arXiv subjects

Jean-Francois Berret

Publications and source records attributed to Jean-Francois Berret.

At least 19 recordsLinked to original sources

arXiv2022

Versatile coating platform for metal oxide nanoparticles: applications to materials and biological science

In this feature article, we provide an overview of our research on statistical copolymers as a coating material for metal oxide nanoparticles and surfaces. These copolymers contain functional groups enabling non-covalent binding to oxide surfaces and poly(ethylene glycol) (PEG) polymers for colloidal stability and stealthiness. The functional groups are organic derivatives of phosphorous acid compounds R-H$_2$PO$_3$, also known as phosphonic acids that have been screened for their strong affinity to metals and their ability to build multidentate binding. Herein we develop a polymer-based coating platform that shares features with the techniques of self-assembled monolayers (SAM) and Layer-by-Layer (L-b-L) deposition. The milestones of this endeavor are the synthesis of PEG-based copolymers containing multiple phosphonic acid groups, the implementation of simple protocols combining versatility with high particle production yields and the experimental demonstration of the colloidal stability of the coated particles. As a demonstration, coating studies are conducted on cerium (CeO$_2$), iron ($γ$-Fe$_2$O$_3$), aluminum (Al$_2$O$_3$) and titanium (TiO$_2$) oxides of different sizes and morphologies. We finally discuss applications in the domain of nanomaterials and nanomedicine. We evaluate the beneficial effects of coating on redispersible nanopowders, contrast agents for In Vitro/Vivo assays and stimuli-responsive particles.

cond-mat.soft↗

arXiv2021

The desalting/salting pathway: a route to form metastable aggre-gates with tuneable morphologies and lifetimes

We investigate the formation/re-dissociation mechanisms of hybrid complexes made from negatively charged PAA2k coated γ-Fe2O3 nanoparticles (NP) and positively charged polycations (PDADMAC) in aqueous solution in the regime of very high ionic strength (I). When the building blocks are mixed at large ionic strength (1M NH4Cl), the electrostatic interaction is screened and complexation does not occur. If the ionic strength is then lowered down to a targeted ionic strength Itarget, there is a critical threshold Ic = 0.62 M at which complexation occurs, that is independent on the charge ratio Z and the pathway used to reduce salinity (drop-by-drop mixing or fast mixing). If salt is added back up to 1M, the transition is not reversible and persistent out-of-equilibrium aggregates are formed. The lifetimes of such aggregates depends on Itarget: the closer Itarget to Ic is, the more difficult it is to dissolve the aggregates. Such peculiar behavior is driven by the inner structure of the complexes that are formed after desalting. When Itarget is far below Ic, strong electrostatic interactions induce the formation of dense, compact and frozen aggregates. Such aggregates can only poorly reorganize further on with time, which makes their dissolution upon resalting almost reversible. Conversely, when Itarget is close to Ic more open aggregates are formed due to weaker electrostatic interactions upon desalting. System can thus rearrange with time to lower its free energy and reach more stable out-of-equilibrium states which are very difficult to dissociate back upon resalting, even at very high ionic strength.

cond-mat.soft↗

arXiv2021

Stimuli-responsive assembly of iron oxide nanoparticles into magnetic flexible filaments

The combination of multiple functionalities in a single material is an appealing strategy for the de-velopment of smart materials with unique features. In this work, we present the preparation of thermoresponsive magnetic nanoparticles and their one-dimensional assembly into transient micro-filaments. The material is based on 9.4 nm iron oxide nanoparticles grafted with poly(N-n-propylacrylamide) via multiphosphonic acid anchoring sites. The hybrid nanoparticles present a low critical solution temperature (LCST) transition between 21 °C and 28 °C, depending on the pH and the ionic strength. When heated above the LCST in defined conditions, the nanoparticles ag-gregate and respond to an external magnetic field. An intrinsic characteristic of the thermorespon-sive particles is an asymmetric transition between cooling and heating cycles, that was favorably exploited to build one-dimensional permanent microstructures, such as magnetic microfilaments and cilia. In summary, we present the development of a nanoplatform responsive to multiple stimu-li, including temperature, magnetic field, pH and ionic strength and its transformation into magneti-cally active microfilaments that could find potential applications in remotely controlled devices.

cond-mat.mtrl-sci↗

arXiv2020

Polymer coated cerium oxide nanoparticles as oxidoreductase-like catalysts

Cerium oxide nanoparticles have been shown to mimic oxidoreductase enzymes by catalyzing the decomposition of organic substrates and reactive oxygen species. This mimicry can be found in superoxide radicals and hydrogen peroxides, harmful molecules produced in oxidative stress asso-ciated diseases. Despite the fact that nanoparticle functionalization is mandatory in the context of nanomedicine, the influence of polymer coatings on their enzyme-like catalytic activity is poorly understood. In this work, six polymer coated cerium oxide nanoparticles are prepared by associa-tion of 7.8 nm cerium oxide cores with two poly(sodium acrylate) and four poly(ethylene glycol) (PEG) grafted copolymers with different terminal or anchoring end groups, such as phosphonic acids. The superoxide dismutase-, catalase-, peroxidase- and oxidase-like catalytic activities of the coated nanoparticles were systematically studied. It is shown that the polymer coatings do not af-fect the superoxide dismutase-like, impair the catalase-like and oxidase-like and surprisingly im-proves peroxidase-like catalytic activities of cerium oxide nanoparticles. It is also demonstrated that the particles coated with the PEG-grafted copolymers perform better than the poly(acrylic acid) coated ones as oxidoreductase-like enzymes, a result that confirms the benefit of having phosphon-ic acids as anchoring groups at the particle surface.

physics.app-ph↗

arXiv2020

Interaction between DNA and the Hfq amyloid-like region triggers a viscoelastic response

Molecular transport of biomolecules plays a pivotal role in the machinery of life. Yet, this role is poorly understood due the lack of quantitative information. Here, the role and properties of the C-terminal region of Escherichia coli Hfq is reported, involved in controlling the flow of a DNA solution. A combination of experimental methodologies has been used to probe the interaction of Hfq with DNA and to measure the rheological properties of the complex. A physical gel with a temperature reversible elasticity modulus is formed due to formation of non-covalent crosslinks. The mechanical response of the complexes shows that they are inhomogeneous soft solids. Our experiments indicate that Hfq C-terminal region could contribute to genome mechanical response. The reported viscoelasticity of the DNA-protein complex might have implications for cellular pro-cesses involving molecular transport of DNA or segments thereof.

cond-mat.soft↗

arXiv2018

Magnetic wire as stress controlled micro-rheometer for cytoplasm viscosity measurements

We review here different methods to measure the bulk viscosity of complex fluids using micron-sized magnetic wires. The wires are characterized by length of a few microns and diameter of a few hundreds of nanometers. We first draw analogies between cone-and-plate rheometry and wire-based microrheology. In particular we highlight that magnetic wires can be operated as stress-controlled rheometers for two types of testing, the creep-recovery and steady shear experiments. In the context of biophysical applications, the cytoplasm of different cell lines including fibroblasts, epithelial and tumor cells is studied. It reveals that the interior of living cells can be described as a viscoelastic liquid with a static viscosity comprised between 10 and 100 Pas. We extend the previous approaches and show that the proposed technique can also provide time resolved viscosity data, which for cells display strong temporal fluctuations. The present work demonstrates the high potential of the magnetic wires for quantitative rheometry in confined espaces.

cond-mat.soft↗

arXiv2014

Superparamagnetic iron oxide polyacrylic acid coated γ-Fe2O3 nanoparticles does not affect kidney function but causes acute effect on the cardiovascular function in healthy mice

This study describes the distribution of intravenously injected polyacrylic acid (PAA) coated γ-Fe2O3 NPs (10 mg kg-1) at the organ, cellular and subcellular levels in healthy BALB/cJ mice and in parallel addresses the effects of NP injection on kidney function, blood pressure and vascular contractility. Magnetic resonance imaging (MRI) and transmission electron microscopy (TEM) showed accumulation of NPs in the liver within 1h after intravenous infusion, accommodated by intracellular uptake in endothelial and Kupffer cells with subsequent intracellular uptake in renal cells, particularly the cytoplasm of the proximal tubule, in podocytes and mesangial cells. The renofunctional effects of NPs were evaluated by arterial acid-base status and measurements of glomerular filtration rate (GFR) after instrumentation with chronically indwelling catheters. Arterial pH was 7.46 and 7.41 in mice 0.5 h after injections of saline or NP, and did not change over the next 12h. In addition, the injections of NP did not affect arterial PCO2 or [HCO3-] either. Twenty-four and 96h after NP injections, the GFR averaged 11.0 and 13.0 ml min-1 g-1, respectively, values which were statistically comparable with controls (14.0 and 14.0 ml min-1 g-1). Mean arterial blood pressure (MAP) decreased 12-24h after NP injections (111 vs 123 min-1) associated with a decreased contractility of small mesenteric arteries revealed by myography to characterise endothelial function. In conclusion, our study demonstrates that accumulation of superparamagnetic iron oxide nanoparticles does not affect kidney function in healthy mice but temporarily decreases blood pressure.

physics.med-ph↗

arXiv2013

Self-assembly of complex salts of cationic surfactants and anionic-neutral block copolymers. Dispersions with liquid-crystalline internal structure

We report the synthesis of complex salts made from the cationic surfactant dodecyltrimethyl-ammonium and diblock copolymers poly(acrylic acid)-block-poly(acrylamide) of different molecular weights. In water, the complex salts self-assemble into stable hierarchical aggregates with a dense core and a diffuse shell. In contrast to earlier reports, the surfactant/polymer aggregates exhibit a liquid crystalline structure of Pm3n cubic symmetry. The crystal structure is analogous to that obtained with homopolymer. Size and aggregation numbers were estimated from a combination of light and small-angle x-ray scattering experiments. It is found that the size of the aggregates decreases with increasing diblock asymmetry. The complex salt methodology presents many advantages, among which to be insensitive to the preparation conditions and to the mixing pathway.

cond-mat.mtrl-sci↗

arXiv2011

Superstructures par agrégation contrôlée de nanocolloïdes: caractérisation structurale par diffusion de neutrons aux petits angles et simulation numérique

The complexation of micelles or charged nanoparticles with neutral-charged block copolymers in aqueous solutions leads to the formation of colloidal superstructures also termed 'colloidal complexes'. Their primary interest relies in their monodispersity in size, and in their increased domain of stability. In this review, the structural characterization by dynamic light scattering, cryo-TEM, and small angle neutron scattering is presented. Small angle neutron scattering results have been analyzed using numerical simulations - Monte Carlo or reverse Monte Carlo (RMC). Such simulations are useful to show the compatibility between different models of colloidal superstructures, and experiment. Our results have allowed us to propose a generic structure of complex colloids, made of a dense core of interacting colloids, bridged by polyelectrolyte blocks, and a hydrated corona. We have shown that such superstructures are formed systematically in these systems, with either micelles or nanoparticles, for different copolymers, and different charges. The text is in French.

cond-mat.soft↗

arXiv2009

Shear-induced transitions and instabilities in surfactant wormlike micelles

In this review, we report recent developments on the shear-induced transitions and instabilities found in surfactant wormlike micelles. The survey focuses on the non-linear shear rheology and covers a broad range of surfactant concentrations, from the dilute to the liquid-crystalline states and including the semi-dilute and concentrated regimes. Based on a systematic analysis of many surfactant systems, the present approach aims to identify the essential features of the transitions. It is suggested that these features define classes of behaviors. The review describes three types of transitions and/or instabilities : the shear-thickening found in the dilute regime, the shear-banding which is linked in some systems to the isotropic-to-nematic transition, and the flow-aligning and tumbling instabilities characteristic of nematic structures. In these three classes of behaviors, the shear-induced transitions are the result of a coupling between the internal structure of the fluid and the flow, resulting in a new mesoscopic organization under shear. This survey finally highlights the potential use of wormlike micelles as model systems for complex fluids and for applications.

cond-mat.soft↗

arXiv2009

Electrostatic co-assembly of magnetic nanoparticles and fluorescent nanospheres: a versatile approach toward bimodal nanorods

The elaboration of multimodal nanoparticles stimulates tremendous interest owing to their numerous potentialities in many applicative fields like optoelectronics, photonics and especially bioimaging. The concomitant association of various properties (optical, electrochemical, magnetic) allows for the use of complementary stimuli in order to probe the interactions between the nanoparticles and their surroundings.Nanoparticles (NPs) have thus become highly praised tools to image cells and tissues with a large contrast compatible with the dimensions of biological materials and the existence of quantum confinement effects induced by the reduced dimensions. In this context, the combination of magnetism and emissive properties such as fluorescence appears particularly attractive for non-invasive investigations, cell sorting or drug vectorization. Therefore, combining both fluorescence and magnetism requires the delicate construction of hybrid assemblies. Most of the magnetic nanoparticles are made of metallic oxides or alloys, e.g. gamma-Fe2O3, Fe3O4, FePt, while the target fluorescent entities are often organic dyes or quantum dots (QDs).

cond-mat.mtrl-sci↗

arXiv2008

Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents

We have studied the phase behavior of the poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible solvents, water and tetrahydrofuran (THF). The techniques used to examine the different polymers, structures and phases formed in mixed solvents were static and dynamic light scattering, small-angle neutron scattering, nuclear magnetic resonance and fluorescence microscopy. By lowering the water/THF mixing ratio X, the sequence unimers, micron-sized droplets, polymeric micelles was observed. The transition between unimers and the micron-sized droplets occurred at X = 0.75, whereas the microstructuration into core-shell polymeric micelles was effective below X = 0.4. At intermediate mixing ratios, a coexistence between the micron-sized droplets and the polymeric micelles was observed. Combining the different aforementioned techniques, it was concluded that the droplet dispersion resulted from a solvent partitioning that was induced by the hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the droplets were rich in THF and concentrated in copolymers and that they were stabilized by the hydrophilic poly(acrylic acid) moieties.

cond-mat.soft↗

arXiv2007

Organic versus Hybrid Coacervate Complexes : Co-Assembly and Adsorption Properties

We report the co-assembly and adsorption properties of coacervate complexes made from polyelectrolyte-neutral block copolymers and oppositely charged nanocolloids. The nanocolloids put under scrutiny were ionic surfactant micelles and highly charged 7 nm cerium oxide (CeO2) nanoparticles. Static and dynamic light scattering was used to investigate the microstructure and stability of the organic and hybrid complexes. The microstructure of the CeO2-based complexes was resolved using cryogenic transmission electronic microscopy (Cryo-TEM), and it revealed that the cores were clusters made from densely packed nanoparticles. In the concentration range of interest, c = 10-4 - 1 wt. %, the surfactant-based complexes were shown to exhibit a critical association concentration (cac) whereas the nanoparticle-polymer hybrids did not. The adsorption properties of the same complexes were investigated above the cac by stagnation point adsorption reflectometry. The adsorbed amount was measured as a function of time for polymers and complexes using anionically charged silica and hydrophobic poly(styrene) substrates. It was found that all complexes adsorbed readily on both types of substrates up to a level of 1 - 2 mg m-2 at stationary state. Upon rinsing however, the adsorbed layer was removed for the surfactant-based systems, but not for the cerium oxide clusters. As for the solution properties, these finding were interpreted in terms of a critical association concentrations which are very different for organic and hybrid complexes.

cond-mat.mtrl-sci↗

arXiv2007

Stability and Adsorption Properties of Electrostatic Complexes : Design of Hybrid Nanostructures for Coating Applications

We report the presence of a correlation between the bulk and interfacial properties of electrostatic coacervate complexes. Complexes were obtained by co-assembly between cationic-neutral diblocks and oppositely charged surfactant micelles or 7 nm cerium oxide nanoparticles. Light scattering and reflectometry measurements revealed that the hybrid nanoparticle aggregates were more stable both through dilution and rinsing (from either a polystyrene or a silica surfaces) than their surfactant counterparts. These findings were attributed to a marked difference in critical association concentration between the two systems and to the frozen state of the hybrid structures.

cond-mat.soft↗

arXiv2007

Use of Superparamagnetic Nanoparticle/Block Copolymer Electrostatic Complexes as Contrast Agents in Magnetic Resonance Imaging

During the past years we have investigated the complexation between nanocolloids and oppositely charged polymers. The nanocolloids examined were ionic surfactant micelles and inorganic oxide nanoparticles. For the polymers, we used homopolyelectrolytes and block copolymers with linear and comb architectures. In general, the attractive interactions between oppositely charged species are strong and as such, the simple mixing of solutions containing dispersed constituents yield to a precipitation, or to a phase separation. We have developed means to control the electrostatically-driven attractions and to preserve the stability of the mixed solution. With these approaches, we designed novel core-shell nanostructures, e.g. as those obtained with polymers and iron oxide superparamagnetic nanoparticles. In this presentation, we show that electrostatic complexation can be used to tailor new functionalized nanoparticles and we provide examples related to biomedical applications in the domain of contrast agents for Magnetic Resonance Imaging.

cond-mat.soft↗

arXiv2006

Polymer-Nanoparticle Complexes : from Dilute Solution to Solid State

We report on the formation and the structural properties of supermicellar aggregates also called electrostatic complexes, made from mineral nanoparticles and polyelectrolyte-neutral block copolymers in aqueous solutions. The mineral particles put under scrutiny are ultra-fine and positively charged yttrium hydroxyacetate nanoparticles. Combining light, neutron and x-ray scattering experiments, we have characterized the sizes and the aggregation numbers of the organic-inorganic complexes. We have found that the hybrid aggregates have typical sizes in the range 100 nm and exhibit a remarkable colloidal stability with respect to ionic strength and concentration variations. Solid films with thicknesses up to several hundreds of micrometers were cast from solutions, resulting in a bulk polymer matrix in which nanoparticle clusters are dispersed and immobilized. It was found in addition that the structure of the complexes remains practically unchanged during film casting.

cond-mat.soft↗

arXiv2005

Controlled Clustering of Superparamagnetic Nanoparticles using Block Copolymers : Design of New Contrast Agents for Magnetic Resonance Imaging

When polyelectrolyte-neutral block copolymers are mixed in aqueous solutions with oppositely charged species, stable complexes are found to form spontaneously. The mechanism is based on electrostatics, and on the compensation between the opposite charges. Electrostatic complexes exhibit a core-shell microstructure. In the core, the polyelectrolyte blocks and the oppositely charged species are tightly bound and form a dense coacervate microphase. The shell is made of the neutral chains and surrounds the core. In this paper, we report on the structural and magnetic properties of such complexes made from 6.3 nm diameter superparamagnetic nanoparticles (maghemite gamma-Fe2O3) and cationic-neutral copolymers. The copolymers investigated are poly(trimethylammonium ethylacrylate methylsulfate)-b-poly(acrylamide), with molecular weights 5000-b-30000 gmol-1 and 110000-b-30000 gmol-1. The mixed copolymer-nanoparticle aggregates were characterized by a combination of light scattering and cryo-transmission electron microscopy. Their hydrodynamic diameters were found in the range 70 - 150 nm and their aggregation numbers (number of nanoparticles per aggregate) between several tens to several hundreds. In addition, Magnetic Resonance Spin-Echo measurements show that the complexes have a better contrast in Magnetic Resonance Imaging than single nanoparticles, and that these complexes could be used for biomedical applications.

cond-mat.soft↗

arXiv2005

Evidence of Overcharging in the Complexation between Oppositely Charged Polymers and Surfactants

We report on the complexation between charged-neutral block copolymers and oppositely charged surfactants studied by small-angle neutron scattering. Two block copolymers/surfactant systems are investigated, poly(acrylic acid)-b-poly(acrylamide) with dodecyltrimethylammonium bromide and poly(trimethylammonium ethylacrylate methylsulfate)-b-poly(acrylamide) with sodium dodecyl sulfate. The two systems are similar in terms of structure and molecular weight but have different electrostatic charges. The neutron scattering data have been interpreted in terms of a model that assumes the formation of mixed polymer-surfactant aggregates, also called colloidal complexes. These complexes exhibit a core-shell microstructure, where the core is a dense coacervate microphase of micelles surrounded by neutral blocks. Here, we are taking advantage of the fact that the complexation results in finite-size aggregates to shed some light on the complexation mechanisms. In order to analyze quantitatively the neutron data, we develop two different approaches to derive the number of surfactant micelles per polymer in the mixed aggregates and the distributions of aggregation numbers. With these results, we show that the formation of the colloidal complex is in agreement with the overcharging predictions. In both systems, the amount of polyelectrolytes needed to build the core-shell colloids always exceeds the number that would be necessary to compensate the charge of the micelles. For the two polymer-surfactant systems investigated, the overcharging ratios are 0.66 and 0.38.

cond-mat.soft↗