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Zhulina E.B.,RAS Institute of Macromolecular Compounds | Leermakers F.A.M.,Laboratory of Physical Chemistry and Colloid Science | Borisov O.V.,University of Pau and Pays de lAdour
Langmuir | Year: 2015

We present a theoretical analysis targeted to describe the structural properties of brushes formed by Ψ-shaped macromolecules tethered by terminal segment of stem to planar surface while exposing multiple free branches to the surrounding solution. We use an analytical self-consistent field approach based on the strong stretching approximation, and the assumption of Gaussian elasticity for linear chain fragments of the tethered macromolecules. The effect of weak and strong polydispersity of branches is analyzed. In the case of weakly polydisperse macromolecules, variations in length of branches lead to a more uniform polymer density distribution with slight increase in the brush thickness compared to the case of monodisperse chains with the same degree of polymerization. We demonstrate that in contrast to linear chains, strong polydispersity of Ψ-shaped macromolecules does not necessarily lead to strong perturbations in polymer density distribution. In particular, mixed brushes of the so-called "mirror" dendrons (in which number of stem monomers in one component coincides with number of monomers in a branch of the other component, and vice versa) give rise to a unified polymer density distribution with shape independent of the brush composition. The predictions of analytical theory are systematically compared to the results of numerical self-consistent field modeling based on the Scheutjens-Fleer approach. © 2015 American Chemical Society. Source


Zhulina E.B.,RAS Institute of Macromolecular Compounds | Leermakers F.A.M.,Laboratory of Physical Chemistry and Colloid Science | Borisov O.V.,University of Pau and Pays de lAdour
Macromolecules | Year: 2015

We predict theoretically that in contrast to composite brushes of end-tethered linear polymers that exhibit vertical stratification, chemically identical branched macromolecules with different molecular weights and selected architectures can distribute their free ends all over the volume of composite brush and produce a unified polymer density profile. As a result of this, we expect the presence of terminal end-groups of all constituent macromolecular species in the vicinity of the external boundary of such composite brush. The predictions of the analytical theory are supported by numerical self-consistent field calculations. Unified brushes offer new possibilities in the design of polymer-decorated surfaces and might improve our understanding of natural biointerfaces. © 2015 American Chemical Society. Source


Trappmann B.,University of Cambridge | Gautrot J.E.,University of Cambridge | Connelly J.T.,University of Cambridge | Connelly J.T.,Queen Mary, University of London | And 14 more authors.
Nature Materials | Year: 2012

To investigate how substrate properties influence stem-cell fate, we cultured single human epidermal stem cells on polydimethylsiloxane (PDMS) and polyacrylamide (PAAm) hydrogel surfaces, 0.1 kPa-2.3 MPa in stiffness, with a covalently attached collagen coating. Cell spreading and differentiation were unaffected by polydimethylsiloxane stiffness. However, cells on polyacrylamide of low elastic modulus (0.5 kPa) could not form stable focal adhesions and differentiated as a result of decreased activation of the extracellular-signal- related kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling pathway. The differentiation of human mesenchymal stem cells was also unaffected by PDMS stiffness but regulated by the elastic modulus of PAAm. Dextran penetration measurements indicated that polyacrylamide substrates of low elastic modulus were more porous than stiff substrates, suggesting that the collagen anchoring points would be further apart. We then changed collagen crosslink concentration and used hydrogel-nanoparticle substrates to vary anchoring distance at constant substrate stiffness. Lower collagen anchoring density resulted in increased differentiation. We conclude that stem cells exert a mechanical force on collagen fibres and gauge the feedback to make cell-fate decisions. © 2012 Macmillan Publishers Limited. All rights reserved. Source


Saglam D.,Top Institute Food and Nutrition | Saglam D.,Wageningen University | Venema P.,Wageningen University | de Vries R.,Laboratory of Physical Chemistry and Colloid Science | And 2 more authors.
Food Hydrocolloids | Year: 2013

In this work heat stability and rheological properties of concentrated whey protein particle dispersions in different dispersing media are studied. Whey protein particles (protein content ∼20% w/v) having an average size of a few microns were formed using a combination of two-step emulsification and heat-induced gelation. Particles were dispersed (volume fraction of particles ∼0.35) in solutions of Na-caseinate, whey protein isolate or gum arabic at different concentrations. The microstructure, particle size distribution and flow behaviour of the dispersions were analyzed before and after heating at 90 °C for 30 min. All dispersions were liquid-like and no significant change in the microstructure was observed after heat treatment. Viscosity measurements showed that both the type and the concentration of the stabilizer influenced the viscosity changes after heat treatment. When 1% (w/w) gum arabic was used as stabilizer no change in the viscosity was observed after heat treatment. However, when Na-caseinate or whey protein isolate was used, viscosity increased in low-shear regime and shear-thickening was observed in high-shear regime. Heat treatment did not significantly alter the zeta potential of the particles, whereas the size of the particles increased after heating due to swelling. The results show that swelling of the particles plays a significant role in the heat stability and rheological properties of these dispersions. © 2012 Elsevier Ltd. Source


Saglam D.,Top Institute Food and Nutrition | Saglam D.,Wageningen University | Venema P.,Wageningen University | de Vries R.,Laboratory of Physical Chemistry and Colloid Science | And 2 more authors.
Food Hydrocolloids | Year: 2014

We have studied the influence of dense whey protein particles on the mechanical properties of whey protein isolate (WPI) gels at high protein concentrations (16-22% (w/w)). Incorporation of dense whey protein particles in the gel, while keeping the total protein concentration constant, leads to a considerably lower storage modulus. By adding protein particles, the total protein concentration of the WPI gels could be increased by 25-55% (w/w), without increasing the storage modulus of the gel. The large deformation properties of the WPI gels were also influenced by the presence of dense protein particles. Gels containing protein particles fractured at a lower strain than pure WPI gels at the same protein concentration. We conclude that protein particles can be used to modulate mechanical properties of WPI gels and are promising candidates for the development of high protein foods with improved textural properties. © 2013 Elsevier Ltd. Source

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