Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Multiscale analysis of structure development in expanded starch snacks
Sman, R.G.M. van der; Broeze, J. - \ 2014
Journal of Physics-Condensed Matter 26 (2014)46. - ISSN 0953-8984
mass-transfer - food materials - bubble-growth - porous-media - systems - polymer - phase - model - simulation - extrusion
In this paper we perform a multiscale analysis of the food structuring process of the expansion of starchy snack foods like keropok, which obtains a solid foam structure. In particular, we want to investigate the validity of the hypothesis of Kokini and coworkers, that expansion is optimal at the moisture content, where the glass transition and the boiling line intersect. In our analysis we make use of several tools, (1) time scale analysis from the field of physical transport phenomena, (2) the scale separation map (SSM) developed within a multiscale simulation framework of complex automata, (3) the supplemented state diagram (SSD), depicting phase transition and glass transition lines, and (4) a multiscale simulation model for the bubble expansion. Results of the time scale analysis are plotted in the SSD, and give insight into the dominant physical processes involved in expansion. Furthermore, the results of the time scale analysis are used to construct the SSM, which has aided us in the construction of the multiscale simulation model. Simulation results are plotted in the SSD. This clearly shows that the hypothesis of Kokini is qualitatively true, but has to be refined. Our results show that bubble expansion is optimal for moisture content, where the boiling line for gas pressure of 4 bars intersects the isoviscosity line of the critical viscosity 10(6) Pa.s, which runs parallel to the glass transition line.
Genetically engineered silk-collagen-like copolymer for biomedical applications: Production, characterization and evaluation of cellular response
Wlodarczyk-Biegun, M.K. ; Werten, M.W.T. ; Wolf, F.A. de; Beucken, J.J.J.P. van den; Leeuwenburgh, S.C.G. ; Kamperman, M.M.G. ; Cohen Stuart, M.A. - \ 2014
Acta Biomaterialia 10 (2014)8. - ISSN 1742-7061 - p. 3620 - 3629.
crystal-structure - protein - scaffolds - biomaterials - polymer - polypeptides - hydrogels - elastin - gels - morphology
Genetically engineered protein polymers (GEPP) are a class of multifunctional materials with precisely controlled molecular structure and property profile. Representing a promising alternative for currently used materials in biomedical applications, GEPP offer multiple benefits over natural and chemically synthesized polymers. However, producing them in sufficient quantities for preclinical research remains challenging. Here, we present results from an in vitro cellular response study of a recombinant protein polymer that is soluble at low pH but self-organizes into supramolecular fibers and physical hydrogels at neutral pH. It has a triblock structure denoted as C2SH48C2, which consists of hydrophilic collagen-inspired and histidine-rich silk-inspired blocks. The protein was successfully produced by the yeast Pichia pastoris in laboratory-scale bioreactors, and it was purified by selective precipitation. This efficient and inexpensive production method provided material of sufficient quantities, purity and sterility for cell culture study. Rheology and erosion studies showed that it forms hydrogels exhibiting long-term stability, self-healing behavior and tunable mechanical properties. Primary rat bone marrow cells cultured in direct contact with these hydrogels remained fully viable; however, proliferation and mineralization were relatively low compared to collagen hydrogel controls, probably because of the absence of cell-adhesive motifs. As biofunctional factors can be readily incorporated to improve material performance, our approach provides a promising route towards biomedical applications.
Structure and dynamics of polyelectrolyte complex coacervates studied by scattering of neutrons, X-rays, and light
Spruijt, E. ; Leermakers, F.A.M. ; Fokkink, R.G. ; Schweins, R. ; Well, A.A. van; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
Macromolecules 46 (2013)11. - ISSN 0024-9297 - p. 4596 - 4605.
gelatin/polyelectrolyte complexes - angle scattering - reversible gels - micelles - polymer - protein - macromolecules - chloride) - interface - hydrogels
We investigate the microscopic structure and density fluctuations of complex coacervates of flexible polyelectrolytes using scattering of neutrons, X-rays, and light. Poly(acrylic acid) and poly(N,N-dimethylaminoethyl methacrylate) offer a well-defined model system that allows for selective labeling and systematic variation of the strength of the attractive electrostatic interactions. Two neutron scattering experiments have been carried out: (i) we use deuterated polymeric tracers in a complex coacervate with an overall neutron scattering length density that is matched to that of the solvent, to probe the conformation of single polymer chains in the complex coacervates, and (ii) we measure complex coacervates in which all polymer chains of one type are deuterated, to probe their overall structure. The single chain static structure factors reveal that both polycations and polyanions have an ideal Gaussian chain conformation in the complex coacervates. At the same time, the overall structure is similar to that of a semidilute polymer solution, with polycations and polyanions strongly overlapping to form a network with a mesh size that is much smaller than the radius of gyration of the polymers. The mesh size decreases with decreasing salt concentration, following a scaling that is in good agreement with predictions from the corresponding salt–polymer phase diagram. These findings are confirmed by complementary X-ray scattering experiments. Finally, in all scattering experiments with light, X-rays, and neutrons, and for all polymer chain lengths and salt concentrations, we find a remarkable low-q excess scattering, following a power law with a slope close to -2. This points to the presence of equilibrium, large-scale density fluctuations in the complex coacervates. Dynamic light scattering experiments reveal two complementary diffusive modes in the complex coacervates, corresponding to fluctuations of the polymer mesh and diffusion of domains of varying density, respectively
Pathway-dependent properties of a multi-stimuli sensitive biosynthetic hybrid network
Pham, T.H.T. ; Wolf, F.A. de; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
Soft Matter 9 (2013)36. - ISSN 1744-683X - p. 8737 - 8744.
inverse temperature transition - triblock copolymers - polymer - gelatin - nacl - gels
We study the self-assembly of an asymmetric triblock copolymer consisting of an elastin-like and a silk-like block bridged by a hydrophilic spacer. The elastin-like block aggregates at high temperature, leading to thermo-reversible micellization. The silk-like block self-assembles at low pH, and forms long fibrils, which dissociate again at high pH. The self-assembly of both blocks is strongly enhanced by increasing the salt concentration. When two blocks are sequentially triggered to self-assemble, the reversibility is lost; the final morphology and mechanical properties depend on the pathway that is chosen. A micellar solution formed at high temperature transforms into a gel network of sticky fibrils when the pH is lowered. Heating a solution of fibrils, formed at low pH, leads to the irreversible formation of bundles and large aggregates
On the Stability and Morphology of Complex Coacervate Core Micelles: From Spherical to Wormlike Micelles
Kooij, H.M. van der; Spruijt, E. ; Voets, I.K. ; Fokkink, R.G. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
Langmuir 28 (2012)40. - ISSN 0743-7463 - p. 14180 - 14191.
block-copolymer micelles - light-scattering - polyelectrolyte complexes - protein adsorption - diblock copolymer - polysulfone surfaces - polystyrene surfaces - silica - delivery - polymer
We present a systematic study of the stability and morphology of complex coacervate core micelles (C3Ms) formed from poly(acrylic acid) (PAA) and poly(N-methyl-2-vinylpyridinium)-b-poly(ethylene oxide) (PM2VP-b-PEO). We use polarized and depolarized dynamic and static light scattering, combined with small-angle X-ray scattering, to investigate how the polymer chain length and salt concentration affect the stability, size, and shape of these micelles. We show that C3Ms are formed in aqueous solution below a critical salt concentration, which increases considerably with increasing PAA and PM2VP length and levels off for long chains. This trend is in good agreement with a mean-field model of polyelectrolyte complexation based on the Voorn-Overbeek theory. In addition, we find that salt induces morphological changes in C3Ms when the PAA homopolymer is sufficiently short: from spherical micelles with a diameter of several tens of nanometers at low salt concentration to wormlike micelles with a contour length of several hundreds of nanometers just before the critical salt concentration. By contrast, C3Ms of long PAA homopolymers remain spherical upon addition of salt and shrink slightly. A critical review of existing literature on other C3Ms reveals that the transition from spherical to wormlike micelles is probably a general phenomenon, which can be rationalized in terms of a classical packing parameter for amphiphiles.
DNA compaction by nonbinding macromolecules
Vries, R.J. de - \ 2012
Polymer science. Series C, Chemistry reviews 54 (2012)1. - ISSN 1811-2382 - p. 30 - 35.
induced condensation - psi-condensation - supercoiled dna - polymer - proteins - bacteria - nanochannel - transition - filaments - dynamics
Compaction of DNA by nonbinding macromolecules such as uncharged flexible polymer chains and negatively charged globular proteins is thought to have various applications in biophysics, for example in the formation of a nucleoid structure in bacteria. A simple experimental model that has been very well studied is the classic DNA ¿-condensation induced by polymers and salt. In recent years, compaction of DNA by nonbinding macromolecules has been reconsidered under conditions that are closer to the biophysical applications, in various respect. This work is reviewed here. Topics that are considered are: DNA compaction by nonbinding globular proteins, the influence of DNA binding proteins and DNA topology on ¿-condensation, and finally, the impact of confinement on DNA ¿-condensation
Pickering emulsions: Wetting and colloidal stability of hairy particles - A self-consistent field theory
Salari, J.W.O. ; Leermakers, F.A.M. ; Klumperman, B. - \ 2011
Langmuir 27 (2011)11. - ISSN 0743-7463 - p. 6574 - 6583.
oil-water interface - interacting chain molecules - statistical-theory - solid particles - stabilization - adsorption - polymer - phase - microcapsules - surfactants
The assembly of sterically stabilized colloids at liquid–liquid interfaces is studied with the self-consistent field (SCF) theory using the discretization scheme that was developed by Scheutjens, Fleer, and co-workers. The model is based on a poly(methyl methacrylate) (pMMA) particle with poly(isobutylene) (pIB) grafted to the surface. The stabilizing groups on the particle surface have a significant effect on the interfacial assembly and, therefore, also on the formation and properties of Pickering emulsions. The wetting behavior of the particle is altered by the presence of the stabilizing groups, which affects the equilibrium position of the particles at the interface. The stabilizing groups can also lead to an activation barrier before interfacial adsorption, analogous to the steric repulsion between two particles. These effects are numerically solved with the SCF theory. It is commonly known that flocculating conditions enhance the interfacial adsorption and yield stable Pickering emulsions, which is confirmed in this work. Additionally, it is concluded that those conditions are not an absolute requirement. There is a window of stabilizer concentrations GpIB, 2.2–3.3 mg/m2 pIB, that shows both partial wetting and colloidal stability. The activation barrier for interfacial assembly is 140–550 kBT and is an order of magnitude higher than the colloidal stability. The difference can be attributed to the unfavorable interaction of pIB with water and a difference in geometry (plate–sphere vs sphere–sphere). This study demonstrates the interplay and provides a quantitative comparison between the wetting behavior and the colloidal stability, and it gives a better understanding of the colloidal assembly at soft interfaces and formation of Pickering emulsions in general
In situ quantification of membrane foulant accumulation by reflectometry
Schroën, C.G.P.H. ; Roosjen, A. ; Tang, K. ; Norde, W. ; Boom, R.M. - \ 2010
Journal of Membrane Science 362 (2010)1-2. - ISSN 0376-7388 - p. 453 - 459.
cross-flow microfiltration - ultrafiltration membranes - protein adsorption - skim milk - performance - filtration - polymer - bioreactors - inhibition - modules
In this paper, we present laser light reflectometry [1] (not to be mistaken with ultrasound reflectometry [2] that uses ultrasound waves) as a tool for quantitative investigation of (the initial stages of) fouling on membrane-like surfaces. Reflectometry allows in situ investigation of adsorption and accumulation of components near a surface However, before the method can be applied, a membrane-resembling layer should be attached to a reflecting surface and this layer should have minimal roughness. This was investigated for the widely used membrane materials polyethersulfone (PES), polyvinylpyrrolidone (PVP), and a blend of both The adsorption of typical foulants, such as BSA, dextrin, and tannin was followed in time Both unmodified and modified surfaces, obtained through pre-adsorption of Tween components were investigated The interactions responsible for adsorption of foulants could be charted, and surface modifications could be proposed that specifically target these interactions (C) 2010 Elsevier B.V All rights reserved
Interfacial tension between a complex coacervate phase and its coexisting aqueous phase
Spruijt, E. ; Sprakel, J.H.B. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2010
Soft Matter 6 (2010). - ISSN 1744-683X - p. 172 - 178.
atomic-force microscope - microencapsulation - thermodynamics - micelles - polymer - system
Complex coacervation is the associative phase separation in a solution of positively and negatively charged macroions. Despite the widespread use of coacervation in e.g. micellar assemblies (complex coacervate core micelles), drug carriers and thin films, there is virtually no experimental data on the interfacial tension between such coacervate phases (polyelectrolyte complexes) and their coexisting aqueous phases or on the influence of salt thereon. In this paper we use colloidal probe AFM measurements of capillary adhesion forces to obtain the interfacial tension between a complex coacervate phase of two polyelectrolytes with high charge density and its coexisting aqueous phase. We find that the interfacial tension is of order 100 µN/m, decreases with increasing salt concentration and vanishes at the critical point. Interestingly, we find that the critical scaling exponent for the interfacial tension found in segregative demixing also applies here
Inhibition of LPS-induced proinflammatory responses of J774.2 macrophages by immobilized enzymatically tailored pectins
Gallet, M. ; Vayssade, M. ; Morra, M. ; Verhoef, R.P. ; Perrone, S. ; Cascardo, G. ; Vigneron, P. ; Schols, H.A. ; Nagel, M.D. - \ 2009
Acta Biomaterialia 5 (2009). - ISSN 1742-7061 - p. 2618 - 2622.
hairy ramified regions - glinus-oppositifolius - rhamnogalacturonan-i - cell - polysaccharides - adhesion - activation - polymer - plant - vitro
The surface of an implant device can be modified by immobilizing biological molecules on it to improve its integration into the host tissue. We have previously demonstrated that enzymatically tailored plant pectins are promising nanocoatings for biomaterials. This study investigates whether a coating of modified hairy region (rhamnogalacturonan-I) from apple pectin (MHR-a) which has anti-adhesive properties can inhibit the generation of inflammatory mediators by lipopolysaccharide (LPS)-activated macrophages. For that purpose, J774.2 murine macrophages were cultured for 24 h on MHR-a-coated Petri dishes and tissue culture polystyrene controls, with and without LPS. Cell morphology, cell growth, nitrite and TNF-a secretion were studied. The results indicate that MHR-a coating inhibits the LPS-induced activation of macrophages.
Hydrolytic stability of water-soluble spruce O-acetyl galactoglucomannans
Xu, C. ; Pranovich, A. ; Hemmimg, J. ; Holmbom, B. ; Albrecht, S.A. ; Schols, H.A. ; Willfor, S. - \ 2009
Holzforschung 63 (2009)1. - ISSN 0018-3830 - p. 61 - 68.
molecular-weight changes - norway spruce - thermomechanical pulp - acid-hydrolysis - picea-abies - degradation - kinetics - chitosan - polymer
Water-soluble native O-acetyl galactoglucomannan (GGM) from spruce is a polysaccharide that can be produced in an industrial scale. To develop GGM applications, information is needed on its stability, particularly under acidic conditions. Therefore, acid hydrolysis of spruce GGM was investigated at various pH levels and temperatures. The results allow an estimation of the stability of GGM under food processing conditions and in biological systems. Determination of the average molar mass demonstrated that spruce GGM was stable at pH 1 and 37°C, as well as at pH 3 and 70°C. GGM was hydrolysed at pH 1 and 90°C. GGM oligomers and monomers were detected after degradation. Some of the oligomers contained O-acetyl groups. Monosaccharides were the predominant products in the hydrolysates after treatment at pH 1 and 90°C for 48 h. Pentoses, present in GGM samples as impurities, were released more easily than GGM hexoses. Glucose was more difficult to release than mannose. Traces of 6-deoxy-mannose and levoglucosan were found in the hydrolysates, indicating further degradation of hydrolysed monosaccharides.
Self-consistent field modeling of adsorption from polymer/surfactant mixtures
Postmus, B.R. ; Leermakers, F.A.M. ; Cohen Stuart, M.A. - \ 2008
Langmuir 24 (2008)13. - ISSN 0743-7463 - p. 6712 - 6720.
silica-water interface - interacting chain molecules - nonionic surfactants - competitive adsorption - statistical-theory - ellipsometry - kinetics - polymer - layer - association
We report on the development of a self-consistent field model that describes the competitive adsorption of nonionic alkyl-(ethylene oxide) surfactants and nonionic polymer poly(ethylene oxide) (PEO) from aqueous solutions onto silica. The model explicitly describes the response to the pH and the ionic strength. On an inorganic oxide surface such as silica, the dissociation of the surface depends on the pH. However, salt ions can screen charges on the surface, and hence, the number of dissociated groups also depends on the ionic strength. Furthermore, the solvent quality for the EO groups is a function of the ionic strength. Using our model, we can compute bulk parameters such as the average size of the polymer coil and the surfactant CMC. We can make predictions on the adsorption behavior of either polymers or surfactants, and we have made adsorption isotherms, i.e., calculated the relationship between the surface excess and its corresponding bulk concentration. When we add both polymer and surfactant to our mixture, we can find a surfactant concentration (or, more precisely, a surfactant chemical potential) below which only the polymer will adsorb and above which only the surfactant will adsorb. The corresponding surfactant concentration is called the CSAC. In a first-order approximation, the surfactant chemical potential has the CMC as its upper bound. We can find conditions for which CMC <CSAC . This implies that the chemical potential that the surfactant needs to adsorb is higher than its maximum chemical potential, and hence, the surfactant will not adsorb. One of the main goals of our model is to understand the experimental data from one of our previous articles. We managed to explain most, but unfortunately not all, of the experimental trends. At the end of the article we discuss the possibilities for improving the model.
Depletion-induced instability in protein-DNA mixtures: Influence of protein charge and size
Vries, R.J. de - \ 2006
Journal of Chemical Physics 125 (2006). - ISSN 0021-9606 - p. 014905 - 1-014905-8.
coil-globule transition - poly(ethylene glycol) - psi-condensation - polymer - particles - molecule - collapse - driven - chain
While there is abundant experimental and theoretical work on polymer-induced DNA condensation, it is still unclear whether globular proteins can condense linear DNA or not. We develop a simple analytical approximation for the depletion attraction between rodlike segments of semiflexible polyelectrolytes such as DNA, induced by nonbinding globular proteins. Monte Carlo simulations show that the approximation works well up to protein volume fractions of at least 20%. From the expression for the depletion attraction we estimate instability thresholds by computing the effective virial coefficient of DNA segments in protein solutions. While globular proteins are found to be much poorer depletion agents than flexible polymers, it should be possible to condense linear DNA with small highly charged globular proteins, at relatively low ionic strengths
Monte Carlo simulations of flexible polyanions complexing with whey proteins at their isoelectric point
Vries, R.J. de - \ 2004
Journal of Chemical Physics 120 (2004)7. - ISSN 0021-9606 - p. 3475 - 3481.
polyelectrolyte-macroion complexation - continuous capillary-electrophoresis - heterogeneously charged surfaces - bovine serum-albumin - light-scattering - chain flexibility - opposite charge - adsorption - polymer - binding
The complexation of globular proteins with flexible polyelectrolytes with homogeneous, oppositely charged spheres was discussed using Monte Carlo simulations. The proteins were considered at their respective isoelectric points. A coarse-grained model of the protein shape was also considered in order to take into account the protein excluded volume. A simple statistical analysis of the surface charge density was found sufficient for identifying potential polyelectrolyte binding regions. The protein-only approach identified only possible regions of polyelectrolyte binding, and did not account for any of the polyelectrolyte properties tha influenced binding.
A small-angle neutron scattering study of cholic acid-based organogel systems
Willemen, H.M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. ; Bouwman, W.G. ; Deme, B. ; Terech, P. - \ 2004
Langmuir 20 (2004)6. - ISSN 0743-7463 - p. 2075 - 2080.
rheological properties - organic liquids - gelators - gels - polymer - fibers - water
Small-angle neutron scattering measurements were performed on some cholic acid-based gel systems in order to gain detailed information about the network structure. The presence of thin fibers with a radius of about 10-20 Å was found for various gelators. Two types of interaction between different sorts of fibers were demonstrated, depending on the molecular structure of the gelator. The first type involves the presence of microcrystalline knots with a dimension of about 100-200 Å between the fibers. Upon heating, this network gradually disintegrates. The second type involves loose entanglements between flattened fibers. The occurrence of these types of interaction is related to the length of the alkyl tail attached to cholic acid.
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