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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The supramolecular organization of a peptide-based nanocarrier at high molecular detail
Rad-Malekshahi, M. ; Visscher, K.M. ; Rodrigues, J.P.G.L.M. ; Vries, R.J. de; Hennink, W.E. ; Baldus, M. ; Bonvin, A.M.J.J. ; Mastrobattista, E. - \ 2015
Journal of the American Chemical Society 137 (2015)24. - ISSN 0002-7863 - p. 7775 - 7784.
solid-state nmr - protein secondary structure - chemical-shift index - force-field - polypeptide vesicles - drug-delivery - beta-sheet - dynamics - nanovesicles - spectroscopy
Nanovesicles self-assembled from amphiphilic peptides are promising candidates for applications in drug delivery. However, complete high-resolution data on the local and supramolecular organization of such materials has been elusive thus far, which is a substantial obstacle to their rational design. In the absence of precise information, nanovesicles built of amphiphilic “lipid-like” peptides are generally assumed to resemble liposomes that are organized from bilayers of peptides with a tail-to-tail ordering. Using the nanocarrier formed by the amphiphilic self-assembling peptide 2 (SA2 peptide) as an example, we derive the local and global organization of a multimega-Dalton peptide-based nanocarrier at high molecular detail and at close-to physiological conditions. By integrating a multitude of experimental techniques (solid-state NMR, AFM, SLS, DLS, FT-IR, CD) with large- and multiscale MD simulations, we show that SA2 nanocarriers are built of interdigitated antiparallel ß-sheets, which bear little resemblance to phospholipid liposomes. Our atomic level study allows analyzing the vesicle surface structure and dynamics as well as the intermolecular forces between peptides, providing a number of potential leads to improve and tune the biophysical properties of the nanocarrier. The herein presented approach may be of general utility to investigate peptide-based nanomaterials at high-resolution and at physiological conditions.
Looped structure of flowerlike micelles revealed by (1)H NMR relaxometry and light scattering
Graaf, A.J. de; Boere, K.W.M. ; Kemmink, J. ; Fokkink, R.G. ; Nostrum, C.F. van; Rijkers, D.T.S. ; Gucht, J. van der; Wienk, H. ; Baldus, M. ; Mastrobattista, E. ; Vermonden, T. ; Hennink, W.E. - \ 2011
Langmuir 27 (2011)16. - ISSN 0743-7463 - p. 9843 - 9848.
block-copolymer micelles - triblock copolymer - aqueous-solution - poly(ethylene glycol) - drug-delivery - aggregation behavior - nmr relaxation - oxide) - micellization - nanoparticles
We present experimental proof that so-called “flowerlike micelles” exist and that they have some distinctly different properties compared to their “starlike” counterparts. Amphiphilic AB diblock and BAB triblock copolymers consisting of poly(ethylene glycol) (PEG) as hydrophilic A block and thermosensitive poly(N-isopropylacrylamide) (pNIPAm) B block(s) were synthesized via atom transfer radical polymerization (ATRP). In aqueous solutions, both block copolymer types form micelles above the cloud point of pNIPAm. Static and dynamic light scattering measurements in combination with NMR relaxation experiments proved the existence of flowerlike micelles based on pNIPAm16kDa-PEG4kDa-pNIPAm16kDa which had a smaller radius and lower mass and aggregation number than starlike micelles based on mPEG2kDa-pNIPAm16kDa. Furthermore, the PEG surface density was much lower for the flowerlike micelles, which we attribute to the looped configuration of the hydrophilic PEG block. 1H NMR relaxation measurements showed biphasic T2 relaxation for PEG, indicating rigid PEG segments close to the micelle core and more flexible distal segments. Even the flexible distal segments were shown to have a lower mobility in the flowerlike micelles compared to the starlike micelles, indicating strain due to loop formation. Taken together, it is demonstrated that self-assemblies of BAB triblock copolymers have their hydrophilic block in a looped conformation and thus indeed adopt a flowerlike conformation.
Macromolecular diffusion in self-assembling biodegradable thermosensitive hydrogels
Vermonden, T. ; Jena, S.S. ; Barriet, D. ; Censi, R. ; Gucht, J. van der; Hennink, W.E. ; Siegel, R.A. - \ 2010
Macromolecules 43 (2010)2. - ISSN 0024-9297 - p. 782 - 789.
concentrated polyelectrolyte solutions - biomedical applications - fluorescence recovery - reversible hydrogels - triblock copolymers - gelling hydrogels - probe diffusion - polymers - gels - proteins
Hydrogel formation triggered by a change in temperature is an attractive mechanism for in situ gelling biomaterials for pharmaceutical applications such as the delivery of therapeutic proteins. In this study, hydrogels were prepared from ABA triblock polymers having thermosensitive poly(N-(2-hydroxypropyl)methacrylamide lactate) flanking A-blocks and hydrophilic poly(ethylene glycol) B-blocks. Polymers with fixed length A-blocks (22 kDa) but differing PEG-midblock lengths (2, 4, and 10 kDa) were synthesized and dissolved in water with dilute fluorescein isothiocyanate (FITC)-labeled dextrans (70 and 500 kDa). Hydrogels encapsulating the dextrans were formed by raising the temperature. Fluorescence recovery after photobleaching (FRAP) studies showed that diffusion coefficients and mobile fractions of the dextran dyes decreased upon elevating temperatures above 25 °C. Confocal laser scanning microscopy and cryo-SEM demonstrated that hydrogel structure depended on PEG block length. Phase separation into polymer-rich and water-rich domains occurred to a larger extent for polymers with small PEG blocks compared to polymers with a larger PEG block. By changing the PEG block length and thereby the hydrogel structure, the mobility of FITC-dextran could be tailored. At physiological pH the hydrogels degraded over time by ester hydrolysis, resulting in increased mobility of the encapsulated dye. Since diffusion can be controlled according to polymer design and concentration, plus temperature, these biocompatible hydrogels are attractive as potential in situ gelling biodegradable materials for macromolecular drug delivery
Sensitive spectroscopic detection of large and denatured protein aggregates in solution by use of the fluorescent dye Nile re
Sutter, M. ; Oliveira, S. ; Sanders, N.N. ; Lucas, B. ; Hoek, A. van; Hink, M.A. ; Visser, A.J.W.G. ; Smedt, S.C. de; Hennink, W.E. ; Jiskoot, W. - \ 2007
Journal of Fluorescence 17 (2007)2. - ISSN 1053-0509 - p. 181 - 192.
galactosidase escherichia-coli - beta-galactosidase - ftir spectroscopy - congo red - immunogenicity - surfaces - probe
The fluorescent dye Nile red was used as a probe for the sensitive detection of large, denatured aggregates of the model protein ß-galactosidase (E. coli) in solution. Aggregates were formed by irreversible heat denaturation of ß-galactosidase below and above the protein¿s unfolding temperature of 57.4°C, and the presence of aggregates in heated solutions was confirmed by static light scattering. Interaction of Nile red with ß-galactosidase aggregates led to a shift of the emission maximum (¿ max) from 660 to 611 nm, and to an increase of fluorescence intensity. Time-resolved fluorescence and fluorescence correlation spectroscopy (FCS) measurements showed that Nile red detected large aggregates with hydrodynamic radii around 130 nm. By steady-state fluorescence measurements, it was possible to detect 1 nM of denatured and aggregated ß-galactosidase in solution. The comparison with size exclusion chromatography (SEC) showed that native ß-galactosidase and small aggregates thereof had no substantial effect on the fluorescence of Nile red. Large aggregates were not detected by SEC, because they were excluded from the column. The results with ß-galactosidase demonstrate the potential of Nile red for developing complementary analytical methods that overcome the size limitations of SEC, and can detect the formation of large protein aggregates at early stages.
Rheological studies of thermosensitive triblock copolymer hydrogels
Vermonden, T. ; Besseling, N.A.M. ; Steenbergen, M.J. van; Hennink, W.E. - \ 2006
Langmuir 22 (2006)24. - ISSN 0743-7463 - p. 10180 - 10184.
aqueous-solutions - gel point - poly(ethylene glycol) - polymeric micelles - viscoelasticity - dependence - systems
Hydrogel formation by physical cross-linking is a developing area of research toward materials suitable for pharmaceutical and biomedical applications. Polymers exhibiting lower critical solution temperature (LCST) behavior in aqueous solution are used in this study to prepare hydrogels. Four triblock copolymers (ABA) with thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) A-blocks and a hydrophilic poly(ethylene glycol) B-block have been synthesized. The molecular weight of the hydrophilic PEG block was fixed at 10 kDa, whereas the molecular weight of the pHPMAm - lactate block was varied between 10 and 20 kDa. The rheological characteristics of these polymer hydrogels were studied as a function of temperature, concentration, and the length of the thermosensitive blocks. Gelation occurred rapidly upon increasing the temperature to 37°C, which makes this system suitable as an injectable formulation. The gels became stronger with increasing temperature and concentration, and moreover they behaved as critical gels, which means that G¿ and G¿ follow power laws over the entire frequency range. Surprisingly, with increasing length of the thermosensitive blocks, weaker hydrogels were formed. This trend can be explained by the cross-link density of the physical network, which increases with decreasing length of the thermosensitive blocks
Linear rheology of water-soluble reversible neodymium (III) coordination polymers
Vermonden, T. ; Steenbergen, M.J. van; Besseling, N.A.M. ; Marcelis, A.T.M. ; Hennink, W.E. ; Sudhölter, E.J.R. ; Cohen Stuart, M.A. - \ 2004
Journal of the American Chemical Society 126 (2004)48. - ISSN 0002-7863 - p. 15802 - 15808.
wormlike micelles - supramolecular polymers - viscoelastic behavior - semidilute solutions - living polymers - dynamics - networks - reptation - copper(i) - chains
The rheology of reversible coordination polymer networks in aqueous solution is studied. The polymers are formed by neodymium(III) ions and bifunctional ligands, consisting of two pyridine-2,6-dicarboxylate groups connected at the 4-positions by an ethylene oxide spacer. Neodymium(III) ions can bind three of these terdendate ligand groups. At high concentrations, the polymer networks yield viscoelastic materials, which can be described with the Maxwell model. The scaling of the elastic modulus, relaxation time, and zero-shear viscosity with concentration are in good agreement with the predictions of Cates' model that describes the dynamics of linear equilibrium polymers. This indicates that the networks have only few cross-links and can be described as linear equilibrium polymers. The gels are also thermo-reversible. At high temperatures, fast relaxation was found, resulting in liquidlike behavior. Upon cooling, the viscoelastic properties returned immediately. From the temperature dependence of the relaxation time, an activation energy of 49 kJ/mol was determined for the breaking and reptation of the polymers.
Permeation of volatile compounds through starch films
Yilmaz, G. ; Jongboom, R.O.J. ; Feil, H. ; Dijk, C. van; Hennink, W.E. - \ 2004
Biomacromolecules 5 (2004)2.. - ISSN 1525-7797 - p. 650 - 656.
controlled-release - glassy-polymers - aroma compounds - free-volume - oxygen permeability - hydrogel membranes - solvent-diffusion - sunflower oil - encapsulation - crystallinity
The aim of this study was to gain insight into the factors that affect the permeation of volatiles through starch films. These films were obtained by casting gelatinized starch/water/glycerol mixtures. The films were dried and conditioned under different conditions (temperature and relative humidity) resulting in films that vary in the degree of starch crystallinity and glycerol and water content. The permeation of two model volatiles (carvone and diacetyl) at 20degreesC and at 30, 60, or 90% relative humidity (RH) was analyzed gravimetrically. Further, the solubility of the two model compounds (under conditions where the permeation experiments were carried out) was determined. From the obtained permeation and solubility data, the diffusion coefficients of these compounds in the different starch films were calculated. The crystallinity in the starch films increased with increasing water content of the films during preparation. The water content of the resulting films in turn increased with increasing glycerol and when the films were exposed to a higher RH during drying or conditioning. For films with the same composition, the flux for diacetyl was greater than for carvone. The solubilities of diacetyl and carvone were slightly dependent on the properties of the films. It was found that with increasing starch crystallinity the diffusion coefficient for both compounds decreases, which is probably due to the impermeability of starch crystallites. Interestingly, in films with about the same extent of crystallinity, the diffusion can be described with the free volume model, with water and glycerol determining the amount of free volume.
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