Polymer-functionalized carbon nanotubes in cancer therapy: a review

The increasing importance of nanotechnology in the field of biomedical applications has encouraged the development of new nanomaterials endowed with multiple functions. Novel nanoscale drug delivery systems with diagnostic, imaging and therapeutic properties hold many promises for the treatment of different types of diseases, including cancer, infection and neurodegenerative syndromes. Carbon nanotubes (CNTs) are both low-dimensional sp² carbon nanomaterials exhibiting many unique physical and chemical properties that are interesting in a wide range of areas including nanomedicine. Since 2004, CNTs have been extensively explored as drug delivery carriers for the intracellular transport of chemotherapy drugs, proteins and genes. In vivo cancer treatment with CNTs has been demonstrated in animal experiments by several different groups. Herein, the recent works on anticancer drug delivery systems based on carbon nanotubes are reviewed and some of more specific and important novel drug delivery devices are discussed in detail. This paper focuses on modifications of CNTs by polymers through covalent and non-covalent attachments: two different methods as critical steps in preparation of anticancer drug delivery systems from CNTs. In this respect the in vivo and in vitro behaviors and toxicity of the CNTs modified by polymers are summarized as well. Well-functionalized CNTs did not show any significant toxicity after injection into mice. Moreover, administration and excretion of CNT-based nanocarriers are discussed. It was concluded that future development of CNT-based nanocarriers may bring novel opportunities to cancer diagnosis and therapy.     

Ways towards the scaleable integration of carbon nanotubes into silicon based technology

The outstanding performance of carbon nanotubes (CNTs) as interconnects and microelectronic devices has been shown in a number of experiments on hand-picked demonstrators. However, for implementation parallel manufacture, which involves the precise placement and the simultaneous control over the properties of millions of CNTs with microelectronic compatible processes is required. Various concepts for the large-scale integration of CNT-based electronics are compared in this presentation. One of them, catalyst mediated CVD growth, allows the direct growth of CNTs on silicon substrates. Methods for structuring the substrates and the catalyst materials on wafer scale as well as the influence of the process parameters are discussed in terms of reproducibility and uniformity. Furthermore, the synthesis of single, isolated multiwalled CNTs with lithographically defined diameters and locations has been established. This resembles the creation of vertical interconnects consisting of individual and multiple multiwalled CNTs. From this base, a concept for the assembly of CNT based, vertical, surrounding-gate transistors is presented.     

功能化碳纳米管/聚合物复合分离膜

碳纳米管不仅具有优异的力学性质和超大的比表面积,同时具有优良的传输特性,将其添加到聚合物中制备复合分离膜,具有广阔的应用前景。通过化学改性将碳纳米管功能化,提高其在聚合物中的分散性,制备碳纳米管/聚合物复合膜。本文在介绍了碳纳米管功能化、碳纳米管/聚合物复合膜制备方法的基础上,综述了功能化碳纳米管的加入对复合分离膜亲水性、水通量、机械稳定性以及分离等性能的影响。总结了近年来对碳纳米管在聚合物膜内定向排列的研究进展及碳纳米管定向对复合膜相关性能的影响。由于碳纳米管材料的各向异性,利用电场、磁场及流场等对碳纳米管在聚合物膜内的分布进行定向,从而充分利用其优异的性能,是该类复合膜的研究方向。     

In situ grown carbon nanotubes on carbon paper as integrated gas diffusion and catalyst layer for proton exchange membrane fuel cells

In situ grown carbon nanotubes (CNTs) on carbon paper as an integrated gas diffusion layer (GDL) and catalyst layer (CL) were developed for proton exchange membrane fuel cell (PEMFC) applications. The effect of their structure and morphology on cell performance was investigated under real PEMFC conditions. The in situ grown CNT layers on carbon paper showed a tunable structure under different growth processes. Scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) demonstrated that the CNT layers are able to provide extremely high surface area and porosity to serve as both the GDL and the CL simultaneously. This in situ grown CNT support layer can provide enhanced Pt utilization compared with the carbon black and free-standing CNT support layers. An optimum maximum power density of 670 mW cm⁻² was obtained from the CNT layer grown under 20 cm³ min⁻¹ C₂H₄ flow with 0.04 mg cm⁻² Pt sputter-deposited at the cathode. Furthermore, electrochemical impedance spectroscopy (EIS) results confirmed that the in situ grown CNT layer can provide both enhanced charge transfer and mass transport properties for the Pt/CNT-based electrode as an integrated GDL and CL, in comparison with previously reported Pt/CNT-based electrodes with a VXC72R-based GDL and a Pt/CNT-based CL. Therefore, this in situ grown CNT layer shows a great potential for the improvement of electrode structure and configuration for PEMFC applications.     

Delivery of drugs and biomolecules using carbon nanotubes

Carbon nanotubes (CNTs) have emerged as one of the most advanced nanovectors for the highly efficient delivery of drugs and biomolecules. They offer several appealing features such as large surface areas with well defined physico-chemical properties as well as unique optical and electrical properties. They can be conjugated non-covalently or covalently with drugs, biomolecules and nanoparticles. Albeit some pending concerns about their toxicity in vitro and in vivo, functionalized CNTs appear to exhibit very low toxicity and are not immunogenic. Thus, they could be promising carriers with a great potential for the development of a new-generation delivery system for drugs and biomolecules. There have been significant advances in the field of CNT-based drug delivery, especially in the specific targeting of anticancer and anti-inflammatory drugs for tissues and organs in the body, where their therapeutic effect is highly required. Other promising applications are the delivery of DNA, RNA and proteins.     

Thermal transport across carbon nanotubes connected by molecular linkers

Nonequilibrium molecular dynamics is applied to investigate thermal transport across two CNTs connected longitudinally by molecular linkers, which is a basic building-block for CNT network structures. We show the effect of different numbers, monomer types, and lengths of molecular linkers on the interfacial thermal conductance between CNTs and molecular linkers. We also analyze the density of vibrational normal modes to further understand the interfacial thermal conductance between different molecular linkers and CNTs. For most of the molecular linker type we simulated, the interfacial thermal conductance decreases with the increasing chain length. We find that aromatic-backbone structures are better than aliphatic-backbone structures to obtain higher interfacial thermal conductance with CNTs. Incorporating double bonds, oxygen atoms and amide groups into polymer chains shifts or redistributes of the density of vibrational normal modes, which in turn tunes the interfacial thermal conductance of molecular linker with CNTs. These results provide guidance for choosing molecular linkers to build up large-scale CNT-based network structures with tunable thermal properties.     

Structure and performance of Si3N4/SiC/CNT composite fibres

Herein, a homogeneously distributed and well-orientated ceramic-CNT composite fibre (Si₃N₄/SiC/CNTs) has been prepared using carbon nanotube fibres (CNTFs) premixed with silicon powder, followed by the reaction-bonded sintering process. The SiC layers around the CNT bundles interspersed in the composite are formed during the silicon reaction stage through the contact of silicon and CNTs, and the densification of the ceramic through the further reaction-bonded silicon carbide and nitride. Due to strong interface bonding, the composite fibres exhibit the potential for CNT-based damage sensing with a tensile strength upto 225 Mpa. Furthermore, the high-volume distribution of CNT sresults in a significant enhancement of the electrical and thermal conductivities as well as photoluminescence properties. Our work provides a useful approach for thefabrication of multifunctional fibres for imaging, engineering, and other complex applications.     

Structural evolution and stability studies of heterostructures comprised of carbon nanotubes decorated with nickel/nickel oxide core/shell nanoparticles

The single-step synthesis of heterostructures, denoted as CNC heterostructures, comprised of carbon nanotubes (CNTs) decorated with nickel (Ni)/nickel oxide (NiO) core/shell nanoparticles through a direct nucleation approach is reported. This approach allowed for a single-parameter and well-controlled structural evolution of Ni/NiO core/shell nanoparticles on CNTs. It was possible to control the size (∼12–52 nm), shape, spatial density, and chemical composition of nanoparticles formed on CNTs by changing the nanoparticle growth time (15 min to 15 h). It was observed that growth time of 15 h led to the reaction between phosphine-based stabilizers and Ni core forming solid and hollow Ni₁₂P₅ nanoparticles directly on CNTs. Thermal stability of CNC heterostructures (in N₂-rich atmosphere) dispersed on a silicon wafer as well as subsequent surface migration of nanoparticles were studied by annealing heterostructures at different temperatures (125–750 °C). In comparison to as-produced CNTs, the surface characteristics, oxidative resistance or thermal stability, and changes in heterostructure compositions were studied using electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The heterostructures showed greater oxidative resistance as compared to as-produced CNTs.     

Can the properties of carbon nanotubes influence their internalization by living cells?

Carbon nanotubes (CNTs) are widely used for biomedical applications as intracellular transporters of (bio)molecules, due to their high propensity to cross cell membranes. However, there is a clear discrepancy in the literature about their uptake mechanism, which should be related to the differences existing in the nanotube materials, as well as the experimental procedures. Despite the fact that there are some studies on the influence of the CNT surface chemistry, the role of the properties of non-functionalized CNTs in cellular uptake has not been much investigated to a great extent. In this work, different kinds of multi-wall CNTs (MWCNTs) are produced and fully characterized, in terms of diameter, length, metal impurity, carbon soot and surface chemistry. These MWCNT samples are tested in vitro, and the cellular uptake is indirectly evaluated by using standard fluorescent probes and confirmed by TEM images. Our assays demonstrate that nanotube length clearly influences their uptake and shorter (sub-1 μm) MWCNTs are easier to be internalized through an energy-independent pathway. The results of this investigation may be useful for the design of promising CNT-based vectors for cell therapy.     

Nanostructured Hybrid Carbon Nanotube/UltraHigh‐Temperature Ceramic Heterostructures: Microstructure Evolution and Forming Mechanism

An original catalytic method has been proposed to synthesize carbon nanotubes (CNTs)–ZrB₂–ZrO₂ heterostructures using ZrB₂ polymeric precursor. The pyrolysized gases from the ZrB₂ polymeric precursor are identified to be the carbon sources for CNTs growth. A parametric study is conducted to control the CNTs growth by optimizing parameters such as synthesis temperature and catalyst content. Observations show that the in situ grown CNTs are homogeneously dispersed in the powders, and the structure and the amount of CNTs are significantly dependent on the synthesis parameters. There are two kinds of grown CNTs existed in the produced hybrid heterostructures: (i) the kinking structured CNTs that are disordered and incomplete graphitization; (ii) the improved and graphitized CNTs. The ZrB₂ polymeric precursor during thermal pyrolysis provides capable of supplying substantial carbon source for CNTs nucleation and growth by homogeneous vapor–liquid–solid reactions.     

Effects of nanotube size and roof-layer coating on viscoelastic properties of hybrid diamond-like carbon and carbon nanotube composites

Hybrid carbon nanobuffers are developed by exploiting the ultra-hardness and wear-resistant properties of diamond-like carbon (DLC) coatings and the inherent viscoelasticity properties of vertically aligned carbon nanotubes (VACNTs). The viscoelastic properties of carbon nanobuffers incorporating thin-walled and thick-walled CNTs, respectively, are characterized by means of nanoindentation dynamic mechanical analysis tests. It is shown that the thin-walled nanobuffer has a better damping performance than the thick-walled nanobuffer due to its buckling-driven friction and post-buckling behaviors; particularly under large displacements. In addition, it is shown that under large indenter displacements, the VACNT arrays with DLC coatings display the improved stress distributions and enhanced strain energy dissipation performances due to the load transfer on the top of VACNTs. Molecular dynamics (MD) simulations are performed to investigate the roof-layer effect on damping behavior and structural deformation of the coated and uncoated VACNTs under nanoindentation. The results confirm that the VACNT with a DLC coating exhibits the significantly damping characterizations than the non-coated VACNT. Overall, the results presented in this study reveal the potential for tuning the damping performance of CNT-based nanobuffers through a careful control of the CNT size.     

Sub-millimeter-long carbon nanotubes repeatedly grown on and separated from ceramic beads in a single fluidized bed reactor

A semi-continuous fluidized-bed process is reported which rapidly converts acetylene into carbon nanotubes (CNTs). Catalysts are first immobilized on ceramic beads and CNTs are then grown on the beads and then separated from them in a repetitive process accomplished within a single reactor simply by switching gases at a fixed temperature. CNTs of 6–10 nm diameter, three walls on average, 0.4 mm length and 99 wt.% purity were synthesized at an yield of over 70% in a reactor residence time shorter than 0.3 s. The easy and efficient production of such CNTs with in situ separation from the catalysts may accelerate the development of CNT-based nanotechnology industries.     

Morphology and processing of aligned carbon nanotube carbon matrix nanocomposites

Intrinsic and scale-dependent properties of carbon nanotubes (CNTs) have led aligned CNT architectures to emerge as promising candidates for next-generation multifunctional applications. Enhanced operating regimes motivate the study of CNT-based aligned nanofiber carbon matrix nanocomposites (CNT A-CMNCs). However, in order to tailor the material properties of CNT A-CMNCs, porosity control of the carbon matrix is required. Such control is usually achieved via multiple liquid precursor infusions and pyrolyzations. Here we report a model that allows the quantitative prediction of the CNT A-CMNC density and matrix porosity as a function of number of processing steps. The experimental results indicate that the matrix porosity of A-CMNCs comprised of ∼1% aligned CNTs decreased from ∼61% to ∼55% after a second polymer infusion and pyrolyzation. The model predicts that diminishing returns for porosity reduction will occur after 4 processing steps (matrix porosity of ∼51%), and that >10 processing steps are required for matrix porosity <50%. Using this model, prediction of the processing necessary for the fabrication of liquid precursor derived A-CMNC architectures, with possible application to other nanowire/nanofiber systems, is enabled for a variety of high value applications.     

Synthesis, characterization, and electrochemical capacitance of amino-functionalized carbon nanotube/carbon paper electrodes

Amino-functionalization of carbon nanotubes (CNTs) attached to carbon paper (CP) has been achieved using one synthesis protocol: (i) chemical oxidation, (ii) acyl chlorination, and (iii) amidation. The amidation reaction of the carboxylic groups in oxidized the CNT/CP hybrids enables the formation of terminal amino groups on the CNT sidewalls. The functionalized CNTs were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, thermal programmed desorption, and N₂ adsorption. The cyclic voltammetry curves of an amino-modified CNT-based capacitor showed a continuum of double-layer and pseudocapacitive behavior. The presence of surface oxides and amides on CNTs imparts not only hydrophilic coverage for the formation of double-layer (double-layer capacitance) but also active sites for the redox reaction (pseudocapacitance). Based on the result of the charge/discharge cycling test, the N-modified CNT/CP capacitor exhibits an enhanced capacitance, high-rate capability, and capacitance stability with high coulombic efficiency.     

Role of polymers in the design of 3D carbon nanotube-based scaffolds for biomedical applications

Since pioneer works by Iijima in 1991, carbon nanotubes (CNTs) have received a great deal of attention as confirmed by the increasing number of papers in the topic. Their unique and attractive properties have made them extensively demanded materials for a wide variety of technological applications, including their promising use as scaffolds in tissue engineering. In this review, we focus on the role that polymers (both natural and synthetic) play on the fabrication of three-dimensional (3D) CNT-based scaffolds for biomedical applications, with emphasis on biocompatible fabrication strategies such as freeze-casting, electrospinning and gel formation. These 3D matrices may be an interesting and alternative platform to circumvent structural limitations and toxicity problems of bare CNTs by the use of biocompatible dispersant polymers that allow the preparation of substrates better resembling native extracellular matrices. In any case, due to the relevance of CNT toxicity in this context, we also discuss significant works concerning cell and tissue responses to CNTs in dispersion, highlighting: (1) the asbestos-like behavior of CNTs, (2) surface functionalization as a tool to reduce CNT toxicity and (3) CNT biodistribution from the blood stream and posterior excretion. In this sense, literature revision has evidenced major toxicity issues related to: (a) the inherent insolubility and tendency to aggregate of pristine CNTs, (b) the rigidity of their structures that makes them resemble asbestos, (c) the presence of residual metal impurities or amorphous carbon from their synthesis, and (d) the depletion of culture media components due to the adsorptive properties of CNTs. Nevertheless, as expected for almost any material, we also illustrate how dose plays a key role in the biological responses induced. Overall, this critic review is expected to help research community working on polymers and CNTs, as well as other carbon nanomaterials such as graphene, to identify useful guidelines that help advancing the use of 3D CNT-based scaffolds in biomedical applications.     

Three-dimensional heterostructure of metallic nanoparticles and carbon nanotubes as potential nanofiller

ABSTRACT: The effect of the dimensionality of metallic nanoparticle-and carbon nanotube-based fillers on the mechanical properties of an acrylonitrile butadiene styrene (ABS) polymer matrix was examined. ABS composite films, reinforced with low dimensional metallic nanoparticles (MNPs, 0-D) and carbon nanotubes (CNTs, 1-D) as nanofillers, were fabricated by a combination of wet phase inversion and hot pressing. The tensile strength and elongation of the ABS composite were increased by 39% and 6%, respectively, by adding a mixture of MNPs and CNTs with a total concentration of 2 wt%. However, the tensile strength and elongation of the ABS composite were found to be significantly increased by 62% and 55%, respectively, upon addition of 3-D heterostructures with a total concentration of 2 wt%. The 3-D heterostructures were composed of multiple CNTs grown radially on the surface of MNP cores, resembling a sea urchin. The mechanical properties of the ABS/3-D heterostructured nanofiller composite films were much improved compared to those of an ABS/mixture of 0-D and 1-D nanofillers composite films at various filler concentrations. This suggests that the 3-D heterostructure of the MNPs and CNTs plays a key role as a strong reinforcing agent in supporting the polymer matrix and simultaneously serves as a discrete force-transfer medium to transfer the loaded tension throughout the polymer matrix.     

Stretchable carbon nanotube conductors and their applications

Stretchable electronics has evolved rapidly in the past decade because of its promising applications, as electronic devices undergo large mechanical deformation (e.g., bending, folding, twisting, and stretching). Stretchable conductors are particularly crucial for the realization of stretchable electronic devices. Therefore, tremendous efforts have been dedicated toward developing stretchable conductors, with a focus on conductive material/polymer composites. This review summarizes the recent progress in stretchable conductors and related stretchable devices based on carbon nanotubes (CNTs), which was enabled by their outstanding electrical and mechanical properties. Various strategies for developing highly stretchable conductors that can deform into nonplanar shapes without significant degradation in their electronic performance are described in terms of preparation processes. Finally, challenges and perspectives for further advances in CNT-based stretchable conductors are discussed.     

Tailoring gas sensing properties of multi-walled carbon nanotubes by in situ modification with Si,P, and N

A simple method for the synthesis of multi-walled carbon nanotubes (MWCNTs) containing Si, P–N and N is reported, and their gas sensing properties were investigated. The MWCNTs were synthesised by the thermal decomposition of aerosols containing mixtures of ferrocene/triphenylsilane, ferrocene/triphenylphosphine/benzylamine, and ferrocene/benzylamine/toluene. Electron microscopy studies revealed that the addition of Si, P, and N alters the structure of CNTs dramatically. Gas sensing experiments were carried out using Si, P–N, N-containing MWCNTs, and were compared with pure MWCNTs synthesised at similar experimental conditions. These experiments showed that the gas sensitivity and selectivity of CNT-based sensors can be indeed tailored without any post-processing of the raw nanotubes. The efficient in situ tailoring of nanotube properties and functionality are important for nanotubes to become viable materials at the industrial scale where low cost processes are required.     

Interfacial bond dependence of damping properties of carbon nanotubes enhanced polymers

The effect of interfacial bond on damping properties of carbon nanotubes (CNTs) enhanced polymers is investigated. To acquire different interfacial bonds (including van der Waals, weak, and strong covalent bond) of CNTs enhanced polymers, different functionalizations of CNTs have been designed through acid treatment and silane termination. CNTs with silanization show superior dispersion state in the matrix regardless of CNTs content. When the CNTs content is lower than 0.2 wt%, a strong interfacial bond of CNTs/epoxy composites has a deleterious effect on the damping properties. When the CNTs content is greater than 0.2 wt%, the strong covalent bond becomes the dominant factor to enhance damping properties and slow down the decreasing rate of the damping properties. POLYM. COMPOS., 35:548–556, 2014. © 2013 Society of Plastics Engineers     

Modeling and characterization of the electrical conductivity of carbon nanotube-based polymer composites

In this research, we investigate both analytically and experimentally the electrical properties of carbon nanotube (CNT)-based polymer composites. An analytical model was developed to predict the electrical conductivity of CNT-based composites. The micro/nanoscale structures of the nanocomposites and the electrical tunneling effect due to the matrix material between CNTs were incorporated within the model. Electrical conductivity measurements were also performed on CNT/polycarbonate composites to identify the dependence of their electrical transport characteristics on the nanotube content. The analytical predictions were compared with the experimental data, and a good correlation was obtained between the predicted and measured results. In addition, the effect of nanotube geometry on the nanocomposite electrical properties at the macroscale was examined.