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Author: Kather, Michael × Type: Article ×

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Now showing 1 - 5 of 5
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    Enabling the measurement of particle sizes in stirred colloidal suspensions by embedding dynamic light scattering into an automated probe head
    (Amsterdam [u.a.] : Elsevier Science, 2016) de Kanter, Martinus; Meyer-Kirschner, Julian; Viell, Jörn; Mitsos, Alexander; Kather, Michael; Pich, Andrij; Janzen, Christoph
    A novel probe head design is introduced, which enables in-line monitoring of particle sizes in undiluted stirred fluids using dynamic light scattering. The novel probe head separates a small sample volume of 0.65 ml from the bulk liquid by means of an impeller. In this sample volume, particle sizing is performed using a commercially available fiber-optical backscatter probe. While conventional light scattering measurements in stirred media fail due to the superposition of Brownian’ motion and forced convection, undistorted measurements are possible with the proposed probe head. One measurement takes approximately 30 s used for liquid exchange by rotation of the impeller and for collection of scattered light. The probe head is applied for in-line monitoring of the particle growth during microgel synthesis by precipitation polymerization in a one liter laboratory reactor. The in-line measurements are compared to off-line measurements and show a good agreement.
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    Dual Stimuli-Responsive Self-Assembly Behavior of a Tailor-Made ABC-Type Amphiphilic Tri-Block Copolymer
    (Hoboken, NJ [u.a.] : Wiley, 2020) Pal, Sanjay; Kather, Michael; Banerjee, Sovan Lal; Saha, Pabitra; Pich, Andrij; Singha, Nikhil K.
    This investigation describes the synthesis of a dual stimuli-responsive, amphiphilic ABC tri-block copolymer (BCP) based on the functional monomers via RAFT polymerization. In this case, ABC-type BCP was prepared based on N-isopropylacrylamide, n-butyl acrylate, and 4-vinylpyridine in DMF solvent using cyanomethyl dodecyl trithiocarbonate as the RAFT agent and azobisisobutyronitrile as a thermal initiator in a subsequent macro-RAFT approach, respectively. The BCPs were characterized by SEC, 1H-NMR, FTIR spectroscopy, and DSC analyses. Temperature and pH-dependent properties of the smart BCP micelles in aqueous medium were investigated using dynamic light scattering. Transmission electron microscopic images were taken at cryogenic and dry conditions to study the morphology of molecular assemblies of block copolymers in an aqueous medium. The phase and topographical images were captured by atomic force microscopy to understand the assembly of block copolymers in solvents of different polarities. The morphology of BCP micelles was transformed from flower-like to spherical in the presence of solvents with different polarities (H2O or CHCl3). © 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc.
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    Synthesis of Polyampholyte Janus-like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization
    (Weinheim : Wiley-VCH, 2020) Xu, Wenjing; Rudov, Andrey; Oppermann, Alex; Wypysek, Sarah; Kather, Michael; Schroeder, Ricarda; Richtering, Walter; Potemkin, Igor I.; Wöll, Dominik; Pich, Andrij
    Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
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    Trypsin-Free Cultivation of 3D Mini-Tissues in an Adaptive Membrane Bioreactor
    (Weinheim : Wiley-VCH, 2020) Djeljadini, Suzana; Lohaus, Theresa; Gausmann, Marcel; Rauer, Sebastian; Kather, Michael; Krause, Bernd; Pich, Andrij; Möller, Martin; Wessling, Matthias
    The production of large scaffold-free tissues is a key challenge in regenerative medicine. Nowadays, temperature-responsive polymers allow intact tissue harvesting without needing proteolytic enzymes. This method is limited to tissue culture plastic with limited upscaling capacity and plain process control. Here, a thermoresponsive hollow fiber membrane bioreactor is presented to produce large scaffold-free tissues. Intact tissues, rich in cell-to-cell connections and ECM, are harvested from a poly(N-vinylcaprolactam) microgel functionalized poly(ether sulfone)/poly(vinylpyrrolidone) hollow fiber membrane by a temperature shift. The harvested 3D tissues adhere in successive cultivation and exhibit high vitality for several days. The facile adsorptive coating waives the need for extensive surface treatment. The research is anticipated to be a starting point for upscaling the production of interconnected tissues enabling new opportunities in regenerative medicine, large-scale drug screening on physiological relevant tissues, and potentially opening new chances in cell-based therapies. © 2020 The Authors. Advanced Biosystems published by Wiley-VCH GmbH
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    Synthesis of Poly(N-vinylcaprolactam)-Based Microgels by Precipitation Polymerization: Pseudo-Bulk Model for Particle Growth and Size Distribution
    (Washington, DC : ACS Publications, 2019) Janssen, Franca A.L.; Kather, Michael; Ksiazkiewicz, Agnieszka; Pich, Andrij; Mitsos, Alexander
    Particle size distribution and in particular the mean particle size are key properties of microgels, which are determined by synthesis conditions. To describe particle growth and particle size distribution over the progress of synthesis of poly(N-vinylcaprolactam)-based microgels, a pseudo-bulk model for precipitation copolymerization with cross-linking is formulated. The model is fitted and compared to experimental data from reaction calorimetry and dynamic light scattering, showing good agreement with polymerization progress, final particle size, and narrow particle size distribution. Predictions of particle growth and reaction progress for different experimental setups are compared to the corresponding experimental data, demonstrating the predictive capability and limitations of the model. The comparison to reaction calorimetry measurements shows the strength in the prediction of the overall polymerization progress. The results for the prediction of the particle radii reveal significant deviations and highlight the demand for further investigation, including additional data. Copyright © 2019 American Chemical Society.