427 research outputs found
Sphere-to-cylinder transition in hierarchical electrostatic complexes
We report the formation of colloidal complexes resulting from the
electrostatic co-assembly between anionic surfactants and cationic
polyelectrolytes or block copolymers. Combining light and x-ray scattering
experiments with cryogenic transmission and optical microscopy, we emphasize a
feature rarely addressed in the formation of the electrostatic complexes,
namely the role of the mixing concentration on the microstructure. At low
mixing concentration, electrostatic complexes made from cationic-neutral
copolymers and alkyl sulfate surfactants exhibit spherical core-shell
microstructures. With increasing concentration, the complexes undergo a
sphere-to-cylinder transition, yielding elongated aggregates with diameter 50
nm and length up to several hundreds of nanometers. From the comparison between
homo- and diblock polymer phase behaviors, it is suggested that the
unidimensional growth is driven by the ability of the surfactant to
self-assemble into cylindrical micelles, and in particular when these
surfactants are complexed with oppositely charged polymers.Comment: 7 pages, 9 figures, 2 tables paper accepted at Colloid and Polymer
Science, 31-Mar-0
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.Comment: 20 pages, 6 figure
Growth mechanism of nanostructured superparamagnetic rods obtained by electrostatic co-assembly
We report on the growth of nanostructured rods fabricated by electrostatic
co-assembly between iron oxide nanoparticles and polymers. The nanoparticles
put under scrutiny, {\gamma}-Fe2O3 or maghemite, have diameter of 6.7 nm and
8.3 nm and narrow polydispersity. The co-assembly is driven by i) the
electrostatic interactions between the polymers and the particles, and by ii)
the presence of an externally applied magnetic field. The rods are
characterized by large anisotropy factors, with diameter 200 nm and length
comprised between 1 and 100 {\mu}m. In the present work, we provide for the
first time the morphology diagram for the rods as a function of ionic strength
and concentration. We show the existence of a critical nanoparticle
concentration and of a critical ionic strength beyond which the rods do not
form. In the intermediate regimes, only tortuous and branched aggregates are
detected. At higher concentrations and lower ionic strengths, linear and stiff
rods with superparamagnetic properties are produced. Based on these data, a
mechanism for the rod formation is proposed. The mechanism proceeds in two
steps : the formation and growth of spherical clusters of particles, and the
alignment of the clusters induced by the magnetic dipolar interactions. As far
as the kinetics of these processes is concerned, the clusters growth and their
alignment occur concomitantly, leading to a continuous accretion of particles
or small clusters, and a welding of the rodlike structure.Comment: 15 pages, 10 figures, one tabl
The effects of aggregation and protein corona on the cellular internalization of iron oxide nanoparticles
Engineered inorganic nanoparticles are essential components in the
development of nanotechnologies. For applications in nanomedicine, particles
need to be functionalized to ensure a good dispersibility in biological fluids.
In many cases however, functionalization is not sufficient : the particles
become either coated by a corona of serum proteins or precipitate out of the
solvent. In the present paper, we show that by changing the coating of iron
oxide nanoparticles from a low-molecular weight ligand (citrate ions) to small
carboxylated polymers (poly(acrylic acid)), the colloidal stability of the
dispersion is improved and the adsorption/internalization of iron towards
living mammalian cells is profoundly affected. Citrate-coated particles are
shown to destabilize in all fetal-calf-serum based physiological conditions
tested, whereas the polymer coated particles exhibit an outstanding
dispersibility as well as a structure devoid of protein corona. The
interactions between nanoparticles and human lymphoblastoid cells are
investigated by transmission electron microscopy and flow cytometry. Two types
of nanoparticle/cell interactions are underlined. Iron oxides are found either
adsorbed on the cellular membranes, or internalized into membrane-bound
endocytosis compartments. For the precipitating citrate-coated particles, the
kinetics of interactions reveal a massive and rapid adsorption of iron oxide on
the cell surfaces. The quantification of the partition between adsorbed and
internalized iron was performed from the cytometry data. The results highlight
the importance of resilient adsorbed nanomaterials at the cytoplasmic membrane.Comment: 21 pages, 11 figures, accepted at Biomaterials (2011
Reorientation kinetics of superparamagnetic nanostructured rods
The attractive interactions between oppositely charged species (colloids,
macromolecules etc) dispersed in water are strong, and the direct mixing of
solutions containing such species generally yields to a precipitation, or to a
phase separation. We have recently developed means to control the
electrostatically-driven attractions between nanoparticles and polymers in
water, and at the same time to preserve the stability of the dispersions. We
give here an account of the formation of supracolloidal aggregates obtained by
co-assembly of 7 nm particles with copolymers. Nanostructured rods of length
comprised between 5 and 50 microns and diameter 500 nm were investigated. By
application of a magnetic field, the rods were found to reorient along with the
magnetic field lines. The kinetics of reorientation was investigated using step
changes of the magnetic field of amplitude 90 degrees. From the various results
obtained, among which an exponential decay of the tangent of the angle made
between the rod and the field, we concluded that the rods are
superparamagnetic.Comment: 12 pages - 452kB 7 - figures - 1 Table will be published in Journal
of Physics : Condensed Matte
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.Comment: 19 pages 9 figure
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