Ellina Kesselman

Spontaneous high-concentration dispersions and liquid crystals of graphene

Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties. Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase. Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as approximately 2 mg ml(-1), which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations ( approximately 20-30 mg ml(-1)). Transparent, conducting films are produced from these dispersions at 1,000 Omega square(-1) and approximately 80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.

Therapeutic ultrasound-mediated DNA to cell and nucleus: bioeffects revealed by confocal and atomic force microscopy

Therapeutic ultrasound (TUS) has the potential of becoming a powerful nonviral method for the delivery of genes into cells and tissues. Understanding the mechanism by which TUS delivers genes, its bioeffects on cells and the kinetic of gene entrances to the nucleus can improve transfection efficiency and allow better control of this modality when bringing it to clinical settings. In the present study, direct evidence for the role and possible mechanism of TUS (with or without Optison) in the in vitro gene-delivery process are presented. Appling a 1 MHz TUS, at 2 W/cm2, 30%DC for 30 min was found to achieve the highest transfection level and efficiency while maintaining high cell viability (>80%). Adding Optison further increase transfection level and efficiency by 1.5 to three-fold. Confocal microscopy studies indicate that long-term TUS application localizes the DNA in cell and nucleus regardless of Optison addition. Thus, TUS significantly affects transfection efficiency and protein kinetic expression. Using innovative direct microscopy approaches: atomic force microscopy, we demonstrate that TUS exerts bioeffects, which differ from the ones obtained when Optison is used together with TUS. Our data suggest that TUS alone affect the cell membrane in a different mechanism than when Optison is used.

Glycodynamers: dynamic polymers bearing oligosaccharides residues--generation, structure, physicochemical, component exchange, and lectin binding properties.

Dynamic glycopolymers have been generated by polycondensation through acylhydrazone formation between components bearing lateral bioactive oligosaccharide chains. They have been characterized as bottlebrush type by cryo-TEM and SANS studies. They present remarkable fluorescence properties whose emission wavelengths depend on the constitution of the polymer and are tunable by constitutional modification through exchange/incorporation of components, thus also demonstrating their dynamic character. Constitution-dependent binding of these glycodynamers to a lectin, peanut agglutinin, has been demonstrated.

Spontaneous dissolution of ultralong single- and multiwalled carbon nanotubes.

We report that chlorosulfonic acid is a true solvent for a wide range of carbon nanotubes (CNTs), including single-walled (SWNTs), double-walled (DWNTs), multiwalled carbon nanotubes (MWNTs), and CNTs hundreds of micrometers long. The CNTs dissolve as individuals at low concentrations, as determined by cryo-TEM (cryogenic transmission electron microscopy), and form liquid-crystalline phases at high concentrations. The mechanism of dissolution is electrostatic stabilization through reversible protonation of the CNT side walls, as previously established for SWNTs. CNTs with highly defective side walls do not protonate sufficiently and, hence, do not dissolve. The dissolution and liquid-crystallinity of ultralong CNTs are critical advances in the liquid-phase processing of macroscopic CNT-based materials, such as fibers and films.

High-performance mussel-inspired adhesives of reduced complexity

Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remains limited or non-existent for diverse applications. Translation of mussel-inspired wet adhesion typically entails catechol functionalization of polymers and/or polyelectrolytes, and solution processing of many complex components and steps that require optimization and stabilization. Here we reduced the complexity of a wet adhesive primer to synthetic low-molecular-weight catecholic zwitterionic surfactants that show very strong adhesion (∼50 mJ m−2) and retain the ability to coacervate. This catecholic zwitterion adheres to diverse surfaces and self-assembles into a molecularly smooth, thin (<4 nm) and strong glue layer. The catecholic zwitterion holds particular promise as an adhesive for nanofabrication. This study significantly simplifies bio-inspired themes for wet adhesion by combining catechol with hydrophobic and electrostatic functional groups in a small molecule.

Solubilization of Hydrophobic Guest Molecules in the Monoolein Discontinuous QL Cubic Mesophase and Its Soft Nanoparticles

Hydrophobic bioactive guest molecules were solubilized in the discontinuous cubic mesophase (QL) of monoolein. Their effects on the mesophase structure and thermal behavior, and on the formation of soft nanoparticles upon dispersion of the bulk mesophase were studied. Four additives were analyzed. They were classified into two types based on their presumed location within the lipid bilayer and their influence on the phase behavior and structure. Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), polarized light microscopy, cryogenic-transmission electron microscopy (cryo-TEM), and dynamic light scattering (DLS) were used for the analysis. We found that carbamazepine and cholesterol (type I molecules) likely localize in the hydrophobic domains, but close to the hydrophobic-hydrophilic region. They induce strong perturbation to the mesophase packing by influencing both the order of the lipid acyl chains and interactions between lipid headgroups. This results in significant reduction of the phase transition enthalpy, and phase separation into lamellar and cubic mesophases above the maximum loading capacity. The inclusion of type I molecules in the mesophase also prevents the formation of soft nanoparticles with long-range internal order upon dispersion. In their presence, only vesicles or sponge-like nanoparticles form. Phytosterols and coenzyme Q10 (type II molecules) present only moderate effects. These molecules reside in the hydrophobic domains, where they cannot alter the lipid curvature or transform the QL mesophase into another phase. Therefore, above maximum loading, excess solubilizate precipitates in crystal forms. Moreover, when type II-loaded QL is dispersed, nanoparticles with long-range order and cubic symmetry (i.e., cubosomes) do form. A model for the growth of the ordered nanoparticles was developed from a series of intermediate structures identified by cryo-TEM. It proposes the development of the internal structure by fusion events between bilayer segments.

Formation of celecoxib nanoparticles from volatile microemulsions.

A new composition of a fully water-dilutable microemulsion system stabilized by natural surfactants is presented as a template for preparation of celecoxib nanoparticles. Nanoparticles are obtained as a dry powder upon rapid conversion of microemulsion droplets with dissolved celecoxib into nanoparticles, followed by evaporation of all the liquid in a spray dryer. The resultant powder is easily re-dispersible in water to form a clear, transparent dispersion. The celecoxib nanoparticles are amorphous and their average size in the dispersion is 17 nm, in agreement with cryo-TEM results and concentration measurements after filtration. As a result of the nanometric size and amorphous state, about 10-fold increase in dissolution of the powder was obtained, compared to that for particulate celecoxib in the presence of surfactants.

Surface characterization and dissolution properties of high amylose corn starch: pectin coatings

Coatings from mixture of pectin and high amylose corn starch (HACS) were prepared on glass slides, and characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), dissolution and enzymatic digestion tests. The surface of pectin–HACS coatings showed increased roughness with increase in HACS content (r2=0.957, p≤0.001). Dissolution of the coatings decreased with increase in HACS content in both stomach (pH 1.6) and intestine (pH 7.0) conditions. HACS coatings also showed high resistance to amylolysis, with degradation of <35% after 3 h of incubation in pancreatic solution. SEM images of enzymatically treated HACS coatings revealed a uniform and practically intact surface. The potential of these coatings for targeted release in the intestine was, therefore, demonstrated.

A simple route to fluids with photo-switchable viscosities based on a reversible transition between vesicles and wormlike micelles

Recently, there has been much interest in photorheological (PR) fluids, i.e., fluids whose rheological properties can be tuned by light. In particular, there is a need for simple, low-cost PR fluids that can be easily created using inexpensive, commercially available ingredients and that show substantial, reversible changes in rheology upon exposure to different wavelengths of light. Towards this end, we report a class of photoreversible PR fluids prepared by combining the azobenzene derivative 4-azobenzene carboxylic acid (ACA) (in its salt form) with the cationic surfactant erucyl bis(2-hydroxyethyl)methyl ammonium chloride (EHAC). We show that certain aqueous mixtures of EHAC and ACA, which are low-viscosity solutions at the outset, undergo nearly a million-fold increase in viscosity when irradiated with UV light. The same solutions revert to their initial viscosity when subsequently exposed to visible light. Using an array of techniques including UV-vis and NMR spectroscopies, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM), we have comprehensively characterized these PR fluids at the molecular, nanostructural, and macroscopic scales. Initially, EHAC–ACA are self-assembled into unilamellar vesicles, which are discrete container structures and give the sample a low viscosity. Upon exposure to UV light, ACA undergoes a trans to cis photoisomerization, which alters the geometry of the EHAC–ACA complex. In turn, the molecules self-assemble into a different structure, viz. wormlike micelles, which are long, entangled chains and impart a high viscosity to the sample. The above changes in viscosity are repeatable, and the sample can be reversibly cycled back and forth between low and high viscosity states. Our photoreversible PR fluids can be easily replicated in any industrial or academic lab, and it is hoped that these “smart” fluids will eventually find a host of applications.

Liposome fusion rates depend upon the conformation of polycation catalysts.

Cryo-TEM and NaCl-leakage experiments demonstrated that the cationic polymer polylysine induces fusion of anionic liposomes but that the cationic polymer poly(N-ethyl-4-vinylpyridinium bromide) (PEVP) does not, although both polymers bind strongly to the liposomes. The difference was traced to the thickness of the coatings at constant charge coverage. Polylysine is believed to form planar β-sheets that are sufficiently thin to allow membrane fusion. In contrast, looping and disorganization among adsorbed PEVP molecules physically prevent fusion. A similar effect is likely to be applicable to important polycation-induced fusion of cell membranes.