132 research outputs found
Salt-induced reentrant stability of polyion-decorated particles with tunable surface charge density
The electrostatic complexation between DOTAP-DOPC unilamellar liposomes and
an oppositely charged polyelectrolyte (NaPA) has been investigated in a wide
range of the liposome surface charge density. We systematically characterized
the "reentrant condensation" and the charge inversion of
polyelectrolyte-decorated liposomes by means of dynamic light scattering and
electrophoresis. We explored the stability of this model
polyelectrolyte/colloid system by fixing each time the charge of the bare
liposomes and by changing two independent control parameters of the
suspensions: the polyelectrolyte/colloid charge ratio and the ionic strength of
the aqueous suspending medium. The progressive addition of neutral DOPC lipid
within the liposome membrane gave rise to a new intriguing phenomenon: the
stability diagram of the suspensions showed a novel reentrance due to the
crossing of the desorption threshold of the polyelectrolyte. Indeed, at fixed
charge density of the bare DOTAP/DOPC liposomes and for a wide range of polyion
concentrations, we showed that the simple electrolyte addition first (low salt
regime) destabilizes the suspensions because of the enhanced screening of the
residual repulsion between the complexes, and then (high salt regime)
determines the onset of a new stable phase, originated by the absence of
polyelectrolyte adsorption on the particle surfaces. We show that the observed
phenomenology can be rationalized within the Velegol-Thwar model for
heterogeneously charged particles and that the polyelectrolyte desorption fits
well the predictions of the adsorption theory of Winkler and Cherstvy. Our
findings unambiguously support the picture of the reentrant condensation as
driven by the correlated adsorption of the polyelectrolyte chains on the
particle surface, providing interesting insights into possible mechanisms for
tailoring complex colloids via salt-induced effects.Comment: 34 pages, 7 figure
Overcharging and reentrant condensation of thermoresponsive ionic microgels
We investigated the complexation of thermoresponsive anionic
poly(N-isopropylacrylamide) (PNiPAM) microgels and cationic
-polylysine (-PLL) chains. By combining electrophoresis,
light scattering, transmission electron microscopy (TEM) and dielectric
spectroscopy (DS) we studied the adsorption of -PLL onto the microgel
networks and its effect on the stability of the suspensions. We show that the
volume phase transition (VPT) of the microgels triggers a large polyion
adsorption. Two interesting phenomena with unique features occur: a
temperature-dependent microgel overcharging and a complex reentrant
condensation. The latter may occur at fixed polyion concentration, when
temperature is raised above the VPT of microgels, or by increasing the number
density of polycations at fixed temperature. TEM and DS measurements
unambiguously show that short PLL chains adsorb onto microgels and act as
electrostatic glue above the VPT. By performing thermal cycles, we further show
that polyion-induced clustering is a quasi-reversible process: within the time
of our experiments large clusters form above the VPT and partially re-dissolve
as the mixtures are cooled down. Finally we give a proof that the observed
phenomenology is purely electrostatic in nature: an increase of the ionic
strength gives rise to the polyion desorption from the microgel outer shell.Comment: 15 Figure
Study of network composition in interpenetrating polymer networks of poly(N isopropylacrylamide) microgels:the role of poly(acrylic acid)
Hypothesis: The peculiar swelling behaviour of poly(N-isopropylacrylamide)
(PNIPAM)-based responsive microgels provides the possibility to tune both
softness and volume fraction with temperature, making these systems of great
interest for technological applications and theoretical implications. Their
intriguing phase diagram can be even more complex if poly(acrylic acid) (PAAc)
is interpenetrated within PNIPAM network to form Interpenetrating Polymer
Network (IPN) microgels that exhibit an additional pH-sensitivity. The effect
of the PAAc/PNIPAM polymeric ratio on both swelling capability and dynamics is
still matter of investigation. Experiments: Here we investigate the role of
PAAc in the behaviour of IPN microgels across the volume phase transition
through dynamic light scattering (DLS), transmission electron microscopy (TEM)
and electrophoretic measurements as a function of microgel concentration and
pH. Findings: Our results highlight that aggregation is favored at increasing
weight concentration, PAAc content and pH and that a crossover PAAc content
C*_{PAAc} exists above which the ionic charges on the microgel become relevant.
Moreover we show that the softness of IPN microgels can be tuned ad hoc by
changing the PAAc/PNIPAM ratio. These findings provide new insights into the
possibility to control experimentally aggregation properties, charge and
softness of IPN microgels by varying PAAc content.Comment: preprint versio
Biophysical and biological contributions of polyamine-coated carbon nanotubes and bidimensional buckypapers in the delivery of miRNAs to human cells
Recent findings in nanomedicine have revealed that carbon nanotubes (CNTs) can be used as potential drug carriers, therapeutic agents and diagnostics tools. Moreover, due to their ability to cross cellular membranes, their nanosize dimension, high surface area and relatively good biocompatibility, CNTs have also been employed as a novel gene delivery vector system. In our previous work, we functionalized CNTs with two polyamine polymers, polyethyleneimine (PEI) and polyamidoamine dendrimer (PAMAM). These compounds have low cytotoxicity, ability to conjugate microRNAs (such as miR-503) and, at the same time, transfect efficiently endothelial cells. The parameters contributing to the good efficiency of transfection that we observed were not investigated in detail. In fact, the diameter and length of CNTs are important parameters to be taken into account when evaluating the effects on drug delivery efficiency. In order to investigate the biophysical and biological contributions of polymer-coated CNTs in delivery of miRNAs to human cells, we decided to investigate three different preparations, characterized by different dimensions and aspect ratios. In particular, we took into account very small CNTs, a suspension of CNTs starting from the commercial product and a 2D material based on CNTs (ie, buckypapers [BPs]) to examine the transfection efficiency of a rigid scaffold. In conclusion, we extensively investigated the biophysical and biological contributions of polyamine-coated CNTs and bidimensional BPs in the delivery of miRNAs to human cells, in order to optimize the transfection efficiency of these compounds to be employed as efficient drug delivery vectors in biomedical applications
Comparative treatments of a green tattoo ink with Ruby, Nd: YAG nano- and picosecond lasers in normal and array mode
The tattoos removal has become an issue upon spread of the tattooing practice worldwide and
hindsight regrets. Lasers are typically used for the purpose, though some colours such as green are
considered “recalcitrant” to the treatment. In the current investigation, we aim at determining the
efcacy of removal of a green ink water dispersion, using 5 laser treatments: Nd:YAG nano- and
picosecond lasers in normal and array mode and Ruby nanosecond laser, keeping the total irradiated
energy constant. The UV–Vis spectroscopy of the treated samples indicate that Nd:YAG picosecond
laser is most efective, and the Ruby nanosecond laser is the least efcient. Fragment compounds
generated from the pigment and siloxanes are common to all treatments, whereas hydrocarbon
emerge by a larger amount upon Nd:YAG nanosecond treatment. Fibres are formed upon picosecond
treatments and when operating in array mode, and lamellae are achieved by Ruby nanosecond laser
treatment. Residual particles suspensions are very heterogeneous upon nanosecond treatments
Proton-driven patterning of bulk transition metal dichalcogenides
At the few-atom-thick limit, transition metal dichalcogenides (TMDs) exhibit
a host of attractive electronic optical, and structural properties. The
possibility to pattern these properties has a great impact on applied and
fundamental research. Here, we demonstrate spatial control over the light
emission, lattice deformation, and hydrogen storage in bulk TMDs. By low-energy
proton irradiation, we create uniquely favorable conditions for the production
and accumulation of molecular hydrogen just one or few monolayers beneath the
crystal basal plane of bulk WS2, WSe2, WTe2, MoSe2, and MoS2 samples. H2
therein produced coalesces to form bubbles, which lead to the localized
swelling of one X-M-X plane prevalently. This results eventually in the
creation of atomically thin domes filled with molecular hydrogen at 10 atm. The
domes emit light strongly well above room temperature and can store H2
indefinitely. They can be produced with the desired density, well-ordered
positions, and size tunable from the nanometer to the micrometer scale, thus
providing a template for the manageable and durable mechanical and electronic
structuring of two-dimensional materials
Laser vs. thermal treatments of green pigment PG36: coincidence and toxicity of processes
Comparative laser and thermal treatments were carried out on PG36, a green phthalocyanine-based pigment, permitted in
European countries where legislation on tattoo composition was issued. Prior to the treatments, PG36 was characterized
by SEM imaging, EDX, IR and UV–Vis spectroscopies, revealing an excess of Si and C and O as compared to the pure
halogenated Cu-phthalocyanine. Laser treatments were carried out with a Nd:YAG device applied to H2O
and propan-2-ol
dispersions. Pyrolysis and calcinations were carried out in air or under N2
flow. The outcome of the different procedures was
analyzed by UV–Vis spectroscopy, GC–mass spectrometry, X-ray diffraction of the solid residues, SEM microscopy and
dynamic light scattering. The comparative analysis indicated the production of different fragment compounds depending
on the treatment, (pyrolysis or laser), and, to some extent, to the solvent of the dispersion, with pyrolysis generating a larger
number of hazardous compounds. Hydrocarbons and cyclic siloxanes present as additives in PG36 were stable or degraded
depending on the treatment. The morphology of the products is also treatment-dependent with nanoparticles < 20 nm and
fibers being produced upon laser treatments only. Based on the experimental findings, the equivalence of laser and thermal
treatments is evaluated
Toward a unified description of the electrostatic assembly of microgels and nanoparticles
The combination of soft responsive particles, such as microgels, with
nanoparticles (NPs) yields highly versatile complexes of great potential for
applications, from ad-hoc plasmonic sensors to controlled protocols for loading
and release. However, the assembly process between these microscale networks
and the co-dispersed nano-objects has not been investigated so far at the
microscopic level, preempting the possibility of designing such hybrid
complexes a priori. In this work, we combine state-of-the-art numerical
simulations with experiments, to elucidate the fundamental mechanisms taking
place when microgels-NPs assembly is controlled by electrostatic interactions.
We find a general behavior where, by increasing the number of interacting NPs,
the microgel deswells up to a minimum size, after which a plateau behavior
occurs. This occurs either when NPs are mainly adsorbed to the microgel corona
via the folding of the more external chains, or when NPs penetrate inside the
microgel, thereby inducing a collective reorganization of the polymer network.
By varying microgel properties, such as fraction of crosslinkers or charge, as
well as NPs size and charge, we further show that the microgel deswelling
curves can be rescaled onto a single master curve, for both experiments and
simulations, demonstrating that the process is entirely controlled by the
charge of the whole microgel-NPs complex. Our results thus have a direct
relevance in fundamental materials science and offer novel tools to tailor the
nanofabrication of hybrid devices of technological interest
Influence of drug/lipid interaction on the entrapment efficiency of isoniazid in liposomes for antitubercular therapy: a multi-faced investigation
Hypothesis. Isoniazid is one of the primary drugs used in tuberculosis
treatment. Isoniazid encapsulation in liposomal vesicles can improve drug
therapeutic index and minimize toxic and side effects. In this work, we
consider mixtures of hydrogenated soy phosphatidylcholine/phosphatidylglycerol
(HSPC/DPPG) to get novel biocompatible liposomes for isoniazid pulmonary
delivery. Our goal is to understand if the entrapped drug affects bilayer
structure.
Experiments. HSPC-DPPG unilamellar liposomes are prepared and characterized
by dynamic light scattering, -potential, fluorescence anisotropy and
Transmission Electron Microscopy. Isoniazid encapsulation is determined by UV
and Laser Transmission Spectroscopy. Calorimetry, light scattering and Surface
Pressure measurements are used to get insight on adsorption and thermodynamic
properties of lipid bilayers in the presence of the drug.
Findings. We find that INH-lipid interaction can increase the entrapment
capability of the carrier due to isoniazid adsorption. The preferential
INH-HSPC dipole-dipole interaction promotes modification of lipid packing and
ordering and favors the condensation of a HSPC-richer phase in molar excess of
DPPG. Our findings highlight the importance of fundamental investigations of
drug-lipid interactions for the optimal design of liposomal nanocarriers.Comment: 28 pages (main manuscript + supplementary information
Rifampicin-liposomes for mycobacterium abscessus infection treatment: intracellular uptake and antibacterial activity evaluation
: Treatment of pulmonary infections caused by Mycobacterium abscessus are extremely difficult to treat, as this species is naturally resistant to many common antibiotics. Liposomes are vesicular nanocarriers suitable for hydrophilic and lipophilic drug loading, able to deliver drugs to the target site, and successfully used in different pharmaceutical applications. Moreover, liposomes are biocompatible, biodegradable and nontoxic vesicles and nebulized liposomes are efficient in targeting antibacterial agents to macrophages. The present aim was to formulate rifampicin-loaded liposomes (RIF-Lipo) for lung delivery, in order to increase the local concentration of the antibiotic. Unilamellar liposomal vesicles composed of anionic DPPG mixed with HSPC for rifampicin delivery were designed, prepared, and characterized. Samples were prepared by using the thin-film hydration method. RIF-Lipo and unloaded liposomes were characterized in terms of size, ζ-potential, bilayer features, stability and in different biological media. Rifampicin's entrapment efficiency and release were also evaluated. Finally, biological activity of RIF-loaded liposomes in Mycobacterium abscessus-infected macrophages was investigated. The results show that RIF-lipo induce a significantly better reduction of intracellular Mycobacterium abscessus viability than the treatment with free drug. Liposome formulation of rifampicin may represent a valuable strategy to enhance the biological activity of the drug against intracellular mycobacteria
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