Effect of particle dimension on biocompatibility of carbon nanomaterials

With various emerging applications ranging from medicine to materials and electronics, the risk of exposure to nanomaterials is rapidly increasing. Several routes of exposure to nanomaterials exist; the most important being dermal contact and inhalation. In this dermal toxicity study, the cellular effects of carbon-based materials with diameters ranging from micro- to nano-dimension were investigated using mouse keratinocytes (HEL-30). The carbon materials tested included carbon fibers (CF; 10 μm diameter), carbon nanofibers (CNF; 100 nm diameter), multi-walled carbon nanotubes (MWCNT; 10 nm diameter), and single-walled carbon nanotubes (SWCNT; 1 nm diameter). CF and CNF did not significantly affect cell viability; however, MWCNT and SWCNT reduced cell viability in a time-dependent manner up to 48 h, with full recovery of mitochondrial function by the 72 h time point. After a 24 h exposure, cells exposed to MWCNT produced up to 3-fold higher increase in reactive oxygen species than those exposed to SWCNT. The results of this study suggest that high-aspect ratio carbon material toxicity is dependent on dimension and composition.     

Nanosilver induces minimal lung toxicity or inflammation in a subacute murine inhalation model

Background

Multi-walled carbon nanotubes (MWCNTs) are new manufactured nanomaterials with a wide spectrum of commercial applications. To address the hypothesis that MWCNTs cause persistent pulmonary pathology, C57BL/6J mice were exposed by pharyngeal aspiration to 10, 20, 40 or 80 μg of MWCNTs (mean dimensions of 3.9 μm × 49 nm) or vehicle. Lungs were preserved at 1, 7, 28 and 56 days post- exposure to determine the potential regions and target cells for impact by MWCNT lung burden. Morphometric measurement of Sirius Red staining was used to assess the connective tissue response.

Results

At 56 days post-exposure, 68.7 ± 3.9, 7.5 ± 1.9 and 22.0 ± 5.1 percent (mean ± SE, N = 8) of the MWCNT lung burden were in alveolar macrophages, alveolar tissue and granulomatous lesions, respectively. The subpleural tissues contained 1.6% of the MWCNT lung burden. No MWCNTs were found in the airways at 7, 28 or 56 days after aspiration The connective tissue in the alveolar interstitium demonstrated a progressive increase in thickness over time in the 80 μg exposure group (0.12 ± 0.01, 0.12 ± 0.01, 0.16 ± 0.01 and 0.19 ± 0.01 μm for 1, 7, 28 and 56 days post-exposure (mean ± SE, N = 8)). Dose-response determined at 56 days post-exposure for the average thickness of connective tissue in alveolar septa was 0.11 ± 0.01, 0.14 ± .02, 0.14 ± 0.01, 0.16 ± 0.01 and 0.19 ± 0.01 μm (mean ± SE, N = 8) for vehicle, 10, 20, 40 and 80 μg dose groups, respectively.

Conclusions

The distribution of lung burden was predominately within alveolar macrophages with approximately 8% delivery to the alveolar septa, and a smaller but potentially significant burden to the subpleural tissues. Despite the relatively low fraction of the lung burden being delivered to the alveolar tissue, the average thickness of connective tissue in the alveolar septa was increased over vehicle control by 45% in the 40 μg and 73% in the 80 μg exposure groups. The results demonstrate that MWCNTs have the potential to produce a progressive, fibrotic response in the alveolar tissues of the lungs. However, the increases in connective tissue per μg dose of MWCNTs to the interstitium are significantly less than those previously found for single-walled carbon nanotubes (SWCNTs).     

Coating carbon nanotubes with a polystyrene-based polymer protects against pulmonary toxicity

Background

Multi-walled carbon nanotubes (MWCNTs) are widely used in many disciplines due to their unique physical and chemical properties. Therefore, some concerns about the possible human health and environmental impacts of manufactured MWCNTs are rising. We hypothesized that instillation of MWCNTs impairs pulmonary function in C57BL/6 mice due to development of lung inflammation and fibrosis.

Methods

MWCNTs were administered to C57BL/6 mice by oropharyngeal aspiration (1, 2, and 4 mg/kg) and we assessed lung inflammation and fibrosis by inflammatory cell infiltration, collagen content, and histological assessment. Pulmonary function was assessed using a FlexiVent system and levels of Ccl3, Ccl11, Mmp13 and IL-33 were measured by RT-PCR and ELISA.

Results

Mice administered MWCNTs exhibited increased inflammatory cell infiltration, collagen deposition and granuloma formation in lung tissue, which correlated with impaired pulmonary function as assessed by increased resistance, tissue damping, and decreased lung compliance. Pulmonary exposure to MWCNTs induced an inflammatory signature marked by cytokine (IL-33), chemokine (Ccl3 and Ccl11), and protease production (Mmp13) that promoted the inflammatory and fibrotic changes observed within the lung.

Conclusions

These results further highlight the potential adverse health effects that may occur following MWCNT exposure and therefore we suggest these materials may pose a significant risk leading to impaired lung function following environmental and occupational exposures.     

Impaired Ciliogenesis in differentiating human bronchial epithelia exposed to non-Cytotoxic doses of multi-walled carbon Nanotubes

Background

Multi-walled carbon nanotubes (MWCNTs) are engineered nanomaterials used for a variety of industrial and consumer products. Their high tensile strength, hydrophobicity, and semi-conductive properties have enabled many novel applications, increasing the possibility of accidental nanotube inhalation by either consumers or factory workers. While MWCNT inhalation has been previously shown to cause inflammation and pulmonary fibrosis at high doses, the susceptibility of differentiating bronchial epithelia to MWCNT exposure remains unexplored. In this study, we investigate the effect of MWCNT exposure on cilia development in a differentiating air-liquid interface (ALI) model. Primary bronchial epithelial cells (BECs) were isolated from human donors via bronchoscopy and treated with non-cytotoxic doses of MWCNTs in submerged culture for 24 h. Cultures were then allowed to differentiate in ALI for 28 days in the absence of further MWCNT exposure. At 28 days, mucociliary differentiation endpoints were assessed, including whole-mount immunofluorescent staining, histological, immunohistochemical and ultrastructural analysis, gene expression, and cilia beating analysis.

Results

We found a reduction in the prevalence and beating of ciliated cells in MWCNT-treated cultures, which appeared to be caused by a disruption of cellular microtubules and cytoskeleton during ciliogenesis and basal body docking. Expression of gene markers of mucociliary differentiation, such as FOXJ1 and MUC5AC/B, were not affected by treatment. Colocalization of basal body marker CEP164 with γ-tubulin during days 1–3 of ciliogenesis, as well as abundance of basal bodies up to day 14, were attenuated by treatment with MWCNTs.

Conclusions

Our results suggest that a single exposure of bronchial cells to MWCNT during a vulnerable period before differentiation may impair their ability to develop into fully functional ciliated cells.

     

A comparative study of superhydrophobicity of 0D/1D/2D thermally functionalized carbon nanomaterials

Superhydrophobic coatings promise various practical applications. A one-step, ingenious yet economical thermal curing method is devised to render the carbon nanomaterials superhydrophobic. This study aims to compare the degree of superhydrophobicity of the carbon/polydimethylsiloxane (PDMS) synthesized from the 2D graphene nanoplatelets (GNPs), 1D multiwalled carbon nanotubes (MWCNTs), and 0D carbon black (CB) nanomaterials. The superhydrophobic GNPs/PDMS, MWCNTs/PDMS and CB/PDMS are synthesized when thermally functionalized with the siloxane groups. The Fourier transform infrared spectroscopy data signifies the successful functionalization of the carbon nanostructures by siloxane chains and the Raman spectroscopy analyses indicate that GNPs/PDMS manifests the highest degree of structural defects due to functionalization. The degree of superhydrophobicity induced on the carbon/PDMS coatings correlates with the dimensions of the carbon nanomaterials (0D, 1D and 2D), which is intimately associated with the effective surface areas of the nanomaterials susceptible of chemical functionalization. The promising applications of the superhydrophobic coatings are demonstrated. This study proposes a novel wettability tuning method and provides insightful analyses and characterization of the superhydrophobicity of the thermally functionalized carbon nanomaterials with different dimensions of varied nano-geometries.     

Morphology and tensile properties of polypropylene‐multiwalled carbon nanotubes composite fibers

In this work, we analyzed tensile properties of polypropylene‐multiwalled carbon nonotubes composite fibers. The multiwalled carbon nanotubes (MWCNTS) were used in different contents of 0, 1, 2, 3, 4, and 5 wt %. Dispersing agents were used to disperse MWCNTs in polypropylene matrix. After the dispersing agent was removed, the mixture was melt mixed. The fibers were spun by a home‐made melt spinning equipment and stretching was done at a draw ratio of 7.5. By using 1–5 wt % of MWCNTs, the modulus of composite fibers increased by 69–84% and tensile strength increased about 39% when compared with the virgin polypropylene fibers. In addition, the MWCNTs dispersion in the matrix was monitored by scanning electron microscopy and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of processing methods and functional groups on the properties of multi-walled carbon nanotube filled poly(dimethyl siloxane) composites

Pristine and functionalized multi-walled carbon nanotubes (MWCNTs) filled poly(dimethyl siloxane) (PDMS) composites were produced by two different methods, namely the solution mixing method and the mini-extruder method. The composites produced using the mini-extruder exhibit relatively higher tensile strength and higher thermal conductivity due to better nanotubes dispersion. On the other hand, the composites prepared via solution mixing have higher electrical conductivity and better thermal stability due to the high aspect ratio of nanotubes. Scanning electron micrographs of composites fracture surface revealed that composites produced by mini-extruder resulted shorter nanotube length, thus lowering the aspect ratio of MWCNTs. In general, functionalization of nanotubes increases the tensile strength, thermal conductivity, and thermal stability of the PDMS composites due to the improved interfacial adhesion and nanotubes dispersion.     

Bomb calorimetry as a bulk characterization tool for carbon nanostructures

Multiwalled carbon nanotubes (MWCNTs) consisting of coaxial graphene cylinders (cylindrical MWCNTs), cones (herringbone MWCNTs) or carbon fibers were combusted in an isothermal bomb calorimeter. Their standard enthalpies of formation were determined to be 16.56 ± 2.76 kJ mol⁻¹(C – per carbon mol) for carbon fibers, 21.70 ± 1.32 kJ mol⁻¹(C) for herringbone MWCNTs and 8.60 ± 0.52 kJ mol⁻¹(C) for cylindrical ones. All materials were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermogravimetry, and elemental analysis. A linear correlation between the standard enthalpies of formation and D/G and G′/G Raman bands ratio (D – band is centered at 1350 cm⁻¹, G – 1585 cm⁻¹, G′ – 2700 cm⁻¹) demonstrates the applicability of bomb calorimetry for characterization of the “defectiveness” of the bulk carbon material in the sense Raman spectroscopy is widely used nowadays. Also, we show that the calorimetry may be used to estimate the oxygen content in the bulk carbon nanomaterials, as there is a linear correlation between the oxygen content (both total content and in carboxyl groups separately) and the standard enthalpies of formation for herringbone nanotubes oxidized by nitric acid.     

Fabrication and characterization of three-dimensional macroscopic all-carbon scaffolds

We report a simple method to fabricate macroscopic, 3-D, free standing, all-carbon scaffolds (porous structures) using multiwalled carbon nanotubes (MWCNTs) as the initial materials. The scaffolds prepared by radical initiated thermal crosslinking, and annealing of MWCNTs possess macroscale interconnected pores, robust structural integrity, stability, and electrical conductivity. The porosity of the three-dimensional structure can be controlled by varying the amount of radical initiator, thereby allowing the design of porous scaffolds tailored towards specific potential applications. This method also allows the fabrication of 3-D scaffolds using other carbon nanomaterials such as single-walled carbon nanotubes, fullerenes, and graphene indicating that it could be used as a versatile method for 3-D assembly of carbon nanostructures with pi bond networks.     

The improved electrical conductivity of carbon nanofibers by fluorinated MWCNTs

In order to increase the conductivity of carbon nanofiber sheet, conductive multi wall carbon nanotubes (MWCNTs) was added into the carbon fibers. The dispersion of MWCNTs into the fibers and adhesion between carbon fibers and MWCNTs were improved through fluorine modification on surface of MWCNTs. By fluorination treatment, hydrophobic functional group was introduced on the surface of MWCNTs improving the affinity on interface between two carbon materials. These nanofibers made by electrospinning method were treated at different temperature in order to investigate the effect of temperature. According to the increment of temperature, the better conductivity of carbon nanofibers sheet was obtained due to the better oriented carbon structure. Eventually, the improved conductivity of carbon nanofiber sheet was resulted showing 27 S/cm.     

Mechanical Reinforcement of Diopside Bone Scaffolds with Carbon Nanotubes

Carbon nanotubes are ideal candidates for the mechanical reinforcement of ceramic due to their excellent mechanical properties, high aspect ratio and nanometer scale diameter. In this study, the effects of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of diopside (Di) scaffolds fabricated by selective laser sintering were investigated. Results showed that compressive strength and fracture toughness improved significantly with increasing MWCNTs from 0.5 to 2 wt %, and then declined with increasing MWCNTs to 5 wt %. Compressive strength and fracture toughness were enhanced by 106% and 21%, respectively. The reinforcing mechanisms were identified as crack deflection, MWCNTs crack bridging and pull-out. Further, the scaffolds exhibited good apatite-formation ability and supported adhesion and proliferation of cells in vitro.     

Universal water-soluble cyclodextrin polymer–carbon nanomaterials with supramolecular recognition

Functionalization of carbon nanomaterials (including fullerenes, single-walled carbon nanotubes, multi-walled carbon nanotubes (MWCNTs), and graphene sheets) dispersed in water with macromolecules was achieved by a one-step strategy using β-cyclodextrin polymer (CDP). CDP-carbon nanomaterials were characterized by ultraviolet–visible, Raman, and Fourier transform infrared spectroscopies, transmission and scanning electron microscopies, and thermogravimetric analysis. These nanomaterials showed high solubility and stability in water because of the noncovalent interaction between carbon nanomaterials and CDP. The supramolecular recognition abilities of CDP-carbon nanomaterials were studied by cyclic voltammetry (CV). CDP-MWCNTs were also decorated by p-aminothiophenol (PATP) which formed inclusion complexes with the CDP. The conjugates (PATP-CDP-MWCNTs) were ideal templates for the highly efficient assembly of noble metal nanoparticles (Au and Pt) with dramatically different properties. Methanol oxidation of Pt-decorated PATP-CDP-MWCNTs in CV analyses indicated its potential application in direct methanol fuel cells, facilitating the feasibility of metal-decorated CDP-carbon nanomaterials in real technological applications. This universal method of producing carbon nanomaterials functionalized with macromolecules is beneficial for investigating the structure–performance relationship of carbon nanomaterials for designing compounds with specialized functions.     

碳纳米管负载层结构对复合膜分离性能的影响研究

采用过滤涂敷法将多壁碳纳米管（MWCNTs）负载于氧化铝微滤（MF）膜表面,构建了一种新型复合膜。通过系统考察碳管投加量、外形尺寸对表面碳层结构的影响,建立了其与复合膜分离性能的响应关系,为传统MF膜的改进提供了重要参考。结果表明,借助高分子表面活性剂和超声波辅助技术,可以实现碳管在水溶液中的充分分散,这有利于在膜表面形成相对均匀的碳负载层。对于同类型碳管而言,增大负载量对碳层孔径分布和过滤比阻（r_c）的影响较小。相比之下,使用低长径比（L/D）的碳管可以有效压缩负载碳层中的孔隙尺寸,导致复合膜渗透率降低。而高L/D比碳管在膜表面形成了高度缠绕的蓬松结构,对应的r_c值最小。利用负载碳层的吸附作用,复合膜对小分子富里酸（FA）的截留能力与碳管负载量和比表面积呈现正相关,同时,碳层结构的致密程度也是影响FA截留率的重要因素。     

Highly conductive multiwall carbon nanotube and epoxy composites produced by three-roll milling

Length and diameter distributions as well as the conductivity of bucky papers made of different multiwalled carbon nanotubes (MWCNTs) have been measured. While the average diameter is in good agreement with the manufacturer specification, the average length is significantly shorter than that given by the manufacturer. Highly conductive and homogeneous dispersions of up to 8 wt% MWCNTs in an epoxy resin are obtained by three-roll milling. The influence of shear intensity and number of passes on the nanotube dispersion and composite conductivity is investigated. The aspect ratio of the MWCNTs is one of the most important parameters that determine the composite conductivity and the percolation behavior. We have found that the composite conductivity increases almost 10 times as the aspect ratio increases 5.5 times. The percolation parameters in conjunction with the optical microscopy revealed a kinetic rather than statistic percolation. We have observed that three-roll milling induces extended alignment of MWCNTs with high aspect ratio at moderate loading (2-4 wt%).     

Improvement in mechanical properties of enamel via carbon nanotube addition

Enameled metal equipment exploits the strength of metal materials and the corrosion resistance of enamel; therefore, it is widely used in the chemical industry. However, the mechanical properties of the enamel restrict its service life. Multi-walled carbon nanotubes (MWCNTs) are one-dimensional nanomaterials with high-specific surface area, C–C bond structure, and SP₂ hybrid orbital. Herein, the effect of the dosage of MWCNTs on the mechanical properties of enamel is studied by adding MWCNTs to improve the mechanical properties of the enamel. Microscopic observation showed that the toughening mechanism of MWCNTs was mainly manifested in fracture and pull out behaviors. According to three-point bending test, when 0.4 wt% carbon nanotubes were added, the reinforcing effect of enamel layer reached the best state. These results provide reference for optimizing the formulation of enamel and extending the service life of enamel.     

Carbon nanotube functionalization effects on thermal properties of multiwall carbon nanotube/polycarbonate composites

The thermal properties of composites based on polycarbonate (PC) filed with ultraviolet/ozone (UVO) treated multiwall carbon nanotubes (MWCNTs) in low limit (less than 0.01) volume fractions have been investigated. The composites were prepared in the form of films of relatively small thickness (23–33 μm) with random orientation of treated MWCNTs. Functionalization of MWCNTs has been confirmed through Fourier transform infrared measurements. Thermal conductivity was obtained by measuring both of thermal diffusivity and thermal effusivity using photoacoustic technique. The results reveal that the addition of UVO treated MWCNTs lead to enhance both the thermal diffusivity and thermal effusivity of the composites. Insertion of 0.95% MWCNTs into PC improves the thermal conductivity of the composites by ∼22%. This enhancement is reasonable using such low content of MWCNTs of moderate aspect ratio. The experimental results were analyzed using a simple model concerning some relevant parameters such as volume fractions, interfacial thermal resistance, aspect ratio, and nonstraightness of nanotubes. An interface thermal resistance in the low limit of about 2.1 × 10⁻⁸ m²K/W has been estimated. In the light of these results, the role of MWCNTs functionalization on the overall thermal transport properties of MWCNTs‐polymer composites has been discussed. POLYM. COMPOS., 36:1242–1248, 2015. © 2014 Society of Plastics Engineers     

Plasma retinol,carotene and vitamin E concentrations and lung function in a crocidolite-exposed cohort from Wittenoom,Western Australia: a cohort study

Background  

Increased rates of death from asbestos related diseases have been reported for people previously employed in the mining and milling operations at Wittenoom (Western Australia), and people who lived in the nearby town, where they were environmentally exposed to crocidolite.     

Facile fabrication of PVA composite fibers with high fraction of multiwalled carbon nanotubes by gel spinning

Poly(vinyl alcohol) (PVA) composite fibers with high fraction of multiwalled carbon nanotubes (MWCNTs) were prepared by gel spinning process. Here, a modified process was introduced to prepare concentrated PVA/MWCNTs/DMSO spinning dope, and to attain good dispersion of MWCNTs in the fibers. The final composite fibers were studied by thermogravimetric analyzer (TGA), Fourier transform infrared spectrometer (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), and WAXD analysis. The total content of MWCNTs in PVA composite fibers, from 5 to 30 wt%, was confirmed by TGA analysis. FTIR and Raman measurements demonstrated the existence of strong hydrogen interaction between MWCNTs and PVA matrix. SEM images of composite fibers showed smooth surface, regular cross‐section shape and good dispersion of MWCNTs in the fibers. DSC analysis showed that the crystallinity first increased and then decreased with the increase of MWCNTs contents. It can be concluded that low concentration of MWNCTs can act as nucleation sites for crystallization of PVA component, and large amount of MWCNTs may impede the crystallization of PVA component. The WAXD analysis results indicated that the crystal orientation of the PVA component in PVA composite fibers is almost identical at the same drawn ratio. Polarized Raman analysis indicated a small increase in MWCNTs orientation for the composite fibers. The mechanical properties tests showed that the composite fibers exhibit significant improvement in tensile strength and modulus as compared to the neat PVA fibers. The composite fibers also showed sustained growth in electrical conductivity. POLYM. ENG. SCI., 58:37–45, 2018. © 2017 Society of Plastics Engineers     

Dispersion and aspect ratio of carbon nanotubes in aqueous suspension and their relationship with electrical resistivity of carbon nanotube filled polymer composites

Multiwalled carbon nanotube (MWCNT)/acrylonitrile butadiene styrene (ABS) composites were prepared by a processing method using solvent–nonsolvent precipitation. Size distributions of MWCNT agglomerates in aqueous suspension were investigated in order to predict aspect ratio of nanotubes by evaluating the effects of sonication time, MWCNT content, and surfactant. Aspect ratios of MWCNTs were predicted on the basis of the size distribution measurements for MWCNT agglomerates. Sonication time or applied sonic energy has a strong effect on the size distribution of MWCNT agglomerates. Compared with simple shear mixing method, it was shown that this processing method is more suitable for the MWCNT/ABS composites. An electrical percolation threshold was observed for the weight fraction of MWCNTs in the range of about 0.5–1.0 wt.%. Shorter MWCNTs are more suitable to induce fine dispersion, but lead to higher percolation threshold weight fraction. It was illustrated that fine dispersion can overcome the handicap of short length or low aspect ratio of MWCNTs.     

Evaluation and mechanism of antifungal effects of carbon nanomaterials in controlling plant fungal pathogen

The antifungal activity of six carbon nanomaterials (CNMs, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), reduced graphene oxide (rGO), fullerene (C₆₀) and activated carbon (AC)) against two important plant pathogenic fungi (Fusarium graminearum (F. graminearum) and Fusarium poae (F. poae)) was evaluated. SWCNTs were found to show the strongest antifungal activity, followed by MWCNTs, GO, and rGO, while C₆₀ and AC showed no significant antifungal activity. The antifungal mechanism of CNMs was deduced to target the spores in three steps: (i) depositing on the surface of the spores, (ii) inhibiting water uptake and (iii) inducing plasmolysis.