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Exploration of Shear Stresses Induced by a Contrast Agent Bubble on the Cell Membrane

Exploration of Shear Stresses Induced by a Contrast Agent Bubble on the Cell Membrane

Alexander Doinikov 1,2 , Ayache Bouakaz 1 1 INSERM U930 CNRS ERL3106, Universite Francois Rabelais, CHU Bretonneau, 2 Boulevard Tonnelle, 37044 Tours Cedex 09, doinikov@bsu.by 2 LE STUDIUM , Institute for Advanced Studies, Orleans and Tours The subject of this study is shear stress exerted on the cell membrane by acoustic microstreaming generated by a contrast microbubble pulsating nearby a cell. This effect is presumed to play a major role in the sonoporation process. Currently, the existing model of this effect is based on an equation that has been derived for a free hemispherical bubble resting on a rigid plane. Such a model is not adequate for an encapsulated bubble such as a contrast agent microbubble. In this study, an improved theory is suggested that assumes an encapsulated bubble to be detached from the cell membrane. The new model allows one to calculate the shear stress distribution on the cell membrane and to determine the position and the magnitude of the peak shear stress at different values of the acoustic parameters. The second problem under consideration is how to apply the model for pairwise bubble-cell interactions to bubble-cell solutions which one has to deal with in experiments. An approach is proposed to evaluate the number of cells undergoing sonoporation in a bubble-cell solution. It is shown that the reaction of a bubble-cell solution to the variation of the acoustic parameters can be different from what is expected from the analysis of pairwise interactions between single bubbles and cells. In particular, the attenuation of the driving acoustic wave caused by bubbles can considerably reduce the total efficiency of sonoporation in the solution at frequencies close to the resonance frequency of bubbles of dominant size. Numerical examples for a polydisperse bubble population are presented.
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Nano-clustering of ligands on surrogate antigen presenting cells modulates T cell membrane adhesion and organization

Nano-clustering of ligands on surrogate antigen presenting cells modulates T cell membrane adhesion and organization

4 Conclusion Here we showed that the cells are able to sense a chemical con- trast on the substrate, presented in the form of dots with ele- vated levels of α-CD3 inside and PEG polymer chains outside. This sensing is at a local level – the cells reorganize the molecular distribution of TCR and ZAP-70 as well as the topography of their membrane in response. Interestingly, the cell spreading response, at the global cell scale, depends not on the local α-CD3 distribu- tion but on the overall ligand density - the cells integrate the sub- micron signal and respond to the average. We established that the repulsive polymer layer not only prevents non-specific adhe- sive interaction of the cell membrane with the glass but also acts as a reservoir for unligated diffusive TCR, with the consequence that on the patterned substrates the TCR clusters are brighter and more numerous. The diffusive TCR is however not coupled to the actin retrograde flow, evidenced by the lack of centralization seen with mobile ligands on supported lipid bilayers 49 . Interestingly, while the spreading response is strongly dependent on the quality of the PEG layer - cell spread more on less dense PEG layer and also fail to show any correspondence between ligand density and area - the membrane organization, both in terms of area of tight contact and assembly of TCR, is independent of PEG density.
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Tacrolimus diffusion across the peripheral mononuclear blood cell membrane impact of drug transporters

Tacrolimus diffusion across the peripheral mononuclear blood cell membrane impact of drug transporters

Accepted Article of two families of influx transporters (OAT and OATP) likely to be expressed in PBMC membranes [21,22] and whom influence on drug pharmacokinetics have been highlighted in several works [13,23– 26]. Neither probenecid (OAT inhibitor according to [26]) nor BSP (OATP inhibitor according to [19]) had any impact on TAC accumulation in our experiments suggesting that these transporters are not involved in TAC uptake in PBMC. Again, the choice of these inhibitors could be discussed since probenecid can also inhibit MRP efflux protein [27,28]. The identification of influx solute carrier transporters (SLC) expressed in PBMC, whom TAC might also be a substrate, remains to be established. Pharmacogenetics studies underlined the potential interest, in TAC pharmacokinetics, of other SLC transporter isoforms which could be candidates for future studies [29,30]. Besides, based on our data, we cannot fully rule out the hypothesis that the decrease of TAC accumulation in cells at 4°C would be due to a lower passive diffusion across the lipid membrane. Indeed, since TAC is a lipophilic drug (Log P≈3.3), it is expected that its concentration measured in PBMC results in the combined effect of passive and active diffusion in both directions across the cell membrane [31]. We postulated that at low temperature, only the passive diffusion phenomenon was observed. However, for some substrates, temperature can alter passive diffusion as well [31] by changing the shape of the cell and the membrane stiffness.
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Investigation of the Cell Membrane Architecture by Single-Molecule Tracking of Peptidic Toxins

Investigation of the Cell Membrane Architecture by Single-Molecule Tracking of Peptidic Toxins

The work presented in this thesis lies at the interface of physics and cell bi- ology. The starting point was previous work by Didier Casanova, who showed in his thesis “Nanoparticules d’oxyde: d´ eveloppements et applications comme sondes biologiques” that rare-earth doped nanoparticles are attractive labels for tracking single molecules due to their photostability and absence of blinking. He observed that the receptors of a peptidic bacterial toxin were confined in the cell membrane and the simple question: “What causes the confinement?”, became the motivation of the work presented here. This work benefited from many different collabora- tions. The nanoparticles were synthesized by the group of Thierry Gacoin and Jean-Pierre Boilot in the Laboratoire de Physique de la Mati`ere Condens´ee at Ecole Polytechnique and based on work that was developed during the thesis of Domitille Giaume and Genevi`eve Mialon. Michel Popoff from the Anaerobe Bacte- ria and Toxins unit at the Institut Pasteur proposed studying pore forming toxins and supplied all the toxins used in this work. The first demonstration of the anal- ysis of experimental single-molecule trajectories using the inference approach was done in the beginning of the thesis in collaboration with Jean-Baptiste Masson, Guillaume Voisinne and Massimo Vergassola at the Physics of Biological Systems Unit at Institut Pasteur [1]. All further developments regarding bias, type of po- tential and comparison with other techniques were performed in the framework of this thesis and in collaboration with Jean-Baptiste Masson. Finally, the appli- cation of an external force using a microfluidic flow was realized in collaboration with Jean-Marc Allain at the Laboratoire de m´ecanique des solides at Ecole Poly- technique.
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Correlation of cell membrane dynamics and cell motility

Correlation of cell membrane dynamics and cell motility

In order to determine which features contributed to the diversity of correlation patterns, or rather influenced the type of motility pattern adapted by any cell, factor analysis was performed on all four sub-clusters. This method has been proven efficient in describing cell shape dynamics in cancer cells [24]. This method postu- lates the existence of a small number of latent factors which explains the systematic contribution of the origi- nal features. The number of factors that should be retained is suggested by the Kaiser criterion (factors with Eigenvalues more than or equal to one should be retained) [25]. For class 1 and class 2, six factors were retained which accounted for 91.6% and 90.1% of the variance respectively. For class 3 and class 4, seven fac- tors were retained and they accounted for 88.2% and 89.0% of the variance respectively (Table 4). Factor 1 indicated the presence of high number of edge fea- tures. In particular, protrusion and retraction features extracted from initial six time points (Table 5 ). Factor 2 had predominantly cell dynamics features. The remaining factors contained edge features sampled from middle to end time points. These findings con- clude that the motility patterns are decided largely by cell membrane features observed in the initial time points.
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STUDY OF PLASMA COMPONENT EFFECT ON CELL MEMBRANE PERMEABILIZATION FOR DRUG DELIVERY APPLICATIONS

STUDY OF PLASMA COMPONENT EFFECT ON CELL MEMBRANE PERMEABILIZATION FOR DRUG DELIVERY APPLICATIONS

cells depends also on the time when the florescence molecular maker is injected into the solution. Finally, to know whether endocytosis could be involved in cell membrane permeabilization as observed for other physical methods, chlorpromazine was used as a clathrin – mediated endocytosis inhibitor. When cells were treated with this compound, the percentage of permeabilized cells decreased, suggesting that endocytosis could be partly responsible for cell membrane permeabilization.

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Correlation of cell membrane dynamics and cell motility

Correlation of cell membrane dynamics and cell motility

In this work, we propose novel morphodynamics con- cepts to quantify the relationship between whole cell movement and edge dynamics. Whole cell movement as a function of space and time and its possible influence on protrusion retraction dynamics have not been studied in detail. Heterogeneous populations exhibiting characteristic protrusion and retraction patterns have been completely exploited by us in order to identify possible correlations with motility features. Such information is helpful in determining overall motility functions of cells in collective migration. Cell membrane movements are extracted and protrusion/retraction dynamics along the cell edges at dif- ferent time points were obtained to correlate with whole cell motility features. An approach to extract such patterns from heterogeneous cell populations is presented. Our experiments show that the cells with similar kinetic pro- files display different edge movements and that features observed in initial time points have profound influence in determining the type of motility patterns as the cell adapts to its motion.
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Cell Membrane Electropermeabilization

Cell Membrane Electropermeabilization

Electrophoresis in the cell membrane Some membrane components are freely mobile in the cell membrane (glycolipids, proteins) as part of the fluidity of the cell membrane matrix. As their polar groups in the external solution are highly charged, as in the case of glycosylated derivatives, a force is present when the external field is present. An electrophoretically driven lateral movement is triggered when the external field pulse is delivered. As a result of this lateral movement along the electric field lines, an accumulation of the affected molecules towards one pole of the cell will result. 29–31 This affects the distribution of the molecules in the membrane matrix and brings the formation of charged domains. Noncovalently bound components of the cell wall are affected. This is obvious in the case of the outer membrane. The drift velocity is under the control of the applied field. The length of the displacement depends on the pulse duration and on the membrane and wall viscosities (that are dif ficult to evaluate).
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Water nano-diffusion through the Nafion fuel cell membrane

Water nano-diffusion through the Nafion fuel cell membrane

120 third cycle up to p max = 50 kbar, and then was reduced stepwise until it reached the final value of p = 1 bar. In a last step, membrane was subsequently hy- drated and 7 hydration levels were defined from the number of water molecules around a sulfonate group (λ), λ = 3, 5, 7, 9, 11, 14.5, 22.5. All hydrated mem- branes were relaxed from 21 MD steps scheme by using similar temperature and

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The Matrix protein M1 from influenza C virus induces tubular membrane invaginations in an in vitro cell membrane model

The Matrix protein M1 from influenza C virus induces tubular membrane invaginations in an in vitro cell membrane model

David Saletti 1,2,* , Jens Radzimanowski 3,* , Gregory Effantin 3 , Daniel Midtvedt 4 , Stéphanie Mangenot 1,2 , Winfried Weissenhorn 3 , Patricia Bassereau 1,2 & Marta Bally 1,2,4 Matrix proteins from enveloped viruses play an important role in budding and stabilizing virus particles. In order to assess the role of the matrix protein M1 from influenza C virus (M1-C) in plasma membrane deformation, we have combined structural and in vitro reconstitution experiments with model membranes. We present the crystal structure of the N-terminal domain of M1-C and show by Small Angle X-Ray Scattering analysis that full-length M1-C folds into an elongated structure that associates laterally into ring-like or filamentous polymers. Using negatively charged giant unilamellar vesicles (GUVs), we demonstrate that M1-C full-length binds to and induces inward budding of membrane tubules with diameters that resemble the diameter of viruses. Membrane tubule formation requires the C-terminal domain of M1-C, corroborating its essential role for M1-C polymerization. Our results indicate that M1-C assembly on membranes constitutes the driving force for budding and suggest that M1-C plays a key role in facilitating viral egress.
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Asymmetric Hybrid Polymer-Lipid Giant Vesicles as Cell Membrane Mimics

Asymmetric Hybrid Polymer-Lipid Giant Vesicles as Cell Membrane Mimics

to our knowledge the association of lipids and polymers has never been investigated so far to develop entirely asymmetric membranes. We herein introduce a versatile method to produce asym- metric giant hybrid polymer–lipid unilamellar vesicles (aGHUV). In the present work, the vesicles are constituted of an inner leaflet of poly(butadiene)-b-poly(ethylene oxide) copoly mer and outer leaflet of lipid type via an emulsion-centrif- ugation method. We also show how we can prepare the reverse structures with the lipid leaflet facing the interior of the vesicle. We demonstrate the asymmetric character of the membrane and follow its stability by fluorescence quenching measurements. In addition, we further investigate lipid dynamic responses such as lateral and transverse diffusion (flip-flop). We thus provide an efficient method to afford aGHUV that exhibit close resem- blance to the architecture and membrane diffusion dynamics of biological cells. This system could serve as a tool and scaffold to better understand the importance of asymmetry and how it is maintained in biological systems.
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Biophysical Insight on the Membrane Insertion of an Arginine-Rich Cell-Penetrating Peptide

Biophysical Insight on the Membrane Insertion of an Arginine-Rich Cell-Penetrating Peptide

As plasma membranes are mainly composed of lipids, the peptide–lipid interactions are crucial for the initial binding of CPPs prior to internalization [ 6 – 8 ]. Polar residues, and especially arginines (Arg), interact with high affinity through their guanidinium group to negatively-charged lipids and lipid phosphate groups, and thus enhance the binding of Arg-rich peptides to membranes [ 9 , 10 ]. In parallel, hydrophobic residues such as tryptophans (Trp) have been shown to establish hydrophobic contacts with lipid acyl chains and play a role on the insertion of MAPs into the membrane [ 11 , 12 ]. Structural plasticity of these peptides during membrane contact may then bring sufficient peptide charge neutralization (e.g., through electrostatic interactions) to help the peptides translocate. However, it has also been suggested that highly hydrophobic residues might prevent peptide internalization, with the peptide trapped in the membrane due to these strong interactions [ 7 , 13 ]. Although CPPs have been broadly reported to have an enhanced affinity for negatively-charged membranes, peptide interaction and insertion in zwitterionic membranes is not fully described. A large amount of studies is performed on anionic systems (negatively-charged membranes) due to the establishment of important electrostatic interactions between the CPP and the cell membrane that are important for their internalization. While lipids in the outer eukaryotic cell membrane leaflet are mainly zwitterionic, with less than 2% anionic lipids, the cell membrane possesses an anionic character due to the glycosaminoglycans. Therefore, study of CPP interaction with zwitterionic lipids is important and most of the studies, to the best of our knowledge, mainly use zwitterionic systems as a comparison model to anionic ones.
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Numerical analysis of water transport through the membrane electrolyte assembly of a polymer exchange membrane fuel cell

Numerical analysis of water transport through the membrane electrolyte assembly of a polymer exchange membrane fuel cell

Keywords: proton exchange membrane fuel cell, membrane electrolyte assembly, water transport, fuel cell model, net water transport coefficient 1 Introduction Successful water management in the proton exchange mem- brane 共PEM兲 fuel cell plays a critical role in terms of reducing the mass transport limitation. Too much water causes flooding in the cathode region, which inhibits oxygen from diffusing to the reac- tion sites of the cathode catalyst layer of a PEM fuel cell. On the other hand, too little water makes the membrane dry out and re- sults in lower proton conductivity because the membrane’s trans- port properties are highly dependent on water content. One com- mon phenomenon occurring in a PEM fuel cell is that cell performance is low under low humidity conditions. Cell perfor- mance gradually improves with an increase in humidity. Once the humidity and liquid water saturation reach certain values, cell performance cannot be improved anymore. Instead, further in- creases in humidity and liquid water saturation will reduce cell performance.
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Numerical predictions of transport phenomena in a proton exchange membrane fuel cell

Numerical predictions of transport phenomena in a proton exchange membrane fuel cell

The hybrid and 3D methodologies were compared under the same average current density and temperature conditions. For mass transfer calculations, precisely the same source and/or sink terms of reactants/products are prescribed, based on Eqs. 共7兲–共9兲. The electro-osmotic drag coefficient and diffusion coefficient are indirectly related to the water vapor mole fraction distribution at the interface between the electrodes and the membrane. As the local membrane current density distribution is presumed constant for the hybrid model, a higher water vapor mole fraction is pre- dicted for this model at the anode interface.
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A general model for air-side proton exchange membrane fuel cell contamination

A general model for air-side proton exchange membrane fuel cell contamination

components, Na, Ca, and S from membranes, and Si from gaskets and cooling fluid. It has been demonstrated that even trace amounts of impurities in the fuel or air stream or the fuel cell system components can severely poison the anode, membrane, and cathode, particularly at low-temperature operation. The contaminants can: strongly or irre- versibly adsorb on the catalyst surface, blocking the reaction sites; enter the membrane, reducing proton conductivity; and change the hydrophobicity/hydrophilicity of the catalyst layer interface,

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Regulating TRAIL receptor-induced cell death at the membrane : a deadly discussion.

Regulating TRAIL receptor-induced cell death at the membrane : a deadly discussion.

pro- caspase-8 cleavage [161]. Caspase-8 is maintained within the DISC and cannot be released to the cytosol because the gen- eration of the p20 subunit of caspase-8 cannot occur in the presence of c-FLIP L . Active caspase-8 therefore remains sequestered within the DISC, where it can still induce the cleavage of a number of substrates including c-FLIP, RIP and as yet to be discovered unidentified proteins, recruited within the DISC or in close proximity [130, 161]. While all isoforms of c-FLIP efficiently inhibit Fas ligand- and TRAIL-induced cell death, subcellular confinement of active caspase-8 is only asscociated with c- FLIP L so far. The find- ing that c-FLIP L induces caspase-8 activation within the DISC represents another degree of control regarding the regulation of TRAIL signaling. RIP cleavage at the DISC level in these circumstances could play a role in controlling TRAIL-induced necrosis [162], NF-kB activation [163-165] or other non-apoptotic functions. The possibility of using of RNA interference to inhibit cFLIP to circumvent TRAIL
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A review of accelerated conditioning for a polymer electrolyte membrane fuel cell

A review of accelerated conditioning for a polymer electrolyte membrane fuel cell

voltage stops increasing. At this point, the break-in procedure is thought to be complete and the cell is broken in and ready to oper- ate under normal use conditions. Depending on the MEAs, this process can take hours and even days to complete, if no special measures are taken. With today’s cell/stack technology, a break-in period of 24 h is not uncommon. This not only consumes a con- siderable amount of hydrogen fuel, but also takes up significant time, resulting in a high cost for operating the fuel cell. Thus, MEA conditioning and testing techniques are required to significantly reduce the break-in period [2] . Ideally, not only would one like to have the highest possible power density after the break-in pro- cedure, but one would also like to minimize the time to reach this point [3] . The US Department of Energy (DOE) has proposed research projects in an attempt to either condition the MEA before stack assembly and thereby significantly reduce the process dura- tion, or develop novel design concepts that eliminate the need for conditioning steps [4] .
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Dynamic Remodeling of membrane composition drives cell cycle through primary cilia excision

Dynamic Remodeling of membrane composition drives cell cycle through primary cilia excision

surface. To determine mid-point of G 0 -G 1 transit, 10-hour time series of nuclear Venus- p27K − and mCherry-hCdt1(30/120) fluorescence signals were subtracted with background signals, divided to obtain Venus-p27K − /mCherry-hCdt1(30/120) signal ratio values, and further normalized with basal ratio values at T=0. For 8xGBS-GFP Gli activity reporter measurements, average nuclear GFP signal in best-focused z-plane was measured for each cell under specified conditions, since: (1) expressed GFP show nuclear enrichment in NIH/3T3 cells (2) high cell densities preclude ability to measure whole-cell signals. It is of note that we occasionally observed primary cilia of fibroblasts extending from the ventral cell surface and adhering to underlying substratum. Subsequent cellular movements could result in mechanical pulling and breaking of primary cilia (Figure S1K). Care was taken to exclude instances of passive cilia breaking throughout all experiments.
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Using silica nanoparticles for modifying sulfonated poly(phthalazinone ether ketone) membrane for direct methanol fuel cell : A significant improvement on cell performance

Using silica nanoparticles for modifying sulfonated poly(phthalazinone ether ketone) membrane for direct methanol fuel cell : A significant improvement on cell performance

silica electrolyte for DMFC. The cell could be operated at a relatively high temperature of 140 ◦ C to show improved cell performance. In our previous work [23,24] colloidal sil- ica nanoparticles showed great compatibility with organic polymers, and the particles could be directly added into the polymer solutions for casting membranes. No alternation in the membrane preparation process is needed with the addi- tion of silica nanoparticles. Therefore, silica nanoparticles are utilized for preparation of organic-inorganic nanocom- posite proton exchange membranes in this work. Sulfonated poly(phthalazinone ether ketone) (sPPEK) with a high con- tent of sulfonic acid groups is utilized as the proton conduct- ing material [2] . Although possessing high ionic conductivity, the pristine polymer did not exhibit satisfactory performance owing to its high methanol and water affinity. The prop- erties of the prepared nanocomposite PEMs and the single cell performance are examined and discussed. A significant improvement in the cell performance is observed with using the sPPEK-silica nanocomposite PEMs.
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Proton exchange membrane fuel cell remaining useful life prognostics considering degradation recovery phenomena

Proton exchange membrane fuel cell remaining useful life prognostics considering degradation recovery phenomena

Dacheng Zhang 1 , Catherine Cadet 1 , Nadia Yousfi-Steiner 2,3,4 and Christophe B ´erenguer 1 Abstract The present work explores the challenges of handling the recovery phenomena in the degradation behavior of the Proton Exchange Membrane Fuel Cells, from the perspective of the prognostics. An adaptive Prognostics and Health Management approach with additional knowledge, such as the Electrochemical Impedance Spectroscopy, from the State of Health characterization, is applied on two fuel cell stacks under both stationary and quasi-dynamic operating regimes. Some improvements in the prognostic performance are obtained in the view of the Remaining Useful Life predictions by comparing with a classical Particle Filtering-based prognostic approach.
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