Magnetic nanoparticles: synthesis, properties and biomedical applications: Part 1: Synthesis and physical properties

MasterMagnetic nanoparticles present some attractive applications in biomedicine. First, they can be prepared from a size ranging from a few nanometers up to hundreds of nanometers, which places the particles at dimensions that are smaller than or comparable to those of cells (10–100 μm), virus (20–450 nm), proteins (5–50 nm) and genes (2 nm wide and 10–100 nm long). As a consequence they can “get close” to these biological entities. Furthermore, when coated with appropriate molecules magnetic nanoparticles can interact or bind to biological entities, which provides a mean of actuating on these entities by noncontact magnetic forces. This ‘action at a distance’, combined with the intrinsic penetrability of magnetic fields into biological tissues, possibilities a number of biomedical applications of magnetic nanoparticles.In this seminar, a revision of the state of the art in the fields of synthesis, properties and biomedical applications of magnetic nanoparticles is presented. This seminar is organized as it follows:1. Chemistry of iron oxides and oxo-hydroxides: Diversity of methods to prepare colloidal nanoparticles, either in non aqueous solvents: hydrothermal synthesis, polyol synthesis, thermal decomposition… or in water: co-precipitation of iron salts2. Magnetic behavior: ferro- /ferri- /antiferro- /superpara– magnetism, magnetophoresis (magnetic guiding)3. Optical properties: UV-vis absorption, circular dichroism (Faraday rotation), magnetic birefringence4. Relaxivity properties (T1/T2 of H spins): Contrast agents in MRI5. Magnetic relaxations in radiofrequency (kHz-MHz) fields: Magnetic hyperthermia and RF-induced drug releas

Nanoparticules magnétiques et structures auto-assemblées avec (ou sans) polymères

This manuscript describes ten years of research performed at the Pierre & Marie Curie University (Paris 6) then at the University of Bordeaux on composite materials based on magnetic iron oxide nanoparticles dispersed in a matrix, most often of polymer, but also sometimes of liquid crystal, with various sizes and shapes (gels, films, micron scale beads, micelles or vesicles...). The projects belong to the domain of medical imaging, and to pharmaceutical active delivery triggered magnetically. The annex file presents works anterior (1995-2001) and posterior (2012-2021) to this habilitation thesis.Ce manuscrit décrit dix années de recherche effectuées à l’université Pierre et Marie Curie puis à l’université de Bordeaux sur des matériaux composites à base de nanoparticules d’oxyde de fer magnétique dispersées dans une matrice, le plus souvent polymère, mais aussi parfois cristal liquide, de tailles et de formes variées (gels, films, billes micrométriques, micelles et vésicules…). Les projets s’inscrivent dans le domaine de l’imagerie médicale et la délivrance d’un actif pharmaceutique contrôlée magnétiquement. Le fichier annexe présente les travaux antérieurs (1995-2001) et postérieurs (2012-2021) à cette HDR

Pores transitoires, adhésion et fusion des vésicules géantes

Giant vesicles are artificial objects used to mimic the lipid envelope of biological cells, or plasma membrane, delimiting the cell interior from the outer medium. Among all the systems modeling biological membranes (monomolecular layers at the air/water interface, bilayers supported on a solid substrate, black lipid membranes, etc.…), giant vesicles are the softest and the easiest to change their shapes. Their membrane is a thin fluid sheet with indeed almost no surface tension. Nevertheless, it can be stretched by an external action. The value of the so created mechanical tension lies far below the usual interfacial tensions of liquids. However, with giant vesicles, the necessity to relax this low tension is a sufficient factor to cause major reorganizations of lipids. This work highlights two types of transformation: i) transient rupture of the membrane, and the leakage of the inner fluid through a giant macroscopic pore; ii) fusion of neighboring membranes, via the steps of hemifusion and then of a fusion pore. Experimental observations have been obtained mainly by fluorescence microscopy. A simple hydrodynamic theory describes the viscous dissipation inside the membrane and in the surrounding solvent. Besides, a novel imaging technique developed recently, namely the second harmonic generation (SHG) microscopy provides complementary information about the distance profile of adhering membranes. Finally, giant vesicles decorated with proteins enable to get a little closer to the reality of cell adhesion.Chapter I presents the general characteristics of vesicles, and the manipulations enabling to put them under tension. The experimental protocols are described in chapter II, to prepare on the one hand suspensions of giant vesicles in various mediums, on the other hand adhesive coatings on glass. Chapter III details the methods of optical microscopy, in order to observe the lipid membranes with the best contrast. After a brief state of the art about the break-down of lipid bilayers, chapter IV describes the complete dynamics of transient pores, both theoretically and experimentally. In particular, we shall see how the increased viscosity of the medium leads to longer lifetimes together with larger sizes. Chapter V just reveals descriptively the foams of giant vesicles. Depending on the type of interaction, vesicles either remain tense as soap bubbles, or they relax their tension by mixing part of their membranes.Les vésicules géantes sont des objets artificiels utilisés pour mimer l’enveloppe lipidique des cellules biologiques, la membrane plasmique, qui sépare l’intérieur de la cellule de son milieu extérieur. Parmi tous les systèmes censés modéliser les membranes biologiques (couches monomoléculaires à l’interface eau/air, bicouches supportées sur un substrat solide, films noirs lipidiques, etc...) les vésicules géantes sont les plus molles et les plus déformables. En effet, leur membrane est une mince couche fluide dont la tension de surface est pratiquement nulle. Néanmoins, elle peut être tendue progressivement par une action extérieure. La tension mécanique qui apparaît alors reste très en deçà des tensions interfaciales usuelles des liquides. Mais, sur des vésicules géantes, la relaxation de cette tension suffit pour provoquer des réorganisations importantes des lipides. Ce travail met en lumière deux types de transformation : i) la rupture transitoire de la membrane, et la fuite du liquide interne à travers un pore macroscopique géant ; ii) la fusion de deux membranes adjacentes, qui passe par les étapes intermédiaires d’hémifusion puis d’un pore de fusion. Les observations expérimentales ont été réalisées principalement en microscopie de fluorescence. Un modèle hydrodynamique simple étudie la dissipation visqueuse à l’intérieur de la membrane et dans le solvant alentour. En parallèle, une nouvelle imagerie mise au point récemment, la microscopie par génération de second harmonique (SHG), apporte des informations complémentaires sur le profil de distance des membranes adhérentes. Enfin, des vésicules géantes décorées par des protéines permettent de s’approcher un peu plus de la réalité de l’adhésion cellulaire.Le chapitre I présente les caractéristiques générales des vésicules, ainsi que les manipulations permettant de les mettre sous tension. Les protocoles expérimentaux sont décrits au chapitre II, pour préparer d’une part des suspensions de vésicules géantes dans différents milieux, d’autre part des traitements de surfaces adhésifs sur le verre. Les méthodes de microscopie optique, nécessaires pour observer les membranes lipidiques avec un contraste optimal, sont détaillées au chapitre III. La suite aborde les deux voies adoptées par les vésicules géantes pour relaxer une tension de surface. Après un bref état de l’art sur les ruptures de bicouches lipidiques, le chapitre IV décrit, sur le plan théorique puis expérimental, la dynamique complète des pores transitoires. Nous verrons en particulier comment la viscosité accrue du milieu augmente à la fois leur durée de vie et leur taille. Le chapitre V ne fait qu’aborder, d’une manière surtout descriptive, les mousses de vésicules géantes. Suivant leur type d’interaction, soit les vésicules restent tendues comme des bulles de savon, soit elles relaxent leur tension, en mélangeant partiellement leurs membranes

Transient pores in vesicles

International audienceWe present our observations of transient pores in giant unilamellar vesicles, placed under tension, by optical illumination. When the membrane tension reached a certain level, transient pores appeared. Pore opening is driven by the membrane tension, s, and its closure by the pore's line tension, T. By use of viscous mixtures of glycerol and water, we slowed down the leak out of the inner liquid in the presence of a pore. This allowed pores to reach large sizes (a few micrometres) and last at least a few seconds so that they could be visualized by fluorescence videomicroscopy. Line tension was inferred from the measurements of the closure velocity of the pores. By addition of cholesterol, which increased T (reducing pore lifetimes), or of surfactants, which decreased T (increasing pore lifetimes), we demonstrate how T , and consequently pore lifetimes, can be controlled over nearly two orders of magnitude. Addition of surfactants also has a dramatic effect on vesicle fusion. We discuss how our results can be extended to less viscous aqueous solutions which are more relevant for liposomal drug delivery formulations

Transient pores in stretched vesicles: role of leak-out

International audienceWe have visualized macroscopic transient pores in mechanically stretched giant vesicles. They can be observed only if the vesicles are prepared in a viscous solution to slow down the leak-out of the internal liquid. We study here theoretically the full dynamics of growth (driven by surface tension) and closure (driven by line tension) of these large pores. We write two coupled equations of the time evolution of the radii r(t) of the hole and R(t) of the vesicle, which both act on the release of the membrane tension. We find four periods in the life of a transient pore: (I) exponential growth of the young pore; (II) stop of the growth at a maximum radius rm; (III) slow closure limited by the leak-out; (IV) fast closure below a critical radius, when leak-out becomes negligible. Ultimately the membrane is completely resealed

Dispersion of magnetic nanoparticles in a nematic liquid crystal host: Phase diagram, Fredericks transition and deformation of droplets

During the seventies when the main properties of magnetic fluids were first understood, (superparamagnetism, birefringence, hydrodynamics instabilities...) theoreticians [1] have imagined the possible advantages of a ferrofluid with a thermotropic nematic liquid crystal (LC) as a solvent. Such a “ferronematic” would indeed combine the properties of two systems which become optically anisotropic (birefringent) under electrical and magnetic fields. The today widely used liquid crystals displays (LCDs) are based on the transition between transparent and opaque state of LCs, controlled by electric fields. For certain applications, magnetic fields could be used instead if we could lower down the threshold magnetic field intensity Hc of the so called Fredericks transition arising from the competition between alignment of LC molecules by surfaces and by an applied magnetic field. This idea motivated our experimental study of dispersion of nanoparticles made of maghemite iron oxide (Γ-Fe2O3) and 5-CB, one of the most standard nematic LCs which is convenient due to its nematic-isotropic temperature (TN-I=35°C) slightly above room temperature. However, we found that a true (monophasic) ferrofluid with 5-CB as solvent can be obtained only in the isotropic phase (above TN-I), whereas in the nematic state, the system separates between two phases: one the one hand magnetic microdroplets made of a high concentration of magnetic nanoparticles (about 18 vol% from SAXS measurements) in isotropic 5-CB and on the other hand a non magnetic 5-CB nematic matrix [2]. This phenomenon was explained by the thermodynamic laws for a ternary system (nanoparticles – LC – surfactant). Two aspect of these highly magnetic droplets in a LC host matrix where studied : i) their influence on the threshold field Hc of the Fredericks transition of a 5-CB layer sandwitched between two plates with homeotropic alignment conditions; ii) their strong ellipsoidal deformation under a magnetic field of low intensity, which – by analogy with ferrofluid droplets in a non magnetic liquid – provides an experimental measurement of the interfacial tension and tentatively of the anchoring energy of LC molecules onto nanoparticles [3]. ___________________________________________________ [1] F. Brochard, P. G. de Gennes, J. Phys. (Paris), 1970, 31, 691. [2] C. Da Cruz, O. Sandre, V. Cabuil, Journal of Phyical Chemistry B (2005) 109, 14292. [3] J. Deseigne, report of ESPCI engineering school short training period (March 2006)

Membrane imaging by simultaneous second-harmonic generation and two-photon microscopy

International audienceWe demonstrate that simultaneous second-harmonic generation (SHG) and two-photon-excited fluorescence (TPEF) can be used to rapidly image biological membranes labeled with a styryl dye. The SHG power is made compatible with the TPEF power by use of near-resonance excitation, in accord with a model based on the theory of phased-array antennas, which shows that the SHG radiation is highly structured. Because of its sensitivity to local asymmetry, SHG microscopy promises to be a powerful tool for the study of membrane dynamics

Magnetic tubules

International audienceDispersion of tubules made of diacetylenic phospholipids (DC8,9PC), in aqueous colloidal dispersions of magnetic nanoparticles is studied as a function of the sign of particles surface charges. In every case the tubule-vesicle transition temperature is decreased by the presence of the magnetic nanoparticles. Electrophoresis experiments on the tubules in pure water permits to conclude on a negative apparent surface charge. We study the magnetic response of the system to a static or stationary rotating field and to a magnetic field gradient. These experiments reveal an excess or a lack of magnetic permeability between tubules and the surrounding medium. Electron microscopy confirms these results showing an electrostatic interaction between the phospholipidic bilayer and the magnetic particles