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See detailGlutaraldehyde - A Subtle Tool in the Investigation of Healthy and Pathologic Red Blood Cells
Abay, Asena; Simionato, Greta; Chachanidze, Revaz et al

in FRONTIERS IN PHYSIOLOGY (2019), 10

Glutaraldehyde is a well-known substance used in biomedical research to fix cells. Since hemolytic anemias are often associated with red blood cell shape changes deviating from the biconcave disk shape ... [more ▼]

Glutaraldehyde is a well-known substance used in biomedical research to fix cells. Since hemolytic anemias are often associated with red blood cell shape changes deviating from the biconcave disk shape, conservation of these shapes for imaging in general and 3D-imaging in particular like confocal microscopy, scanning electron microscopy or scanning probe microscopy is a common desire. Along with the fixation comes an increase in the stiffness of the cells. In the context of red blood cells this increased rigidity is often used to mimic malaria infected red blood cells because they are also stiffer than healthy red blood cells. However, the use of glutaraldehyde is associated with numerous pitfalls: (i) while the increase in rigidity by an application of increasing concentrations of glutaraldehyde is an analog process, the fixation is a rather digital event (all or none); (ii) addition of glutaraldehyde massively changes osmolality in a concentration dependent manner and hence cell shapes can be distorted; (iii) glutaraldehyde batches differ in their properties especially in the ratio of monomers and polymers (iv) handling pitfalls, like inducing shear artifacts of red blood cell shapes or cell density changes that needs to be considered, e.g., when working with cells in flow; (v) staining glutaraldehyde treated red blood cells need different approaches compared to living cells, for instance, because glutaraldehyde itself induces a strong fluorescence. Within this paper we provide documentation about the subtle use of glutaraldehyde on healthy and pathologic red blood cells and how to deal with or circumvent pitfalls. [less ▲]

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See detailMacro- and Microrheological Properties of Mucus Surrogates in Comparison to Native Intestinal and Pulmonary Mucus
Huck, Benedikt C.; Hartwig, Olga; Biehl, Alexander et al

in BIOMACROMOLECULES (2019), 20(9), 3504-3512

Mucus is a complex hydrogel that acts as a protective barrier in various parts of the human body. Both composition and structural properties play a crucial role in maintaining barrier properties while ... [more ▼]

Mucus is a complex hydrogel that acts as a protective barrier in various parts of the human body. Both composition and structural properties play a crucial role in maintaining barrier properties while dictating diffusion of molecules and (nano)materials. In this study, we compare previously described mucus surrogates with the native human airway and pig intestinal mucus. Oscillatory shear rheology was applied to characterize mucus on the bulk macrorheological level, revealing that the artificial airway surrogate deviates from the elastic-dominant behavior of native mucus samples. We circumvented this limitation through the addition of a cross-linking polymer to the surrogate adjusting the rheological properties closer to those of native mucus. Applying particle tracking microrheology, we further demonstrated that the mechanical properties at the microscale differ significantly between artificial and native mucus. We conclude that proper characterization of mucus and its surrogates is vital for a reliable investigation of nanoparticle-based mucosal drug delivery. [less ▲]

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See detailSwimming of bacterium Bacillus subtilis with multiple bundles of flagella
Najafi, Javad; Altegoer, Florian; Bange, Gert et al

in SOFT MATTER (2019), 15(48), 10029-10034

We characterize the bundle properties for three different strains of B. subtilis bacteria with various numbers of flagella. Our study reveals that, surprisingly, the number of bundles is independent of ... [more ▼]

We characterize the bundle properties for three different strains of B. subtilis bacteria with various numbers of flagella. Our study reveals that, surprisingly, the number of bundles is independent of the number of flagella, and the formation of three bundles is always the most frequent case. We assume that this relates to the fact that different mutants have the same body length. There is no significant difference between the bundle width and length for distinct strains, but the projected angle between the bundles increases with the flagellar number. Furthermore, we find that the swimming speed is anti-correlated with the projected angle between the bundles, and the wobbling angle between the swimming direction and cell body increases with the number of flagella. Our findings highlight the impact of geometrical properties of bacteria such as body length and bundle configuration on their motility. [less ▲]

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See detailThe Evolution of Erythrocytes Becoming Red in Respect to Fluorescence
Hertz, Laura; Ruppenthal, Sandra; Simionato, Greta et al

in FRONTIERS IN PHYSIOLOGY (2019), 10

Very young red blood cells, namely reticulocytes, can be quite easily recognized and labeled by cluster of differentiation antibodies (CD71 transferrin receptor) or by staining remnant RNA with thiazol ... [more ▼]

Very young red blood cells, namely reticulocytes, can be quite easily recognized and labeled by cluster of differentiation antibodies (CD71 transferrin receptor) or by staining remnant RNA with thiazol orange. In contrast, age specific erythrocyte labeling is more difficult in later periods of their life time. While erythrocytes contain band 4.1 protein a molecular clock, so far it has not been possible to read this clock on individual cells. One concept to track erythrocytes during their life time is to mark them when they are young, either directly in vivo or ex vivo followed by a transfusion. Several methods like biotinylation, use of isotopes or fluorescent labeling have proved to be useful experimental approaches but also have several inherent disadvantages. Genetic engineering of mice provides additional options to express fluorescent proteins in erythrocytes. To allow co-staining with popular green fluorescent dyes like Fluo-4 or other fluorescein-based dyes, we bred a mouse line expressing a tandem red fluorescent protein (tdRFP). Within this Brief Research Report, we provide the initial characterisation of this mouse line and show application examples ranging from transfusion experiments and intravital microscopy to multicolour flow cytometry and confocal imaging. We provide a versatile new tool for erythrocyte research and discuss a range of experimental opportunities to study membrane processes and other aspects of erythrocyte development and aging with help of these animals. [less ▲]

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See detailStatistics of Colloidal Suspensions Stirred by Microswimmers
Ortlieb, Levke; Rafai, Salima; Peyla, Philippe et al

in Physical Review Letters (2019), 122(14),

We present a statistical analysis of the experimental trajectories of colloids in a dilute suspension of the green algae Chlamydomonas reinhardtii. The measured probability density function (pdf) of the ... [more ▼]

We present a statistical analysis of the experimental trajectories of colloids in a dilute suspension of the green algae Chlamydomonas reinhardtii. The measured probability density function (pdf) of the displacements of colloids covers 7 orders of magnitude. The pdfs are characterized by non-Gaussian tails for intermediate time intervals, but nevertheless they collapse when scaled with their standard deviation. This diffusive scaling breaks down for longer time intervals and the pdf becomes Gaussian. However, the mean squared displacements of tracer positions are linear over the complete measurement time interval. Experiments are performed for various tracer diameters, swimmer concentrations, and mean swimmer velocities. This allows a rigorous comparison with several theoretical models. We can exclude a description based on an effective temperature and other mean field approaches that describe the irregular motion as a sum of the fluctuating far field of many microswimmers. The data are best described by the microscopic model by J.-L. Thiffeault, Distribution of particle displacements due to swimming microorganisms, Phys. Rev. E 92, 023023 (2015). [less ▲]

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See detailVesicle dynamics in confined steady and harmonically modulated Poiseuille flows
Boujja, Z.; Misbah, C.; Ez-Zahraouy, H. et al

in Physics Reviews (2018)

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See detailNumerical–experimental observation of shape bistability of red blood cells flowing in a microchannel
Guckenberger, A.; Kihm, A.; John, T. et al

in European Physical Journal E. Soft Matter (2018)

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See detailEffect of spectrin network elasticity on the shapes of erythrocyte doublets
Hoore, M.; Yaya, F.; Podgorski, T. et al

in European Physical Journal E. Soft Matter (2018)

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See detailDetermination of the rheological properties of Matrigel for optimum seeding conditions in microfluidic cell cultures
Kane, K. I. W.; Moreno, E. Lucumi; Lehr, Claudius Moritz UL et al

in AIP ADVANCES (2018), 8(12),

Hydrogels are increasingly used as a surrogate extracellular matrix in three-dimensional cell culture systems, including microfluidic cell culture. Matrigel is a hydrogel of natural origin widely used in ... [more ▼]

Hydrogels are increasingly used as a surrogate extracellular matrix in three-dimensional cell culture systems, including microfluidic cell culture. Matrigel is a hydrogel of natural origin widely used in cell culture, particularly in the culture of stem cell-derived cell lines. The use of Matrigel as a surrogate extracellular matrix in microfluidic systems is challenging due to its biochemical, biophysical, and biomechanical properties. Therefore, understanding and characterising these properties is a prerequisite for optimal use of Matrigel in microfluidic systems. We used rheological measurements and particle image velocimetry to characterise the fluid flow dynamics of liquefied Matrigel during loading into a three-dimensional microfluidic cell culture device. Using fluorescence microscopy and fluorescent beads for particle image velocimetry measurements (velocity profiles) in combination with classical rheological measurements of Matrigel (viscosity versus shear rate), we characterised the shear rates experienced by cells in a microfluidic device for three-dimensional cell culture. This study provides a better understanding of the mechanical stress experienced by cells, during seeding of a mixture of hydrogel and cells, into three-dimensional microfluidic cell culture devices. (C) 2018 Author(s). [less ▲]

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See detailFlagellar number governs bacterial spreading and transport efficiency
Najafi, Javad; Shaebani, Mohammad Reza; John, Thomas et al

in SCIENCE ADVANCES (2018), 4(9),

Peritrichous bacteria synchronize and bundle their flagella to actively swim, while disruption of the bundle leads to a slow motility phase with a weak propulsion. It is still not known whether the number ... [more ▼]

Peritrichous bacteria synchronize and bundle their flagella to actively swim, while disruption of the bundle leads to a slow motility phase with a weak propulsion. It is still not known whether the number of flagella represents an evolutionary adaptation toward optimizing bacterial navigation. We study the swimming dynamics of differentially flagellated Bacillus subtilis strains in a quasi-two-dimensional system. We find that decreasing the number of flagella N-f reduces the average turning angle between two successive run phases and enhances the run time and the directional persistence of the run phase. As a result, having fewer flagella is beneficial for long-distance transport and fast spreading while having a lot of flagella is advantageous for the processes that require a slower spreading, such as biofilm formation. We develop a two-state random walk model that incorporates spontaneous switchings between the states and yields exact analytical expressions for transport properties, in remarkable agreement with experiments. The results of numerical simulations based on our two-state model suggest that the efficiency of searching and exploring the environment is optimized at intermediate values of N-f. The optimal choice of N-f, for which the search time is minimized, decreases with increasing the size of the environment in which the bacteria swim. [less ▲]

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See detailAntimargination of microparticles and platelets in the vicinity of branching vessels
Bächer, C.; Kihm, A.; Schrack, L. et al

in Biophysical Journal (2018)

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See detailClassification of red blood cell shapes in flow using outlier tolerant machine learning
Kihm, A.; Kaestner, L.; Wagner, Christian UL et al

in PLoS Computational Biology (2018)

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See detailDextran adsorption onto red blood cells revisited: single cell quantification by laser tweezers combined with microfluidics
Lee, K.; Shirshin, E.; Rovnyagina, N. et al

in Biomedical Optics Express (2018)

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See detailIn-phase and anti-phase flagellar synchronization by waveform compliance and basal coupling
Klindt, Gary; Ruloff, Christian; Wagner, Christian UL et al

in New Journal of Physics (2017)

Cilia and flagella exhibit regular bending waves that perform mechanical work on the surrounding fluid, to propel cellular swimmers and pump fluids inside organisms. Here, we quantify a force-velocity ... [more ▼]

Cilia and flagella exhibit regular bending waves that perform mechanical work on the surrounding fluid, to propel cellular swimmers and pump fluids inside organisms. Here, we quantify a force-velocity relationship of the beating flagellum, by exposing flagellated Chlamydomonas cells to controlled microfluidic flows. A simple theory of flagellar limit-cycle oscillations, calibrated by measurements in the absence of flow, reproduces this relationship quantitatively. We derive a link between the energy efficiency of the flagellar beat and its ability to synchronize to oscillatory flows. [less ▲]

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See detail3D tomography of cells in micro-channels
Wagner, Christian UL; Quint, Serket; Guckenberger, A. et al

in Applied Physics Letters (2017)

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See detailThe buckling instability of aggregating red blood cells
Flomann, Daniel; Othmane, Aouane; Kaestner, Lars et al

in Scientific Reports (2017)

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See detailA foam model highlights the differences of the macro- and microrheology of respiratory horse mucus
Wagner, Christian UL; Gross, Andreas; Schaefer, Ulrich F. et al

in Journal of the Mechanical Behavior of Biomedical Materials (2017)

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See detailA Model for the Transient Subdiffusive Behavior of Particles in Mucus
Ernst, Matthias; John, Thomas; Guenther, Marco et al

in Biophysical Journal (2017)

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