different styrene contents (from 30 wt.% to 80 wt.%) in the statistical copolymer middle block and different block architectures (20-60-20 and 30-40-30) were characterised to study the influence of S/B middle block composition and segregation strength on the morphology and mechanical behaviour. The morphological investigations, i.e. TEM and SAXS, exhibited ordered lamellar and lamellar-like morphologies for both block architectures at low styrene contents between 30 wt.% and 50 wt.% in the S/B middle block. The increase in the styrene content in the middle block to 70 wt.% resulted in phase separated structures without long range order due to the enhanced miscibility between the PS and P(S-co-B) phase as observed from dynamic mechanical analysis. Further it was observed that the glass transition of the butadiene-rich phase is mainly determined by the S/B composition of the st atistical copolymer block as confirmed by the Fox-equation. The alteration of the glass transition of the PS-rich phase and the observed PS-softening with raise in styrene content might be correlated to the increasing interphase width due to the enhanced miscibility as shown by calculations based on a simple model for diblock copolymers. Tensile testing revealed a transition from ductile to semi-ductile to brittle behaviour that strongly depends on the styrene content in the S/B middle block, chain architecture and the resulting morphology. Block copolymers (BCPs) with lamellar structure exhibited ductile behaviour with extensive strain hardening, whereas BCPs forming segregated structures without long range order were semi-ductile or brittle depending on the type of block architecture and on the hard-phase content. The transition in the mechanical behaviour was confirmed by fracture mechanical investigations based on the essential work of fracture approach and SEM-characterizations

    Insulin mRNA is stored in RNA granules in resting beta cells

    No full text
    The glucose-stimulated biosynthesis of insulin in pancreatic islet beta cells is post-transcriptionally regulated. Several RNA-binding proteins (RBPs) that regulate Insulin mRNA stability and translation also bind mRNAs coding for other insulin secretory granule (ISG) proteins. However, an overview of these interactions and their glucose-induced remodelling is still missing. Here we identify two distinct sets of RBPs that were preferentially pulled down with the 5’-UTRs of mouse Ins1, Ins2, spliced Ins2, Ica512/Ptprn and Pc2/Pcsk2 mRNAs from extracts of either resting or stimulated mouse insulinoma MIN6 cells. Among RBPs binding to all tested transcripts in resting conditions was hnRNP A2/B1. Hnrnpa2b1 KO MIN6 cells contained lower levels of Ins1 mRNA, proinsulin and insulin, and had reduced insulin secretion. In resting cells, both hnRNP A2/B1 and Insulin mRNAs localized to stress granules, which dissolved upon glucose stimulation. Insulin mRNA-positive RNA granules were also found in human pancreatic beta cells in situ. Our results suggest that resting beta cells store mRNAs for insulin secretory granule proteins in stress granules through specific RNA protein interactions. Glucose stimulation remodels these interactions, releasing the transcripts, and another set of RBPs coordinates their translation
    corecore