Structure-property relations of highly ordered bio-nanocomposites

Bio-nanocomposites with superior mechanical, transport and flame-retardant properties can be produced from the combination of biopolymers and silicate nanoclay platelets, such as montmorillonite (MMT) [1,2,4]. The highly ordered nanostructure observed in such systems is often compared to natural ones, such as in the brick-and-mortar arrangement of aragonite plates in nacreous materials [3]. Previous work on nacre-mimetic alginate/MMT nanocomposites has shown good compatibility between the biopolymer and inorganic filler and a dependence on MMT concentration to the level of alignment [4]. In this study, we investigate the effect of gelation on the orientation of nanoparticles and its impact on clay stacking and effective aspect ratio. Thermo-reversible gelling biopolymers, i.e. gelatin and carrageenan, were used as matrices to induce early gelation; and compared to sodium alginate (late gelling reaction). Self-supporting bio-nanocomposite films based on gelatin or carrageenan, with a wide range of Na-montmorillonite concentration – up to 80 wt.% MMT – were successfully prepared by solvent casting. The obtained films display a highly aligned nacre-like structure (Fig. 1). To investigate the effect of MMT ordering on the mechanical properties, we have analyzed the obtained films with dynamic mechanical thermal analysis. The bio-nanocomposite films display exceptional mechanical properties, with storage modulus as high as 33 GPa (carrageenan/MMT); and high reinforcement depending on MMT concentration (Fig. 2). At remarkably high inorganic fraction, 80 wt.% MMT, early gelling biopolymers showed a continued increase in material reinforcement, whereas late gelation shows a slight decrease. This suggests that early gelling might reduce restacking of MMT platelets, thus, improving the effective aspect ratio of the filler. The highly ordered structure observed in the gelatin 80 wt.% MMT composite was also reflected in its high heat distortion temperature, implying lower oxygen diffusivity. To better understand the influence of gelation and MMT addition on the mechanical properties, we further applied a conventional composite theory (Halpin-Tsai model), which considers the individual contributions of filler, such as the level of alignment, aspect ratio, volume fraction, and the modulus of the MMT platelets. Please click Additional Files below to see the full abstract

Supramolecular materials: molecular packing of tetranitrotetrapropoxycalix[4]arene in highly stable films with second-order nonlinear optical properties

Highly stable films of tetranitrotetrapropoxycalix[4]arene (9) with second-order nonlinear optical (NLO) properties and a noncentrosymmetric structure were obtained by a novel crystallization process at 130-140 degrees C in a de electric field. The packing of 9 in these films was elucidated by a combination of X-ray diffraction, angle-dependent second- harmonic generation, and scanning force microscopy (SFM). The experimental results agree well with solid-state molecular dynamics calculations for these films. No crystalline phase was observed for nitrocalix[4]arene derivatives with longer or branched alkyl chains; this explains the limited NLO stability of films of these calixarenes. Scanning force microscopy o­n the aligned films of 9 showed two distinct surface lattice structures: a rectangular lattice (a = 9.3, b = 11.7 Angstrom) and a pseudohexagonal lattice (d approximate to 11.4 Angstrom). The combination of these data with the interlayer distance of 8.9 Angstrom (X-ray diffraction) allowed the packing of molecules of 9 in these structures to be fully elucidated at the molecular level

Automated High-Content Live Animal Drug Screening Using C. elegans Expressing the Aggregation Prone Serpin α1-antitrypsin Z

The development of preclinical models amenable to live animal bioactive compound screening is an attractive approach to discovering effective pharmacological therapies for disorders caused by misfolded and aggregation-prone proteins. In general, however, live animal drug screening is labor and resource intensive, and has been hampered by the lack of robust assay designs and high throughput work-flows. Based on their small size, tissue transparency and ease of cultivation, the use of C. elegans should obviate many of the technical impediments associated with live animal drug screening. Moreover, their genetic tractability and accomplished record for providing insights into the molecular and cellular basis of human disease, should make C. elegans an ideal model system for in vivo drug discovery campaigns. The goal of this study was to determine whether C. elegans could be adapted to high-throughput and high-content drug screening strategies analogous to those developed for cell-based systems. Using transgenic animals expressing fluorescently-tagged proteins, we first developed a high-quality, high-throughput work-flow utilizing an automated fluorescence microscopy platform with integrated image acquisition and data analysis modules to qualitatively assess different biological processes including, growth, tissue development, cell viability and autophagy. We next adapted this technology to conduct a small molecule screen and identified compounds that altered the intracellular accumulation of the human aggregation prone mutant that causes liver disease in α1-antitrypsin deficiency. This study provides powerful validation for advancement in preclinical drug discovery campaigns by screening live C. elegans modeling α1-antitrypsin deficiency and other complex disease phenotypes on high-content imaging platforms

Cooperative and non-cooperative dynamics in ultra-thin films of polystyrene studied by dielectric spectroscopy and capacitive dilatometry

The effect of thickness reductions on the glass transition dynamics in ultrathin films of polystyrene has been studied by dielectric spectroscopy (DS) and capacitive dilatometry (CD). Upon reduction of the film thickness, a systematic decrease in the dilatometric glass transition temperatures, Tg (dil), was observed via CD, while DS revealed a continuous speed-up and broadening of the α-process, accompanied by only minor reductions in the fragility index. A good agreement between 'spectroscopic' and the dilatometric glass transition temperatures was found for films thicker than 20 nm, while for thinner films both quantities diverge increasingly. A likely explanation for this discrepancy is the presence of another dynamic process showing Arrhenius-behavior (Ea ∼ 72 kJ/mol) with a pre-exponential factor of 10-12 s being indicative for non-cooperative dynamics. Such a new process might be assigned to distinct surface dynamics in polystyrene films as suggested in recent papers. © 2006 Elsevier B.V. All rights reserved.status: publishe

Dynamics of T(2)G(2) helices in atactic and syndiotactic polystyrene: New evidence from dielectric spectroscopy and FTIR

The local and cooperative dynamics in atactic (a-PS) and syndiotactic (s-PS) polystyrene were studied by broadband dielectric spectroscopy. Besides the known alpha-relaxation, two additional relaxation processes beta(1) and beta(2) were revealed in various samples of a-PS and s-PS films cast from solvent solutions. These new dynamic processes show Arrhenius behavior, a common activation energy around 80 kJ/mol, and cross the alpha-relaxation region without merging, indicating a molecular origin being phase-separated from the amorphous PS fraction. By Fourier transform infrared spectroscopy (FTIR) measurements, a clear link between the existence of T(2)G(2) helix conformation and the occurrence of the beta(1) and beta(2)-processes was established. Symmetry arguments and systematic differences in the relaxation parameters between a-PS and s-PS favor the assignment of the fast, beta(1), process to a helix defect mechanism (helix inversion), while the slow mode, beta(2), likely originates from cooperative helix inversion events that would point to spatially organized aggregates of helices, as suggested earlier for PS gels. The occurrence of such solvent-induced structures and their dynamics might have important implication for the interpretation of T-g reductions found in ultrathin PS films.status: publishe

Supplementary data for PhD thesis "Biopolymer nanocomposites: lessons from structure-property relationships"

Supplementary information accompanying Ph.D. thesis "Biopolymer nanocomposites: lessons from structure-property relationships"</p

Systematic study of the nanostructures of exfoliated polymer nanocomposites

High-performance bioinspired materials have shown rapid development over the last decade. Examples are brick-and-mortar hierarchical structures, which are often achieved via solvent evaporation. Although good properties are claimed, most systems are composed of stacked or intercalated platelets. Exfoliation is a crucial step to give ultimate anisotropic properties, e.g. thermal, mechanical and barrier properties. We propose a general framework for all the various types of micro-scale structures that should be distinguished for 2D-filler nanocomposites. In particular, the exfoliated state is systematically explored by the immobilization of montmorillonite platelets via (gelatin) hydrogelation. Scattering techniques were used to evaluate this strategy at the level of the particle dispersion and the regularity of spatial arrangement. The gelatin/montmorillonite exfoliated nanostructures are fully controlled by the filler volume fraction since the observed gallery d-spacings perfectly fall onto the predicted values. Surprisingly, X-ray analysis also revealed short- and quasi long-range arrangement of the MMT at high loading

Supplementary data for PhD thesis "Biopolymer nanocomposites: lessons from structure-property relationships"

Supplementary information accompanying Ph.D. thesis "Biopolymer nanocomposites: lessons from structure-property relationships"</p

Mechanisms involved in down-regulation of intestinal IgA in rats by high cocoa intake

Previous studies have shown that rat intestinal immunoglobulin A (IgA) concentration and lymphocyte composition of the intestinal immune system were influenced by a highly enriched cocoa diet. The aim of this study was to dissect the mechanisms by which a long-term high cocoa intake was capable of modifying gut secretory IgA in Wistar rats. After 7 weeks of nutritional intervention, Peyer's patches, mesenteric lymph nodes and the small intestine were excised for gene expression assessment of IgA, transforming growth factor ß, C-C chemokine receptor-9 (CCR9), interleukin (IL)-6, CD40, retinoic acid receptors (RAR¿ and RARß), C-C chemokine ligand (CCL)-25 and CCL28 chemokines, polymeric immunoglobulin receptor and toll-like receptors (TLR) expression by real-time polymerase chain reaction. As in previous studies, secretory IgA concentration decreased in intestinal wash and fecal samples after cocoa intake. Results from the gene expression showed that cocoa intake reduced IgA and IL¿6 in Peyer's patches and mesenteric lymph nodes, whereas in small intestine, cocoa decreased IgA, CCR9, CCL28, RAR¿ and RARß. Moreover, cocoa-fed animals presented an altered TLR expression pattern in the three compartments studied. In conclusion, a high-cocoa diet down-regulated cytokines such as IL-6, which is required for the activation of B cells to become IgA-secreting cells, chemokines and chemokine receptors, such as CCL28 and CCR9 together with RAR¿ and RARß, which are involved in the gut homing of IgA-secreting cells. Moreover, cocoa modified the cross-talk between microbiota and intestinal cells as was detected by an altered TLR pattern. These overall effects in the intestine may explain the intestinal IgA down-regulatory effect after the consumption of a long-term cocoa-enriched diet