Polymeric Nanoparticles Limit the Collective Migration of Cellular Aggregates

Controlling the propagation of primary tumors is fundamental to avoiding the epithelial to mesenchymal transition process leading to the dissemination and seeding of tumor cells throughout the body. Here we demonstrate that nanoparticles (NPs) limit the propagation of cell aggregates of CT26 murine carcinoma cells used as tumor models. The spreading behavior of these aggregates incubated with NPs is studied on fibronectin-coated substrates. The cells spread with the formation of a cell monolayer, the precursor film, around the aggregate. We study the effect of NPs added either during or after the formation of aggregates. We demonstrate that, in both cases, the spreading of the cell monolayer is slowed down in the presence of NPs and occurs only above a threshold concentration that depends on the size and surface chemistry of the NPs. The density of cells in the precursor films, measured by confocal microscopy, shows that the NPs stick cells together. The mechanism of slowdown is explained by the increase in cell-cell interactions due to the NPs adsorbed on the membrane of the cells. The present results demonstrate that NPs can modulate the collective migration of cells; therefore, they may have important implications for cancer treatment.Peer reviewe

Compact and highly stable quantum dots through optimized aqueous phase transfer

International audienceA large number of different approaches for the aqueous phase transfer of quantum dots have been proposed. Surface ligand exchange with small hydrophilic thiols, such as L-cysteine, yields the lowest hydrodynamic diameter. However, cysteine is prone to dimer formation, which limits colloidal stability. We demonstrate that precise pH control during aqueous phase transfer dramatically increases the colloidal stability of InP/ZnS quantum dots. Various bifunctional thiols have been applied. The formation of disulfides, strongly diminishing the fluorescence QY has been prevented through addition of appropriate reducing agents. Bright InP/ZnS quantum dots with a hydrodynamic diameter <10 nm and longterm stability have been obtained. Finally we present in vitro studies of the quantum dots functionalized with the cellpenetrating peptide maurocalcin

Spontaneous migration of cellular aggregates from giant keratocytes to running spheroids

Despite extensive knowledge on the mechanisms that drive singlecell migration, those governing the migration of cell clusters, as occurring during embryonic development and cancer metastasis,remain poorly understood. Here, we investigate the collective migration of cell on adhesive gels with variable rigidity, using 3D cellular aggregates as a model system. After initial adhesion to the substrate, aggregates spread by expanding outward a cell monolayer, whose dynamics is optimal in a narrowrange of rigidities. Fast expansion gives rise to the accumulation of mechanical tension that leads to the rupture of cell–cell contacts and the nucleation of holes within the monolayer, which becomes unstable and undergoes dewetting like a liquid film. This leads to a symmetry breaking and causes the entire aggregate to move as a single entity. Varying the substrate rigidity modulates the extent of dewetting and induces different modes of aggregate motion: “giant keratocytes,” where the lamellipodium is a cell monolayer that expands at the front and retracts at the back; “penguins,” characterized by bipedal locomotion; and “running spheroids,” for nonspreading aggregates. We characterize these diverse modes of collectivemigration by quantifying the flows and forces that drive them, andwe unveil the fundamental physical principles that govern these behaviors, which underscore the biological predisposition of living material to migrate, independent of length scale

Magnétoliposomes pour l'imagerie et l'étude des membranes lipidiques

La première partie de ce travail de thèse porte sur l élaboration de vésicules multifonctionnelles encapsulant différents types de nanoparticules ayant un intérêt pour l imagerie ou la thérapie médicale : des nanoparticules magnétiques, des quantum dots et des nanoparticules d or. Ces nanoparticules sont co-encapsulées dans des liposomes par émulsions multiples et émulsion en phase inverse. Ces dernières sont étudiées d un point de vue morphologique par microscopie (optique et confocale) et leurs propriétés (magnétiques, de fluorescence, d échauffement) sont explorées. La deuxième partie est consacrée à l utilisation des magnétoliposomes géants (GUV) comme modèle membranaire. L encapsulation de particules bifonctionnelles ( Fe2O3-rhodamine) dans les GUV a mis en évidence une interaction préférentielle des particules avec la membrane liée à la fois à la présence de rhodamine et à la force ionique du ferrofluide encapsulé. D autre part, l insertion d un tensioactif catanionique sous forme monomérique dans la membrane ou sa fusion sous forme vésiculaire avec la membrane des GUV a été prouvée par des mesures d élasticité de membrane sous champ magnétique et par des modifications de morphologie des liposomes.The first part of this work concerns ths synthesis of multifunctional vesicles encapsulating nanoparticles with potential applications in the fields of imagery and therapy : magnetic nanoparticles, quantum dots and gold nanoparticles. The liposomes are synthesized using two emulsion processes. Their morphology is characteized by confocal and optical microscopy and their properties (magnetic, fluorescent and overheating properties) are investigated. The second part is devoted to the use of giant and magnetic liposomes (GUV) as a membrane model. The encapsulation of bifunctionnal particles inside GUV highlights a specific interaction between nanoparticles and the membrane of th eGUV due to rhodamine and th eionic strength of the encapsulated magnetic fluid. We also studied the insertion of catanionic surfactant, in the monomeric or vesicular state, inside the membrane of the GUV. It has been demonstrated by th eimportant shape modifications of GUV and their membrane elasticity measurements under a magnetic field.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Aqueous phase transfer of InP/ZnS nanocrystals conserving fluorescence and high colloidal stability

Small thiol-containing amino acids such as cysteine are appealing surface ligands for transferring semiconductor quantum dots (QDs) from organic solvents to the aqueous phase. They provide a compact hydrodynamic diameter and low nonspecific binding in biological environment. However, cysteine-capped QDs generally exhibit modest colloidal stability in water and their fluorescence quantum yield (QY) is significantly reduced as compared to organics. We demonstrate that during phase transfer the deprotonation of the thiol group by carefully adjusting the pH is of crucial importance for increasing the binding strength of cysteine to the QD surface. As a result, the colloidal stability of cysteine-capped InP/ZnS core/shell QDs is extended from less than one day to several months. The developed method is of very general character and can be used also with other hydrophilic thiols and various other types of QDs, e.g., CdSe/CdS/ZnS and CuInS(2)/ZnS QDs as well as CdSe and CdSe/CdS nanorods. We show that the observed decrease of QY upon phase transfer with cysteine is related to the generation of cysteine dimer, cystine. This side-reaction implies the formation of disulfide bonds, which efficiently trap photogenerated holes and inhibit radiative recombination. On the other hand, this process is not irreversible. By addition of an appropriate reducing agent, tris(2-carboxyethyl)phosphine hydrochloride (TCEP), the QY can be partially recovered. When TCEP is already added during the phase transfer, the QY of cysteine-capped InP/ZnS QDs can be maintained almost quantitatively. Finally, we show that penicillamine is a promising alternative to cysteine for the phase transfer of QDs, as it is much less prone to disulfide formatio

Ferrofluidic aqueous two-phase system with ultralow interfacial tension and micro-pattern formation

| openaire: EC/H2020/803937/EU//InterActive Funding Information: J.V.I.T. acknowledges funding from ERC (803937) and Academy of Finland (316219). We acknowledge the facilities and technical support by Aalto University at OtaNano Nanomicroscopy Centre (Aalto-NMC). Publisher Copyright: © 2022, The Author(s).Ferrofluids are magnetic liquids known for the patterns they form in external magnetic fields. Typically, the patterns form at the interface between a ferrofluid and another immiscible non-magnetic fluid with a large interfacial tension γ ∼ 10−2 N m−1, leading to large pattern periodicities. Here we show that it is possible to reduce the interfacial tension several orders of magnitude down to ca. γ ∼ 10−6 N m−1 by using two immiscible aqueous phases based on spontaneous phase separation of dextran and polyethylene glycol and the asymmetric partitioning of superparamagnetic maghemite nanoparticles into the dextran-rich phase. The system exhibits classic Rosensweig instability in a uniform magnetic field with a periodicity of ∼200 μm, significantly lower than in traditional systems (∼10 mm). This system paves the way towards the science of pattern formation at the limit of vanishing interfacial tension and ferrofluid applications driven by small external magnetic fields.Peer reviewe

Self-Coacervation of a Silk-Like Protein and Its Use As an Adhesive for Cellulosic Materials

Liquid-liquid phase separation of biomacromolecules plays a critical role in many of their functions, both as cellular components and in structural assembly. Phase separation is also a key mechanism in the assembly of engineered recombinant proteins for the general aim to build new materials with unique structures and properties. Here the phase separation process of an engineered protein with a block-architecture was studied. As a central block, we used a modified spider silk sequence, predicted to be unstructured. In each terminus, folded globular blocks were used. We studied the kinetics and mechanisms of phase formation and analyzed the evolving structures and their viscoelastic properties. Individual droplets were studied with a micropipette technique, showing both how properties vary between individual drops and explaining overall bulk rheological properties. A very low surface energy allowed easy deformation of droplets and led to efficient infiltration into cellulosic fiber networks. Based on these findings, we demonstrated an efficient use of the phase-separated material as an adhesive for cellulose. We also conclude that the condensed state is metastable, showing an ensemble of properties in individual droplets and that an understanding of protein phase behavior will lead to developing a wider use of proteins as structural polymers.Peer reviewe