arXiv subjects

J. -F. Berret

Publications and source records attributed to J. -F. Berret.

At least 19 recordsLinked to original sources

arXiv2024

Magnetic sub-micron rods for quantitative viscosity imaging using heterodyne holography

Many processes in microfluidics and biology are driven or affected by viscosity. While several methods are able to measure this parameter globally, very few can provide high resolution viscosity images. Optimizing the locality of viscosity measurements demands smaller probes but also shorter lateral diffusion lengths and measurement times. Here, we propose to use sub-micrometer magnetic rods to perform high resolution viscosity imaging. An external magnetic field forces the oscillation of superparamagnetic iron oxide rods. Under linearly polarized illumination, the rotation of these highly anisotropic optical scatterers induces a blinking which is analyzed by heterodyne holography. The spectral analysis of the rotation dynamics yields a regime transition frequency from which the local viscosity is deduced. Holography provides a 3D optical field reconstruction and 3D superlocalization of the rods, which allows super-resolved viscosity measurements. Relying on the fast Brownian rotation instead of the slower translation component of nanorods therefore allows faster measurements and, crucially, smaller effective voxels for viscosity determination. We thus demonstrate that viscosity imaging is possible with a 0.5 (micron)^3 3D-resolution.

physics.optics↗

arXiv2023

Magnetic nanorods for quantitative viscosity imaging using heterodyne holography

Many processes in microfluidics and biology are driven or affected by viscosity. While several methods are able to measure this parameter globally (AFM, surface acoustic waves, DLS, ...), very few can provide high resolution viscosity images, particularly in living cells. Here, we propose to use sub-micrometer magnetic rods to perform high resolution viscosity imaging. An external magnetic field forces the oscillation of superparamagnetic iron oxide nanorods. Under linearly polarized illumination, the rotation of these highly anisotropic optical scatterers induces a blinking which is analyzed by heterodyne holography. The spectral analysis of the rotation dynamics yields a regime transition frequency f t from which the local viscosity is deduced. Holography provides 3D image reconstruction and 3D superlocalization of the nanorods, which allows super-resolved viscosity measurements. Relying on the fast Brownian rotation of nanorods instead of their slower translation therefore allows faster measurements and, crucially, smaller effective voxels for viscosity determination. Viscosity imaging is demonstrated with a 0.5 μm 3 3D resolution.

physics.ins-det↗

arXiv2020

Pulmonary surfactant inhibition of nanoparticle uptake by alveolar epithelial cells

Pulmonary surfactant forms a sub-micrometer thick fluid layer that covers the surface of alveolar lumen and inhaled nanoparticles therefore come in to contact with surfactant prior to any interaction with epithelial cells. We investigate the role of the surfactant as a protective physical barrier by modeling the interactions using silica-Curosurf-alveolar epithelial cell system in vitro. Electron microscopy displays that the vesicles are preserved in the presence of nanoparticles while nanoparticle-lipid interaction leads to the formation of mixed aggregates. Fluorescence microscopy reveals that the surfactant decreases the uptake of nanoparticles by up to two orders of magnitude in two models of alveolar epithelial cells, A549 and NCI-H441, irrespective of immersed culture on glass or air-liquid interface culture on transwell. Confocal microscopy corroborates the results by showing nanoparticle-lipid colocalization interacting with the cells. Our work thus supports the idea that pulmonary surfactant plays a protective role against inhaled nanoparticles. The effect of surfactant should therefore be considered in predictive assessment of nanoparticle toxicity or drug nanocarrier uptake. Models based on the one presented in this work may be used for preclinical tests with engineered nanoparticles.

cond-mat.soft↗

arXiv2019

Effect of Nanoparticles on the Bulk Shear Viscosity of a Lung Surfactant Fluid

Inhaled nanoparticles (< 100 nm) reaching the deep lung region first interact with the pulmonary surfactant, a thin lipid film lining the alveolar epithelium. To date, most biophysical studies have focused on particle induced modifications of the film interfacial properties. In comparison, there is less work on the surfactant bulk properties, and on their changes upon particle exposure. Here we study the viscoelastic properties of a biomimetic pulmonary surfactant in the presence of various engineered nanoparticles. The microrheology technique used is based on the remote actuation of micron-sized wires via the application of a rotating magnetic field and on time-lapse optical micros-copy. It is found that particles strongly interacting with lipid vesicles, such as cationic silica (SiO2, 42 nm) and alumina (Al2O3, 40 nm) induce profound modifications of the surfactant flow proper-ties, even at low concentrations. In particular, we find that silica causes fluidification, while alumi-na induces a liquid-to-soft solid transition. Both phenomena are described quantitatively and ac-counted for in the context of colloidal physics models. It is finally suggested that the structure and viscosity changes could impair the fluid reorganization and recirculation occurring during breath-ing.

cond-mat.soft↗

arXiv2019

On the rheology of pulmonary surfactant: effects of concentration and consequences for the surfactant replacement therapy

The role of pulmonary surfactant is to reduce the surface tension in the lungs and to facilitate breathing. Surfactant replacement therapy (SRT) aims at bringing a substitute by instillation into the airways, a technique that has proven to be efficient and lifesaving for preterm infants. Adapting this therapy to adults requires to scale the administered dose to the patient body weight and to in-crease the lipid concentration, whilst maintaining its surface and flow properties similar. Here, we exploit a magnetic wire-based microrheology technique to measure the viscosity of the exogenous pulmonary surfactant Curosurf in various experimental conditions. The Curosurf viscosity is found to increase exponentially with lipid concentration following the Krieger-Dougherty law of colloids. The Krieger-Dougherty behavior also predicts a divergence of the viscosity at the liquid-to-gel transition. For Curosurf the transition concentration is found close to the concentration at which it is formulated (117 g L-1 versus 80 g L-1). This outcome suggests that for SRT the surfactant rheological properties need to be monitored and kept within a certain range. The results found here could help in producing suspensions for respiratory distress syndrome adapted to adults. The present work also demonstrates the potential of the magnetic wire microrheology tech-nique as an accurate tool to explore biological soft matter dynamics.

cond-mat.soft↗

arXiv2019

Mono- versus multi-phosphonic acid based PEGylated polymers for functionalization and stabilization of metal (Ce, Fe, Ti, Al)oxide nanoparticles in biological media

For applications in nanomedicine, particles need to be functionalized to prevent protein corona formation and or aggregation. Most advanced strategies take advantage of functional polymers and assembly techniques. Nowadays there is an urgent need for coatings that are tailored according to a broad range of surfaces and that can be produced on a large scale. Herein, we synthesize mono- and multi-phosphonic acid based poly(ethylene glycol) (PEG) polymers with the objective of producing efficient coats for metal oxide nanoparticles. Cerium, iron, titanium and aluminum oxide nanoparticles of different morphologies (spheres, platelets, nanoclusters) and sizes ranging from 7 to 40 nm are studied in physiological and in protein rich cell culture media. It is found that the particles coated with mono-functionalized polymers exhibit a mitigated stability over time, whereas the multi-functionalized copolymers provide resilient coatings and long-term stability (months). With the latter, PEG densities in the range 0.2 - 0.5 nm-2 and layer thickness about 10 nm provide excellent performances. The study suggests that the proposed coating allows controlling nanomaterial interfacial properties in biological environments.

physics.app-ph↗

arXiv2018

Nanoparticle-lipid interaction: Job scattering plots to differentiate vesicle aggregation from supported lipid bilayer formation

The impact of nanomaterials on lung fluids or on the plasma membrane of living cells has prompted researchers to examine the interactions between nanoparticles and lipid vesicles. Recent studies have shown that nanoparticle-lipid interaction leads to a broad range of structures including supported lipid bilayers (SLB), particles adsorbed at the surface or internalized inside vesicles, and mixed aggregates. Today, there is a need to have simple protocols that can readily assess the nature of structures obtained from particles and vesicles. Here we apply the method of continuous variation for measuring Job scattering plots and provide analytical expressions for the scattering intensity in various scenarios. The result that emerges from the comparison between modeling and experimental measurements is that electrostatics plays a key role in the association, but it is not sufficient to induce the formation of supported lipid bilayers.

cond-mat.soft↗

arXiv2018

The role of surface charge in the interaction of nanoparticles with model pulmonary surfactants

Inhaled nanoparticles traveling through the airways are able to reach the respiratory zone of the lungs. In such event, the incoming particles first enter in contact with the liquid lining the alveolar epithelium, the pulmonary surfactant. The pulmonary surfactant is composed of lipids and proteins that are assembled into large vesicular structures. The question of the nature of the biophysicochemical interaction with the pulmonary surfactant is central to understand how the nanoparticles can cross the air-blood barrier. Here we explore the phase behavior of sub-100 nm particles and surfactant substitutes in controlled conditions. Three types of surfactant mimetics, including the exogenous substitute Curosurf, a drug administred to infants with respiratory distress syndrome are tested together with aluminum oxide (Al2O3), silicon dioxide (SiO2) and polymer (latex) nanoparticles. The main result here is the observation of the spontaneous nanoparticle-vesicle aggregation induced by Coulombic attraction. The role of the surface charges is clearly established. We also evaluate the supported lipid bilayer formation recently predicted and find that in the cases studied these structures do not occur. Pertaining to the aggregate internal structure, fluorescence microscopy ascertains that the vesicles and particles are intermixed at the nano- to microscale. With particles acting as stickers between vesicles, it is anticipated that the presence of inhaled nanomaterials in the alveolar spaces could significantly modify the interfacial and bulk properties of the pulmonary surfactant and interfere with the lung physiology.

cond-mat.soft↗

arXiv2018

Design of eco-friendly fabric softeners: structure, rheology and interaction with cellulose nanocrystals

Concentrated fabric softeners are water-based formulations containing around 10 - 15 wt. % of double tailed esterquat surfactants primarily synthesized from palm oil. In recent patents, it was shown that a significant part of the surfactant contained in today formulations can be reduced by circa 50 % and replaced by natural guar polymers without detrimental effects on the deposition and softening performances. We presently study the structure and rheology of these softener formulations and identify the mechanisms at the origin of these effects. The polymer additives used are guar gum polysaccharides, one cationic and one modified through addition of hydroxypropyl groups. Formulations with and without guar polymers are investigated using optical and cryo-transmission electron microscopy, small-angle light and Xray scattering and finally rheology. Similar techniques are applied to study the phase behavior of softener and cellulose nanocrystals considered here as a model for cotton. The esterquat surfactants are shown to assemble into micron-sized vesicles in the dilute and concentrated regimes. In the former, guar addition in small amounts does not impair the vesicular structure and stability. In the concentrated regime, cationic guars induce a local crowding associated to depletion interactions and leads to the formation of a local lamellar order. In rheology, adjusting the polymer concentration at one tenth that of the surfactant is sufficient to offset the decrease of the elastic property associated with the surfactant reduction. In conclusion, we have shown that through an appropriate choice of natural additives it is possible to lower the concentration of surfactants in fabric conditioners by about half, a result that could represent a significant breakthrough in current home care formulations.

cond-mat.soft↗

arXiv2018

The enzyme-like catalytic activity of cerium oxide nanoparticles and its dependency on Ce3+ surface area concentration

Cerium oxide nanoparticles are known to catalyze the decomposition of reactive oxygen species such as superoxide radical and hydrogen peroxide. Herein, we examine the superoxide dismutase (SOD) and catalase (CAT) mimetic catalytic activities of nanoceria and demonstrate the existence of generic behaviors. For particles of size 4.5, 7.8, 23 and 28 nm, the SOD and CAT catalytic activities exhibit the characteristic shape of a Langmuir isotherm as a function of cerium concentration. Results show that the catalytic effects are enhanced for smaller particles and for the particles with the largest Ce3+ fraction. The SOD-like activity obtained from the different samples is found to superimpose on a single master curve using the Ce3+ surface area concentration as a new variable, indicating the existence of particle independent redox mechanisms. For the CAT assays the adsorption of H2O2 molecules at the particle surface modulates the efficacy of the decomposition process and must be taken into account. We design an amperometry-based experiment to evaluate the H2O2 adsorption at nanoceria surfaces, leading to the renormalization of the particle specific area. Depending on the particle type the amount of adsorbed H2O2 molecules varies from 2 to 20 nm-2. The proposed scalings are predictive and allow determining SOD and CAT catalytic properties of cerium oxide solely from physico-chemical features.

cond-mat.mtrl-sci↗

arXiv2017

Supported pulmonary surfactant bilayers on silica nanoparticles: Formulation, stability and impact on lung epithelial cells

Studies have shown that following exposure to particulate matter, the ultrafine fraction (< 100 nm) may deposit along the respiratory tract down to the alveolar region. To assess the effects of nanoparticles in the lungs, it is essential to address the question of their biophysicochemical interaction with the different pulmonary environments, including the lung lining fluids and the epithelia. Here we examine one of these interactive scenarios and study the role of supported lipid bilayers (SLB) on the fate of 40 nm fluorescent silica particles towards living cells. We first study the particle phase behavior in presence of Curosurf, a pulmonary surfactant substitute used in replacement therapies. It is found that Curosurf vesicles interact strongly with the nanoparticles, but do not spontaneously form SLBs. To achieve this goal, we use sonication to reshape the vesicular membranes and induce the lipid fusion around the particles. Centrifugal sedimentation and electron microscopy are carried out to determine the optimum coating conditions and layer thickness. We then explore the impact of surfactant SLBs on the cytotoxic potential and interactions towards a malignant epithelial cell line. All in vitro assays indicate that SLBs mitigate the particle toxicity and internalization rates. In the cytoplasm, the particle localization is also strongly coating dependent. It is concluded that SLBs profoundly affect cellular interactions and functions in vitro and could represent an alternative strategy for particle coating. The current data also shed some light on potential mechanisms pertaining to the particle or pathogen transport through the air-blood barrier.

cond-mat.soft↗

arXiv2017

Fabric Softener/Cellulose Nanocrystal Interaction: A Model For Assessing Surfactant Deposition On Cotton

There is currently a renewed interest for improving household and personal care formulations to provide more environment friendly products. Fabric conditioners used as softeners have to fulfill a number of stability and biodegradability requirements. They should also display significant adsorption on cotton in the conditions of use. The quantification of surfactant adsorption remains however difficult because the fabric woven structure is complex and deposited amounts are generally small. Here we propose a method to evaluate cellulose/sur-factant interactions with increased detection sensitivity. The method is based on the use of cellulose nanocrystals in lieu of micron-sized fibers or yarns, combined with different techni-ques including light scattering, optical and electron microscopy, and electrophoretic mobili-ty. Cellulose nanocrystals are rod-shaped nano-particles in the form of 200 nm laths that are negatively charged and can be dispersed in bulk solutions. In this work, we use a double-tailed cationic surfactant present in fabric softener. Results show that the surfactants self-assemble into unilamellar, multivesicular and multilamellar vesicles, and interaction with cellulose nanocrys-tals is driven by electrostatics. Mutual interac-tions are strong and lead to the formation of large-scale aggregates, where the vesicles remain intact at the cellulose surface. The technique developed here could be exploited to rapidly assess fabric conditioner efficiency obtained by varying the nature and content of their chemical additives.

cond-mat.soft↗

arXiv2016

Wire active microrheology to differentiate viscoelastic liquids from soft solids

Viscoelastic liquids are characterized by a finite static viscosity and a zero yield stress, whereas soft solids have an infinite viscosity and a non-zero yield stress. The rheological nature of viscoelastic materials has long been a challenge, and it is still a matter of debate. Here, we provide for the first time the constitutive equations of linear viscoelasticity for magnetic wires in yield stress materials, together with experimental measurements using Magnetic Rotational Spectroscopy (MRS). With MRS, the wires are submitted to a rotational magnetic field as a function of frequency and the wire motion is monitored by time-lapse microscopy. The soft solids studied are gel-forming polysaccharide aqueous dispersions (gellan gum) at concentrations above the gelification point. It is found that soft solids exhibit a clear and distinctive signature compared to viscous and viscoelastic liquids. In particular, the wire average rotation velocity equals zero over a broad frequency range. We also show the MRS technique is quantitative. From the wire oscillation amplitudes, the equilibrium elastic modulus is retrieved and agrees with polymer dynamics theory.

cond-mat.soft↗

arXiv2016

Delayed hepatic uptake of multi-phosphonic acid poly(ethylene glycol) coated iron oxide measured by real-time Magnetic Resonance Imaging

We report on the synthesis, characterization, stability and pharmacokinetics of novel iron based contrast agents for magnetic resonance imaging (MRI). Statistical copolymers combining multiple phosphonic acid groups and poly(ethylene glycol) (PEG) were synthesized and used as coating agents for 10 nm iron oxide nanocrystals. In vitro, protein corona and stability assays show that phosphonic acid PEG copolymers outperform all other coating types examined, including low molecular weight anionic ligands and polymers. In vivo, the particle pharmacokinetics is investigated by monitoring the MRI signal intensity from mouse liver, spleen and arteries as a function of the time, between one minute and seven days after injection. Iron oxide particles coated with multi-phosphonic acid PEG polymers are shown to have a blood circulation lifetime of 250 minutes, i.e. 10 to 50 times greater than that of recently published PEGylated probes and benchmarks. The clearance from the liver takes in average 2 to 3 days and is independent of the core size, coating and particle stability. By comparing identical core particles with different coatings, we are able to determine the optimum conditions for stealth MRI probes.

q-bio.BM↗

arXiv2016

Viscoelasticity of model surfactant solutions determined by rotational magnetic spectroscopy

Being able to reduce the size of a rheometer down to the micron scale is a unique opportunity to explore the mechanical response of expensive and/or confined liquids and gels. To this aim, we synthesize micron size wires with magnetic properties and examine the possibility of using them as microrheology probes. In this work, we exploit the technique of rotational magnetic spectroscopy by placing a wire in a rotating magnetic field and monitor its temporal evolution by time-lapse microscopy. The wire-based microrheology technique is tested on wormlike micellar surfactant solutions showing very different relaxation dynamics and viscosities. A model for the wire rotation is also developed and used to predict the wire behavior. It is shown that the rheological parameters of the surfactant solutions including the static shear viscosity, the entangled micellar network relaxation time and the elastic modulus are in good agreement with those of conventional rheometry.

cond-mat.soft↗

arXiv2016

Polyelectrolyte assisted charge titration spectrometry: applications to latex and oxide nanoparticles

The electrostatic charge density of particles is of paramount importance for the control of the dispersion stability. Conventional methods use potentiometric, conductometric or turbidity titration but require large amount of samples. Here we report a simple and cost-effective method called polyelectrolyte assisted charge titration spectrometry or PACTS. The technique takes advantage of the propensity of oppositely charged polymers and particles to assemble upon mixing, leading to aggregation or phase separation. The mixed dispersions exhibit a maximum in light scattering as a function of the volumetric ratio X, and the peak position XMax is linked to the particle charge density according to σ ~ D0 XMax where D0 is the particle diameter. The PACTS is successfully applied to organic latex, aluminum and silicon oxide particles of positive or negative charge using poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). The protocol is also optimized with respect to important parameters such as pH and concentration, and to the polyelectrolyte molecular weight. The advantages of the PACTS technique are that it requires minute amounts of sample and that it is suitable to a broad variety of charged nano-objects.

cond-mat.mtrl-sci↗

arXiv2015

Local viscoelasticity of living cells measured by rotational magnetic spectroscopy

When submitted to a magnetic field, micron size wires with superparamagnetic properties behave as embedded rheometers and represent interesting sensors for micro-rheology. Here we use rotational magnetic spectroscopy to measure the shear viscosity of the cytoplasm of living cells. We address the question of whether the cytoplasm is a viscoelastic liquid or a gel. The main result of the study is the observation of a rotational instability between a synchronous and an asynchronous regime of rotation, found for murine fibroblasts and human cancer cells. For wires of susceptibility 3.6, the transition occurs in the range 0.01...1 rad s-1. The determination of the shear viscosity (10...100 Pa s) and elastic modulus (5...20 Pa) confirms the viscoelastic character of the cytoplasm. In contrast to earlier studies, it is concluded that the interior of living cells can be described as a viscoelastic liquid, and not as an elastic gel.

cond-mat.soft↗

arXiv2015

Biophysicochemical interaction of a clinical pulmonary surfactant with nano-alumina

We report on the interaction of pulmonary surfactant composed of phospholipids and proteins with nanometric alumina (Al2O3) in the context of lung exposure and nanotoxicity. We study the bulk properties of phospholipid/nanoparticle dispersions and determine the nature of their interactions. The clinical surfactant Curosurf, both native and extruded, and a protein-free surfactant are investigated. The phase behavior of mixed surfactant/particle dispersions was determined by optical and electron microscopy, light scattering and zeta potential measurements. It exhibits broad similarities with that of strongly interacting nanosystems such as polymers, proteins or particles, and supports the hypothesis of electrostatic complexation. At a critical stoichiometry, micron sized aggregates arising from the association between oppositely charged vesicles and nanoparticles are formed. Contrary to the models of lipoprotein corona or of particle wrapping, our work shows that vesicles maintain their structural integrity and trap the particles at their surfaces. The agglomeration of particles in surfactant phase is a phenomenon of importance since it could change the interactions of the particles with lung cells.

physics.bio-ph↗