Wendelin J. Stark

ETH Zurich, Zürich, Zurich, Switzerland

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Publications (288)1176.73 Total impact

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    ABSTRACT: Ferromagnetic nanoparticles are covalently modified in order to enhance the dispersion stability as well as the antifouling properties. Insertion of an azide moiety allows “click”-reaction of a relevant tag molecule. This and the high saturation magnetization of the presented nanocomposite offer a promising platform for magnetic biosensors.
    Chemical Communications 12/2014; 51(10). DOI:10.1039/C4CC06126H · 6.72 Impact Factor
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    ABSTRACT: Although silica particles are among the widest utilized engineered nanoparticles, the measurement of silica particles at low exposure concentrations is impeded by the high background concentrations of silicates in the environment. To circumvent this analytical limitation, we describe a new method for tracing submicrometer silica particles in water by the usage of silica particles fully encapsulating unique DNA codes. Because DNA can be detected at extremely low concentrations by quantitative polymerase chain reaction (PCR), the encapsulation of DNA in silica allows an indirect measure of the concentration of silica particles down to the sub-parts per billion range (micrograms per liter). To provide insight into the capability of this novel technology, we utilized DNA-loaded submicrometer silica particles to follow the fate of silica particles in the analytically most demanding biological stages of wastewater treatment solutions (activated sludge). At various initial particle concentrations ranging from 10 ppb (10 μg/L) to 10 ppm (10 mg/L) and under both aerobic and anoxic conditions, we are able to show that >97% of the particles were removed from the wastewater by incorporation into sludge biomass.
    12/2014; 1(12):484. DOI:10.1021/ez5003506
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    ABSTRACT: Magnetic hybrid materials have been synthesized as recyclable catalysts for alkene hydrogenation. The materials consist of magnetic nanobeads functionalized with imidazolium-based ionic liquids and optional polymer shells. Palladium nanoparticles (NPs) were synthesized on the surface of these supports by two different methods and evaluated as catalysts for alkene hydrogenation. Deposition of palladium(0) onto the magnetic nanobeads by microwave decomposition of Pd2(dba)(3)center dot CHCl3 leads to more efficient catalysts than the reduction of a Pd(II) precursor. Reactivity, recycling ability and ease of separation of the catalysts are compared. A hybrid material without polymer shells and a quite flexible ionic liquid was identified as the most promising for stabilizing Pd NPs resulting in a catalyst that shows high activity (TOF up to 330 h(-1)), good recycling ability, and minor metal leaching into the product. Notably, the activity of this catalyst increases with an enhanced Pd loading, contrasting related systems for which a decrease of activity is observed due to agglomeration. Therefore, this recyclable, highcapacity system is especially attractive for large-scale applications, requiring just a minimal amount of supporting material for the recycling of expensive Pd that is readily achieved by magnetic decantation.
    ChemInform 11/2014; 45(46). DOI:10.1002/chin.201446039
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    ABSTRACT: Limestone nanoparticles can be used as nanopore template to prepare porous polymeric films. Their application as membranes was so far strongly limited by the fact that these films were highly hydrophobic. In this study, a simple method is reported to directly produce self-wetting membranes by the template removal method. Triethyl citrate modified polyethersulfone and cellulose acetate membranes were produced using dissolvable limestone nanoparticles as pore templates. The nanoporous polymer films were used as dialysis membranes and characterized by means of buffer exchange rate, molecular weight cut-off, protein adsorption, pore size distribution and water contact angle. The herein prepared membranes were further benchmarked against commercially available dialysis membranes with comparable average pore size. They showed narrow pore size distributions, fast dialysis rates at low protein adsorption and molecular weight cut-off of around 12 kDa. Interestingly, the triethyl citrate modified polyethersulfone membranes displayed only moderate change in pore size distribution as a result of the plasticizer additive compared to pure polyethersulfone membranes. This is a matter of substantial interest considering the fact that additive modifications of membranes produced by the predominant phase inversion process typically show alterations in morphology that lead to undesired changes in membrane performance. Furthermore, dextran recovery analysis proved to meet the specific requirements for dialysis membrane characterization and benchmarking.
    RSC Advances 11/2014; DOI:10.1039/C4RA12613K · 3.71 Impact Factor
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    ABSTRACT: The effects of an exposure to three mass-produced metal oxide nanoparticles – similar in size and specific surface area, but different in redox activity and solubility – were studied in rat alveolar macrophages (MAC) and epithelial cells (AEC). We hypothesized that the cell response depends on the particle redox activity and solubility determining the amount of reactive oxygen species formation (ROS) and subsequent inflammatory response. MAC and AEC were exposed to different amounts of Mn3O4 (soluble, redox-active), CeO2 (insoluble, redox-active), and TiO2 (insoluble, redox-inert) up to 24 hours. Viability and inflammatory response were monitored with and without co-incubation of a free-radical scavenger (trolox). In MAC elevated ROS levels, decreased metabolic activity and attenuated inflammatory mediator secretion were observed in response to Mn3O4. Addition of trolox partially resolved these changes. In AEC, decreased metabolic activity and an attenuated inflammatory mediator secretion were found in response to CeO2 exposure without increased production of ROS, thus not sensitive to trolox administration. Interestingly, highly redox-active soluble particles did not provoke an inflammatory response. The data reveal that target and effector cells of the lung react in different ways to particle exposure making a prediction of the response depending from redox activity and intracellular solubility difficult.
    Environmental Science & Technology 10/2014; DOI:10.1021/es504011m · 5.48 Impact Factor
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    ABSTRACT: Work-up in organic synthesis can be very time consuming, particularly when using reagents of solubility similar to the desired products and a low tendency to crystallize. In this respect, reactions involving organic bases would strongly profit from a tremendously simplified separation. Therefore, we synthesized a derivative of the superbasic proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) and covalently linked it to the strongest currently available nanomagnets based on carbon-coated cobalt metal nanoparticles. The immobilized magnetic superbase reagent was tested in Knoevenagel and Claisen-Schmidt type condensations and showed conversions up to 99%. In a particular example, high yields up to 97 % of isolated product could be obtained by simple recrystallization without using column chromatography. Recycling of the catalyst was simple and fast with insignificant decrease in catalytic activity.
    The Journal of Organic Chemistry 10/2014; DOI:10.1021/jo501913z · 4.64 Impact Factor
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    ABSTRACT: The capability of tracing a food product along its production chain is important to ensure food safety and product authenticity. For this purpose and as an application example, recently developed Silica Particles with Encapsulated DNA (SPED) were added to milk at concentrations ranging from 0.1 to 100 ppb (µg per kg milk). Thereby the milk, as well as the milk derived products yoghurt and cheese, could be uniquely labeled with a DNA tag. Procedures for the extraction of the DNA tags from the food matrixes were elaborated and allowed identification and quantification of previously marked products by quantitative polymerase chain reaction (qPCR) with detection limits below 1 ppb of added particles. The applicability of both synthetic as well as naturally occurring DNA sequences was shown. The usage of approved food additives as DNA carrier (silica = E551) and the low cost of the technology (< 0.1 USD per ton of milk labeled with 10 ppb of SPED) display the technical applicability of this food labeling technology.
    Journal of Agricultural and Food Chemistry 10/2014; 62(43). DOI:10.1021/jf503413f · 3.11 Impact Factor
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    ABSTRACT: From environmental modeling of engineered nanomaterial (ENM) release, it is clear that ENMs will enter soils, where they interact with soil compounds as well as plant roots. We analyzed three different size groups of cerium dioxide nanoparticles (CeO2-NPs) in respect to chemical changes in the most common plant growth medium, Hoagland solution. We created a simple environmental model using liquid dispersions of 9-, 23-, and 64-nm-uncoated CeO2-NPs. We found that CeO2-NPs release dissolved Ce when the pH of the medium is below 4.6 and in the presence of strong chelating agents even at pH of 8. In addition, we found that in reaction with Fe2+-ions, equimolar amounts of Ce were released from NPs. We could elucidate the involvement of the CeO2-NPs surface redox cycle between Ce3+ and Ce4+ to explain particle transformation. The chemical transformation of CeO2-NPs was summarized in four probable reactions: dissolution, surface reduction, complexation, and precipitation on the NP surface. The results show that CeO2-NPs are clearly not insoluble as often stated but can release significant amounts of Ce depending on the composition of the surrounding medium.
    Journal of Nanoparticle Research 10/2014; 16(10). DOI:10.1007/s11051-014-2668-8 · 2.28 Impact Factor
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    ABSTRACT: Gelatin is an exceptional and versatile biopolymer with applications in various industries. As the most abundant structural protein in vertebrates it is available in megaton quantities. On these grounds, it would be a plausible substitute for synthetic polymers. Gelatin processing into fibers seems promising as continuous protein filaments do not have the limitation of natural fibers, i.e., small staple fiber length. Instead of spinning an aqueous gelatin solution, a protein precipitate from a phase-separated system is used. Robust wet spinning with subsequent fiber drawing allows production of a gelatin filament with similar mechanical properties as sheep wool. Different degrees of fiber drawing and addition of plasticizers enable to tailor the mechanical and thermal fiber properties and demonstrate the versatility of the proposed spinning process.
    Macromolecular Materials and Engineering 10/2014; 300(2). DOI:10.1002/mame.201400240 · 2.78 Impact Factor
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    ABSTRACT: We present a design and parameter study on 3D-printed, lost-wax-casted and combustion-powered soft silicone pumps, which are internally cooled by the conveyed liquid. Important factors influencing the pumping performance such as gas mixtures, feed rates, and actuation frequencies were thoroughly studied. Furthermore, we reinforced some of the here presented pumps with aramid fabrics in order to achieve partial blocking of the elastomeric flexibility upon combustion expansion. This design measure dramatically increased the pumping capabilities and allowed continuous conveying of water to 13 m (corresponding to 42 ft) of height. We were able to stably operate these novel pumps for more than 30 000 combustion cycles. Therefore, they represent a further step toward long-term stable soft machines with dense power characteristics.
    Industrial & Engineering Chemistry Research 08/2014; 53(31):12519-12526. DOI:10.1021/ie501991d · 2.24 Impact Factor
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    ABSTRACT: There is a strong interest in studying the cellular uptake of silica nanoparticles, particularly at medically relevant concentrations (ppb-ppm range) to understand their toxicology. At present, uptake analysis at these exposure levels is impeded by the high silica background concentration. Here we describe the use of DNA encapsulated within silica particles as a tool to quantify silica nanoparticles in in vitro cell-uptake experiments at low concentrations (down to 10 fg cell(-1)).
    Chemical Communications 07/2014; 50(73). DOI:10.1039/c4cc04480k · 6.72 Impact Factor
  • R. A. Raso, P. R. Stoessel, W. J. Stark
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    ABSTRACT: Removal of volatile organic compounds (VOC) and indoor air quality regulation through adsorbers required exchange or maintenance of active materials. In this work, we combine well known VOC adsorbers with oxidation catalysts as intimate particulate mixtures. We demonstrate how typical VOC can subsequently adsorb on such mixed material fixed beds (usually days to weeks; the common state of the system, adsorption phase) using small organic compounds (diethyl ether, triethylamine), monoterpenes such as linalool and limonene, and hexanoic acid. Occasional regeneration runs through heat up of the fixed bed results in simultaneous desorption and oxidation of the accumulated VOC, thus regenerating full adsorption capacity for a next adsorption phase. We investigated both small pore zeolites (H-ZSM-5) and larger pore zeolites (13X) and found a distinct interplay between the pore size and the type of VOC. Thermogravimetry coupled with mass spectroscopy was used to quantitatively study the effects of mixing composition and temperature on adsorber performance and regeneration. The here investigated bi-functional systems combine very low maintenance costs and materials requirement with low air flow and exchange costs, thus suggesting mixed (two-functional) bed adsorbers with catalytic function as sustainable alternatives to currently used single use systems based on granulated zeolites or activated carbon. In this work we show the ability of zeolite/cerium oxide physical mixtures to adsorb and capture different classes of VOC at room temperature and release them for oxidation at higher temperatures in a regenerative and sustainable process.
    07/2014; 2(34). DOI:10.1039/C4TA02317J
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    ABSTRACT: Elastic silicone composites with mechanically switchable transparency are generated by incorporating micron‐sized aluminum platelets into a highly flexible silicone. Physisorbing Fe3O4 nanoparticles onto the platelets surface allow magnetic pre‐alignment during the polymer curing. One‐dimensional or two‐dimensional stretching of the resulting silicone composites permits orientation of the incorporated flakes and alters light transmittance of the polymer coating.
    Advanced Engineering Materials 07/2014; 16(7). DOI:10.1002/adem.201300478 · 1.51 Impact Factor
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    ABSTRACT: To investigate chemo-mechanical effects of incorporating alkaline bioactive glass nanoparticles into a light-curable dental resin matrix.
    Dental materials: official publication of the Academy of Dental Materials 06/2014; DOI:10.1016/j.dental.2014.05.029 · 4.16 Impact Factor
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    ABSTRACT: A novel technique for transforming cubic α-NaYF4 phosphors into the hexagonal modification is presented for the removal of O impurities that hinder upconversion luminescence.
    ChemInform 06/2014; 45(22). DOI:10.1002/chin.201422215
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    ABSTRACT: Background Fractures with a critical size bone defect are associated with high rates of delayed- and non-union. The treatment of such complications remains a serious issue in orthopedic surgery. Adipose derived stem cells (ASCs) combined with biomimetic materials can potentially be used to increase fracture healing. Nevertheless, a number of requirements have to be fulfilled; in particular the insufficient vascularization of the bone constructs. Here, the objectives were to study the impact of ASC-derived osteoblasts on ASC-derived endothelial cells in a 3D co-culture and the effect of 40 wt % of amorphous calcium phosphate nanoparticles on the proliferation and differentiation of ASC-derived endothelial cells when present in PLGA. Materials and Methods Five primary ASC lines were differentiated towards osteoblasts (OB) and endothelial cells (EC) and two of them were chosen based on quantitative PCR results. Either a mono-culture of ASC-derived EC or a co-culture of ASC-derived EC with ASC-derived OB (1:1) was seeded on an electrospun nanocomposite of poly-(lactic-co-glycolic acid) and amorphous calcium phosphate nanoparticles (PLGA/a-CaP; reference: PLGA). The proliferation behavior was determined histomorphometrically in different zones and the expression of von Willebrand Factor (vWF) was quantified. Results Independently of the fat source (biologic variability), ASC-derived osteoblasts decelerated the proliferation behavior of ASC-derived endothelial cells in the co-culture compared to the mono-culture. However, expression of vWF was clearly stronger in the co-culture, indicating further differentiation of the ASC-derived EC into the EC lineage. Moreover, the presence of a-CaP nanoparticles in the scaffold slowed the proliferation behavior of the co-culture cells, too, going along with a further differentiation of the ASC-derived OB, when compared to pure PLGA scaffolds. Conclusions This study revealed significant findings for bone tissue-engineering. Co-cultures of ASC-derived EC and ASC-derived OB stimulate each other's further differentiation. A nanocomposite with a-CaP nanoparticles offers higher mechanical stability, bioactivity and osteoconductivity compared to mere PLGA and can easily be seeded with pre-differentiated EC and OB.
    Injury 06/2014; 45(6). DOI:10.1016/j.injury.2014.02.035 · 2.46 Impact Factor
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    ABSTRACT: The bombardier beetle uses attack-triggered mixing of reactants (hydrochinone, hydrogen peroxide (H2O2) and enzymes as catalysts) to defend itself against predators. Using multi-layer polymer sheets with H2O2 and catalyst (MnO2) filled compartments we developed a 2D analogous bio-inspired chemical defence mechanism for anti-vandalism applications. The reactants were separated by a brittle layer that ruptures upon mechanical attack and converts the mechanical energy trigger (usually a few Joules) into a chemical self-defence reaction involving release of steam, and optionally persistent dyes and a DNA-based marker for forensics. These surfaces effectively translate a weak mechanical trigger into an energetic chemical reaction with energy amplification of several orders of magnitude. Since the responsive materials presented here do not depend on electricity, they may provide a cost effective alternative to currently used safety systems in the public domain, automatic teller machines and protection of money transport systems. Anti-feeding protection in forestry or agriculture may similarly profit from such mechanically triggered chemical self-defending polymer surfaces.
    05/2014; 2(22). DOI:10.1039/C3TA15326F
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    ABSTRACT: Purpose: A low direct current can be used to disinfect dental titanium implants in simulated physiologic environments. The aim of this study was to determine whether this treatment affects implant surface structure and cytocompatibility. Materials and Methods: Titanium test disks with a sandblasted, acid-etched, large-grit (SLA) surface were placed as anodes in an electrolytic bath with physiologic saline and treated with 15 mA of current for 15 minutes. Surfaces were analyzed by light and electron microscopy and contact angle measurement. Depth profile analyses of SLA disks were run at subsurface levels from 0 to 1,000 nm. The proliferation and viability of preosteoblastic cells and human foreskin fibroblasts on implant surfaces were assessed. Alkaline phosphatase (ALP) activity was determined with and without exposure to bone morphogenetic protein-2 (BMP-2). Mineralization was determined after 4 weeks. Results: A blue discoloration was observed after treating the SLA disks, but no damage was recognized microscopically. An oxidation layer formed on the surface and the wettability of the disks increased significantly. Cell proliferation and initial maturation were not affected by the treatment. Mineralization and ALP activity of BMP-exposed cells, however, were slightly but significantly reduced on test disks. Conclusions: The current study showed that the alterations in implant color after electrochemical treatment did not reflect significant surface changes, which would preclude cell adhesion and growth or have a major impact on osteoblastic differentiation or maturation.
    The International journal of oral & maxillofacial implants 05/2014; 29(3):735-42. DOI:10.11607/jomi.3342 · 1.49 Impact Factor
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    ABSTRACT: Intravascular application of magnetic nanocarriers is a critical step in the development of new therapeutic strategies, including magnetic drug targeting or hyperthermia. However, injection of particulate matter bears the intrinsic risk of contact activation of the blood coagulation cascade. In this work, we use point-of-care assays to study coagulation dynamics and clotting parameters in blood samples exposed to relevant concentrations of surface-functionalized carbon-coated iron carbide nanomagnets using unmodified nanomagnets and poly(ethylene)glycol-functionalized nanomagnets with different end-groups, including –OCH3, –NH2, –COOH, –IgG, and –ProteinA-protected-IgG (–IgG-ProtA). Silica nanoparticles with a comparable surface area are used as a reference material. For magnetic nanoparticles, we observe a decrease in clotting time by 25% compared to native blood at concentrations of 1 mg mL−1, independent of the surface functionalization, and only minor differences in receptor expression on platelets (GP-IIb-IIIa, CD62, and CD63) relative to control samples were observed. Interestingly, the inter-subject variance of the clotting time is similar to the nanoparticle-induced effect in a single subject with average clotting time. Whilst the present study is based on in vitro assays and a small group of healthy blood donors, the comparison to broadly used silica nanoparticles, and the fact that experimental intergroup variability is comparable to the observed effects from the carbon-coated nanomagnets suggests continuing investigations on their potential clinical use.
    Journal of Materials Chemistry 04/2014; DOI:10.1039/C4TB00208C · 7.44 Impact Factor
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    ABSTRACT: Due to their porous structure, angora rabbit fibers make for some of the highest quality wool. The application of these fibers on a technical scale is not feasible due to their limited availability and high price. Here, a robust fiber preparation method is reported based on an unusual spinning process, where a non-equilibrated, ternary system of protein, solvent, and non-solvent is continuously processed into strong fibers with minimal energy input and harmless solvents. Gelatin - the degradation product of collagen - is chosen as the protein component because of its immense availability from slaughterhouse waste. Due to the sponge-like structure of the ternary gelatin/water/2-propanol spinning mixture, fibers with internal cavities are produced. The porous nature of these fibers resembles the morphology of angora rabbit fibers. Despite their high porosity, the here-obtained gelatin fibers show clear re-orientation of the fibrous protein and attain a mechanical performance similar to other bio- (e.g., wool, tendon collagen) and synthetic polymers (e.g., polytetrafluoroethylene, polyamide 6). These promising results motivate for broader investigations on the spinning of non-equilibrium protein mixtures and suggest the use of porous gelatin fibers in textiles.
    Advanced Functional Materials 04/2014; 24(13). DOI:10.1002/adfm.201303321 · 10.44 Impact Factor

Publication Stats

7k Citations
1,176.73 Total Impact Points


  • 2003–2015
    • ETH Zurich
      • • Institute for Chemical and Bioengineering
      • • Department of Mechanical and Process Engineering
      Zürich, Zurich, Switzerland
  • 2010–2014
    • Universität Regensburg
      • Institute of Organic Chemistry
      Ratisbon, Bavaria, Germany
    • Imperial College London
      • Department of Materials
      London, ENG, United Kingdom
  • 2011
    • University of Zurich
      • Institut für Anästhesiologie
      Zürich, ZH, Switzerland
  • 2002
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland