75 research outputs found
Directed collective motion of bacteria under channel confinement
Dense suspensions of swimming bacteria are known to exhibit collective behaviour arising from the
interplay of steric and hydrodynamic interactions. Unconfined suspensions exhibit transient,
recurring vortices and jets, whereas those confined in circular domains may exhibit order in the form
of a spiral vortex. Here we show that confinement into a long and narrow macroscopic ‘racetrack’
geometry stabilises bacterial motion to form a steady unidirectional circulation. This motion is
reproduced in simulations of discrete swimmers that reveal the crucial role that bacteria-driven fluid
flows play in the dynamics. In particular, cells close to the channel wall produce strong flows which
advect cells in the bulk against their swimming direction.Weexamine in detail the transition from a
disordered state to persistent directed motion as a function of the channel width, and show that the
width at the crossover point is comparable to the typical correlation length of swirls seen in the
unbounded system. Our results shed light on the mechanisms driving the collective behaviour of
bacteria and other active matter systems, and stress the importance of the ubiquitous boundaries
found in natural habitats.This is the final published version. It first appeared at http://dx.doi.org/10.1088/1367-2630/18/7/075002
Driven Topological Transitions in Active Nematic Films
The topological properties of many materials are central to their behavior,
with the dynamics of topological defects being particularly important to
intrinsically out-of-equilibrium, active materials. In this paper, local
manipulation of the ordering, dynamics, and topological properties of
microtubule-based extensile active nematic films is demonstrated in a joint
experimental and simulation study. Hydrodynamic stresses created by
magnetically actuated rotation of disk-shaped colloids in proximity to the
films compete with internal stresses in the active nematic, enabling local
control of the motion of the +1/2 charge topological defects that are intrinsic
to spontaneously turbulent active films. Sufficiently large applied stresses
drive the formation of +1 charge topological vortices in the director field
through the merger of two +1/2 defects. The directed motion of the defects is
accompanied by ordering of the vorticity and velocity of the active flows
within the film that is qualitatively unlike the response of passive viscous
films. Many features of the film's response to the disk are captured by Lattice
Boltzmann simulations, leading to insight into the anomalous viscoelastic
nature of the active nematic. The topological vortex formation is accompanied
by a rheological instability in the film that leads to significant increase in
the flow velocities. Comparison of the velocity profile in vicinity of the
vortex with fluid-dynamics calculations provides an estimate of film viscosity
Topological sound in active-liquid metamaterials
Liquids composed of self-propelled particles have been experimentally
realized using molecular, colloidal, or macroscopic constituents. These active
liquids can flow spontaneously even in the absence of an external drive. Unlike
spontaneous active flow, the propagation of density waves in confined active
liquids is not well explored. Here, we exploit a mapping between density waves
on top of a chiral flow and electrons in a synthetic gauge field to lay out
design principles for artificial structures termed topological active
metamaterials. We design metamaterials that break time-reversal symmetry using
lattices composed of annular channels filled with a spontaneously flowing
active liquid. Such active metamaterials support topologically protected sound
modes that propagate unidirectionally, without backscattering, along either
sample edges or domain walls and despite overdamped particle dynamics. Our work
illustrates how parity-symmetry breaking in metamaterial structure combined
with microscopic irreversibility of active matter leads to novel
functionalities that cannot be achieved using only passive materials
Functional Evidence of Multidrug Resistance Transporters (MDR) in Rodent Olfactory Epithelium
Background: P-glycoprotein (Pgp) and multidrug resistance-associated protein (MRP1) are membrane transporter proteins which function as efflux pumps at cell membranes and are considered to exert a protective function against the entry of xenobiotics. While evidence for Pgp and MRP transporter activity is reported for olfactory tissue, their possible interaction and participation in the olfactory response has not been investigated. Principal Findings: Functional activity of putative MDR transporters was assessed by means of the fluorometric calcein acetoxymethyl ester (calcein-AM) accumulation assay on acute rat and mouse olfactory tissue slices. Calcein-AM uptake was measured as fluorescence intensity changes in the presence of Pgp or MRP specific inhibitors. Epifluorescence microscopy measured time course analysis in the olfactory epithelium revealed significant inhibitor-dependent calcein uptake in the presence of each of the selected inhibitors. Furthermore, intracellular calcein accumulation in olfactory receptor neurons was also significantly increased in the presence of either one of the Pgp or MRP inhibitors. The presence of Pgp or MRP1 encoding genes in the olfactory mucosa of rat and mouse was confirmed by RT-PCR with appropriate pairs of speciesspecific primers. Both transporters were expressed in both newborn and adult olfactory mucosa of both species. To assess a possible involvement of MDR transporters in the olfactory response, we examined the electrophysiological response to odorants in the presence of the selected MDR inhibitors by recording electroolfactograms (EOG). In both animal species
ATP-binding cassette (ABC) transporters in normal and pathological lung
ATP-binding cassette (ABC) transporters are a family of transmembrane proteins that can transport a wide variety of substrates across biological membranes in an energy-dependent manner. Many ABC transporters such as P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP) are highly expressed in bronchial epithelium. This review aims to give new insights in the possible functions of ABC molecules in the lung in view of their expression in different cell types. Furthermore, their role in protection against noxious compounds, e.g. air pollutants and cigarette smoke components, will be discussed as well as the (mal)function in normal and pathological lung. Several pulmonary drugs are substrates for ABC transporters and therefore, the delivery of these drugs to the site of action may be highly dependent on the presence and activity of many ABC transporters in several cell types. Three ABC transporters are known to play an important role in lung functioning. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene can cause cystic fibrosis, and mutations in ABCA1 and ABCA3 are responsible for respectively Tangier disease and fatal surfactant deficiency. The role of altered function of ABC transporters in highly prevalent pulmonary diseases such as asthma or chronic obstructive pulmonary disease (COPD) have hardly been investigated so far. We especially focused on polymorphisms, knock-out mice models and in vitro results of pulmonary research. Insight in the function of ABC transporters in the lung may open new ways to facilitate treatment of lung diseases
A comprehensive overview of radioguided surgery using gamma detection probe technology
The concept of radioguided surgery, which was first developed some 60 years ago, involves the use of a radiation detection probe system for the intraoperative detection of radionuclides. The use of gamma detection probe technology in radioguided surgery has tremendously expanded and has evolved into what is now considered an established discipline within the practice of surgery, revolutionizing the surgical management of many malignancies, including breast cancer, melanoma, and colorectal cancer, as well as the surgical management of parathyroid disease. The impact of radioguided surgery on the surgical management of cancer patients includes providing vital and real-time information to the surgeon regarding the location and extent of disease, as well as regarding the assessment of surgical resection margins. Additionally, it has allowed the surgeon to minimize the surgical invasiveness of many diagnostic and therapeutic procedures, while still maintaining maximum benefit to the cancer patient. In the current review, we have attempted to comprehensively evaluate the history, technical aspects, and clinical applications of radioguided surgery using gamma detection probe technology
The pore structure of Clostridium perfringens epsilon toxin
Epsilon toxin (Etx), a potent pore forming toxin (PFT) produced by Clostridium perfringens, is responsible for the pathogenesis of enterotoxaemia of ruminants and has been suggested to play a role in multiple sclerosis in humans. Etx is a member of the aerolysin family of β-PFTs (aβ-PFTs). While the Etx soluble monomer structure was solved in 2004, Etx pore structure has remained elusive due to the difficulty of isolating the pore complex. Here we show the cryo-electron microscopy structure of Etx pore assembled on the membrane of susceptible cells. The pore structure explains important mutant phenotypes and suggests that the double β-barrel, a common feature of the aβ-PFTs, may be an important structural element in driving efficient pore formation. These insights provide the framework for the development of novel therapeutics to prevent human and animal infections, and are relevant for nano-biotechnology applications
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Directed collective motion of bacteria under channel confinement
Dense suspensions of swimming bacteria are known to exhibit collective behaviour arising from the
interplay of steric and hydrodynamic interactions. Unconfined suspensions exhibit transient,
recurring vortices and jets, whereas those confined in circular domains may exhibit order in the form
of a spiral vortex. Here we show that confinement into a long and narrow macroscopic ‘racetrack’
geometry stabilises bacterial motion to form a steady unidirectional circulation. This motion is
reproduced in simulations of discrete swimmers that reveal the crucial role that bacteria-driven fluid
flows play in the dynamics. In particular, cells close to the channel wall produce strong flows which
advect cells in the bulk against their swimming direction.Weexamine in detail the transition from a
disordered state to persistent directed motion as a function of the channel width, and show that the
width at the crossover point is comparable to the typical correlation length of swirls seen in the
unbounded system. Our results shed light on the mechanisms driving the collective behaviour of
bacteria and other active matter systems, and stress the importance of the ubiquitous boundaries
found in natural habitats.This is the final published version. It first appeared at http://dx.doi.org/10.1088/1367-2630/18/7/075002
Magneto-optical Faraday imaging with an apertureless scanning near field optical microscope
We have developed an apertureless Scanning Near field Optical Microscope (SNOM) in
transmission, devoted to near field magneto-optics. Our apertureless SNOM combines an inverted
optical microscope, which has been adapted to Faraday effect imaging, with a commercial
stand-alone Scanning Probe Microscope, used in Atomic Force Microscope (AFM) mode. Two
different probes are validated as apertureless SNOM tips: a home-made etched tungsten wire and
a commercial AFM silicon probe. We present and analyze preliminary images of the doMayn
structure in iron garnets. They indicate a SNOM resolution clearly in the sub-micrometric range.
Besides, the near field magneto-optical image presents some unexpected features, not revealed in
far field images
Near field optical microscopy and spectroscopy with STM and AFM probes
This article deals with a new generation of scanning near field optical microscopes (SNOM), called apertureless SNOM, based on metallic, semi-conductive or dielectric probes. The classification of the apertureless probe among the usual SNOM probes is discussed in the first part. Then, we present the different apertureless SNOM configurations that we develop, with various commercial AFM and home-made tungsten tips, and several illumination and collection modes. Finally, after a preliminary result in near field imaging, we propose a promising application of such microscopes dedicated to the near field fluorescence spectroscopy
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