Macroporous hybrid Pickering foams based on carbon nanotubes and cellulose nanocrystals.

The association of nanoparticles with complementary properties to produce hybrids is an underestimated way to develop multifunctional original architectures. This strategy is used to prepare simple, low-cost, and environmentally friendly method to fabricate ultra-low density alveolar foam reinforced with carbon nanotubes (CNTs). This paper investigates the ability of cellulose nanocrystals (CNCs) to produce highly stable oil-in-water Pickering emulsions and to efficiently disperse carbon nanotubes in water to form three-dimensional macroporous conductive foam. It is shown that both single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) are strongly linked to CNCs by non-covalent interactions, preserving the intrinsic properties of both nanoparticles. Homogeneous surfactant-free emulsions with a droplet diameter of 6 µm are produced. Once concentrated, they can form stable high internal phase emulsions. Incorporating CNTs into these CNC-based emulsions was shown to improve their rheological properties. Freeze-drying the concentrated emulsions produces ultra-low density solid foams (14 mg·cm-3) with several levels of porosity controlled by the emulsification step. Loading CNCs with only 2-4 wt% of CNTs, decreases the electrical resistivity of the foam to 104 Ω cm in high relative humidity. The mechanical and electrical properties are studied and discussed in light of the resulting specific foam structure.

pH-Sensitive photoinduced energy transfer from bacteriorhodopsin to single-walled carbon nanotubes in SWNT-bR hybrids.

Energy transfer mechanisms in noncovalently bound bacteriorhodopsin/single-walled carbon nanotube (SWNT) hybrids are investigated using optical absorption and photoluminescence excitation measurements. The morphology of the hybrids was investigated by atomic force microscopy. In this study, proteins are immobilized onto the sidewall of the carbon nanotubes using a sodium cholate suspension-dialysis method that maintains the intrinsic optical and fluorescence properties of both molecules. The hybrids are stable in aqueous solutions for pH ranging from 4.2 to 9 and exhibit photoluminescence properties that are pH-dependent. The study reveals that energy transfer from bacteriorhodopsin to carbon nanotubes takes place. So, at pH higher than 5 and up to 9, the SWNTs absorb the photons emitted by the aromatic residues of the protein, inducing a strong increase in intensity of the E11 emissions of SWNTs through their E33 and E44 excitations. From pH = 4.2 to pH = 5, the protein fluorescence is strongly quenched whatever the emission wavelengths, while additional fluorescence features appear at excitation wavelengths ranging from 660 to 680 nm and at 330 nm. The presence of these features is attributed to a resonance energy transfer mechanism that has an efficiency of 0.94 ± 0.02. More, by increasing the pH of the dispersion, the fluorescence characteristics become those observed at higher pH values and vice versa.

Nanocomposite hydrogels for cartilage tissue engineering: mesoporous silica nanofibers interlinked with siloxane derived polysaccharide.

Injectable materials for mini-invasive surgery of cartilage are synthesized and thoroughly studied. The concept of these hybrid materials is based on providing high enough mechanical performances along with a good medium for chondrocytes proliferation. The unusual nanocomposite hydrogels presented herein are based on siloxane derived hydroxypropylmethylcellulose (Si-HPMC) interlinked with mesoporous silica nanofibers. The mandatory homogeneity of the nanocomposites is checked by fluorescent methods, which show that the silica nanofibres dispersion is realized down to nanometric scale, suggesting an efficient immobilization of the silica nanofibres onto the Si-HPMC scaffold. Such dispersion and immobilization are reached thanks to the chemical affinity between the hydrophilic silica nanofibers and the pendant silanolate groups of the Si-HPMC chains. Tuning the amount of nanocharges allows tuning the resulting mechanical features of these injectable biocompatible hybrid hydrogels. hASC stem cells and SW1353 chondrocytic cells viability is checked within the nanocomposite hydrogels up to 3 wt% of silica nanofibers.

Cellulose nanocrystal-assisted dispersion of luminescent single-walled carbon nanotubes for layer-by-layer assembled hybrid thin films.

Highly stable single-walled carbon nanotube (SWNT) dispersions are obtained after ultrasonication in cellulose nanocrystal (CN) aqueous colloidal suspensions. Mild dispersion conditions were applied to preserve the SWNT length in order to facilitate the identification of hybrid objects. This led to a moderate dispersion of 24% of the SWNTs. Under these conditions, atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments succeeded in demonstrating the formation of hybrid particles in which CNs are aligned along the nanotube axis by a self-assembly process. These SWNT/CN dispersions are used to create multilayered thin films with the layer-by-layer method using polyallylamine hydrochloride as a polyelectrolyte. Homogeneous films from one to eight bilayers are obtained with an average bilayer thickness of 17 nm. The presence of SWNTs in each bilayer is attested to by characteristic Raman signals. It should be noted that these films exhibit a near-infrared luminescence signal due to isolated and well-separated nanotubes. Furthermore, scanning electron microscopy (SEM) suggests that the SWNT network is percolating through the film.

The 2C putative helicase of echovirus 30 adopts a hexameric ring-shaped structure.

The 2C protein, which is an essential ATPase and one of the most conserved proteins across the Picornaviridae family, is an emerging antiviral target for which structural and functional characterization remain elusive. Based on a distant relationship to helicases of small DNA viruses, piconavirus 2C proteins have been predicted to unwind double-stranded RNAs. Here, a terminally extended variant of the 2C protein from echovirus 30 has been studied by means of enzymatic activity assays, transmission electron microscopy, atomic force microscopy and dynamic light scattering. The transmission electron-microscopy technique showed the existence of ring-shaped particles with ∼12 nm external diameter. Image analysis revealed that these particles were hexameric and resembled those formed by superfamily 3 DNA virus helicases.

Conformational structural changes of bacteriorhodopsin adsorbed onto single-walled carbon nanotubes.

The interaction between purple membranes, composed of proteins of bacteriorhodopsin (bR) and their native surrounding lipids, and single-walled carbon nanotubes (SWNT) has been investigated. In this work, sonication has been used to debundle SWNT in buffer solution without surfactant before the addition of native purple membranes. The sample was then sonicated in a bath for a short time, followed by a centrifugation. The supernatants contain proteins in excess and SWNT as individual and small bundles covered by a bR layer with an average thickness of 1.5 nm. TEM and AFM observations support the idea that only a protein monolayer surrounds the tubes. Optical absorption and infrared spectroscopy measurements provide evidence that the proteins adsorbed onto the SWNT undergo orientational changes of the helical segments in bR and helix conformational changes. We ascribe the main driving force to the hydrophobic interactions between the sidewall of the SWNT and the hydrophobic residues of the alpha-helices of bR.

Kinetic studies of a composite carbon nanotube-hydrogel for tissue engineering by rheological methods.

Here we used rheological methods to study the gelation kinetics of silanized hydroxypropylmethylcellulose (HPMC-Si) hydrogel for tissue engineering. Firstly, the gelation time was determined from the independence of tan delta on frequency, and the Arrhenius law was applied to obtain the apparent activation energy of gelation, which was found to be about 109.0 kJ/mol. Secondly, the gelation process was monitored by measuring the sample storage modulus. The results showed that the gelation process could be well classified as a second-order reaction. In addition, a composite HPMC-Si/MWNTs hydrogel system for potential cartilage tissue engineering was investigated. The comparison of pure HPMC-Si hydrogel and composite HPMC-Si/MWNTs systems indicated that the addition of MWNTs could increase the mechanical strength of hydrogel without changing the gelation mechanism of the system.

Electric-Pulse-driven Electronic Phase Separation, Insulator-Metal Transition, and Possible Superconductivity in a Mott Insulator.

Experimental evidence of a nonvolatile electric-pulse-induced insulator-to-metal transition and possible superconductivity in the Mott insulator GaTa4 Se8 is reported. Scanning tunneling microscopy experiments show that this unconventional response of the system to short electric pulses arises from a nanometer-scale electronic phase separation generated in the bulk material.

Solid-state NMR study of Na versus K doping of para-phenylene oligomers.

13C solid-state nuclear magnetic resonance (NMR) experiments were performed on p-terphenyl, p-quaterphenyl, and p-sexiphenyl either in their pristine or doped with alkali metals form. The 13C NMR spectra of doped materials show new resonances by comparison with pristine compounds. For the K-doped materials, these resonances appear in the 90-135 ppm range, while for Na-doped materials, they are observed in the larger 20-150 ppm range. It suggests that the interaction between the alkali ions and the oligomers depends on the nature of the alkali. It is corroborated by 13C NMR experiments after exposure to air that show different behaviors. As expected, air exposure of K-doped samples restores the pristine spectra. This is not the case for Na doping, where the signature of the doped material persists even after exposure to air. In the latter case, some 13C resonances can be assigned to sp3 hybridized carbons and to the quinoid group. It suggests that Na doping induces a polymerization of the oligophenylenes.