Papers by Vladimir Baulin
Biophysical chemistry, Jan 25, 2015
Directional growth caused by gravitropism and corresponding bending of plant cells has been explo... more Directional growth caused by gravitropism and corresponding bending of plant cells has been explored since 19th century, however, many aspects of mechanisms underlying the perception of gravity at the molecular level are still not well known. Perception of gravity in root and shoot gravitropisms is usually attributed to gravisensitive cells, called statocytes, which exploit sedimentation of macroscopic and heavy organelles, amyloplasts, to sense the direction of gravity. Gravity stimulus is then transduced into distal elongation zone, which is several mm far from statocytes, where it causes stretching. It is suggested that gravity stimulus is conveyed by gradients in auxin flux. We propose a theoretical model that may explain how concentration gradients and/or stretching may indirectly affect the global orientation of cortical microtubules, attached to the cell membrane and induce their dynamic reorientation perpendicular to the gradients. In turn, oriented microtubule arrays direct...
Hydrophobic nanoparticles introduced into living systems may lead to increased toxicity, can acti... more Hydrophobic nanoparticles introduced into living systems may lead to increased toxicity, can activate immune cells, or can be used as nanocarriers for drug or gene delivery. It is generally accepted that small hydrophobic nanoparticles are blocked by lipid bilayers and accumulate in the bilayer core, whereas big nanoparticles can only penetrate cells through slow energy-dependent processes, such as endocytosis, lasting minutes. In contrast to expectations, we demonstrate that lipid-covered hydrophobic nanoparticles may translocate through lipid membranes by direct penetration within milliseconds. We identified the threshold size for translocation: nanoparticles with diameters smaller than 5 nm stay trapped in the bilayer, whereas those with diameters larger than 5 nm insert into the bilayer, opening pores in the bilayer. The direct proof of this size-dependent translocation was provided by an in situ observation of a single event of a nanoparticle quitting the bilayer. This was achieved with a specially designed microfluidic device combining optical fluorescence microscopy with simultaneous electrophysiological measurements. A quantitative analysis of the kinetic pathway of a single nanoparticle translocation event demonstrated that the translocation is irreversible and that the nanoparticle can translocate only once. This newly discovered one-way translocation mechanism provides numerous opportunities for biotechnological applications, ranging from targeted biomaterial elimination and/or delivery to precise and controlled trapping of nanoparticles.
Hydrophobic nanoparticles introduced into living systems may lead to increased toxicity, can acti... more Hydrophobic nanoparticles introduced into living systems may lead to increased toxicity, can activate immune cells, or can be used as nanocarriers for drug or gene delivery. It is generally accepted that small hydrophobic nanoparticles are blocked by lipid bilayers and accumulate in the bilayer core, whereas big nanoparticles can only penetrate cells through slow energy-dependent processes, such as endocytosis, lasting minutes. In contrast to expectations, we demonstrate that lipid-covered hydrophobic nanoparticles may translocate through lipid membranes by direct penetration within milliseconds. We identified the threshold size for translocation: nanoparticles with diameters smaller than 5 nm stay trapped in the bilayer, whereas those with diameters larger than 5 nm insert into the bilayer, opening pores in the bilayer. The direct proof of this size-dependent translocation was provided by an in situ observation of a single event of a nanoparticle quitting the bilayer. This was achieved with a specially designed microfluidic device combining optical fluorescence microscopy with simultaneous electrophysiological measurements. A quantitative analysis of the kinetic pathway of a single nanoparticle translocation event demonstrated that the translocation is irreversible and that the nanoparticle can translocate only once. This newly discovered one-way translocation mechanism provides numerous opportunities for biotechnological applications, ranging from targeted biomaterial elimination and/or delivery to precise and controlled trapping of nanoparticles.
Biophysical Chemistry, 2015
Directional growth caused by gravitropism and corresponding bending of plant cells has been explo... more Directional growth caused by gravitropism and corresponding bending of plant cells has been explored since 19th century, however, many aspects of mechanisms underlying the perception of gravity at the molecular level are still not well known. Perception of gravity in root and shoot gravitropisms is usually attributed to gravisensitive cells, called statocytes, which exploit sedimentation of macroscopic and heavy organelles, amyloplasts, to sense the direction of gravity. Gravity stimulus is then transduced into distal elongation zone, which is several mm far from statocytes, where it causes stretching. It is suggested that gravity stimulus is conveyed by gradients in auxin flux. We propose a theoretical model that may explain how concentration gradients and/or stretching may indirectly affect the global orientation of cortical microtubules, attached to the cell membrane and induce their dynamic reorientation perpendicular to the gradients. In turn, oriented microtubule arrays direct the growth and orientation of cellulose microfibrils, forming part of the cell external skeleton and determine the shape of the cell. Reorientation of microtubules is also observed in reaction to light in phototropism and mechanical bending, thus suggesting universality of the proposed mechanism.
Langmuir : the ACS journal of surfaces and colloids, Jan 10, 2016
The protein adsorption of two human plasma proteins-albumin (Alb) and fibronectin (Fn)-onto synth... more The protein adsorption of two human plasma proteins-albumin (Alb) and fibronectin (Fn)-onto synthetic nanostructured bactericidal material-black silicon (bSi) surfaces (that contain an array of nanopillars) and silicon wafer (nonstructured) surfaces-was investigated. The adsorption behavior of Alb and Fn onto two types of substrata was studied using a combination of complementary analytical techniques. A two-step Alb adsorption mechanism onto the bSi surface has been proposed. At low bulk concentrations (below 40 μg/mL), the Alb preferentially adsorbed at the base of the nanopillars. At higher bulk concentrations, the Alb adsorbed on the top of the nanopillars. In the case of Fn, the protein preferentially adsorbed on the top of the nanopillars, irrespective of its bulk concentration.
ACS Nano, 2015
Pristine graphene, its derivatives and composites have been widely reported to possess antibacter... more Pristine graphene, its derivatives and composites have been widely reported to possess antibacterial properties. Most of the studies simulating the interaction between bacterial cell membranes and the surface of graphene have proposed that the graphene-induced bacterial cell death is caused either by (1) the insertion of blade-like graphene-based nanosheets or (2) by the destructive extraction of lipid molecules by the presence of the lipophilic graphene. These simulation studies have, however, only take into account graphene-cell membrane interactions where the graphene is in a dispersed form. In this paper we report the antimicrobial behavior of graphene sheet surfaces in an attempt to further advance the current knowledge pertaining to graphene cytotoxicity, using both experimental and computer simulation approaches. Graphene nanofilms were fabricated to exhibit different edge lengths and different angles of orientation in the graphene sheets. These substrates were placed in contact with Pseudomonas aeruginosa and Staphylococcus aureus bacteria, whereby it was seen that these substrates exhibited variable bactericidal efficiency towards these two pathogenic bacteria. It was demonstrated that the density of the edges of the graphene was one of the principal parameters that contributed to the antibacterial behavior of the graphene nano-sheet films. The study provides both experimental and theoretical evidence that the antibacterial behavior of graphene nano-sheets arises from the formation of pores in the bacterial cell wall, causing a subsequent osmotic imbalance and cell death.
Langmuir : the ACS journal of surfaces and colloids, Jan 10, 2016
The protein adsorption of two human plasma proteins-albumin (Alb) and fibronectin (Fn)-onto synth... more The protein adsorption of two human plasma proteins-albumin (Alb) and fibronectin (Fn)-onto synthetic nanostructured bactericidal material-black silicon (bSi) surfaces (that contain an array of nanopillars) and silicon wafer (nonstructured) surfaces-was investigated. The adsorption behavior of Alb and Fn onto two types of substrata was studied using a combination of complementary analytical techniques. A two-step Alb adsorption mechanism onto the bSi surface has been proposed. At low bulk concentrations (below 40 μg/mL), the Alb preferentially adsorbed at the base of the nanopillars. At higher bulk concentrations, the Alb adsorbed on the top of the nanopillars. In the case of Fn, the protein preferentially adsorbed on the top of the nanopillars, irrespective of its bulk concentration.
PloS one, 2016
The mechanisms by which various biological effects are triggered by exposure to an electromagneti... more The mechanisms by which various biological effects are triggered by exposure to an electromagnetic field are not fully understood and have been the subject of debate. Here, the effects of exposing typical representatives of the major microbial taxa to an 18 GHz microwave electromagnetic field (EMF)were studied. It appeared that the EMF exposure induced cell permeabilisation in all of the bacteria and yeast studied, while the cells remained viable (94% throughout the exposure), independent of the differences in cell membrane fatty acid and phospholipid composition. The resulting cell permeabilisation was confirmed by detection of the uptake of propidium iodine and 23 nm fluorescent silica nanospheres using transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Upon EMF exposure, the bacterial cell membranes are believed to become permeable through quasi-endocytosis processes. The dosimetry analysis revealed that the EMF threshold level required to induc...
Soft matter, Jan 14, 2015
An original coarse-grained model for peroxidised phospholipids is presented, based on the MARTINI... more An original coarse-grained model for peroxidised phospholipids is presented, based on the MARTINI lipid force field. This model results from a combination of thermodynamic modelling and structural information on the area per lipid, which have been made available recently. The resulting coarse-grained lipid molecules form stable bilayers, and a set of elastic coefficients (compressibility and bending moduli) is obtained. We compare the compressibility coefficient to the experimental values [Weber et al., Soft Matter, 2014, 10, 4241]. Predictions for the mechanical properties, membrane thickness and lateral distribution of hydroperoxide groups in the phospholipid bilayer are presented.
Computational Electrostatics for Biological Applications, 2014
ACS Nano, 2015
Pristine graphene, its derivatives and composites have been widely reported to possess antibacter... more Pristine graphene, its derivatives and composites have been widely reported to possess antibacterial properties. Most of the studies simulating the interaction between bacterial cell membranes and the surface of graphene have proposed that the graphene-induced bacterial cell death is caused either by (1) the insertion of blade-like graphene-based nanosheets or (2) by the destructive extraction of lipid molecules by the presence of the lipophilic graphene. These simulation studies have, however, only take into account graphene-cell membrane interactions where the graphene is in a dispersed form. In this paper we report the antimicrobial behavior of graphene sheet surfaces in an attempt to further advance the current knowledge pertaining to graphene cytotoxicity, using both experimental and computer simulation approaches. Graphene nanofilms were fabricated to exhibit different edge lengths and different angles of orientation in the graphene sheets. These substrates were placed in contact with Pseudomonas aeruginosa and Staphylococcus aureus bacteria, whereby it was seen that these substrates exhibited variable bactericidal efficiency towards these two pathogenic bacteria. It was demonstrated that the density of the edges of the graphene was one of the principal parameters that contributed to the antibacterial behavior of the graphene nano-sheet films. The study provides both experimental and theoretical evidence that the antibacterial behavior of graphene nano-sheets arises from the formation of pores in the bacterial cell wall, causing a subsequent osmotic imbalance and cell death.
Applied Microbiology and Biotechnology, 2015
The surface nanotopography and architecture of medical implant devices are important factors that... more The surface nanotopography and architecture of medical implant devices are important factors that can control the extent of bacterial attachment. The ability to prevent bacterial attachment substantially reduces the possibility of a patient receiving an implant contracting an implant-borne infection. We now demonstrated that two bacterial strains, Staphylococcus aureus and Pseudomonas aeruginosa, exhibited different attachment affinities towards two types of molecularly smooth titanium surfaces each possessing a different nanoarchitecture. It was found that the attachment of S. aureus cells was not restricted on surfaces that had an average roughness (S a ) less than 0.5 nm. In contrast, P. aeruginosa cells were found to be unable to colonise surfaces possessing an average roughness below 1 nm, unless sharp nanoprotrusions of approximately 20 nm in size and spaced 35.0 nm apart were present. It is postulated that the enhanced attachment of P. aeruginosa onto the surfaces possessing these nanoprotrusions was facilitated by the ability of the cell membrane to stretch over the tips of the nanoprotrusions as confirmed through computer simulation, together with a concomitant increase in the level of extracellular polymeric substance (EPS) being produced by the bacterial cells.
Journal of Materials Chemistry B, 2014
Microscale devices are increasingly being developed for diagnostic analysis although conventional... more Microscale devices are increasingly being developed for diagnostic analysis although conventional lysis as an initial step presents limitations due to its scale or complexity. Here, we detail the physical response of erythrocytes to the surface nanoarchitecture of black Si (bSi) and foreshadow their potential in microanalysis. The physical interaction brought about by the spatial convergence of the two topologies:
Nature Communications, 2013
Black silicon is a synthetic nanomaterial that contains high aspect ratio nanoprotrusions on its ... more Black silicon is a synthetic nanomaterial that contains high aspect ratio nanoprotrusions on its surface, produced through a simple reactive-ion etching technique for use in photovoltaic applications. Surfaces with high aspect-ratio nanofeatures are also common in the natural world, for example, the wings of the dragonfly Diplacodes bipunctata. Here we show that the nanoprotrusions on the surfaces of both black silicon and D. bipunctata wings form hierarchical structures through the formation of clusters of adjacent nanoprotrusions. These structures generate a mechanical bactericidal effect, independent of chemical composition. Both surfaces are highly bactericidal against all tested Gram-negative and Gram-positive bacteria, and endospores, and exhibit estimated average killing rates of up to B450,000 cells min À 1 cm À 2 . This represents the first reported physical bactericidal activity of black silicon or indeed for any hydrophilic surface. This biomimetic analogue represents an excellent prospect for the development of a new generation of mechano-responsive, antibacterial nanomaterials. *Cicada wing values are based on previously published data 7-9 . wValues represent the number of average killing rate (cells killed per cm À 2 min À 1 ) over 3 h.
The Journal of Chemical Physics, 2014
Coarse-grained model for saturated (DCPC, DLPC, DMPC, DPPC, DSPC) and unsaturated (POPC, DOPC) ph... more Coarse-grained model for saturated (DCPC, DLPC, DMPC, DPPC, DSPC) and unsaturated (POPC, DOPC) phospholipids is introduced within the Single Chain Mean Field theory. A single set of parameters adjusted for DMPC bilayers gives an adequate description of equilibrium and mechanical properties of a range of saturated lipid molecules that differ only in length of their hydrophobic tails and unsaturated (POPC, DOPC) phospholipids which have double bonds in the tails. A double bond is modeled with a fixed angle of 120 degrees, while the rest of the parameters are kept the same as saturated lipids. The thickness of the bilayer and its hydrophobic core, the compressibility and the equilibrium area per lipid correspond to experimentally measured values for each lipid, changing linearly with the length of the tail. The model for unsaturated phospholipids also fetches main thermodynamical properties of the bilayers. This model is used for an accurate estimation of the free energies of the compressed or stretched bilayers in stacks or multilayers and gives reasonable estimates for free energies. The proposed model may further be used for studies of mixtures of lipids, small molecule inclusions, interactions of bilayers with embedded proteins.
IPEC Solver is a Windows program designed to analyze the stability of core–shell inter-polyelectr... more IPEC Solver is a Windows program designed to analyze the stability of core–shell inter-polyelectrolyte complexes formed by complexation of oppositely charged block copolymers. The two-dimensional size distribution of the complexes composed by different numbers of positively or negatively charged polyelectrolytes is calculated based on the scaling model of block copolymer aggregation and Poisson–Boltzmann theory for electrostatic interactions [V.A. Baulin, E. Trizac, Self-assembly of spherical inter-polyelectrolyte complexes from oppositely charged polymers, Soft Matter 8 (25) (2012) 6755–6766]. Salt effects, charge distribution and distributions of labile cations and anions around the complexes are calculated numerically as a function of chain composition and solvent properties.Program title: IPEC SolverCatalogue identifier: AEPM_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPM_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 53802No. of bytes in distributed program, including test data, etc.: 4582576Distribution format: tar.gzProgramming language: C++ (VS.10)Computer: PCOperating system: WinXP, Win7Has the code been vectorized or parallelized?: Supports parallel computation through OpenMPRAM: 1 GBClassification: 16.11Nature of problem:This free software is designed to illustrate physical mechanisms of self-assembly of inter-polyelectrolyte complexes in the presence of salt. It can suggest an optimal structure of the aggregates as a function of the structure of block copolymers.Solution method:The distribution of the complexes composed by a different number of positively or negatively charged polyelectrolytes is calculated based on a scaling model of block copolymer aggregation and Poisson–Boltzmann theory for electrostatic interactions [V.A. Baulin, E. Trizac, Self-assembly of spherical inter-polyelectrolyte complexes from oppositely charged polymers, Soft Matter, 8 (25) (2012) 6755–6766]. Salt effects, charge distribution and distributions of labile ions around the complexes are provided.Restrictions:IPEC complex is assumed to have a core–shell structure: a spherical core containing charged polymers is surrounded by a neutral corona. To insure stability of the solution, salt concentration, ka>0.2ka>0.2Additional comments:Solves the Poisson–Boltzmann equation in a broad range of parameters.Running time:From seconds to several hours.
The behavior of polymeric globule in a solution containing surfactants is analyzed within the fra... more The behavior of polymeric globule in a solution containing surfactants is analyzed within the framework of the Flory lattice theory. The amphiphilic structure of surfactant molecule is modeled as two adjacent lattice cells with opposite interaction parameters. Therefore, model surfactants prefer the globule–solvent interface rather than regions inside and outside the globule.
A single chain mean field theory is used to quantitatively describe the micellization process of ... more A single chain mean field theory is used to quantitatively describe the micellization process of the nonionic polyethylene oxide alkyl ether, C n E m class of surfactants at 25°C. An explicit but simple microscopic model with only three interaction parameters is shown to be able to reproduce with high accuracy the critical micelle concentrations of a wide range of head and tail surfactant lengths. In addition, the aggregation number of the micelles is studied, the effect of the number of the hydrophobic and hydrophilic segments on CMC and aggregation number of the micelles are discussed and volume fraction profiles are given. B dx.
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Papers by Vladimir Baulin