In vitro studies of carbon nanotubes biocompatibility

Cellular tests have been applied to study the biocompatibility of high purity multiwalled carbon nanotubes (MWNTs). The viability of fibroblasts, osteoblasts and osteocalcin concentrations in osteoblasts cultures in the presence of nanotubes has been examined, as well as the degree of cells stimulation, based on the amount of released collagen type I, IL-6 and oxygen free radicals. The high level of viability of the examined cells in contact with the nanotubes, the slight increase of collagen formation, the lack of pro-inflammatory IL-6 cytokine as well as the induction of free radicals, confirm a good biocompatibility of nanotubes, which is similar to that of polysulfone currently used in medicine. The collagen synthesis induced on nanotubes by both fibroblasts and osteoblasts may be significant for future medical applications of nanotubes, in particular as substrates for the regeneration of tissues.     

Decoration of carbon nanotubes with chitosan

In this letter, a non-destroyable surface decoration of carbon nanotubes with biopolymer chitsoan via a controlled surface-deposition and crosslinking process is described. The method utilizes the emulsifying capacity of chitosan, the completely different water-solubility of chitosan in acidic and basic solutions, and the crosslinking reaction among chitosan polymers. As the pristine structures of the carbon nanotubes are not recomposed under those treatments, the unique properties of the pristine carbon nanotubes have not been compromised. Combining the properties of carbon nanotubes and the versatility and biocompatibility of chitosan, these chitosan surface-decorated carbon nanotubes could find potential applications in biosensing, gene and drug delivering as well as other chemical and biological applications.     

Differential biocompatibility of carbon nanotubes and nanodiamonds

Carbon nanomaterials are being produced in increasingly larger quantities for many applications due to their novel characteristics such as enhanced thermal, electrical, mechanical, and biological properties. However, there is a lack of data on biological interactions to assess their biocompatibility before they will be accepted as non-toxic in industrial or biomedical arenas. In the present study, we examined both neuronal and lung cell lines for biocompatibility in aqueous suspensions of carbon nanomaterials, such as nanodiamonds (NDs), single- and multi-walled carbon nanotubes (SWNTs, MWNTs), and carbon black (CB), at concentrations ranging from 25–100 μg/ml for 24 h. Our results indicated that these carbon nanomaterials displayed differential biocompatibility in these two different cell lines. The greatest biocompatibility was found after incubation with NDs and both cell types followed the trend: ND > CB > MWNT > SWNT. Macrophages were found to be more sensitive to the nanomaterials with up to five times the generation of reactive oxygen species after incubation with MWNTs or SWNTs. However, there was a lack of ROS generation from either cell line incubated with ND-raw, as well as intact mitochondrial membranes, suggesting that NDs may be useful as a benchmark nanoparticle non-toxic control in replacement of CB, and should be further investigated for use in medical applications.     

Effects of fullerenes and single-wall carbon nanotubes on murine and human macrophages

The discovery in 1985 of C-fullerenes, a novel carbon allotrope with a polygonal structure made up solely by 60 carbon atoms, and in 1991 of C-nanotubes, thin carbon filaments (1-3 μm in length and 0.001 μm in diameter) with extraordinary mechanical properties, opened a wide field of activity in carbon research. While toxicity and biocompatibility of C-fullerenes have been widely investigated, literature data concerning the biological properties and biotoxicity of C-nanotubes are poor and contradictory. Here we test the ability of highly purified C-Single-Walled-Nanotubes (SWNTs) and C-fullerenes to elicit an inflammatory response by murine and human macrophage cells in vitro. In order to determine the potential of these C-derivatives as biological inducers of inflammatory reactions we evaluate the ability of C-single-walled nanotubes and C-fullerenes to induce the release of NO by murine macrophages cells, to stimulate the phagocytic activity of human macrophage cells and to be cytotoxic against these cells. We show that SWNTs-C-nanotubes, when highly purified, as well as C-fullerenes, do not stimulate the release of NO by murine macrophage cells in culture, their uptake by human macrophage cells is very low, and they possess a very low toxicity against human macrophage cells.     

Functionalization of multiwalled carbon nanotubes by reversible addition fragmentation chain-transfer polymerization

In this study, a new way was used to chemically synthesize polymer-connected MWNT nanocomposites. Reversible addition fragmentation chain-transfer (RAFT) agent was successfully grafted onto the surface of multiwalled carbon nanotubes (MWNTs). Polystyrene (PS) chains were successfully grafted from the surface of MWNTs via RAFT process by using RAFT agent immobilized on MWNTs. FTIR, XPS and TGA were used to determine chemical structure and the grafted PS quantities of the resulting products. TEM images of the samples provide direct evidence for the formation of a core-shell nanostructure, i.e. the MWNT coated with polymer layer and the solubility be improved.     

Metal-particle-induced enhancement of the photoluminescence from biomolecule-functionalized carbon nanotubes

The effect of metal particles on the photoluminescence (PL) and the Raman spectra of functionalized SWCNTs in aqueous solutions was systematically investigated by studying three different metal particles (gold, cobalt, and nickel) on three different SWCNT suspensions (DNA-, RNA-, and sodium deoxycholate salt (DOC)-functionalized SWCNTs). Substantial enhancement of the PL intensities was observed, while the Raman spectra remained unchanged, after gold, cobalt, or nickel particles were introduced into RNA-SWCNT aqueous suspensions. Almost the same results were obtained after the same metal particles were added to DNA-SWCNT aqueous suspensions. However, both the PL and the Raman spectra did not exhibit any change at all after the same metal particles were introduced into DOC-SWCNT aqueous suspensions. The unusual PL enhancements observed in this work cannot be accounted for by the three well-known mechanisms in the literature: surface-enhanced Raman scattering effect, Förster resonance energy transfer in a rebundling of isolated SWCNTs, and pH changes of the aqueous solutions.     

In situ electropolymerization of conducting polypyrrole/carbon nanotubes composites on stainless steel: Role of carbon nanotubes types

In situ electropolymerization was used to prepare polypyrrole-oxidized multi-walled carbon nanotubes and polypyrrole-oxidized single-walled carbon nanotubes composites on a stainless steel surface from 0.1 M oxalic acid by using cyclic voltammetry. The electropolymerization process was investigated and discussed, and the results showed that the addition of the oxidized carbon nanotubes greatly enhanced the electropolymerization process, especially in the case of oxidized single walled carbon nanotubes. The results also showed that increasing the pyrrole monomer concentration leads to increasing the amount of polypyrrole electrodeposited, and this is more pronounced in the presence of the carbon nanotubes. The electropolymerization process was mainly under diffusion control as the process was inhibited by increasing the scan rate. In general, the presence of oxidized carbon nanotubes improved the electropolymerization of the polypyrrole and greatly enhanced its thermal and morphological properties.     

A comparison of reinforcement efficiency of various types of carbon nanotubes in polyacrylonitrile fiber

Polyacrylonitrile (PAN)/carbon nanotubes (CNTs) composite fibers were spun from solutions in dimethyl acetamide (DMAc), using single wall (SWNTs), double wall (DWNTs), multi wall (MWNTs) carbon nanotubes, and vapor grown carbon nanofibers (VGCNFs). In each case, CNT content was 5 wt% with respect to the polymer. Structure, morphology, and properties of the composite fibers have been characterized using X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, tensile tests, dynamic mechanical tests, as well as thermal shrinkage. While all nanotubes contributed to property improvements, maximum increase in modulus (75%) and reduction in thermal shrinkage (up to 50%) was observed in the SWNT containing composites, and the maximum improvement in tensile strength (70%), strain to failure (110%), and work of rupture (230%) was observed in the MWNTs containing composites. PAN orientation is higher in the composite fiber (orientation factor up to 0.62) than in the control PAN fiber (orientation factor 0.52), and the PAN crystallite size in the composite fiber is up to 35% larger than in the control PAN (3.7 nm), while the overall PAN crystallinity diminished slightly. Nanotube orientation in the composite fibers is significantly higher (0.98 for SWNTs, 0.88 for DWNTs, and 0.91 for MWNTs and VGCNFs) than the PAN orientation (0.52-0.62). Improvement in low strain properties (modulus and shrinkage) was attributed to PAN interaction with the nanotube, while the improvement in high strain properties (tensile strength, elongation to break, and work of rupture) at least in part is attributed to the nanotube length. Property improvements have been analyzed in terms of nanotube surface area and orientation.     

碳纳米管增强陶瓷基复合材料研究进展

鉴于其优良的力学性能、独特的物理和化学性能,碳纳米管被认为是最理想的增韧材料。本文主要从制备方法和力学性能两方面综述了碳纳米管增韧陶瓷基复合材料的研究现状,并针对研究中存在的问题,提出了相应的设想和发展趋势。     

Investigation of the cytotoxicity of CCVD carbon nanotubes towards human umbilical vein endothelial cells

The cytotoxicity of different samples of carbon nanotubes synthesised by catalytic chemical vapour deposition was investigated towards human umbilical vein endothelial cells, using two cytotoxicity standard assays (neutral red assay for the cell viability and MTT assay—tetrazolinium salt—for the cell metabolic activity). No cytotoxicity was found for any sample.     

Metal-semiconductor heterojunctions in T-shaped carbon nanotubes

We report a possible metal-semiconductor carbon nanotube heterojunction which can be done fusing perpendicularly a metallic nanotube to a semiconducting one. Octagonal defects help to make the 90° bend necessary for T-junctions. These molecules could be used as building blocks of nanoelectronic devices.     

Inclusion of carbon nanotubes in a hydroxyapatite sol–gel matrix

In this study, the inclusion of multi-walled carbon nanotubes as the second phase in the hydroxyapatite matrix, in order to improve the mechanical strength, has been performed via the sol–gel process. The stability of carbon nanotube sol with the changes of pH and dispersant values (sodium dodecyl sulfate) was evaluated by zeta potential analysis. The results indicated that synthesis of hydroxyapatite particles in the presence of the carbon nanotubes had the best result in homogenization of the carbon nanotube dispersion and faster crystallization of hydroxyapatite. The crystallization of hydroxyapatite phase was investigated with differential scanning calorimetry (DSC) and X-ray diffraction and the microstructure of the obtained composite powder was studied by electron microscopy.     

Conversion of carbon nanotubes to diamond by spark plasma sintering

The diamond phase has been converted directly from carbon nanotubes by spark plasma sintering (SPS), at 1500 °C under 80 MPa pressure, without any catalyst being involved. Well-crystallized diamond crystals, with particle sizes ranging from 300 nm to 10 μm were obtained. After sintering at 1200 °C, the tips of the carbon nanotubes were found to be open and the conversion from carbon nanotubes to diamond started. The mechanism for carbon nanotube to diamond conversion in SPS may be described as that from carbon nanotubes to an intermediate phase of carbon nano-onion, and then to diamond. It is believed that the plasmas generated by the low-voltage, vacuum spark, via a pulsed DC in the SPS process, played a critical role in the low pressure diamond formation. This SPS process provides an alternative approach to diamond synthesis.     

Recent applications of carbon nanotubes in hydrogen production and storage

Hydrogen is actually of great interest because it is the cleanest, sustainable and renewable energy carrier with a significantly reduced impact on the environment. In the future, hydrogen energy systems are expected to progressively replace the existing fossil fuels. Although hydrogen possesses significant advantages, it also exhibits major drawbacks in its utilization. The most important of them are production costs and storage characteristics. Carbon nanotubes (CNTs) have proven to possess ability as support for the fabrication of efficient heterogeneous catalysts in hydrogen production processes. Moreover, CNTs represent convenient adsorbent material that could form the basis of technologically viable hydrogen storage systems. This paper gives an overview of technologies used in the carbon nanotubes production and in the production and storage of hydrogen. In particular, it investigates the feasibility of CNTs and CNTs based catalyst materials in the mentioned processes. Our purpose is to overview the challenges of hydrogen production and storage technologies based on CNTs, to discuss and compare the different results published, and to emphasize recently developed modifications of CNTs that show potential to enhance hydrogen production and storage.     

Electron transfer chemistry of octadecylamine-functionalized single-walled carbon nanotubes

Single-walled carbon nanotubes were chemically functionalized by virtue of the interactions between the nanotube-bound carboxylic moieties and octadecylamine ligands. The electronic conductivity properties of the resulting nanotubes were probed voltammetrically. Two approaches were employed. The first entailed the fabrication of a nanotube monolayer at the air|water interface and the conductivity was measured in situ with a vertically aligned interdigitated arrays (IDAs) electrode. The overall current profiles are analogous to those of a Coulomb blockade and the conducting current pathways are found to be one-dimensional within the two-dimensional arrays of nanotubes. The second technique was taking advantage of the dispersibility of the nanotubes in a solution where conventional electrochemical methods were used. From these measurements, the nanotube bandgap energy could also be estimated, which was quite comparable to that determined by spectroscopic measurements.     

Stable superhydrophobic surface of hierarchical carbon nanotubes on Si micropillar arrays

It is of great importance to construct a stable superhydrophobic surface with low sliding angle (SA) for various applications. We used hydrophobic carbon nanotubes (CNTs) to construct the superhydrophobic hierarchical architecture of CNTs on silicon micropillar array (CNTs/Si-μp), which have a large contact angle of 153° to 155° and an ultralow SA of 3° to 5°. Small water droplets with a volume larger than 0.3 μL can slide on the CNTs/Si-μp with a tilted angle of approximately 5°. The CNTs growing on planar Si wafer lose their superhydrophobic properties after exposing to tiny water droplets. However, the CNTs/Si-μp still show superhydrophobic properties even after wetting using tiny water droplets. The CNTs/Si-μp still have a hierarchical structure after wetting, resulting in a stable superhydrophobic surface.     

Catalyst optimization and reduction condition of continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were synthesized under different catalyst compositions and reduction conditions. The effects of the catalyst, reduction temperature and reduction time on the surface morphology, graphitization, and single filament tensile strength of the prepared CNTs/CF samples were investigated. When nickel was used as the catalyst and copper as the catalyst promoter, with the increase of copper concentration, the catalytic activity increased. Thus, the carbon source was consumed more completely, improving the abundance of CNTs with good graphitization. And the effect of repairing CF defects was more obvious, hence the single filament tensile strength accordingly increased. Besides, the increase of catalyst reduction temperature and reduction time intensified the etching of CF by catalyst, and decreased the single filament tensile strength of CF. With the deposition of CNTs, the tensile strength of CF was enhanced in varying degrees. When the concentration of cooper was 0.01 mol/L with the reduction time of 10 min and reduction temperature of 450 °C, CNTs/CF had the highest tensile strength, which can reach up to 4.51 GPa. We determined that bimetallic catalysts could adjust the catalytic activity of nickel. The change of reduction time and temperature would affect the quality of CNTs, which was helpful to obtain high quality CNTs on CF surface and improve the mechanical properties of CNTs/CF and its composites.     

Influence of carbon nanotubes on thermal and electrical conductivity of zirconia-based composite

Carbon nanotubes (CNTs) are widely used in ceramic-matrix composites (CMC) as a filler. An individual carbon nanotube exhibits extremely high thermal conductivity, however, the influence of CNTs on the thermal conductivity of CMCs is moderate. In contrast, even a small quantity of CNTs significantly increases the electrical conductivity of CMCs. The present paper studies this contradictory influence for ZrO₂-CNTs composites with 3, 5, 10 and 20 vol% multi-wall carbon nanotubes (MWCNTs). Their thermal and electrical conductivity was studied by the laser flash method and electrochemical impedance spectroscopy. The analysis reveals that the moderate influence of MWCNTs on the thermal conductivity of composites originates from the similar thermal conductivity of MWCNTs in a bundle and zirconia. On the other hand, the substantial difference in the electrical conductivity of MWCNTs and zirconia leads to an exponential increase in the electrical conductivity of the ZrO₂-CNTs composite even with small additions of nanotubes.