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Teubl BJ, Stojkovic B, Docter D, Pritz E, Leitinger G, Poberaj I, Prassl R, Stauber RH, Fröhlich E, Khinast JG, Roblegg E. The effect of saliva on the fate of nanoparticles. Clin Oral Investig 2018; 22:929-940. [PMID: 28691145 PMCID: PMC5820401 DOI: 10.1007/s00784-017-2172-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Accepted: 06/26/2017] [Indexed: 11/01/2022]
Abstract
OBJECTIVES The design of nanocarriers for local drug administration to the lining mucosa requires a sound knowledge of how nanoparticles (NPs) interact with saliva. This contact determines whether NPs agglomerate and become immobile due to size- and interaction-filtering effects or adsorb on the cell surface and are internalized by epithelial cells. The aim of this study was to examine the behavior of NPs in saliva considering physicochemical NP properties. MATERIALS AND METHODS The salivary pore-size distribution was determined, and the viscosity of the fluid inside of the pores was studied with optical tweezers. Distinct functionalized NPs (20 and 200 nm) were dispersed in saliva and salivary buffers and characterized, and surface-bound MUC5B and MUC7 were analyzed by 1D electrophoresis and immunoblotting. NP mobility was recorded, and cellular uptake studies were performed with TR146 cells. RESULTS The mode diameter of the salivary mesh pores is 0.7 μm with a peak width of 1.9 μm, and pores are filled with a low-viscosity fluid. The physicochemical properties of the NPs affected the colloidal stability and mobility: compared with non-functionalized particles, which did not agglomerate and showed a cellular uptake rate of 2.8%, functionalized particles were immobilized, which was correlated with agglomeration and increased binding to mucins. CONCLUSION The present study showed that the salivary microstructure facilitates NP adsorption. However, NP size and surface functionalization determine the colloidal stability and cellular interactions. CLINICAL RELEVANCE The sound knowledge of NP interactions with saliva enables the improvement of current treatment strategies for inflammatory oral diseases.
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Affiliation(s)
- Birgit J Teubl
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology and Biopharmacy, University of Graz, Universitätsplatz 1, 8010, Graz, Austria
- BioTechMed, 8010, Graz, Austria
| | - Biljana Stojkovic
- Faculty of Mathematics and Physics, University of Ljubljana, 1000, Ljubljana, Slovenia
| | - Dominic Docter
- Department of Nanobiomedicine, Mainz University Medical Center, 55131, Mainz, Germany
| | - Elisabeth Pritz
- Institute of Cell Biology, Histology and Embryology, Research Unit Electron Microscopic Techniques, Medical University of Graz, 8010, Graz, Austria
| | - Gerd Leitinger
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology and Biopharmacy, University of Graz, Universitätsplatz 1, 8010, Graz, Austria
- Institute of Cell Biology, Histology and Embryology, Research Unit Electron Microscopic Techniques, Medical University of Graz, 8010, Graz, Austria
| | - Igor Poberaj
- Faculty of Mathematics and Physics, University of Ljubljana, 1000, Ljubljana, Slovenia
| | - Ruth Prassl
- BioTechMed, 8010, Graz, Austria
- Institute of Biophysics, Medical University of Graz, 8010, Graz, Austria
| | - Roland H Stauber
- Department of Nanobiomedicine, Mainz University Medical Center, 55131, Mainz, Germany
| | - Eleonore Fröhlich
- BioTechMed, 8010, Graz, Austria
- Center for Medical Research, Medical University of Graz, 8010, Graz, Austria
| | - Johannes G Khinast
- BioTechMed, 8010, Graz, Austria
- Institute for Process and Particle Engineering, Graz University of Technology, 8010, Graz, Austria
- Research Center Pharmaceutical Engineering, 8010, Graz, Austria
| | - Eva Roblegg
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology and Biopharmacy, University of Graz, Universitätsplatz 1, 8010, Graz, Austria.
- BioTechMed, 8010, Graz, Austria.
- Research Center Pharmaceutical Engineering, 8010, Graz, Austria.
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Sretenovic S, Stojković B, Dogsa I, Kostanjšek R, Poberaj I, Stopar D. An early mechanical coupling of planktonic bacteria in dilute suspensions. Nat Commun 2017; 8:213. [PMID: 28790301 PMCID: PMC5548916 DOI: 10.1038/s41467-017-00295-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 06/19/2017] [Indexed: 11/13/2022] Open
Abstract
It is generally accepted that planktonic bacteria in dilute suspensions are not mechanically coupled and do not show correlated motion. The mechanical coupling of cells is a trait that develops upon transition into a biofilm, a microbial community of self-aggregated bacterial cells. Here we employ optical tweezers to show that bacteria in dilute suspensions are mechanically coupled and show long-range correlated motion. The strength of the coupling increases with the growth of liquid bacterial culture. The matrix responsible for the mechanical coupling is composed of cell debris and extracellular polymer material. The fragile network connecting cells behaves as viscoelastic liquid of entangled extracellular polymers. Our findings point to physical connections between bacteria in dilute bacterial suspensions that may provide a mechanistic framework for understanding of biofilm formation, osmotic flow of nutrients, diffusion of signal molecules in quorum sensing, or different efficacy of antibiotic treatments at low and high bacterial densities.Planktonic bacteria are untethered to surfaces or to each other, and thus are expected to move independently when at low cell densities. Here Sretenovic et al. show, using optical tweezers, that bacteria in dilute suspensions are mechanically coupled and show long-range correlated motion.
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Affiliation(s)
- Simon Sretenovic
- Biotechnical Faculty, University of Ljubljana, Vecna pot 111, Ljubljana, 1000, Slovenia
| | - Biljana Stojković
- Medical Faculty, Institute of Biophysics, University of Ljubljana, Vrazov trg 2, Ljubljana, 1000, Slovenia
| | - Iztok Dogsa
- Biotechnical Faculty, University of Ljubljana, Vecna pot 111, Ljubljana, 1000, Slovenia
| | - Rok Kostanjšek
- Biotechnical Faculty, University of Ljubljana, Vecna pot 111, Ljubljana, 1000, Slovenia
| | - Igor Poberaj
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, 1000, Slovenia
- Aresis Ltd., Ulica Franca Mlakarja 1a, Ljubljana, 1000, Slovenia
| | - David Stopar
- Biotechnical Faculty, University of Ljubljana, Vecna pot 111, Ljubljana, 1000, Slovenia.
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Stojković B, Sretenovic S, Dogsa I, Poberaj I, Stopar D. Viscoelastic properties of levan-DNA mixtures important in microbial biofilm formation as determined by micro- and macrorheology. Biophys J 2015; 108:758-65. [PMID: 25650942 DOI: 10.1016/j.bpj.2014.10.072] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Revised: 10/14/2014] [Accepted: 10/30/2014] [Indexed: 12/12/2022] Open
Abstract
We studied the viscoelastic properties of homogeneous and inhomogeneous levan-DNA mixtures using optical tweezers and a rotational rheometer. Levan and DNA are important components of the extracellular matrix of bacterial biofilms. Their viscoelastic properties influence the mechanical as well as molecular-transport properties of biofilm. Both macro- and microrheology measurements in homogeneous levan-DNA mixtures revealed pseudoplastic behavior. When the concentration of DNA reached a critical value, levan started to aggregate, forming clusters of a few microns in size. Microrheology using optical tweezers enabled us to measure local viscoelastic properties within the clusters as well as in the DNA phase surrounding the levan aggregates. In phase-separated levan-DNA mixtures, the results of macro- and microrheology differed significantly. The local viscosity and elasticity of levan increased, whereas the local viscosity of DNA decreased. On the other hand, the results of bulk viscosity measurements suggest that levan clusters do not interact strongly with DNA. Upon treatment with DNase, levan aggregates dispersed. These results demonstrate the advantages of microrheological measurements compared to bulk viscoelastic measurements when the materials under investigation are complex and inhomogeneous, as is often the case in biological samples.
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Affiliation(s)
- Biljana Stojković
- Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
| | - Simon Sretenovic
- Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia
| | - Iztok Dogsa
- Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia
| | - Igor Poberaj
- Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
| | - David Stopar
- Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
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4
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Rogelj N, Poberaj I, Gunde MK. Goniospectrophotometric space curves of diffraction gratings and their applicability as appearance fingerprints. Appl Opt 2013; 52:8355-8362. [PMID: 24513838 DOI: 10.1364/ao.52.008355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 10/26/2013] [Indexed: 06/03/2023]
Abstract
The bidirectional reflectance distribution functions of diffraction gratings were calculated by applying diffraction theory and transformed into goniospectrophotometric space curves. Gratings with parallel sinusoidal grooves having periods of 1-3.5 μm and amplitudes below 0.2 μm were analyzed. The obtained goniospectrophotometric space curves consist of lines with different slopes and possible interconnections. The slope of the lines is directly connected to the grating period and the length to the period and the amplitude. Such curves could be regarded as a simple appearance fingerprint of a diffraction grating. The ability of portable multiangle spectrophotometers to provide them for diffraction gratings is analyzed.
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Mur J, Kavčič B, Poberaj I. Fast and precise Laguerre-Gaussian beam steering with acousto-optic deflectors. Appl Opt 2013; 52:6506-6511. [PMID: 24085126 DOI: 10.1364/ao.52.006506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2013] [Accepted: 07/15/2013] [Indexed: 06/02/2023]
Abstract
Novel fluorescence microscopy techniques and two-color laser direct imaging photolithography methods that enable resolution an order of magnitude beyond the diffraction limit require Laguerre-Gaussian beams and a fast and precise laser beam steering device to obtain images and produce microstructures. An acousto-optic deflector (AOD) is a suitable choice and provides high-speed random access beam positioning with subnanometer precision as well as beam intensity control in a single element. In high-resolution applications, the impact of an AOD on beam quality plays a major role. We study the transfer function of an AOD for a fundamental Gaussian and a doughnut-shaped Laguerre-Gaussian beam by measuring the beam quality as a function of the diffraction angle after passing through the device. It is demonstrated that an AOD introduces negligible distortion and degradation to the beam profile and is therefore highly suitable for use in super-resolution imaging and photolithography techniques where manipulation of Laguerre-Gaussian doughnut-shaped beams is required.
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Vilfan M, Kokot G, Vilfan A, Osterman N, Kavčič B, Poberaj I, Babič D. Analysis of fluid flow around a beating artificial cilium. Beilstein J Nanotechnol 2012; 3:163-71. [PMID: 22428106 PMCID: PMC3304323 DOI: 10.3762/bjnano.3.16] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2011] [Accepted: 01/31/2012] [Indexed: 05/07/2023]
Abstract
Biological cilia are found on surfaces of some microorganisms and on surfaces of many eukaryotic cells where they interact with the surrounding fluid. The periodic beating of the cilia is asymmetric, resulting in directed swimming of unicellular organisms or in generation of a fluid flow above a ciliated surface in multicellular ones. Following the biological example, externally driven artificial cilia have recently been successfully implemented as micropumps and mixers. However, biomimetic systems are useful not only in microfluidic applications, but can also serve as model systems for the study of fundamental hydrodynamic phenomena in biological samples. To gain insight into the basic principles governing propulsion and fluid pumping on a micron level, we investigated hydrodynamics around one beating artificial cilium. The cilium was composed of superparamagnetic particles and driven along a tilted cone by a varying external magnetic field. Nonmagnetic tracer particles were used for monitoring the fluid flow generated by the cilium. The average flow velocity in the pumping direction was obtained as a function of different parameters, such as the rotation frequency, the asymmetry of the beat pattern, and the cilium length. We also calculated the velocity field around the beating cilium by using the analytical far-field expansion. The measured average flow velocity and the theoretical prediction show an excellent agreement.
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Affiliation(s)
- Mojca Vilfan
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Gašper Kokot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Andrej Vilfan
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Natan Osterman
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Blaž Kavčič
- LPKF Laser & Elektronika d.o.o, Polica 33, 4202 Naklo, Slovenia
| | - Igor Poberaj
- Department of Physics, Jadranska 19, University of Ljubljana, 1000 Ljubljana, Slovenia
| | - Dušan Babič
- Department of Physics, Jadranska 19, University of Ljubljana, 1000 Ljubljana, Slovenia
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7
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Kokot G, Vilfan M, Osterman N, Vilfan A, Kavčič B, Poberaj I, Babič D. Measurement of fluid flow generated by artificial cilia. Biomicrofluidics 2011; 5:34103-341039. [PMID: 22662034 PMCID: PMC3364822 DOI: 10.1063/1.3608139] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2011] [Accepted: 06/02/2011] [Indexed: 05/23/2023]
Abstract
We observed and measured the fluid flow that was generated by an artificial cilium. The cilium was composed of superparamagnetic microspheres, in which magnetic dipole moments were induced by an external magnetic field. The interaction between the dipole moments resulted in formation of long chains-cilia, and the same external magnetic field was also used to drive the cilia in a periodic manner. Asymmetric periodic motion of the cilium resulted in generation of fluid flow and net pumping of the surrounding fluid. The flow and pumping performance were closely monitored by introducing small fluorescent tracer particles into the system. By detecting their motion, the fluid flow around an individual cilium was mapped and the flow velocities measured. We confirm that symmetric periodic beating of one cilium results in vortical motion only, whereas asymmetry is required for additional translational motion. We determine the effect of asymmetry on the pumping performance of a cilium, verify the theoretically predicted optimal pumping conditions, and determine the fluid behaviour around a linear array of three neighbouring cilia. In this case, the contributions of neighbouring cilia enhance the maximal flow velocity compared with a single cilium and contribute to a more uniform translational flow above the surface.
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8
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Osterman N, Poberaj I, Dobnikar J, Frenkel D, Ziherl P, Babić D. Field-induced self-assembly of suspended colloidal membranes. Phys Rev Lett 2009; 103:228301. [PMID: 20366126 DOI: 10.1103/physrevlett.103.228301] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2009] [Indexed: 05/29/2023]
Abstract
We report experiments that probe the self-assembly of micrometer-size colloids into one-particle-thick, robust, and self-healing membranes. In a magic-angle precessing magnetic field, superparamagnetic spheres experience isotropic pair attraction similar to the van der Waals force between atoms. But the many-body polarization interactions among them steer an ordered aggregation pathway consisting of growth of short chains, cross-linking and network formation, network coarsening, and consolidation of membrane patches. This generic aggregation scenario can be induced in any particles of large enough susceptibility.
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Affiliation(s)
- N Osterman
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
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9
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Vilfan M, Osterman N, Copic M, Ravnik M, Zumer S, Kotar J, Babic D, Poberaj I. Confinement effect on interparticle potential in nematic colloids. Phys Rev Lett 2008; 101:237801. [PMID: 19113594 DOI: 10.1103/physrevlett.101.237801] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2008] [Indexed: 05/27/2023]
Abstract
We studied the confinement effect on the interaction force in nematic liquid crystal colloids with spherical particles inducing planar anchoring. Using magneto-optical tweezers, we measured the spatial dependence of the quadrupolar structural interparticle force over 4 orders of magnitude. For small separations, the interparticle potential follows the power law, whereas for separations larger than the sample thickness, it decreases exponentially with the decay length proportional to the sample thickness. Experimental results are reproduced by using the Landau-de Gennes free-energy minimization approach.
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Affiliation(s)
- Mojca Vilfan
- J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
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10
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Humar M, Skarabot M, Ravnik M, Zumer S, Poberaj I, Babic D, Musevic I. Electrically tunable diffraction of light from 2D nematic colloidal crystals. Eur Phys J E Soft Matter 2008; 27:73-79. [PMID: 19230228 DOI: 10.1140/epje/i2008-10353-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We show that diffraction of visible light from 2D dipolar nematic colloidal crystals can be tuned electrically. When the external electric field of approximately 1 V/microm is applied in a direction perpendicular to the plane of the 2D colloidal crystal, the induced strain is highly anisotropic, and the inter-colloidal spacing changes by as much as 20% along one direction and approximately 2% along the perpendicular one. Although the speed of response is in the range of several seconds, this novel mechanism could provide interesting photonic applications.
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Affiliation(s)
- M Humar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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11
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Skarabot M, Ravnik M, Zumer S, Tkalec U, Poberaj I, Babic D, Musevic I. Hierarchical self-assembly of nematic colloidal superstructures. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:061706. [PMID: 18643286 DOI: 10.1103/physreve.77.061706] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Indexed: 05/26/2023]
Abstract
We show that colloidal superstructures could be assembled in mixtures of large and small colloidal particles dispersed in a nematic liquid crystal. Using elastic interaction of small colloidal particles with the disclination lines we succeed to demonstrate how one can decorate with small particles a topological matrix of defect rings and loops formed by an array of large colloidal particles. Our simulations show that this concept of colloidal self-assembly in nematics could be extended down to the nanoscale particles.
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Affiliation(s)
- M Skarabot
- J Stefan Institute, Jamova 39, Ljubljana, Slovenia
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12
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Ognysta U, Nych A, Nazarenko V, Musevic I, Skarabot M, Ravnik M, Zumer S, Poberaj I, Babic D. 2D interactions and binary crystals of dipolar and quadrupolar nematic colloids. Phys Rev Lett 2008; 100:217803. [PMID: 18518636 DOI: 10.1103/physrevlett.100.217803] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Indexed: 05/26/2023]
Abstract
In this Letter, we demonstrate that the symmetry of the elastic interaction between the dipolar and quadrupolar colloidal particles in the nematic liquid crystal leads to a novel variety of 2D nematic "binary" colloidal crystals, which have not been observed in any colloidal system. The dipolar-quadrupolar interaction is highly anisotropic and shows a power-law dependence when the particles approach each other along the director field with a pair-binding energy of the order of several thousands of k(B)T for 4 microm diameter colloids.
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Affiliation(s)
- U Ognysta
- Institute of Physics, 46 Nauky avenue, Kyiv 680028, Ukraine
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13
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Skarabot M, Ravnik M, Zumer S, Tkalec U, Poberaj I, Babic D, Osterman N, Musevic I. Interactions of quadrupolar nematic colloids. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:031705. [PMID: 18517404 DOI: 10.1103/physreve.77.031705] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2008] [Indexed: 05/26/2023]
Abstract
We present experimental and theoretical study of colloidal interactions in quadrupolar nematic liquid crystal colloids, confined to a thin planar nematic cell. Using the laser tweezers, the particles have been positioned in the vicinity of other colloidal particles and their interactions have been determined using particle tracking video microscopy. Several types of interactions have been analyzed: (i) quadrupolar pair interaction, (ii) the interaction of an isolated quadrupole with a quadrupolar chain, and (iii) the interaction of an isolated quadrupolar colloidal particle with a two-dimensional (2D) quadrupolar crystallite. In all cases, the interactions are of the order of several 100k(B)T for 2 microm particles, which gives rise to relatively stable 2D colloidal crystals. The experimental results are compared to the predictions of Landau-de Gennes theory and we find a relatively good qualitative agreement.
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Affiliation(s)
- M Skarabot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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14
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Ravnik M, Skarabot M, Zumer S, Tkalec U, Poberaj I, Babic D, Osterman N, Musevic I. Entangled nematic colloidal dimers and wires. Phys Rev Lett 2007; 99:247801. [PMID: 18233489 DOI: 10.1103/physrevlett.99.247801] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Indexed: 05/25/2023]
Abstract
It has been predicted, but never confirmed, that colloidal particles in a nematic liquid crystal could be self-assembled by delocalized topological defects and entangled disclinations. We show experimentally and theoretically that colloidal dimers and 1D structures bound by entangled topological defect loops can indeed be created by locally thermally quenching a thin layer of the nematic liquid crystal around selected colloidal particles. The topological entanglement provides a strong stringlike binding, which is ten thousand times stronger compared to water-based colloids. This unique binding mechanism could be used to assemble resonator optical waveguides and robust chiral and achiral structures of topologically entangled colloids that we call colloidal wires.
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Affiliation(s)
- M Ravnik
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
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15
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Osterman N, Babic D, Poberaj I, Dobnikar J, Ziherl P. Observation of condensed phases of quasiplanar core-softened colloids. Phys Rev Lett 2007; 99:248301. [PMID: 18233495 DOI: 10.1103/physrevlett.99.248301] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2007] [Indexed: 05/25/2023]
Abstract
We experimentally study the condensed phases of repelling core-softened spheres in two dimensions. The dipolar pair repulsion between superparamagnetic spheres trapped in a thin cell is induced by a transverse magnetic field and softened by suitably adjusting the cell thickness. We scan a broad density range and we materialize a large part of the theoretically predicted phases in systems of core-softened particles, including expanded and close-packed hexagonal, square, chainlike, stripe or labyrinthine, and honeycomb phase. Further insight into their structure is provided by Monte Carlo simulations.
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Affiliation(s)
- N Osterman
- Department of Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
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16
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Skarabot M, Ravnik M, Zumer S, Tkalec U, Poberaj I, Babic D, Osterman N, Musevic I. Two-dimensional dipolar nematic colloidal crystals. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 76:051406. [PMID: 18233658 DOI: 10.1103/physreve.76.051406] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2007] [Indexed: 05/25/2023]
Abstract
We study the interactions and directed assembly of dipolar nematic colloidal particles in planar nematic cells using laser tweezers. The binding energies for two stable configurations of a colloidal pair with homeotropic surface alignment are determined. It is shown that the orientation of the dipolar colloidal particle can efficiently be controlled and changed by locally quenching the nematic liquid crystal from the laser-induced isotropic phase. The interaction of a single colloidal particle with a single colloidal chain is determined and the interactions between pairs of colloidal chains are studied. We demonstrate that dipolar colloidal chains self-assemble into the two-dimensional (2D) dipolar nematic colloidal crystals. An odd-even effect is observed with increasing number of colloidal chains forming the 2D colloidal crystal.
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Affiliation(s)
- M Skarabot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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17
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Lev B, Nych A, Ognysta U, Chernyshuk SB, Nazarenko V, Skarabot M, Poberaj I, Babic D, Osterman N, Musevic I. Anisotropic laser trapping in nematic colloidal dispersion. Eur Phys J E Soft Matter 2006; 20:215-9. [PMID: 16779526 DOI: 10.1140/epje/i2006-10015-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2006] [Accepted: 05/26/2006] [Indexed: 05/10/2023]
Abstract
The interaction between a colloidal particle and a focused laser beam in a nematic liquid crystal reveals an unusual anisotropic Coulomb-like character. Experiments demonstrate two opposite directions in which the particle is attracted to and repelled from the nematic region deformed by the light-induced director reorientation. In this work we present analytical analysis of such behavior and derive the energy of interaction between colloidal particle and deformed director field. The analytical solution is in good agreement with recent results obtained by computer simulation.
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Affiliation(s)
- B Lev
- Institute of Physics, 46 Nauky ave., 03039, Kyiv-39, Ukraine
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Kotar J, Vilfan M, Osterman N, Babic D, Copic M, Poberaj I. Interparticle potential and drag coefficient in nematic colloids. Phys Rev Lett 2006; 96:207801. [PMID: 16803208 DOI: 10.1103/physrevlett.96.207801] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Indexed: 05/10/2023]
Abstract
Magneto-optic tweezers were used for measurements of liquid-crystal-mediated forces between spherical beads with tangential anchoring in thin nematic samples. Repulsive force, which results from the quadrupolar symmetry of defects around the immersed beads, decreases proportionally to 1/x6, with x being the bead separation. The velocity with which the particles are pushed apart also follows the same separation dependence. We thus find the effective drag coefficient gamma(eff) independent of x for surface-to-surface distances as small as 10% of the bead diameter.
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Affiliation(s)
- Jurij Kotar
- Department of Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
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Skarabot M, Ravnik M, Babic D, Osterman N, Poberaj I, Zumer S, Musevic I, Nych A, Ognysta U, Nazarenko V. Laser trapping of low refractive index colloids in a nematic liquid crystal. Phys Rev E Stat Nonlin Soft Matter Phys 2006; 73:021705. [PMID: 16605354 DOI: 10.1103/physreve.73.021705] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2005] [Revised: 01/06/2006] [Indexed: 05/08/2023]
Abstract
We describe and analyze laser trapping of small colloidal particles in a nematic liquid crystal, where the index of refraction of colloids is smaller compared to the indices of the liquid crystal. Two mechanisms are identified that are responsible for this anomalous trapping: (i) below the optical Fréedericksz transition, the trapping is due to the anisotropic dielectric interaction of the polarized light with the inhomogeneous director field around the colloid, (ii) above the optical Fréedericksz transition, the optical trapping is accompanied by the elasticity-mediated interaction between the optically distorted region of a liquid crystal and the colloid. In the majority of the experiments, the trapping above the Fréedericksz transition is highly anisotropic. Qualitative agreement is found with a numerical analysis, considering the nematic director elastic distortion, dielectric director-light field coupling and optical repulsion due to low refraction index colloid in high index surroundings.
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Affiliation(s)
- M Skarabot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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Abstract
Hormones are released from neuroendocrine cells by passing through an exocytotic pore that forms after vesicle and plasma membrane fusion. An elegant way to study this process at the single-vesicle level is to use styryl dyes, which stain not only the membrane, but also the matrix of individual vesicles in some neuroendocrine cells. However, the mechanism by which the vesicle matrix is stained is not completely clear. One possibility is that molecules of the styryl dye in the bath solution dissolve first in the plasma membrane and are then transported into the vesicle by lateral diffusion in the plane of the membrane, and finally the vesicle matrix is stained from the vesicle membrane. On the other hand, these molecules may enter the vesicle lumen and reach the vesicle matrix by permeation through an open aqueous fusion pore. To address these questions, we exposed pituitary lactotrophs to different concentrations of FM 4-64 to monitor the fluorescence increase of single vesicles by confocal microscopy after the stimulation of cells by high K(+). The results show that the membrane and the vesicle matrix exhibit different concentration-dependent properties: the plasma membrane staining by FM 4-64 has a higher affinity in comparison to the vesicle matrix. Moreover, the kinetics of vesicle loading by FM 4-64 exhibited a concentration-dependent process, which indicates that FM 4-64 molecules stain the vesicle matrix by aqueous permeation through an open fusion pore.
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Musevic I, Skarabot M, Babic D, Osterman N, Poberaj I, Nazarenko V, Nych A. Laser trapping of small colloidal particles in a nematic liquid crystal: clouds and ghosts. Phys Rev Lett 2004; 93:187801. [PMID: 15525209 DOI: 10.1103/physrevlett.93.187801] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Indexed: 05/24/2023]
Abstract
We show that, contrary to intuition, small (< or =1 microm) transparent particles can be trapped and manipulated in a nematic liquid crystal using an intense laser beam, although their index of refraction is lower than both refractive indices of the surrounding birefringent fluid. Two mechanisms are identified that are responsible for this anomalous trapping: (i) surface-induced distortion of the birefringent media around the particle, creating a high-index "cloud" around the colloid, and (ii) laser-induced distortion or (partial) melting of a nematic, creating a ghost colloid.
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Affiliation(s)
- I Musevic
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia.
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Abstract
Hormones are released from cells by passing through an exocytotic pore that forms after vesicle and plasma membrane fusion. In stimulated exocytosis vesicle content is discharged swiftly. Although rapid vesicle discharge has also been proposed to mediate basal secretion, this has not been studied directly. We investigated basal hormone release by preloading fluorescent peptides into single vesicles. The hormone discharge, monitored with confocal microscopy, was compared with the simultaneous loading of vesicle by FM styryl dye. In stimulated vesicles FM 4-64 (4 microM), loading and hormone discharge occurs within seconds. In contrast, in approximately 50% of spontaneously releasing vesicles, the vesicle content discharge and the FM 4-64 loading were slow (approximately 3 min). These results show that in peptide secreting neuroendocrine cells the elementary vesicle content discharge differs in basal and in stimulated exocytosis. It is proposed that the view dating back for some decades, which is that, at rest, the vesicle discharge of hormones and neurotransmitters is similar to that occurring after stimulation, needs to be extended. In addition to the classical paradigm that secretory capacity of a cell is determined by controlling the probability of occurrence of elementary exocytotic events, one will have to consider activity modulation of elementary exocytotic events as well.
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Abstract
We have used the patch-clamp technique to monitor changes in membrane capacitance (C(m)) elicited by fast and spatially homogeneous rises in cytosolic calcium concentration ([Ca(2+)](i)) using flash photolysis of NP-EGTA. Average peak [Ca(2+)](i) amplitudes of 20-25 microM triggered three different types of responses in C(m): (i) In 42% of cells, a rise in [Ca(2+)](i) activated a monotonic increase in C(m) followed by a slow decline to resting values; (ii) In 30% of cells, the rise in C(m) was clearly characterized by two dynamic components, consisting of a rapid and a slow exo-endocytosis cycle; (iii) In 28% of cells, after the initial rapid rise in C(m), endocytosis exhibited excess retrieval that was characterized by a decline in C(m) below resting C(m). The aim of this work is to develop a unified mathematical model with a minimum number of parameters that would describe all the observed types of responses. Three models were considered: Model A, a model with a single component of exo-endocytosis cycle; model B, a model consisting of a sum of two independent dynamic components; and model C, a model in which, in addition to the two dynamic components as in model B, excess retrieval due to a lipid flow through the reversal closing of the fusion pore during the rapid component of exo-endocytosis cycle was considered. The results show that the latter model describes all the types of responses in C(m) recorded in rat melanotrophs. The association of excess retrieval exclusively with the rapid, but not the slow, exocytosis indicates that some fusing vesicles mediate a lipidic flux during the reversal closing of the fusion pore, whereas those entering the slow phase of exocytosis may fuse with the plasma membrane completely and are retrieved by other endocytic machinery, independent of the lipid flow that might have occurred as the fusion pore opened permanently.
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Affiliation(s)
- Igor Poberaj
- Department of Physics, Faculty of Mathematics and Physics, 1001 Ljubljana, Slovenia
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Poberaj I, Mihailovic D. Electron-phonon interactions of nonequilibrium charge carriers in YBa2Cu3O7- delta investigated by picosecond resonance Raman spectroscopy. Phys Rev B Condens Matter 1994; 50:6426-6430. [PMID: 9977022 DOI: 10.1103/physrevb.50.6426] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Mihailovic D, Poberaj I, Mertelj A. Characterization of the pyroelectric effect in YBa2Cu3O7- delta. Phys Rev B Condens Matter 1993; 48:16634-16640. [PMID: 10008248 DOI: 10.1103/physrevb.48.16634] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Mihailovic D, Foster CM, Voss KF, Mertelj T, Poberaj I, Herron N. Anomalous shifts of oxygen-mode frequencies in La2-xSrxCuO4, YBa2Cu3O7- delta and Tl2Ba2Ca1-xGdxCu2O8 studied by photoinduced infrared absorption and Raman spectroscopy. Phys Rev B Condens Matter 1991; 44:237-241. [PMID: 9998240 DOI: 10.1103/physrevb.44.237] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Poberaj I, Mihailovic D, Bernik S. Room-temperature oxygen diffusion and ordering in YBa2Cu3O7-y studied with time-resolved Raman spectroscopy. Phys Rev B Condens Matter 1990; 42:393-398. [PMID: 9994552 DOI: 10.1103/physrevb.42.393] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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