Jean-Paul Salvetat

Carbon Nanotubes as Structural Nanofibers for Hyaluronic Acid Hydrogel Scaffolds

We have successfully dispersed functionalized single-walled carbon nanotubes (SWNTs) within hyaluronic acid-water solutions. Hybrid hyaluronic acid (HA) hydrogels with SWNTs were then formed by cross-linking with divinyl sulfone. We have found a considerable change in the morphology of the lyophilized hybrid hydrogels compared to HA hydrogels. The high water uptake capacity, an important property of HA hydrogels, remained almost unchanged after 2 wt % SWNT (vs HA) incorporation, despite a dramatic enhancement in the dynamic mechanical properties of the hybrid hydrogels compared to native ones. We have found a 300% enhancement in the storage modulus of hybrid hydrogel with only 2 wt % of SWNTs vs HA (0.06 wt % vs total weight including water content). This apparent contradiction can be explained by a networking effect between SWNTs, mediated by HA chains. As in biological tissue, HA plays a dual role of matrix and linker for the rigid reinforcing nanofibers.

Mesoporous silica nanoparticles enhance MTT formazan exocytosis in HeLa cells and astrocytes.

We report on the observation that mesoporous silica nanoparticles (MSNs), after being endocytosed, interfere with the MTT test in HeLa cells and astrocytes by accelerating the exocytosis of formazan crystals. The stimulation of MTT formazan exocytosis is probably related to perturbation of intracellular vesicle trafficking by MSN uptake as revealed by experiments in presence of chloroquine and genistein. Similar effect has been previously observed with a number of chemicals, especially with neurotoxic beta amyloid peptides, but not with nanoparticles. We showed also that MTT reduction test gives an overestimation of the cytotoxicity of mesoporous silica nanoparticles compared to other tests such as LDH activity, WST-1 test and flow cytometry. These findings show that MTT assay should not be used for the study of MSN toxicity, and that perturbation of intracellular trafficking has to be taken into account in evaluating biocompatibility of MSNs.

Protein-functionalized carbon nanotube-polymer composites

We have developed fully integrated nanotube composite materials through the functionalization of multiwall carbon nanotubes (MWCNTs) by covalently attaching ferritin protein molecules onto the surface of MWCNTs. The investigation of the thermomechanical behavior was performed by dynamic mechanical thermal analysis. Results demonstrated dramatic enhancement in the mechanical properties of PVA, for example a 100%–110% increase in the modulus with the addition of 1.5 wtu2009% of ferritin functionalized MWCNTs. Samples containing functionalized nanotubes showed a stronger influence on glass transition temperature in comparison to composites containing the same amount of nonfunctionalized nanotubes.

Reinforcement of semicrystalline polymers with collagen-modified single walled carbon nanotubes

We report on the enhancement of the mechanical properties of single wall carbon nanotube (SWNT)-polyvinyl alcohol (PVA) composites through functionalization of SWNTs with denatured collagen. In addition to improving compatibility with the matrix, the denatured collagen layer was found to increase the PVA matrix crystallinity, which results in a dramatic enhancement of the Young’s modulus (260%), tensile strength (300%), and toughness (700%) well above what can be expected with the classical rule of mixture. A supramolecular organization at the interface is associated with an increase of PVA crystallinity as shown by the x-ray diffraction and differential scanning calorimetry.

One step synthesis of highly crystalline and high coercive cobalt-ferrite nanocrystals

Highly crystalline and almost monodisperse spinel cobalt-ferrite nanocrystals are synthesized in a one step process, which has very high coercivity at 10 K and exhibits superparamagnetic behaviour at 300 K.

Thermal stability of metal nanoclusters formed by low-pressure plasma sputtering

Abstract In this paper we present the morphological characterization of palladium (Pd) nanoclusters obtained by low-pressure plasma sputtering and dedicated to catalytic carbon nanotube growth. It is shown that small Pd clusters deposited on silicon are not stable at the processing temperature (873 K); they tend to migrate and coalesce with their close neighbors. Heat treatment in fact leads to a bimodal cluster size distribution (2 nm and 10–30 nm), starting from 5-nm as-deposited nanoclusters. Another consequence is the appearance on the silicon substrate of areas containing low (isolated aggregates) or high cluster density. Knowledge of the metal cluster thermal evolution is of great importance in understanding the nanotube growth mechanism. First results indicate that the carbon structures grow only on particles of large size.

Catalyst consumption during growth of carbon nanofilaments on Pd seeds

Carbon nanofilaments are produced at 600degreesC by catalytic decomposition of acetylene on palladium nanoparticles. We observe that nanofilament length is limited to a few hundreds of nm when the size of Pd germs is less than 10 nm, possibly due to the incorporation of Pd atoms during growth. We propose a growth model, supported by first-principles calculations which show that Pd atoms are stable when adsorbed on graphene and that a charge transfer occurs, modifying significantly the electronic properties