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Poly(acrylamide)- b -complex salts made from a symmetric poly(acrylate- b -acrylamide) block copolymer, where the acrylate charges are neutralized by cationic surfactant counterions, form kinetically stable aqueous dispersions of hierarchical aggregates with a liquid-crystalline complex salt core and a diffuse hydrated shell. By the addition of suitable amounts of long-chain alcohols, such as octanol or decanol, the structure of the internal phase can be varied, producing micellar cubic, hexagonal, lamellar, or reverse hexagonal liquid-crystalline phases. In addition, a disordered reverse micellar phase forms at the highest content of octanol. These core structures are the same as those previously obtained for macroscopic homopolymer poly(acrylate) complex salt/water/ n -alcohol systems at the corresponding compositions. The poly(acrylamide)- b -complex salt dispersions are kinetically stable for several weeks, with their colloidal properties and internal structures remaining unchanged. The methodology described here establishes an easy and robust protocol for the preparation of colloidal nanoparticles with variable but controlled internal structures.

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BackgroundNanoparticles’ unique features have been highly explored in cellular therapies. However, nanoparticles can be cytotoxic. The cytotoxicity can be overcome by coating the nanoparticles with an appropriated surface modification. Nanoparticle coating influences biocompatibility between nanoparticles and cells and may affect some cell properties. Here, we evaluated the biocompatibility of gold and maghemite nanoparticles functionalized with 2,3-dimercaptosuccinic acid (DMSA), Au-DMSA and γ-Fe2O3-DMSA respectively, with human mesenchymal stem cells. Also, we tested these nanoparticles as tracers for mesenchymal stem cells in vivo tracking by computed tomography and as agents for mesenchymal stem cells magnetic targeting.ResultsSignificant cell death was not observed in MTT, Trypan Blue and light microscopy analyses. However, ultra-structural alterations as swollen and degenerated mitochondria, high amounts of myelin figures and structures similar to apoptotic bodies were detected in some mesenchymal stem cells. Au-DMSA and γ-Fe2O3-DMSA labeling did not affect mesenchymal stem cells adipogenesis and osteogenesis differentiation, proliferation rates or lymphocyte suppression capability. The uptake measurements indicated that both inorganic nanoparticles were well uptaken by mesenchymal stem cells. However, Au-DMSA could not be detected in microtomograph after being incorporated by mesenchymal stem cells. γ-Fe2O3-DMSA labeled cells were magnetically responsive in vitro and after infused in vivo in an experimental model of lung silicosis.ConclusionIn terms of biocompatibility, the use of γ-Fe2O3-DMSA and Au-DMSA as tracers for mesenchymal stem cells was assured. However, Au-DMSA shown to be not suitable for visualization and tracking of these cells in vivo by standard computed microtomography. Otherwise, γ-Fe2O3-DMSA shows to be a promising agent for mesenchymal stem cells magnetic targeting.

Block copolymer–surfactant “complex salts” (BCPCS), containing one neutral water-soluble block and one polyion/surfactant-ion block, were prepared from poly­(acrylamide)-block-poly­(acrylic acid) block copolymers by neutralizing the acrylate charges with cationic dodecyl- or hexadecyl­trimethyl­ammonium surfactant counterions. The BCPCS were studied in hydrated samples containing 20–99 wt % water (and no additional ions) employing small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and visual inspection. Selected samples in D2O were also investigated. The results reveal for the first time, for hydrated samples, the formation of ordered hierarchical structures on both block copolymer and surfactant length scales, analogous to structures that have previously been reported for solvent-free block copolymer–surfactant complexes in the solid or melt. The BCPCS structures do not dissolve but display a finite swelling also in the presence of excess water. The structure on the BCP length scale (lamellar or hexagonal) depends only on the BCP, whereas the structure on the CS length scale (hexagonal or micellar cubic) depends on both the surfactant ion and the water content. The results strongly suggest that the observed concentrated hierarchical structures are the equilibrium states for BCPCS in water, although small aggregates formed reproducibly in the dilute regime have been reported for BCPCS and similar systems, collectively known as complex coacervate core micelles (C3Ms).

Phase behavior of surfactants in water may be affected by the addition of a third component, and the present study discusses how long-chain n-alcohols affect phase transitions of systems formed by the surfactant hexadecyltrimethylammonium bromide, CTAB, or its complex salts formed with polyacrylate, CTAPA, as well as other previously reported complex salts/water/alcohol systems. Structural characterization by X-ray diffraction patterns at small and wide angles and different temperatures was performed for samples containing n-decanol, n-dodecanol, or n-tetradecanol. Differential scanning calorimetry (DSC) was also used to study the phase transition. The results allowed us to observe and understand the coexistence of lamellar gel (L) and lamellar liquid-crystal (L) phases, elucidating the structure of a previously reported mesophase, proposing an alternative assignment. Whereas the chain-melting transition is well-known to be sharp for lipids, we have found that it is broader for CTAB and CTAPA in the presence of these n-alcohols. We have investigated the effects of their composition and chain length on the temperature and enthalpy of transition. This elucidates why the addition of n-alcohols with chains slightly shorter than that of the surfactants leads to the formation of an ordered gel-like lamellar phase (L). n-Alcohols act as neutral cosurfactants, leading to more packing, and all of the factors converge to a limit situation, associated with a common critical area occupied by each alkyl chain. We compared our results with other mesophase systems from the literature, demonstrating that the same trends of phase behavior occur for complex salts of other polyelectrolytes with alkyltrimethylammonium surfactants.

Internally structured block copolymer-surfactant particles are formed when the complex salts of ionic-neutral block copolymers neutralized by surfactant counterions are dispersed in aqueous media. Here, we report the 1H NMR signal intensities and self-diffusion coefficients (D, from pulsed field gradient nuclear magnetic resonance, PFG NMR) of trimethyl alkylammonium surfactant ions and the poly(acrylamide)-block-poly(acrylate) (PAAm-b-PA) polyions forming such particles. The results reveal the presence of an “NMR-invisible” (slowly exchanging) fraction of aggregated surfactant ions in the particle core and an “NMR-visible” fraction consisting of surface surfactant ions in rapid exchange with the surfactant ions dissociated into the aqueous domain. They also confirm that the neutral PAAm blocks are exposed to water at the particle surface, while the PA blocks are buried in the particle core. The self-diffusion of the polyions closely agree with the self-diffusion of a hydrophobic probe molecule solubilized in the particles, showing that essentially all copolymer chains are incorporated in the aggregates. Through centrifugation, we prepared macroscopically phase-separated systems with a phase concentrated in particles separated from a clear dilute phase. D values for the surfactant and block copolymer indicated that the dilute phase contained small aggregates (ca. 5 nm) of surfactant ions and a few anionic-neutral block copolymer chains. Regardless of the overall concentration of the sample, the fraction of block copolymer found in the dilute phase was nearly constant. This indicates that the dilute fraction represented a tail of small particles created by the dispersion process rather than a true thermodynamic solubility of the complex salts.

comprises the planet and the metal NPs, the satellites. [6,15,16] The fabrication of polymer-based planet-satellite nanostructures is particularly interesting because it was shown that the surface-exposed metal NPs can be easily accessed by species in the surrounding media, a step that is crucial for catalysis and sensing purposes. Such a strategy also allows the control of the interparticle distance of surfacelocated metal NPs which is well known to impact on their optical, electronic, and magnetic properties. [6] Using this approach, several nanoconjugate systems have been described in the recent years, aiming at different potential applications. Block copolymer micelles: [2][3][4][5][6] pH-and temperature-responsive microgels [7,8] and crosslinked polymer particles [9,10] are examples of polymeric nanomaterials assembled with Au and Ag NPs which have been used for catalytic, stimuli-responsive, and drug delivery purposes.The potential uses of the planet-satellite nanostructures in a variety of fields strongly depends on their colloidal stability, regarding both polymer and metal NPs, because in most of the cases, the nanoconjugates are finely tuned to display specific properties that must remain unchanged upon suitable variations in environment conditions, specially the pH and ionic strength. Hence, the fabrication of new polymer-based nanoconjugates with excellent colloidal stability is highly desired.Core-shell particles, collectively known as complex coacervate core micelles (C3Ms), made from charged−neutral block copolymers and oppositely charged surfactant ions have been widely reported in the last years and the most studied systems are comprised of alkyltrimethylammonium cationic surfactants and the block copolymer poly(acrylamide)-block-poly(acrylic acid) (PAAm-b-PAA). [17][18][19][20][21][22][23][24] The particles core contains several densely packed-surfactant micelles surrounded by the anionic block of the copolymer and the outer part consists in a corona composed by the neutral PAAm chains. By using the "complex salt" (CS) approach, [21][22][23] the production of dispersed particles with a variety of surfactant-rich liquid crystalline cores were shown to be achieved. In addition, these particles, refereed here as CS, were shown to display enhanced colloidal stability. [21][22][23] It was noted that the CS particles display different properties, such as size, surface charge, and core structure, if compared with those typically found for particles, referred Gold (Au) and silver (Ag) nanoparticles (NPs) are covalently conjugated onto the surface of thiol-functionalized block copolymer particles containing surfactant-rich liquid crystalline cores. The resulting planet-satellite nanoconjugates display enhanced colloidal stability upon changes in solution pH or ionic strength and interfacial properties that result in the stabilization of oil-in-water emulsions. These biphasic systems are used as medium for catalyzed aerobic oxidation of benzyl alcohol to benzoic acid and the nanoconjugates display catalyt...