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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    Improving the limits of detection in sensor systems
    Bent, J.F. van der - \ 2017
    Wageningen University. Promotor(en): C.J.M. van Rijn. - Wageningen : Wageningen University - ISBN 9789463430555 - 127
    sensors - data processing - nanotechnology - potentiometers - detection - sensors - gegevensverwerking - nanotechnologie - potentiometers - detectie

    Nowadays, sensors are designed to consume less power with decreased size, making them suitable for application in low-power wireless sensor networks (WSN) systems. The challenge is not to compromise on the sensor’s sensitivity and selectivity towards the target. This thesis studies various options to improve the limits of detection. Usually, sensors are limited in detection range and resolution; they are also restricted by cross sensitivity towards other target agents and other parameters. This cross sensitivity, towards humidity and temperature, for instance, reduces the sensor’s detection limit and, therefore, its usability. This work discusses three examples where the limit of detection has been investigated, localised and improved with nanotech-based sensors.

    The first example is a nanowire-based hydrogen sensor. The second example was based on a potentiometric-sensor principle, capable of sensing CO2. The third example is an Inter-Digitated Electrode (IDE) sensor, capable of selective sensing through the coating of an active layer.

    In vitro assays for hazard identification of nanoparticles
    Kloet, Samantha K. - \ 2016
    Wageningen University. Promotor(en): Ivonne Rietjens; Jochem Louisse; Nico van den Brink. - Wageningen : Wageningen University - ISBN 9789462579415 - 213
    nanotechnology - particles - in vitro - models - hazards - toxicity - toxicokinetics - nanotechnologie - deeltjes - in vitro - modellen - gevaren - toxiciteit - toxicokinetiek

    The production of nanoparticles (NPs) has increased in the last decades and the number of products in which NPs are being incorporated is still growing. The rapid increase of nanotechnology has several benefits for society, yet there is an increasing concern that exposure to NPs may result in significant adverse health effects. Since NPs are incorporated in a variety of consumer products, it is likely that the general population will be exposed to NPs. It would be desirable that the safety and risk assessment of NPs could be largely based on studies using in vitro models instead of in vivo models as this would reduce the use of test animals, costs and time required to test the large numbers of NPs. The aim of the present thesis was to investigate the potential of in vitro testing strategies to detect hazards of NPs, focusing on toxicokinetic as well as toxicodynamic endpoints. Toxicokinetic studies focused on translocation of NPs in in vitro models of the placental barrier, while toxicodynamic studies were directed at two endpoints that represent potential hazards of NPs that have not yet been well characterized including: developmental toxicity and immunotoxicity.

    In the present thesis different types of NPs were used. Polystyrene nanoparticles (PS-NPs) were selected because of their commercial availability, with high quality and a wide variety of available physicochemical properties like surface charge, and fluorescent labeling enabling easy detection in toxicokinetic (translocation) studies. Several metal (oxide) NPs were selected as well, of which some are possible constituents of food additives like TiO2, Fe2O3, SiO2 and Ag. Other metal oxide NPs that were selected were Mn­2O3, CuO, Cr2O3, CoO and NiO to which we may be exposed via products like paints, catalysts, construction materials, coatings and batteries.

    Placental translocation of NPs was studied as an important toxicokinetic aspect, since part of the toxicodynamic studies of the present thesis were directed at developmental toxicity testing of NPs. In order to obtain insight in toxicity and translocation of NPs across the placental barrier, cytotoxicity and translocation was studied for one positively and two negatively charged PS-NPs of 50 nm in an in vitro model of the placenta. In this study it appeared that in spite of similar size, surface charge and type of proteins in the protein corona, the differently charged NPs displayed a remarkable difference in cytotoxicity, with only the PS-NPs with an original positive charge inducing cytotoxicity. Translocation of PS-NPs appeared not to be related to PS-NP charge alone. A remarkable difference in translocation was found between the two 50 nm negatively charged PS-NPs that were obtained from different manufacturers. Since none of the characterized parameters, including size, surface charge and protein corona revealed remarkable differences between the two negatively charged NPs, the difference may originate from the chemical groups on the surface of the NPs generating the negative charge. The general conclusion from this study was that the in vitro BeWo b30 model can be used as a fast method to get an initial qualitative impression about the capacity of NPs to translocate across the placental barrier and to set priorities for further in vivo studies on translocation of NPs to the fetus.

    The same PS-NPs as tested for placental translocation were investigated whether they are able to cause in vitro developmental toxicity in the ES-D3 cell differentiation assay of the embryonic stem cell test (EST) focusing also on the effect that charge may have. The study showed that the two negatively charged PS-NPs did not show any effect in the ES-D3 cell differentiation assay up to the highest concentration tested while the positively charged PS-NP showed a concentration-dependent inhibition of ES-D3 cell differentiation. However, effect concentrations in the ES-D3 cell differentiation assay were close to cytotoxic concentrations, which indicated that the inhibition of the ES-D3 cell differentiation may be due to cytotoxic effects of the positively charged PS-NPs. This indicated that the inhibition of the ES-D3 cell differentiation by the positively charged PS-NPs may be caused by non-specific effects. Although the experiments on placental translocation of the present thesis showed that positively charged PS-NPs are more toxic than negatively charged PS-NPs, it appeared that this may not be generalizable to other NPs. This follows from the fact that in SiO2, Ag and TiO2 NPs that were reported in other studies to inhibit ES-D3 cell differentiation were negatively charged, while the negatively charged PS-NPs of the present study did not affect ES-D3 cell differentiation. Although the limited data available indicate that charge, size and coating of NPs may be important characteristics that determine the developmental toxicity potential of NPs, more (systematic) studies are needed to assess how physicochemical characteristics of NPs relate to their developmental toxicity. This information may help to prioritize NPs for in vitro and in vivo developmental toxicity testing.

    In addition, toxic effects of a series of metal (oxide) NPs were tested in macrophage RAW264.7 cells in order to obtain insight in effect of these NPs on cells of the innate immune response. In these macrophage RAW264.7 cells the effects of the metal (oxide) NPs were characterized on cell viability, TNF-α production and mitochondria-related parameters like production of reactive oxygen species (ROS), mitochondrial permeability transition pore (MPTP) opening, and intracellular ATP levels. Altogether, results obtained showed no or limited effects of the NP formulations of metal (oxide) food additives on cell viability, ROS production, MPTP opening, ATP levels and TNF-α production in RAW264.7 macrophages. Effects were only observed at high concentrations that may not be physiologically relevant, indicating that related adverse effects upon exposure to the respective NPs in vivo may be limited.

    Taken together, the present thesis provided further evidence of the influence of physicochemical properties of NPs in driving toxicity in in vitro models. However, the determination of the fate and toxicity of NPs using in vitro or in vivo models is a challenge that needs further evaluation. A combination of several factors likely play a role in determining the outcome of exposure including factors like NP core material and presence and type of coating agents resulting in various physicochemical properties (size, charge, etc.). This appears to hamper conclusive evaluation of the role of physicochemical characteristics of NPs in their potential hazards and risks so far. The results obtained do show however that in vitro assays can detect differences in potential hazards posed by NPs. Therefore it is concluded that the results of the work presented in this thesis will contribute to the further development and use of non-animal based testing strategies for safety testing of NPs providing insight into selected potential hazards of the tested NPs.

    Controlling the self-assembly of protein polymers via heterodimer-forming modules
    Domeradzka, Natalia Eliza - \ 2016
    Wageningen University. Promotor(en): Frans Leermakers, co-promotor(en): Renko de Vries; Frits de Wolf. - Wageningen : Wageningen University - ISBN 9789462578661 - 166
    polymers - nanotechnology - pichia pastoris - modules - mass spectrometry - microscopy - sds-page - rheology - fluorescence emission spectroscopy - protein purification - fermentation - chromatography - polymeren - nanotechnologie - pichia pastoris - modules - massaspectrometrie - microscopie - sds-page - reologie - fluorescentie-emissiespectroscopie - eiwitzuivering - fermentatie - chromatografie

    Supramolecular assemblies formed by protein polymers are attractive candidates for future biomaterials. Ideally, one would like to be able to define the nanostructure, in which the protein polymers should self-assemble, and then design protein polymer sequences that assemble exactly into such nanostructures. Despite progress towards ‘programmability’ of protein polymer self-assembly, we do not yet have such control. This holds especially for hierarchical structures such as self-assembled fibril bundles, where one would like to have independent control over the structures at the different length-scales. In this thesis we explore the use of heterodimerization as a strategy to control self-assembly of protein polymers at multiple length-scales. We tested a selected set of heterodimer-forming peptide modules. The heterodimer-forming modules are genetically incorporated at the C-terminus of protein polymers with a previously characterized self-assembly behavior. Several newly constructed protein polymers were biosynthesized in the yeast Pichia pastoris and, for these new protein polymers we investigated whether the inclusion of the heterodimer-forming blocks improved the control over the assembly of nanostructures.

    The incorporation of heterodimer-forming modules into protein polymers is not the only tool that can be used for improving programmability of assembly. In Chapter 2 we present an overview of several tools that can be use, and we highlighted their advantages and disadvantages.

    In Chapter 3 we test de novo designed heterodimerizing coiled coils DA = LEIRAAFLRQRNTALRTEVAELEQEVQRLENEVSQYETRYGPLGGGK and DB = LEIEAAFLERENTALETRVAELRQRVQRLRNRVSQYRTRYGPLGGGK. These peptides were fused to hydrophilic random coil protein polymer (CP4) and homotrimer forming protein polymer (T9-CP4). We present data on the production, characterization and functionality for four new protein polymers: CP4-DA, CP4-DB, T9-CP4-DA and T9-CP4-DB. When the new protein polymers were produced using the fermentation process established previously for other protein polymers such as CP4 (i.e. standard fermentation), we found the new protein polymers to be partly degraded. The use of a protease deficient strain, as well as changes in aeration or pH were found ineffective in preventing degradation, but nearly intact products were obtained from a fermentation in which the induction was done at 20 ˚C and in which the medium was supplemented with casamino acids. With respect to the physical properties of the new protein polymers, size exclusion chromatography (SEC) showed that an equimolar mixture of CP4-DA and CP4-DB contained mostly dimers, whereas unmixed CP4-DA and CP4-DB contained only monomers. However, we also found that CP4-DB forms homooligomers at concentrations ≥100 µM. A mixture of T9-CP4-DA and T9-CP4-DB forms a hydrogel, most probably due to both homotypic and heterotypic DA/DB associations. We conclude that when used at low concentration, this pair of coiled coils seems to be suitable to control self-assembly of protein polymers produced in Pichia Pastoris.

    Next, in Chapter 4 we test another pair of de novo designed coiled coils. These are much shorter and have lower reported values of the association constant as compared to the DA/DB coiled coils. The systems consist of a peptide DE = (EIAALEK)3 and a peptide DK = (KIAALKE)3. The two peptides were C-terminally fused to protein polymers CP4 and T9-CP4. The standard fermentations resulted in intact CP4-DE and T9-CP4-DE, but protein polymers CP4-DK and T9-CP4-DK were found to be partly degraded. The degradation of variants with DK module could not be readily resolved by fermentation at higher pH or using proteases deficient strain. For CP4-DK, ion exchange chromatography showed that about 40% of protein polymer (by mass) was intact. We find that for this pair of coiled-coils, homotypic interactions are so strong that they can drive gel formation in the case of T9-CP4-DE, and a strong increase in viscosity for T9-CP4-DK. Mixtures of the complimentary triblocks also form hydrogels, but it is not yet clear to what extent this is due to homotypic DE/ DE and DK/ DK associations, and to what extent it is due to DE/ DK heterodimer formation.

    A very different type of heterodimer-forming block is the so-called WW domain that is found in many natural proteins, and which forms heterodimers with proline-rich peptides PPxY. In Chapter 5 we test the interaction between a naturally occurring WW domain (DWW) and its proline-rich ligand (DPPxY). Both were C-terminally fused to the hydrophilic random coil protein polymer CP4. The new protein polymers CP4-DWW and CP4-DPPxY were produced intact during standard fermentations, but CP4-DPPxY was shown to be glycosylated. Using genetic engineering, we mutated the CP4-DPPxY protein polymer sequence by the substitution Ser12→Ala. A standard fermentation resulted in an intact and non-glycosylated protein polymer CP4-DPPxY*. Interaction studies (ITC and steady state tryptophan fluorescence quenching), showed that both CP4-DPPxY and CP4-DPPxY* bind to CP4-DWW with an equilibrium dissociation constant on the order of mM.

    Finally, to demonstrate that heterodimer-forming blocks can be used to independently control protein polymer self-assembly at multiple length-scales, we selected the heterodimer-forming modules DA and DB to control the lateral interactions of fibrils self-assembled from the previously designed triblock protein polymer C2-SH48-C2. In Chapter 6 we construct the protein polymers C2-SH48-C2-DA and C2-SH48-C2-DB. The C2-SH48-C2 protein polymers assemble into long and stiff fibrils at neutral pH. The aim of the C-terminal attachment of the DA/DB blocks was to be able to control subsequent physical cross-linking and bundling of the fibrils. Both protein polymers C2-SH48-C2-DA and C2-SH48-C2-DB were produced intact and with high yield during fermentation at optimal conditions as discussed in Chapter 3. Using Atomic Force Microscopy (AFM) we show that at neutral pH, fibrils consisting of 100% C2-SH48-C2-DA or C2-SH48-C2-DB protein polymers bundle up and cross-link via homotypic DA/DA and DB/DB associations. Control over the degree of cross-linking and bundling can be obtained by using mixed fibrils consisting of C2-SH48-C2 with controlled amounts of the newly developed protein polymers C2-SH48-C2-DA and C2-SH48-C2-DB. While the effect of the heterodimers on the structure of the fibril network as judged from AFM is very strong, oscillation rheology shows that the inclusion of the heterodimer forming blocks merely leads to a moderate increase in gel stiffness.

    In order to place the research discussed in this thesis into the broader perspective, in Chapter 7 we provide a General Discussion. We discuss several general strategies that can be used to control protein polymer self-assembly and discuss why and when there is a need for using heterodimer forming blocks. After providing an overview over results obtained in this thesis, we highlight the most urgent questions that need to be answered next. This is followed by a discussion on the benefits that heterodimer-driven self-assembly may bring to possible future applications of protein polymers as biomaterials. We also discuss the possible risks for human health end environment that might arise from the use of protein polymers technology. Finally we present some speculations about the future of the field of self-assembling protein polymers.

    An in vitro – in vivo integrated approach for hazard and risk assessment of silver nanoparticles for soil organisms
    Makama, S.I. - \ 2016
    Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Nico van den Brink. - Wageningen : Wageningen University - ISBN 9789462578432 - 190
    particles - nanotechnology - toxicity - earthworms - gene expression - soil - coatings - deeltjes - nanotechnologie - toxiciteit - aardwormen - genexpressie - bodem - afdeklagen

    Owing to their small sizes, nanoparticles (NPs) exhibit completely different and novel characteristics compared to their bulk counterparts of the same chemical composition. These novel properties include increased reactivity due to large specific surface area, fluorescence and colour changes, increased biological barrier crossings and increased material strengthening combined with light-weight. Virtually all fields of human endeavours are exploiting nanotechnology to combat different challenges. This has led to an increase in the production and potential release of NPs into the environment. The novel properties of these NPs however, mean an enhanced potential for interactions with biological systems that are different from the interactions of known conventional chemicals, thus raising environmental and public health/safety concerns. Available literature has reported NP uptake in different organisms along with associated hazards. Therefore, to safeguard human and environmental health and safety, regulatory measures are necessary. Such measures must be based on sound scientific evidence and be risk-based rather than hazard-based. As such, the need to understand the fate of NPs after environmental release and their potential to pose hazards and risks to the environment is critical for a proper risk assessment and further development of policy strategies on the future regulation of the use of NPs.

    Some studies have demonstrated different and sometimes conflicting effects of NP properties on their uptake in different organisms. Given that exposure determines whether hazards will turn into risks, there is a critical need for further systematic evaluation of the physico-chemical properties of engineered or manufactured NPs that influence uptake in terrestrial organisms, and also of how soil properties may affect these processes. The objective of this project was to determine the influence of size and surface coating (charge), two important physico-chemical properties of NPs, on their bioavailability, uptake and toxicity. The red earthworm Lumbricus rubellus, common in most parts of Europe, was used as a model soil organism. Silver nanoparticles (AgNPs) have been identified as one of the most commonly used NPs in many products, and their production is expected to continue to increase. Therefore, we selected AgNPs as our model NPs. For our investigations, we applied an integrated in vitro - in vivo approach, utilising high throughput in vitro methods as well as well-established in vivo toxicity end-points in the earthworm. A systematic experimental approach was developed for which AgNPs were synthesized in three sizes: 20, 35 and 50 nm. Surface-coating with bovine serum albumin (AgNP_BSA), chitosan (AgNP_Chit), or polyvinylpyrrolidone (AgNP_PVP) resulted in negative, positive and neutral particles respectively.

    Firstly, macrophage cells (RAW 264.7) were exposed to AgNPs at 0 – 200 µg/mL (nominal concentrations) and uptake dynamics, cell viability, as well as induction of tumour necrosis factor (TNF)-α and reactive oxygen species (ROS) were assessed (Chapter 2). Generally, the adverse effects of exposure to the tested AgNPs resulted in reduced overall viability of the cells, which was similar for all AgNPs tested. On adenosine triphosphate (ATP) production and specific mechanisms of toxicity (TNF-α and ROS production) however, we observed that the AgNPs differed significantly, with the negatively charged AgNP_BSA being the most toxic. Significant ROS induction was only observed after exposure to the 20 nm positively charged AgNP_Chit. Effect of size was less prominent than that of surface coating, showing mostly limited differences that were not statistically significant under our experimental conditions. Live confocal imaging of exposed cells allowed the monitoring of the uptake dynamics and subcellular cytoplasmic accumulation of AgNPs. We observed fast uptake of AgNPs within 2.5 hours which is essential in case of exposure durations of 6 and 24 hours, as applied in our experiments. However, similar uptake did not always result in similar effects.

    With the insights obtained from the in vitro assessments, we investigated the effects of size and surface coating (charge) of AgNPs on the bioaccumulation in, and toxicity (survival, growth, cocoon production) to the earthworm L. rubellus. Currently, metal engineered NPs in tissues are generally quantified based on total metal concentrations after acid destruction of samples. Such destructive methods are limited in providing information on the speciation and the forms of NPs which is essential for characterising the fate of NPs. In the present thesis, we developed a method using a combination of enzymatic tissue processing and single particle inductively coupled plasma–mass spectrometry (sp-ICP-MS) to characterise and quantify AgNPs in tissues of earthworms (Chapter 3). Subcellular fractionation of tissues was also applied to investigate potential association of AgNPs with the cellular metallothionein (MT) containing fraction of the earthworm tissues. This study provided, to the best of our knowledge, the first estimates of tissue Ag concentrations in both particulate and ionic forms in earthworms exposed in vivo to AgNPs via soil. The results obtained showed fairly low uptake of AgNPs, with earthworms exposed to a commercially obtained PVP-coated AgNP showing approximately 34% of their total Ag tissue burden being in particulate form. This indicates that although AgNPs accumulated in tissues of earthworms in their primary form, the dissolution of Ag in the soil, organism, or both played an important role in determining the ultimate fate of the AgNPs. Although the biological uptake of AgNPs was generally low, the method described in Chapter 3 was still capable of extracting NPs in quantities sufficient for identification, quantification and characterisation. It should be noted however, that the lower size detection threshold for the ICP-MS instrument used for these analyses is approximately 30 nm. Consequently, information on NPs smaller than 30 nm was not available. With the increasing optimisation of analytical systems that combine sp-ICP-MS, or other detection methods with, for example, asymmetric flow field-flow fractionation (AF4) which pre-sort different particle sizes, the potential for application of methods described in this thesis will be even greater.

    Having developed a method for extracting Ag from tissues, we exposed earthworms to all nine synthesized AgNPs as well as to AgNO3 at two concentrations below known EC50s to control for ionic effects of Ag in a 28-day sub-chronic reproduction toxicity test in soil in Chapter 4. Uptake was observed to be generally highest for the negatively charged AgNP_BSA especially at the lower exposure concentration ranges. Total Ag concentrations in earthworm tissues reached a plateau level of about 80 mg Ag/kg dry weight (DW) for exposure concentrations between 15 – 100 mg Ag/kg soil DW. Reproduction was impaired at high nominal soil concentrations of all AgNPs tested, with AgNP_BSA particles being the most toxic. Size had an influence on uptake of the AgNP_PVP, showing both uptake and effect on reproduction of the 20 nm sized group to be significantly more than those of the 35 and 50 nm AgNP_PVP. This size effect however, did not hold for AgNP_BSA nor AgNP_Chit. Higher uptake from the soil may consequently lead to a higher potential for toxicity in organisms. Interestingly, internal total Ag tissue concentrations measured after 72 hour exposure were better at predicting the effect on reproduction than tissue concentrations after 28 days exposure. It is likely therefore, that reproduction was affected already in the 72 hour exposure window.

    In order to further elucidate the likely mechanisms by which these AgNPs were exerting their effects, we conducted a toxicogenomic study in Chapter 5. Although AgNPs have been increasingly investigated, information regarding their effect on the gene expression profile of especially soil organisms is yet inadequate. Using RNAseq, we investigated the transcriptome and gene expression profiles of the earthworm L. rubellus, following exposure to the nine AgNPs. Overall, exposure to medium sized AgNPs at a concentration close to the EC50 for effects on cocoon production caused most pronounced responses at the transcriptional level. There was a correlation however, between the numbers of differentially expressed genes (DEGs) and internal Ag concentrations in the earthworms. Within the medium size AgNPs, AgNP_BSA caused extensive transcriptional responses, with 684 genes affected. In contrast ionic silver (AgNO3) did not affect gene expression at low as well as higher exposure levels. Only one gene was regulated by all AgNP and Ag+ treatments, indicating that there was hardly any functional overlap between the responses of the organisms to AgNPs with different coatings. Remarkably, this gene was metallothionein, a cysteine-rich peptide known to strongly bind free metal ions for chelation and detoxification, which was strongly up-regulated. Gene ontology enrichment analysis for 35 nm AgNP_BSA exposures revealed a total of 33 significantly enriched gene ontology terms related to biological processes. These included responses to pH, proton transport, cell differentiation, microtubule organisation, and and MT induction. Surface coating (BSA) was important in triggering the AgNP-induced differential gene expression profiles in earthworms. The importance of physicochemical properties of NPs in influencing their fate and toxicity is thus elucidated in the current study.

    The studies reported in the current thesis showed that within the range of 20 to 50 nm, effects of the size of AgNPs on toxicokinetics and toxicodynamics are limited. However, effects of surface coating were consistent over the different levels of biological integration. Generally, the negatively charged AgNP_BSA accumulated to a higher extent in the earthworms, especially at lower concentrations. The in vitro uptake was fast for all NPs, but also showed the highest uptake of AgNP_BSA. The negatively charged AgNPs were also the most toxic, likely related to their increased uptake. This was evident at all levels: gene expression, cellular, and individual (population dynamic parameters) levels. At the in vitro level, this applied mostly to effects on specific modes of action (TNF-α induction, ROS production). For more general cytotoxic effects, the effects of surface coatings were less evident. Except in cells exposed to AgNP_Chit 20 nm, where there was a slight increase in ROS production, this set of AgNPs under the experimental conditions applied, did not appear to induce the production of ROS. This was supported by the lack of expression of any ROS-related gene in the gene expression profile analyses.

    Based on the results of the current research, it can be concluded that the physico-chemical properties of NPs do influence their environmental fate and toxicity. It should be noted however that general predictions on the outcome of exposure to NPs are difficult to make, and NPs should be evaluated on a case by case basis. Our research supports the use of in vitro models to limit and prioritize further in vivo studies. Studies investigating the fate and effects of NPs for soil organisms are vital for a holistic approach towards a comprehensive and adequate environmental risk assessment (ERA). The studies described in this thesis contribute to this knowledge, thereby improving our understanding of the hazards and risks due to exposure to AgNPs, thus enabling their adequate and comprehensive ERA.

    Bioinspired nanopatterned surfaces via colloidal templating; a pathway for tuning wetting and adhesion
    Akerboom, Sabine - \ 2016
    Wageningen University. Promotor(en): Frans Leermakers, co-promotor(en): Marleen Kamperman. - Wageningen : Wageningen University - ISBN 9789462578470 - 198
    surface chemistry - surfaces - particles - water - nanotechnology - unimolecular films - adhesion - colloidal properties - oppervlaktechemie - oppervlakten - deeltjes - water - nanotechnologie - unimoleculaire films - adhesie - colloïdale eigenschappen

    We can learn from nature that, next to chemistry, surface structures can be used for tuning different functions of surfaces. In this thesis we present a novel fabrication method using colloidal templating on the air/water interface. Two distinct ways to obtain nanopatterned surfaces are described, namely (i) addition of PDMS on top of the colloidal monolayer and (ii) synthesis of polypyrrole around the particles of the monolayer. An increase in adhesion is found for the nanopatterned PDMS surfaces, and the contact angle of water on the nanopatterned polypyrrole surface is increased.

    Statistical modelling of variability and uncertainty in risk assessment of nanoparticles
    Jacobs, R. - \ 2016
    Wageningen University. Promotor(en): Cajo ter Braak, co-promotor(en): Hilko van der Voet. - Wageningen : Wageningen University - ISBN 9789462578197 - 205
    modeling - statistics - particles - risk assessment - uncertainty - uncertainty analysis - nanotechnology - probabilistic models - modelleren - statistiek - deeltjes - risicoschatting - onzekerheid - onzekerheidsanalyse - nanotechnologie - waarschijnlijkheidsmodellen

    Engineered nanoparticles (ENPs) are used everywhere and have large technological and economic potential. Like all novel materials, however, ENPs have no history of safe use. Insight into risks of nanotechnology and the use of nanoparticles is an essential condition for the societal acceptance and safe use of nanotechnology.

    Risk assessment of ENPs has been hampered by lack of knowledge about ENPs, their environmental fate, toxicity, testing considerations, characterisation of nanoparticles and human and environmental exposures and routes. This lack of knowledge results in uncertainty in the risk assessment. Moreover, due to the novelty of nanotechnology, risk assessors are often confronted with small samples of data on which to perform a risk assessment. Dealing with this uncertainty and the small sample sizes are main challenges when it comes to risk assessment of ENPs. The objectives of this thesis are (i) to perform a transparent risk assessment of nanoparticles in the face of large uncertainty in such a way that it can guide future research to reduce the uncertainty and (ii) to evaluate empirical and parametric methods to estimate the risk probability in the case of small sample sizes.

    To address the first objective, I adapted an existing Integrated Probabilistic Risk Assessment (IPRA) method for use in nanoparticle risk assessment. In IPRA, statistical distributions and bootstrap methods are used to quantify uncertainty and variability in the risk assessment in a two-dimensional Monte Carlo algorithm. This method was applied in a human health (nanosilica in food) and an environmental (nanoTiO2 in water) risk context. I showed that IPRA leads to a more transparent risk assessment and can direct further environmental and toxicological research to the areas in which it is most needed.

    For the second objective, I addressed the problem of small sample size of the critical effect concentration (CEC) in the estimation of R = P(ExpC > CEC), where ExpC is the exposure concentration. First I assumed normality and investigated various parametric and non-parametric estimators. I found that, compared to the non-parametric estimators, the parametric estimators enable us to better estimate and bound the risk when sample sizes and/or small risks are small. Moreover, the Bayesian estimator outperformed the maximum likelihood estimators in terms of coverage and interval lengths. Second, I relaxed the normality assumption for the tails of the exposure and effect distributions. I developed a mixture model to estimate the risk, R = P(ExpC > CEC), with the assumption of a normal distribution for the bulk data and generalised Pareto distributions for the tails. A sensitivity analysis showed significant influence of the tail heaviness on the risk probability, R, especially for low risks.

    In conclusion, to really be able to focus the research into the risks of ENPs to the most needed areas, probabilistic methods as used and developed in this thesis need to be implemented on a larger scale. With these methods, it is possible to identify the greatest sources of uncertainty. Based on such identification, research can be focused on those areas that need it most, thereby making large leaps in reducing the uncertainty that is currently hampering risk assessment of ENPs.

    Nanoparticle diffusometry in hydrogels
    Kort, D.W. de - \ 2016
    Wageningen University. Promotor(en): John van Duynhoven, co-promotor(en): Henk van As. - Wageningen University - ISBN 9789462577459 - 178
    nanotechnology - particles - gels - diffusion - nuclear magnetic resonance spectroscopy - rheology - nanotechnologie - deeltjes - gels - diffusie - kernmagnetische resonantiespectroscopie - reologie

    In order to understand food product functionality such as elastic and flow behavior and mass transport properties, one first has to understand the multi-length-scale structure of the material. The aim of this work is to explore novel methodologies to study and characterize multi-length-scale structures of food hydrogels under static and dynamic conditions. The focus lies on hydrogels comprising polysaccharides, because they show a rich variation in elastic and flow behavior.

    The largest part of the thesis focuses on the use of nanoparticles (3–30 nm diameter) that are dissolved into the water phase of hydrogels, and whose mobility is reduced due to the presence of the polymer network. This retardation of nanoparticle self-diffusion in hydrogels relative to self-diffusion in neat water can be used to infer structural information about the microstructure of the polymer network.

    In chapter 2, an in-depth review of existing literature on this method, known as “nanoparticle diffusometry”, is provided, with an emphasis on physical models of self-diffusion in polymer gels and applications in food gels. In that chapter, we distinguish between (1) nanoparticle diffusion in (heterogeneous) polymer gels and (2) nanoparticle diffusion in solutions of (semi)flexible polymers. We adhere to this categorization throughout the rest of the thesis.

    In chapters 3 and 4 we first describe the design and manufacturing of tailor-made nanoparticles that are functionalized with spectroscopic labels, and the implementation of pulsed-field gradient (PFG) NMR and optical spectroscopy toolboxes for nanoparticle diffusometry. We then use these toolboxes to measure nanoparticle self-diffusion in heterogeneous κ-carrageenan (a polysaccharide) gels. These experiments reveal bimodal nanoparticle self-diffusion (i.e., there are two nanoparticle fractions with different diffusion coefficients) as previously observed in these gels by Lorén et al. The results suggest that the sub-micron structure of these gels is heterogeneous with a wide distribution of pore sizes at the sub-micron scale, leading to “sieving” of nanoparticles resulting in the observation of bimodal self-diffusion.

    This hypothesis is further explored in chapter 5, where besides PFG NMR and optical spectroscopy, Overhauser dynamic nuclear polarization (ODNP)-enhanced NMR spectroscopy is employed. This method can determine the local viscosity of water surrounding the two fractions of particles. It turns out that the particle fraction with the lower apparent diffusion coefficient is in fact trapped in small, nanoscopic interstitials within the gel. The ODNP NMR experiments show that the viscosity of water surrounding the trapped particles is significantly lower than the viscosity within the larger interstitials.

    Chapter 6 describes a study of nanoparticle diffusion in solutions of poly(ethylene glycol), a flexible polymer with well defined compositions and chain lengths. We use scaling laws to understand the relation between macroviscosity and “microviscosity” as apparent from the nanoparticle diffusivity. We show that the particles probe (near-)macroviscosity only if their size is larger than the size of the PEG polymer coils.

    Another topic of this thesis is a study of the behavior of food hydrogels under dynamic conditions. To this end we use rheo-MRI velocimetry, which allows us to study the complex shear flow behavior of hydrogels that (per definition) have a yield stress. In chapter 7, we first employ nanoparticle diffusometry to study the sub-micron structure of dispersions of rigid cellulose microfibrils in the presence of carboxymethyl cellulose. Carboxymethyl cellulose is a charged cellulose derivative that succeeds to disperse the aggregation-prone cellulose microfibrils homogeneously at the sub-micron scale. Rheological characterization shows that the resulting dispersions are thixotropic yield-stress fluids. The flow properties of such fluids are well understood, but rheo-MRI experiments show that shear flow of apparently homogeneous cellulose dispersions does not resemble the flow behavior of typical thixotropic yield-stress fluids. We explain the differences by using a fluidity model to show that persistent micron-scale heterogeneity still dominates the flow behavior.

    Supramolecular nanoparticle interactions and biomolecule detection
    Oikonomou, M.E. - \ 2016
    Wageningen University. Promotor(en): Aldrik Velders. - Wageningen : Wageningen University - ISBN 9789462576605 - 158
    nanotechnology - particles - nuclear magnetic resonance spectroscopy - supramolecular chemistry - lectins - interactions - nanotechnologie - deeltjes - kernmagnetische resonantiespectroscopie - supramoleculaire chemie - lectinen - interacties

    Manipulating and understanding matter at the nanoscale describes best the interdisciplinary field of nanotechnology. Nanotechnology is entering, a new era, which is described by Jean-Marie Lehn as the era of “complex matter”. Complex matter is the combination of nanomaterials that together give rise to superstructures, “structures beyond nanostructures”. In this thesis, the motivation was to progressively discover and understand molecular interactions that govern nanoscale natural systems and beyond, and the goal was to acquire the ability to design, direct and control complex matter. In this context, supramolecular ligand interactions on nanoparticle surfaces were designed and implemented with an emphasis on biomolecule sensing. Three main topics were addressed:

    1. NMR as a tool in Nanotechnology to study reactions and supramolecular interactions between molecules, nanoparticles and biomacromolecules.

    2. Supramolecular Orthogonal Interactions at nanoparticle surfaces.

    3. Applications of Supramolecular Orthogonal Interactions for biomolecule recognition and sensing.

    Lipid bilayer stability in relation to oxide nanoparticles
    Pera, H. - \ 2015
    Wageningen University. Promotor(en): Frans Leermakers, co-promotor(en): Mieke Kleijn. - Wageningen : Wageningen University - ISBN 9789462574670 - 144
    lipids - membranes - stability - nanotechnology - particles - analytical methods - models - modeling - lipiden - membranen - stabiliteit - nanotechnologie - deeltjes - analytische methoden - modellen - modelleren
    Lipid bilayer stability in relation to oxide nanoparticles

    All living organisms are composed of cells that are filled with a thick molecular soup. These molecules constitute a complex machinery that brings these cells to life. To contain these molecules, and to protect them from the hostile outer environment, a phospholipid bilayer envelopes the cell. It is essential that this lipid bilayer, also known as the cell membrane, should remain intact and form a perfect barrier at all times. Industrially manufactured nanoparticles are suspect to be able to penetrate this barrier, and thus endanger living organisms in the environment. This thesis deals with some aspects of the structural integrity of lipid bilayers, and especially how this integrity is affected by the interaction with nanoparticles.

    Experiments were performed with silica and titanium dioxide nanoparticles, interacting with lipid bilayers, using a variety of experimental techniques. In addition, a theoretical model was applied that is based on the Scheutjens-Fleer Self Consistent Field (SCF) theory. This model delivered detailed structural and thermodynamic information about the lipid bilayer. The modelling work helped us to improve our understanding of lipid bilayer stability, and showed the effect of the interaction with the nanoparticles on the phospholipid bilayer. These latter results could be related directly to our experiments.

    Let us first experimentally regard the interaction of lipid bilayers with synthetic oxide nanoparticles. We developed a protocol for high-throughput screening of the nanoparticle-bilayer interaction using a fluorescence technique. Results from this method were combined with reflectometry measurements and atomic force microscopy (AFM). The combination of these methods allowed us to relate lipid bilayer integrity to its interaction with nanoparticles and their adsorption onto the bilayer. In addition, the AFM results yielded detailed structural information at the nano-scale. We found that the interaction strongly depends on both lipid bilayer and nanoparticle charge. However, the specific interaction that depends on the nanoparticle type, starts to play a role when the charges are low. When the total interaction strength is regarded, a regime was found at which interaction is strong enough for the nanoparticles to adsorb onto the bilayer, but too weak to disrupt the bilayer. If, however, the bilayer is disrupted by the nanoparticles, the particle may steal away some lipid molecules from the bilayer, and leave again to disrupt the bilayer elsewhere.

    Let us now go into more detail on the SCF modelling. Bilayers are composed of phospholipids, which consist of a hydrophilic head group, and a hydrophobic tail. These bilayers were modelled using a single lipid molecule type, of which the head group structure and lipid tail length could be varied. We thus obtained bilayers that varied in their thickness, and the space that a single lipid takes within the bilayer. Changes in bilayer composition affect the bilayer mechanical properties, such as those constants that describe bilayer stretching or bending. This thesis shows how vesicles, which are bilayers in a globular shape, may become unstable if the bilayer lipid composition is changed. Under certain conditions, a vesicle would prefer to fall apart into many smaller vesicles, which is when highly charged head groups start to repel each other. Or the bilayer may form continuous cubic phases, which might occur if lipids with uncharged head groups but with very long tails are used to form the bilayer. Under very specific and finely tuned conditions, a lipid bilayer may become unstable to form stable pores in the membrane, or to fall apart into tiny lipid discs.

    Affect and cognition in attitude formation towards familiar and unfamiliar attitude objects: the case of nanotechnology
    Giesen, R.I. van - \ 2015
    Wageningen University. Promotor(en): Hans van Trijp, co-promotor(en): Arnout Fischer. - Wageningen : Wageningen University - ISBN 9789462573390 - 187
    nanotechnologie - houding van consumenten - attitudes - besluitvorming - technologie - voedseltechnologie - kennisniveau - kenvermogen - nanotechnology - consumer attitudes - attitudes - decision making - technology - food technology - knowledge level - cognition
    Together, the chapters in this thesis show that although the default is to rely on affect, in attitude formation toward unfamiliar attitude objects, people are able to draw on cognitive inferences provided that there are enough cues available (e.g. product context, high Need for Cognition, or being more often exposed). In addition, whether people rely on affect or cognition depends on which process is the easiest. The attitude component which is decisive in the attitude formation process requires the least elaborate process. This thesis contributes to a better process understanding as both affective-cognitive and deliberative-intuitive dimensions were simultaneously studied. Finally, it is concluded that attitudes toward unfamiliar attitude objects, in this case nanotechnology applications, are still subject to change. This has implications for communication about new technologies, as it is important to address both affective and cognitive aspects.
    Mesoscale structure and techno-functional properties of enzymatically cross-linked a-lactalbumin nanoparticles
    Dhayal, S.K. - \ 2015
    Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Peter Wierenga. - Wageningen : Wageningen University - ISBN 9789462572812 - 152
    enzymatische cross-linking - eiwitten - nanotechnologie - deeltjes - functionele eigenschappen - polymerisatie - peroxidase - enzymatic cross-linking - proteins - nanotechnology - particles - functional properties - polymerization - peroxidase

    Abstract

    The aim of this thesis is to understand the connection between molecular, meso and macroscales of enzymatically cross-linked proteins. It was hypothesised that the techno-functional properties at macroscale, such as bulk rheology and foam stability, are affected by the structure of nanoparticles at mesoscale. The approach was to make α-lactalbumin (α-LA) nanoparticles by using two different enzymes, horseradish peroxidase (HRP) or microbial transglutaminase (mTG), to produce an open and compact mesoscale structure, respectively. In addition to the control over the mesoscale structure, the size of the nanoparticles can be independently controlled by varying the dosage of hydrogen peroxide in the case of HRP and by thermal inactivation in the case of mTG. The other important parameters determining the size are protein concentration and ionic strength. The size (radius of gyration) range that could be achieved by varying the above mentioned control parameters is 20 – 200 nm. The polydispersed nanoparticles were separated by asymmetrical flow field flow fractionation (AF4) and characterised inline with multi angle light scattering (MALS). Polymerization of apo α-LA with HRP and mTG proceeds in a step growth way i.e. first monomers react to form oligomers and the oligomers are cross-linked to form polymers (nanoparticles). Extensive cross-linking of α-LA with HRP gives rise to not only di-tyrosine cross-links, but also tri–octa tyrosine cross-links, which was hitherto unknown. The two different mesoscale structures result in gels of different storage moduli. The storage modulus of gels made by concentrating the α-LA/mTG nanoparticles was around ten times higher than that made with open nanoparticles. The half-life time (t0.5) of the foam made with α-LA nanoparticles was two to six times higher than that of the monomeric α-LA. The higher foam-stability of the α-LA nanoparticles as compared to the monomeric α-LA is due to their higher thickness of the interfacial layer and thin films. In conclusion, it is shown that the techno-functional properties of α-LA are directly correlated to the size and meso-scale structures of the nanoparticles and enzymatic cross-linking is an effective way to control them.

    Development of an integrated in vitro model for the prediction of oral bioavailability of nanoparticles
    Walczak, A.P. - \ 2015
    Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Hans Bouwmeester; Peter Hendriksen. - Wageningen : Wageningen University - ISBN 9789462572201 - 153
    nanotechnologie - deeltjes - in vitro - inname - biologische beschikbaarheid - voedingsonderzoek bij de mens - risicoschatting - nanotechnology - particles - in vitro - ingestion - bioavailability - human nutrition research - risk assessment

    Title of the PhD thesis: Development of an integrated in vitro model for the prediction of oral bioavailability of nanoparticles

    The number of food-related products containing nanoparticles (NPs) increases. To understand the safety of such products, the potential uptake of these NPs following consumption needs to be assessed. In normal safety assessment studies this is investigated using animal models. For scientific, ethical and economical reasons, there is a demand to refine, reduce and replace animal testing by developing in vitro alternatives for hazard characterization. In this thesis an in vitro model for the prediction of the uptake of NPs in the human body after consumption was developed. The model consists of two parts. The first part is a laboratory incubation model mimicking human digestion in mouth, stomach and intestine. For the second part, human intestinal wall cells are used to assess the uptake of nanoparticles. The two models were combined into the integrated in vitro model to take into consideration the potential effect of digestion on nanoparticle uptake in the gut. The main outcome of the work is that the cell-based integrated in vitro model can be used to evaluate which NPs are likely taken up by the body at the highest rate. The size of NPs and the type of chemical groups on their surface greatly influenced the uptake of NPs. The developed model can be used to prioritize the NPs for additional investigations. Using this model in the safety assessment of NPs would reduce the number of animals used in safety assessment.

    New insight into enzymatic cross-linking of globular proteins: from nanostructure to functionality
    Sariçay, Y. - \ 2014
    Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Renko de Vries; Peter Wierenga. - Wageningen : Wageningen University - ISBN 9789462571211 - 217
    enzymatische cross-linking - eiwitten - chemische reacties - alfa-lactalbumine - lactalbumine - nanotechnologie - enzymatic cross-linking - proteins - chemical reactions - alpha-lactalbumin - lactalbumin - nanotechnology

    ABSTRACT

    In last two decades, enzymatic cross-linking of proteins has a growing interest in food technology for better tailoring protein functionality. However, the relation between physical and functional properties of enzymatically cross-linked proteins has been hardly addressed so far. The aim of this thesis was to elucidate the effect of enzymatic protein cross- linking on the physical and functional properties of protein nanoparticles at multiple lengthscale. In the first part of this thesis, as a model system, the enzymatic cross-linking of globular whey protein apo-α-lactalbumin (α-LA) by horseradish peroxidase (HRP) was discussed in details. In comparison with HRP, in the second part of the thesis, we also addressed to what extent both laccase (LC) (from trametes versicolor) and tyrosinase (TYR) (from agaricus bisporus) differ in catalyzing oxidative cross-linking of α-LA. Both HRP and LC were capable of creating self-similar large α-LA nanoparticles that have an open architecture at similar lengthscales whereas TYR led to the formation of α-LA oligomers only. All HRP-, LC-nanoparticles and TYR-oligomers exhibited a high extent of secondary structure content preserved whereas their almost all tertiary structure was lost upon enzymatic cross-linking. HRP-catalyzed cross-linking of α-LA resulted in more hydrophilic nanoparticles than LC-cross-linked α-LA nanoparticles. Whereas both HRP- and LC-nanoparticles exhibited very high colloidal and thermal stability against protein aggregation at pH 5.8 and 7.0, HRP- nanoparticles were more stable than LC-nanoparticles upon heating and in the presence of dithiothreitol (DTT). This suggests that, unlike HRP- nanoparticles, not only the dityrosine bonds but also disulfide cross-linking stabilizes LC-nanoparticles. Dilute dispersions of HRP-nanoparticles exhibited a high viscosity and a hydrophilic nature. As these dispersions were concentrated, they jammed above their critical overlapping concentration and thus created physical transparent protein hydrogels at relatively low protein concentration (4% w/v). These properties of HRP- nanoparticle dispersions offer high thickening properties that are comparable with polysaccharide in food applications as protein-based thickeners.

    Groepsgedrag op de nanoschaal
    Gucht, J. van der - \ 2014
    Wageningen : Wageningen University, Wageningen UR - ISBN 9789461739711 - 23
    nanotechnologie - colloïden - groepsgedrag - polymeren - nanotechnology - colloids - group behaviour - polymers
    Implications of nanoparticles in the aquatic environment
    Velzeboer, I. - \ 2014
    Wageningen University. Promotor(en): Bart Koelmans. - Wageningen : Wageningen University - ISBN 9789461739506 - 253
    microplastics - polychloorbifenylen - nanotechnologie - adsorptie - ecotoxicologie - aquatisch milieu - verontreinigde sedimenten - aquatische ecologie - microplastics - polychlorinated biphenyls - nanotechnology - adsorption - ecotoxicology - aquatic environment - contaminated sediments - aquatic ecology
    De productie en het gebruik van synthetische nanodeeltjes (ENPs) nemen toe en veroorzaken toenemende emissies naar het milieu. Dit proefschrift richt zich op de implicaties van ENPs in het aquatisch milieu, met de nadruk op het sediment, omdat er wordt verwacht dat ENPs hoofdzakelijk in het aquatisch sediment terecht zullen komen. ENPs kunnen directe effecten veroorzaken op organismen in het aquatisch milieu, indirecte effecten op het levensgemeenschap niveau en/of voedselweb en kunnen effecten op het gedrag en de risico’s van andere contaminanten hebben. Om de risico’s van ENPs vast te stellen, is niet alleen informatie nodig over het gevaar, oftewel de kans op een effect, maar ook over de kans op blootstelling.
    Towards colloidal size control by precipitation
    Lebouille, J.G.J.L. - \ 2014
    Wageningen University. Promotor(en): Martien Cohen Stuart; Frans Leermakers; R. Tuinier. - Wageningen : Wageningen University - ISBN 9789461738677 - 151
    micellen - colloïden - nanotechnologie - deeltjesgrootte - deeltjesgrootteverdeling - micelles - colloids - nanotechnology - particle size - particle size distribution

    Many active ingredients like drugs, preservatives and vitamins are hydrophobic. In most applications for food and pharma, however, they need to be functional in aqueous environments. In order to facilitate their usage in aqueous environments one needs a way to enable the dispersion of hydrophobic compounds into submicron particles in water in a controlled manner. We investigated the stabilization by surfactants and encapsulation into micelles of hydrophobic compounds using the nanoprecipitation method. The research described in this thesis is about building more understanding of the nanoprecipitation method in relation to the relevant physical chemical parameters. The theoretical results led to predictions that were compared to experimental data. For water-soluble surfactants as stabilizers in the nanoprecipitation process a new theory was developed to relate the process parameters to the final particle size. For non-water-soluble surfactants self-consistent field theory was used in order to unravel the structure-function relationship between used copolymer chemistry and the form and morphology of the obtained particles, spherical micelles and their size.

    We analyzed new and existing experiments on the nanoprecipitation method using water-soluble surfactants as stabilizers in a systematic manner. These were interpreted in terms of a new theory that links the process and material properties to the final particle size. The nanoprecipitation procedure consists of quenching a polymer solution from a good to a poor solvent containing surfactant solution. Three characteristic time scales can be identified which affect the final particle size. First, the mixing time (τmix) was identified; the time needed to mix the polymer solution (polymer in good solvent) into the surfactant solution (poor solvent). Second, the coalescence time (τcls) was identified; the time needed for the collapsed polymer chains to coalesce into bigger droplets and subsequently to harden out into particles with long term storage stability. Last, the protection time (τpro) was identified; the time that the surfactant molecules need to completely cover the coalescing droplets and by this stop the coalescence of the collapsed polymer chains/droplets. The two latter characteristic times are intrinsic properties of the used solvents, surfactants and polymers and cannot be changed without addition of extra/new molecules. However, the mixing time is the only parameter which can be changed without modifying the material properties of the system. The mixing time can be easily varied by the method of mixing the good and the poor solvent. Using a pipette to mix the two solutions will result in a 'slow' mixing time regime and utilizing for instance an impingent jet mixer can result in a 'fast' mixing regime. For both mixing regimes a clear analytical expression could be derived enabling more efficient experimentation in order to obtain a specific final particle size. For the 'slow' mixing regime the relation between final particle size ()was found only to be dependent of the used polymer concentration (cmp) as ~cmpThe practical interpretation of this analytical expression is rather simple; an eight times higher polymer concentration will result in a two times bigger final particle size. For the 'fast' mixing regime the analytical expression can be interpreted also in an easy way; the faster the mixing the smaller the final particle size. Below a certain value for the mixing time the final particle size attains a plateau value; even faster mixing will not further decrease the final particle size. When using water-soluble surfactants the release of the cargo, which in practice often takes place after significant dilution, is expected to be fast. In order to increase the release of the encapsulated compound(s) in time we incorporated the surfactant functionality into a non-water soluble triblock copolymer. This results, even upon huge dilution, in an extended release profile in time.

    We employed self-consistent field theory for non-water-soluble surfactants in order to relate the (block copolymer) surfactant chemistry to the size and composition of the resulting spherical equilibrium micelles. The surfactants, triblock copolymers synthesized via ring-opening polymerization, were employed in the nanoprecipitation process in order to make spherical micelles. The theoretical predictions were compared to the experimental results and it was concluded that self-consistent field theory is an accurate theoretical tool to predict the size of spherical micelles given a certain chemistry and composition of the copolymers and the conditions required to form these micelles.

    We experimentally studied whether hydrophobic compounds (polymers, different active ingredients or a mixture of the two) were added in order to verify whether these spherical micelles could be loaded by these compounds. We investigated the encapsulation behavior of these micelles for hydrophobic compounds both theoretically and experimentally and considered the influence of the size for the micelles. From both the theoretical predictions and the experimentally obtained data it followed that these micelles can be used for encapsulation of hydrophobic compounds. Moreover, the theoretical predictions matched with the experimentally obtained data. It was concluded that self-consistent field predictions can be used to predict the size and stability of spherical micelles with encapsulated hydrophobic compounds.

    Tuning size and loading is mandatory for passive targeting applications because the particle size mainly determines the biologic faith. In order to enable active targeting, utilizing a targeting moiety and (specific) receptor interaction is needed while maintaining the stealthy nature of the spherical particles. We performed a theoretical self-consistent field study on spherical block copolymer micelles to investigate whether it is feasible to hide the targeting moiety within the micellar corona while maintaining receptor interaction. We determined the maximum interaction distance wherefrom targeting moiety receptor connection can be established and the required energy barrier at different distances. The outcome of these calculations was used to design a (theoretical) optimized system for active targeting.

    We used self-consistent field theory to calculate the size, loading and targeting capability of triblock copolymer based micelles enabling both passive and active targeting and verified our calculation results experimentally. Although the active targeting predictions were not verified experimentally we established a design for passive and active targeting micellar applications for, for instance, drug delivery applications while maintaining the stealthy nature of these micelles.

    Governing nano foods : Principles-Based Responsive Regulation
    Meulen, B.M.J. van der; Bremmers, H.J. ; Purnhagen, K. ; Gupta, N. ; Bouwmeester, H. ; Geyer, L. - \ 2014
    Amsterdam, Boston, Heidelberg, London, New York, Oxford, Paris, San Diego, San Francisco, Singapore, Sydney, Tokyo : Academic Press (EFFoST Critical Reviews 3) - ISBN 9780124201569 - 100
    nanotechnologie - voedselvoorziening - voedingsmiddelenwetgeving - wetgeving - risicoschatting - regelingen - nanotechnology - food supply - food legislation - legislation - risk assessment - regulations
    Food which nanotechnology has impacted or to which nanotechnology is applied is referred to as nanofood. From treatment of the soil in which a crop plant is grown to the caring of a food, nanotechnology is a growing factor in the food supply. At this point, however, there is no definitive, effective global method for regulating the use of nanotechnology as it relates to the food suply. Legislation on nanotechnologies is still evolving, as is understanding what data is needed for effective, efficient and appropriate risk assessment associated with nanotechnology impacted foods. Due to the emerging nature of nanotechnology and its role in the food supply, case-by-case studies are the current norm, but the need for wide-scale testing and broad-based regulatory standards is urgent. This project is based on an EFFoST study designed to provide a comparative study of nanofood regulations in order to guide regulation development in this rapidly expanding market.
    Protein-based polymers that bond to DNA : design of virus-like particles and supramolecular nanostructures
    Hernandez Garcia, A. - \ 2014
    Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Renko de Vries; P. Schoot. - Wageningen : Wageningen University - ISBN 9789461738233 - 242
    polymeren - polymeerchemie - eiwitten - dna - dna-bindende eiwitten - virussen - nanotechnologie - virusreplicatie - virusachtige deeltjes - polymers - polymer chemistry - proteins - dna - dna binding proteins - viruses - nanotechnology - viral replication - virus-like particles

    In this thesis it is demonstrated that it is possible to use Protein-based Polymers (PbPs) as synthetic binders of DNA (or any other negatively charged polyelectrolyte). The PbPs co-assemble with their DNA templates to form highly organized virus-like particles and supramolecular structures. A range of PbPs have been developed over the last decades that can be used as precision functional polymers, and which integrate the unique properties of both proteins and polymers. Many PbPs are based on nature-inspired simple repetitive amino acid sequences. In this thesis, different kinds of such sequences have been combined into PbPs that mimic complex natural functionalities. Being intermediate between proteins and polymers, it has been able to mimic complex functionalities typically found for folded proteins, while retaining the tunability and ease of control that is more characteristic for (synthetic) polymers. Indeed, using clear design rules, biosynthetic PbPs sequences have been obtained and produced that co-assemble with nucleic acids to form true artificial viruses, which mimic their natural counterparts in many respects.

    The motivation for developing artificial viruses derives among others from the growing interest in exploiting natural self-assembled virus structures to develop nanostructured materials. In addition, natural viruses are being used as scaffolds for delivering DNA in the context of gene therapy, to serve as vaccines (by displaying antigens), to template diverse materials, to produce energy, to catch light, to catalyze reactions, to serve as contrasting agents, etc. Developing artificial viruses would serve not only to advance our capabilities to understand and control the co-assembly of nanostructures, but would also generate useful synthetic biomaterials that are even more suited than natural viruses to be used as building blocks for nanostructured materials. In short, the successful development of artificial viruses may be expected to give rise not only to new insights on templated self-assembly, but will also be very important for a range of applications.

    The main part of the thesis is divided into three parts. In part I, “Complexation of DNA into virus-like particles”, we describe details of the molecular biomimetic strategy to design and produce PbPs with functionalities that mimic those of natural viruses. Part II, “Applications of protein-DNA complexes”, deals with the development of diblock PbP that coat DNA, and with their applications in gene delivery and optical mapping of long DNA. Finally, in part III: “Supramolecular nanostructures beyond DNA” we consider the co-assembly of our PbPs with templates other than DNA, and also consider their self-assembly in the absence of DNA.

    Formation of alginate nanospheres
    Paques, J.P. - \ 2014
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Cees van Rijn; Leonard Sagis. - Wageningen : Wageningen University - ISBN 9789461738349 - 178
    alginaten - nanotechnologie - deeltjes - gelering - alginates - nanotechnology - particles - gelation
    WU thesis, no. 5669
    Heteroaggregation and sedimentation rates for nanomaterials in natural waters
    Quik, J.T.K. ; Velzeboer, I. ; Wouterse, M. ; Koelmans, A.A. ; Meent, D. van de - \ 2014
    Water Research 48 (2014)1. - ISSN 0043-1354 - p. 269 - 279.
    sedimentatie - zwevende deeltjes - aggregatie - nanotechnologie - emissie - schatting - colloïden - waterstroming - zeewater - oppervlaktewaterkwaliteit - sedimentation - suspended solids - aggregation - nanotechnology - emission - estimation - colloids - water flow - sea water - surface water quality - engineered nanomaterials - silver nanoparticles - carbon nanotubes - manufactured nanoparticles - aggregation kinetics - aquatic environments - ceo2 nanoparticles - organic-matter - fate - exposure
    Exposure modeling of engineered nanomaterials requires input parameters such as sedimentation rates and heteroaggregation rates. Here, we estimate these rates using quiescent settling experiments under environmentally relevant conditions. We investigated 4 different nanomaterials (C60, CeO2, SiO2-Ag and PVP-Ag) in 6 different water types ranging from a small stream to seawater. In the presence of natural colloids, sedimentation rates ranged from 0.0001md-1 for SiO2-Ag to 0.14md-1 for C60. The apparent rates of heteroaggregation between nanomaterials and natural colloids were estimated using a novel method that separates heteroaggregation from homoaggregation using a simplified Smoluchowski-based aggregation-settling equation applied to data from unfiltered and filtered waters. The heteroaggregation rates ranged between 0.007 and 0.6Lmg-1 day-1, with the highest values observed in seawater. We argue that such system specific parameters are key to the development of dedicated water quality models for ENMs.
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