Carbon Nanotubes – Interactions with Biological Systems

Carbon nanotubes (CNTs) possess exceptional mechanical, thermal, and electrical properties, facilitating their use as reinforcements or additives in various materials to improve the properties of the materials. Furthermore, chemically modified CNTs can introduce novel functionalities. In the medical field, biomaterials are expected to be developed using CNTs for clinical use. Biomaterials often are placed adjacent to bone. The use of CNTs is anticipated in these biomaterials applied to bone mainly to improve their overall mechanical properties, for applications such as high-strength arthroplasty prostheses or fixation plates and screws that will not fail. In addition, CNTs are expected to be used as local drug delivery systems (DDS) and/or scaffolds to promote and guide bone tissue regeneration. However, studies examining the use of CNTs as biomaterials still are in the preliminary stages. In particular, the influence of CNTs on osteoblastic cells or bone tissue is extremely important for the use of CNTs in biomaterials placed in contact with bone, and some studies have explored this. This review paper clarifies the current state of knowledge in the context of the relationship between CNTs and bone to determine whether CNTs might perform in biomaterials in contact with bone, or as a DDS and/or scaffolding for bone regeneration.

Introduction: The need for biocompatible and bioactive scaffolds to accelerate the regeneration and repair of fractured bones has been considered for bone tissue engineering applications during recent decades. The new methods were developed to produce scaffolds to improve the tissue quality, size of cavities, control the porosity and increase the scaffold compressive strength under different loads. The presence of compounds such as hydroxyapatite (HA), which contains calcium and phosphorus ions, is essential for bone marrow transplantation. The use of carbon nanotubes can be considered to improve mechanical, chemical and biological properties, much like bone collagen. However, the construction of bio-nanocomposite scaffold which includes all of the above properties is very important in accelerating bone repair and also in reducing the problems of using other conventional scaffold methods. Materials and Methods: In this paper, the fabrication of a bio-nanocomposite scaffold with a three-dimensional printing method, digital light processing (DLP) has been investigated. The used compounds of photopolymer resin, carbon nanotubes and hydroxyapatite are solvent by ultrasonic and magnet stirrer, then a scaffold model designed in SOLIDWORKS software applied to the DLP 3D printer. Results: The addition of single wall carbon nanotubes (SWCNT) increases the compressive strength of the samples more than two times, beside it leads to an increase in the porosity of the samples due to the addition of SWCNTs. The scaffold porosity was recorded around 75 and 85%, which is associated with a proper compressive strength around 2 -4 MPa. Addition of 2.5 to 5 wt% SWCNT to HA and photopolymer resin can leads to a better mechanical performance compared to the pure sample. Conclusion: The results obtained from this work showed that the above process was successful methodology in preparation of novel scaffold bio-nanocomposites using DLP technique for using in bone tissue engineering.

Control of the conductivity of single wall carbon nanotubes (SWNTs) is crucial for the use of carbon nanotubes in molecular electronics. We report a new fundamental characteristic of semiconducting SWNTs: the persistent photoconductivity of chemically modified carbon nanotube films. Illumination of carboxylated semiconducting SWNTs with ultraviolet or visible light causes a persistent decrease in the conductivity of semiconducting films. The photoinduced conductivity persists in the dark with a characteristic half-life of 35 s to 1.2 × 103 s at room temperature and an activation energy of 0.35 eV. Infrared illumination restores the conductivity of SWNT films. Ultraviolet and visible light illumination partially refills empty valence band states of chemically modified SWNTs by electron injection from the dopant sites. Photoinduced injection of electrons is accompanied by a decrease of the conductivity of the p-doped SWNT film, because of neutralization of holes by injected electrons. Covalent attachment o...

Cardiovascular disease is currently the top global cause of death, however, research into new therapies is in decline. Tissue engineering is a solution to this crisis and in combination with the use of carbon nanotubes (CNTs), which have drawn recent attention as a biomaterial, could facilitate the development of more dynamic and complex in vitro models. CNTs’ electrical conductivity and dimensional similarity to cardiac extracellular proteins provide a unique opportunity to deliver scaffolds with stimuli that mimic the native cardiac microenvironment in vitro more effectively. This systematic review aims to evaluate the use and efficacy of CNTs for cardiac tissue scaffolds and was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Three databases were searched: PubMed, Scopus, and Web of Science. Papers resulting from these searches were then subjected to analysis against pre-determined inclusion and quality appraisal criteria. From 249 results, 27 manuscripts met the criteria and were included in this review. Neonatal rat cardiomyocytes were most commonly used in the experiments, with multi-walled CNTs being most common in tissue scaffolds. Immunofluorescence was the experimental technique most frequently used, which was employed for the staining of cardiac-specific proteins relating to contractile and electrophysiological function.

Higher concentrations of long carbon nanotubes (CNTs) that are aligned and functionalized can improve the mechanical properties of CNT composites. For this purpose, pristine/random CNT sheets were mechanically stretched at different strains of 40 %, 60 % and up to 80 %. The higher degree of CNT alignment was confirmed by scanning electron microscope (SEM) images and the degree of alignment was quantified by X-ray scattering and polarized Raman spectroscopy. The highest degree of alignment of 0.93 was achieved by using this method. Aligned CNT sheets were functionalized and CNT/bismaleimide (BMI) composites were fabricated. The mechanical properties of the composites were improved with a higher degree of alignment achieving a modulus of 252 GPa and tensile strength of over 1.4 GPa for an 80% stretched CNT/BMI composite. To understand the internal CNT packing and the CNT/resin interface, thin composite cross sections that are perpendicular to the alignment direction were prepared using focused ion beam (FIB) with a lift-out process. Using a high-resolution transmission electron microscopy (HRTEM), relatively large diameter CNTs (> 5 nm) cross sections and double-walled CNT bundles were observed. An increased number of densely packed and collapsed CNT structures were also observed with higher stretch ratio, which confirmed the CNT alignment and dense packing along the stretch direction. The CNT/resin interface was also analyzed by electron energy loss spectroscopy (EELS). Carbon K-edge peak was used to identify the functionalization of CNT, and a ratio of 1s-* to 1s-* transition was mapped by a scanning TEM. A decreased */* transition ratio was observed at the edge of CNT packing and could be related to the reduced sp2 bonding after functionalization. This leads efficient load transfer between CNT and resin, thus higher mechanical properties.

Chapter 27 - Wastewater treatments using carbon nanotubes: recent developments

Single-walled carbon nanotubes (CNTs) convert absorbed near infrared (NIR) light intoheat. The use of CNTs in the NIR-mediated photothermal ablation of tumor cells isattractive because the penetration of NIR light through normal tissues is optimal and theside effects are minimal. Targeted thermal ablation with minimal collateral damage can beachieved by using CNTs attached to tumor-specific monoclonal antibodies (MAbs).However, the role that the cellular internalization of CNTs plays in the subsequentsensitivity of the target cells to NIR-mediated photothermal ablation remains undefined.To address this issue, we used CNTs covalently coupled to an anti-Her2 or a controlMAb and tested their ability to bind, internalize, and photothermally ablateHer2 + butnot Her2 − breast cancer cell lines. Using flow cytometry, immunofluorescence, and confocal Raman microscopy,we observed the gradual time-dependent receptor-mediated endocytosis of anti-Her2–CNTswhereas a control MAb–CNT conjugate did not bind to the cells. Most importantly, theHer2 + cells that internalized the MAb–CNTs were more sensitive to NIR-mediated photothermaldamage than cells that could bind to, but not internalize the MAb–CNTs. These resultssuggest that both the targeting and internalization of MAb–CNTs might result in themost effective thermal ablation of tumor cells following their exposure to NIRlight.

Νέα προσέγγιση στην παρακολούθηση της αναπτυσσόμενης βλάβης υπό μηχανική φόρτιση σε ινώδη σύνθετα υλικά με μήτρα ενισχυμένη με νανοσωληνίσκους άνθρακα

The clinical application of carbon nanotube (CNT) based solutions has sparked debate within the scientific community, primarily due to concerns about their non-biodegradability, potential long-term toxicity and bioaccumulation in organs and tissues. A significant challenge in evaluating the health risks of CNTs is the lack of standardized guidelines for reliably assessing CNT concentrations in biological systems. Here, we explore the use of time-resolved Raman spectroscopy in association with partial least square (PLS) regression models to detect and quantify CNTs in biological systems. This study included a comprehensive assessment of the structural and chemical characteristics of different types and sources of CNTs. The results revealed that separate PLS models must be developed for each CNT source, as the same CNT type from different suppliers exhibited unique principal components due their varying characteristics. This study highlights the benefits of utilizing the unique Raman signature of CNTs in combination with PLS models to establish a standardized method for detecting and quantifying CNTs, potentially opening precedents for the regulatory frameworks concerning clinical use of CNTs.

Electro-Active Paper (EAPap) materials based on cellulose are attractive for many applications because of their low voltage operation, lightweight, dryness, low power consumption, bio-degradable. The construction of EAPap actuator has been achieved using the cellulose paper film coated with thin electrode layers. This actuator showed a reversible and reproducible bending movement. In order to improve both force and displacement of this, EAPap actuator efforts are made to construct the device using increasing number of complementary conducting polymer layers and carbon nanotubes. A hybrid EAPap actuator is developed using single-wall carbon nanotubes (CNT)/Polyaniline (PANi) electrodes, as a replacement to gold electrodes. It is expected that the use of CNT can enhance the stiffness of the tri-layered actuator, thus improving the force output. Furthermore, the presence of the CNT may increase the actuation performance of the EAPap material. CNT is dispersed in NMP(1-Methyl-2-pyrrolidine), and the resulting solution is used as a solvent for PANi. The CNT/PANi/NMP solution is then cast on the EAPap by spin coating. The coated EAPap is dried in an oven. The effect of processing parameters on the final performance of the CNT/PANi electrodes is assessed. The final performance of the electrodes is quantified in terms of the electrical conductivity under dc and ac measurement conditions. The actuation output of the CNT/PANi/EAPap samples is tested in an environmental chamber in terms of free displacement and blocked force. The performance of the hybrid actuators is also investigated in terms of frequency, voltage, humidity and temperature to help shed light on the mechanism responsible for actuation. Comparison of these results in that of the EAPap with PANi and gold electrodes are also accomplished. EAPap materials are bio-degradable that is important property for artificial muscle actuators for biomimetic with controlled properties and shape.

The potential use of carbon nanotubes (CNTs) in aerospace structures is considered in this chapter. Various studies are presented on how carbon nanotubes may be the driving force of a new generation of aerospace structures with superior damage tolerance properties, which in turn will lead to novel composite structures for the aerospace industry. This chapter examines the inclusion of CNTs in aerospace grade resins and their reinforcing mechanisms. The conclusion reached is that the main reinforcing mechanisms of carbon nanotubes are: fibre breakage, fibre pull-out, crack bridging and crazing. These are responsible for the improvement of the mechanical properties of composite materials and their structures. In other words, the use of carbon nanotubes in aerospace composite structures has been proven to increase fracture toughness, impact strength, post-impact properties and the fatigue life of composites, all these attributes making them more damage tolerant. Finally, a new generation of fibres and fabrics with CNTs grafted or grown on them are presented. They are expected to play a key role in evolution of aerospace composite structures, overcoming any processing issues that have risen due to high CNT-polymer viscosities.

Chapter 2 - Plasma produced by carbon nanotube-generated electron beam

Carbon Nanotubes (CNTs) grown on substrates are potential electron sources in field emission applications. Several studies have reported the use of CNTs in field emission devices, including field emission displays, X-ray tube, electron microscopes, cathode-ray lamps, etc. Also, in recent years, conventional cold field emission cathodes have been realized in micro-fabricated arrays for medical X-ray imaging. CNT-based field emission cathode devices have potential applications in a variety of industrial and medical applications, including cancer treatment. Field emission performance of a single isolated CNT is found to be remarkable, but the situation becomes complex when an array of CNTs is used. At the same time, use of arrays of CNTs is practical and economical. Indeed, such arrays on cathode substrates can be grown easily and their collective dynamics can be utilized in a statistical sense such that the average emission intensity is high enough and the collective dynamics lead to longer emission life. The authors in their previous publications had proposed a novel approach to obtain stabilized field emission current from a stacked CNT array of pointed height distribution. A mesoscopic modeling technique was employed, which took into account electro-mechanical forces in the CNTs, as well as transport of conduction electron coupled with electron–phonon induced heat generation from the CNT tips. The reported analysis of pointed arrangements of the array showed that the current density distribution was greatly localized in the middle of the array, the scatter due to electrodynamic force field was minimized, and the temperature transients were much smaller compared to those in an array with random height distribution. In the present paper we develop a method to compute the emission efficiency of the CNT array in terms of the amount of electrons hitting the anode surface using trajectory calculations. Effects of secondary electron emission and parasitic capacitive nonlinearity on the current-voltage signals are accounted. Field emission efficiency of a stacked CNT array with various pointed height distributions are compared to that of arrays with random and uniform height distributions. Effect of this parasitic nonlinearity on the emission switch-on voltage is estimated by model based simulation and Monte Carlo method.

This chapter discusses about the behavior of Carbon Nanotube (CNT) different structures which can be used as interconnect in Very Large Scale (VLSI) circuits in nanoscale regime. Also interconnect challenges in VLSI circuits which lead to use CNT as interconnect instead of Cu, is reviewed. CNTs are classified into three main types including Single-walled Carbon Nanotube (SWCNT), CNT Bundle, and Multi-walled Carbon Nanotube (MWCNT). Because of extremely high quantum resistance of a SWCNT which is about 6.45 kΩ, rope or bundle of CNTs are used which consist of parallel CNTs in order to overcome the high delay time due to the high intrinsic (quantum) resistance. Also MWCNTs which consist of parallel shells, present much less delay time with respect to SWCNTs, for the application as interconnects. In this chapter, first a short discussion about interconnect challenges in VLSI circuits is presented. Then the repeater insertion technique for the delay reduction in the global interconnects will be studied. After that, the parameters and circuit model of a CNT will be discussed. Then a brief review about the different structures of CNT interconnects including CNT bundle and MWCNT will be presented. At the continuation, the time domain behavior of a CNT bundle interconnect in a driver-CNT bundle-load configuration will be discussed and analyzed. In this analysis, CNT bundle is modeled as a transmission line circuit model. At the end, a brief study of stability analysis in CNT interconnects will be presented.

A critical review of the recent progress on carbon nanotubes-based nanogenerators