Ref HAL: hal-01601702_v1
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Wheat gluten proteins are among the most complex protein networks in nature, due in particular to their poor solubility in water and to their viscoelastic behavior. Gluten networks are often considered as transient networks comprising extensible biopolymer segments of flexible or semiflexible chains between junction points. However, the exact structure of the network, the nature of the junction points and the way it get structured under shear remain to be clarified. Here we report the visco-elastic behavior of model systems composed of gluten proteins near gelation. We build model systems by dispersing in ethanol-water mixtures two major protein groups, gliadins and glutenins, that we have purified from gluten. Rheological properties show a slow evolution over time scales of the order of days of the linear frequency dependence complex modulus of the samples, with a concentration-dependent liquid to solid transition. Interestingly, we find that all data acquired at different protein concentrations and different times after sample preparation can be scaled onto a master curve showing a cross-over from a soft solid behavior at low frequency to a visco-elastic fluid at high frequency.Rheological data are completed by scattering experiments in order to elucidate the complex structure of the materials. For gel samples, the scattering profiles display at small length scales features typical of polymer and evidences at larger length scale a fractal structure that we interpret as being due to the highly disordered state of the junction points. Biochemical assays are also performed to elucidate the origin of the sample aging.

Ref HAL: hal-00912585_v1
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By adding nanoparticles to polymer melts, nanocomposites with improved mechanical and thermal properties are obtained. For a given polymer-filler couple, the improvement of properties appears related to the filler size, volume fraction and dispersion. Nevertheless no universal model is established at the present time. Whereas the filler size and volume fraction are determined by the formulation, the dispersion is more difficult to control and investigate. In the first part of the talk, we will show how we can tune the particles dispersion in model nanolatex systems (polymethacrylate-silica) using different strategies: the control of the filler charge, the modulation of the latex/filler size ratio (R) and the use of different polymer chain length. Using small angle scattering and TEM analysis we will demonstrate that repulsive aggregates of varying size can be obtained playing with the pH of the casting solution1. A good filler dispersion is obtained for R=1, whereas a network of well-organized silica particles around the latex beads is highlighted for high latex/filler size ratio. Finally, decreasing the polymer molecular weight, fractals aggregates of increasing size are generated. The effect of these various structures on mechanical properties will be discussed. The mechanical properties of nanocomposite materials are controlled to a large extent by the filler-filler interactions, nevertheless, another important contribution - less well understood - is due to the polymer chain-filler interactions. In a second part, we will display results of an investigation of the polymer chains in such nanocomposites2. Small angle neutron scattering experiments performed in zero average contrast conditions (mixing hydrogenated and deuterated latex beads) enabled to follow the latex beads dissolution using an original model. Experimental results demonstrate that the dissolution dynamic of polymer chains is significantly slowed down by the presence of silica nanoparticles.

Ref HAL: hal-00831515_v1
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Wheat gluten proteins are insoluble in water and are among the most complex protein networks in nature. In spite of their extensively use in particular for bread making, their viscoelastic properties and their structuration are still largely unknown. Here we report the visco-elastic behavior of model systems composed of gluten proteins near the liquid-solid transition. We build model systems by dispersing in ethanol-water mixtures two major protein groups, gliadin and glutenin, that we have purified from gluten. We find a slow evolution over time scales of the order of days of the linear frequency dependence complex modulus of the samples. Interestingly, we find that all data acquired at different protein concentrations and different times after sample preparation can be scaled onto a master curve, showing a cross-over from a soft solid at low frequency to a visco-elastic fluid at high frequency. We are currently using scattering techniques to unveil the peculiar structure of the protein network that would lead to the self-similar visco-elasticity.

Résumé:

Distribution de particules et conformation de chaînes dans des matériaux nanocomposites

Ref HAL: hal-00747635_v1
PMID 22617741
Ref Arxiv: 1211.0301
DOI: 10.1016/j.actbio.2012.05.015
WoS: 000307625900012
Ref. & Cit.: NASA ADS
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15 Citations
Résumé:

Designing synthetic microenvironments for cellular investigations is a very active area of research at the crossroads of cell biology and materials science. The present work describes the design and functionalization of a three-dimensional (3D) culture support dedicated to the study of neurite outgrowth from neural cells. It is based on a dense self-assembled collagen matrix stabilized by 100-nm-wide interconnected native fibrils without chemical crosslinking. The matrices were made suitable for cell manipulation and direct observation in confocal microscopy by anchoring them to traditional glass supports with a calibrated thickness of ∼50μm. The matrix composition can be readily adapted to specific neural cell types, notably by incorporating appropriate neurotrophic growth factors. Both PC-12 and SH-SY5Y lines respond to growth factors (nerve growth factor and brain-derived neurotrophic factor, respectively) impregnated and slowly released from the support. Significant neurite outgrowth is reported for a large proportion of cells, up to 66% for PC12 and 49% for SH-SY5Y. It is also shown that both growth factors can be chemically conjugated (EDC/NHS) throughout the matrix and yield similar proportions of cells with longer neurites (61% and 52%, respectively). Finally, neurite outgrowth was observed over several tens of microns within the 3D matrix, with both diffusing and immobilized growth factors.

Résumé:

Observation of chain structure in nanocomposites