Electrodeless direct current dielectrophoresis using reconfigurable field-shaping oil barriers

We demonstrate dielectrophoretic (DEP) potential wells using pairs of insulating oil menisci to shape the DC electric field. These oil menisci are arranged in a configuration similar to the quadrupolar electrodes, typically used in DEP, and are shown to produce similar field gradients. While the one-pair well produces a focusing effect on particles in flow, the two-pair well results in creating spatial traps against crossflows. Uncharged polystyrene particles were used to map the DEP force fields and the experimental observations were compared against the field profiles obtained by numerically solving Maxwell's equations. We demonstrate trapping of a single particle due to negative DEP against a pressure-driven crossflow. This can be easily extended to trap and hold cells and other objects against flow for a longer time. We also show the results of particle trapping experiments performed to observe the effect of adjusting the oil menisci and the gap between two pairs of menisci in a four-menisci configuration on the nature of the DEP well formed at the center. A design parameter, Θ, capturing the dimensions of the DEP energy well, is defined and simulations exploring the effects of different geometric features on Θ are presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57515/1/4572_ftp.pd

Towards an understanding of induced-charge electrokinetics at large applied voltages in concentrated solutions

The venerable theory of electrokinetic phenomena rests on the hypothesis of a dilute solution of point-like ions in quasi-equilibrium with a weakly charged surface, whose potential relative to the bulk is of order the thermal voltage (kT/e ≈ 25 mV at room temperature). In nonlinear electrokinetic phenomena, such as AC or induced-charge electro-osmosis (ACEO, ICEO) and induced-charge electrophoresis (ICEP), several V ≈ 100 kT/e are applied to polarizable surfaces in microscopic geometries, and the resulting electric fields and induced surface charges are large enough to violate the assumptions of the classical theory. In this article, we review the experimental and theoretical literatures, highlight discrepancies between theory and experiment, introduce possible modifications of the theory, and analyze their consequences. We argue that, in response to a large applied voltage, the “compact layer” and “shear plane” effectively advance into the liquid, due to the crowding of counterions. Using simple continuum models, we predict two general trends at large voltages: (i) ionic crowding against a blocking surface expands the diffuse double layer and thus decreases its differential capacitance, and (ii) a charge-induced viscosity increase near the surface reduces the electro-osmotic mobility; each trend is enhanced by dielectric saturation. The first effect is able to predict high-frequency flow reversal in ACEO pumps, while the second may explain the decay of ICEO flow with increasing salt concentration. Through several colloidal examples, such as ICEP of an uncharged metal sphere in an asymmetric electrolyte, we show that nonlinear electrokinetic phenomena are generally ion-specific. Similar theoretical issues arise in nanofluidics (due to confinement) and ionic liquids (due to the lack of solvent), so the paper concludes with a general framework of modified electrokinetic equations for finite-sized ions.National Science Foundation (U.S.) (contract DMS-0707641

An AC electroosmotic micropump for circular chromatographic applications

Flow rates of up to 50 µm s−1 have been successfully achieved in a closed-loop channel using an AC electroosmotic pump. The AC electroosmotic pump is made of an interdigitated array of unequal width electrodes located at the bottom of a channel, with an AC voltage applied between the small and the large electrodes. The flow rate was found to increase linearly with the applied voltage and to decrease linearly with the applied frequency. The pump is expected to be suitable for circular chromatography for the following reasons: the driving forces are distributed over the channel length and the pumping direction is set by the direction of the interdigitated electrodes. Pumping in a closed-loop channel can be achieved by arranging the electrode pattern in a circle. In addition the inherent working principle of AC electroosmotic pumping enables the independent optimisation of the channel height or the flow velocity

Characterization of similar Marshak waves observed at the LMJ

International audienceWe detail results of two experiments performed at the Laser Mégajoule (LMJ) facility aimed atstudying similar supersonic Marshak waves propagating in a low-density SiO2 aerogel enclosedin metallic tubes. Similar means here that these two experiments, driven by the same inputradiation temperature history, use purposely very different tubes in term of length (L = 1200μm or 2000 μm), diameter (2R = 1000 μm or 2000 μm), nature of the wall (gold or copper) andaerogel densities ( = 30 mg/cm3 or 20 mg/cm3), yet the transit time and the radiationtemperature of the fronts at the tube exit are the same for both shots. Marshak waves arecharacterized at the exit using simultaneously for the first time to our knowledge, a onedimensional soft x-ray imager from which the radiation front transit time and curvature aremeasured and also a broadband x-ray spectrometer to infer its temperature history. Theseconstraining results are then successfully compared to those from simple analytical models[A.P. Cohen et al., Phys. Rev. Research 2, 023007 (2020) and O. A. Hurricane et al., Phys.Plasmas 13, 113303 (2006)] and from the three dimensional Lagrangian radiationhydrodynamicscode TROLL to get information on x-ray energy losses. Controlledcompensation effects between the length, diameter and nature of the tubes (governing theselosses) are such that the radiation temperature drop along the tubes is eventually the same forthese two similar shots

TNFR2 blockade of regulatory T cells unleashes an antitumor immune response after hematopoietic stem-cell transplantation

Background targeting immune checkpoints that inhibit antitumor immune responses has emerged as a powerful new approach to treat cancer. We recently showed that blocking the tumor necrosis factor receptor-type 2 (tnfr2) pathway induces the complete loss of the protective function of regulatory t cells (tregs) in a model of graft-versus-host disease (gvhd) prevention that relies on treg-based cell therapy. Here, we tested the possibility of amplifying the antitumor response by targeting tnfr2 in a model of tumor relapse following hematopoietic stem-cell transplantation, a clinical situation for which the need for efficient therapeutic options is still unmet. Method we developed appropriate experimental conditions that mimic patients that relapsed from their initial hematological malignancy after hematopoietic stem-cell transplantation. This consisted of defining in allogeneic bone marrow transplantation models developed in mice, the maximum number of required tumor cells and t cells to infuse into recipient mice to develop a model of tumor relapse without inducing gvhd. We next evaluated whether anti-tnfr2 treatment could trigger alloreactivity and consequently antitumor immune response. In parallel, we also studied the differential expression of tnfr2 on t cells including treg from patients in post-transplant leukemia relapse and in patients developing gvhd. Results using experimental conditions in which neither donor t cells nor tnfr2-blocking antibody per se have any effect on tumor relapse, we observed that the coadministration of a suboptimal number of t cells and an anti-tnfr2 treatment can trigger alloreactivity and subsequently induce a significant antitumor effect. This was associated with a reduced percentage of activated cd4+ and cd8+ tregs. Importantly, human tregs over-expressed tnfr2 relative to conventional t cells in healthy donors and in patients experiencing leukemia relapse or cortico-resistant gvhd after hematopoietic stem cell transplantation. Conclusions these results highlight tnfr2 as a new target molecule for the development of immunotherapies to treat blood malignancy relapse, used either directly in grafted patients or to enhance donor lymphocyte infusion strategies. More widely, they open the door for new perspectives to amplify antitumor responses against solid cancers by directly targeting tregs through their tnfr2 expression

Nucleolin Targeting by N6L Inhibits Wnt/β-Catenin Pathway Activation in Pancreatic Ductal Adenocarcinoma

International audiencePancreatic ductal adenocarcinoma (PDAC) is a highly aggressive and resistant cancer with no available effective therapy. We have previously demonstrated that nucleolin targeting by N6L impairs tumor growth and normalizes tumor vessels in PDAC mouse models. Here, we investigated new pathways that are regulated by nucleolin in PDAC. We found that N6L and nucleolin interact with β-catenin. We found that the Wnt/β-catenin pathway is activated in PDAC and is necessary for tumor-derived 3D growth. N6L and nucleolin loss of function induced by siRNA inhibited Wnt pathway activation by preventing β-catenin stabilization in PDAC cells. N6L also inhibited the growth and the activation of the Wnt/β-catenin pathway in vivo in mice and in 3D cultures derived from MIA PaCa2 tumors. On the other hand, nucleolin overexpression increased β-catenin stabilization. In conclusion, in this study, we identified β-catenin as a new nucleolin interactor and suggest that the Wnt/β-catenin pathway could be a new target of the nucleolin antagonist N6L in PDAC