Toxicity of Multiwalled Carbon Nanotubes with End Defects Critically Depends on Their Functionalization Density

Modified toxic potential of multi-walled carbon nanotubes to zebrafish (Danio rerio) following a two-year incubation in water

Multi-walled carbon nanotubes (MWCNTs), widely used in several industrial fields, are not readily degradable thus, persist in environmental matrices, serving as a source of environmental toxicity to organisms. However, the effects of environmental weathering on nanomaterial toxicity remain unclear. Herein, we prepared aged-MWCNTs (a-CNTs) by incubating commercial pristine-MWCNTs (p-CNTs) for two years and compared their changes in physicochemical properties and toxic effects on zebrafish. The characterization of a-CNTs by transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and Fourier-transform infrared spectroscopy showed an increased surface area, pore size, structural defects, and surface oxidation than those of p-CNTs. Zebrafish were exposed to 100 mg/L p-CNT and a-CNT for four days. Subsequently, the mRNA expression of antioxidant enzymes, including cat, gst, and sod, in a-CNT group increased by 1.5- to 1.7-fold, consistent with increased expression of genes associated with inflammation (interleukin-8) and apoptosis (p53) compared to control. The higher toxicity of a-CNTs to zebrafish than p-CNT might be due to the increased oxidative potential by altered physicochemical properties. These findings provide new insights into the risk assessment and environmental management of MWCNTs in the aquatic environment. However, further testing at environmentally relevant doses, different exposure durations, and diverse weathering parameters is warranted.

Photothermal therapy of papillary thyroid cancer tumor xenografts with targeted thyroid stimulating hormone receptor antibody functionalized multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs) are being widely investigated in multiple biomedical applications including, and not limited to, drug delivery, gene therapy, imaging, biosensing, and tissue engineering. Their large surface area and aspect ratio in addition to their unique structural, optical properties, and thermal conductivity also make them potent candidates for novel hyperthermia therapy. Here we introduce thyroid hormone stimulating receptor (TSHR) antibody–conjugate–MWCNT formulation as an enhanced tumor targeting and light-absorbing device for the photoablation of xenografted BCPAP papillary thyroid cancer tumors. To ensure successful photothermal tumor ablation, we determined three key criteria that needed to be addressed: (1) predictive pre-operational modeling; (2) real-time monitoring of the tumor ablation process; and (3) post-operational follow-up to assess the efficacy and ensure complete response with minimal side effects. A COMSOL-based model of spatial temperature distributions of MWCNTs upon selected laser irradiation of the tumor was prepared to accurately predict the internal tumor temperature. This modeling ensured that 4.5W of total laser power delivered over 2 min, would cause an increase of tumor temperature above 45 ℃, and be needed to completely ablate the tumor while minimizing the damage to neighboring tissues. Experimentally, our temperature monitoring results were in line with our predictive modeling, with effective tumor photoablation leading to a significantly reduced post 5-week tumor recurrence using the TSHR-targeted MWCNTs. Ultimately, the results from this study support a utility for photosensitive biologically modified MWCNTs as a cancer therapeutic modality. Further studies will assist with the transition of photothermal therapy from preclinical studies to clinical evaluations.

Attributes of Nanomaterials and Nanotopographies for Improved Bone Tissue Engineering and Regeneration

Bone tissue engineering (BTE) is a multidisciplinary area that can solve the limitation of conventional grafting methods by developing viable and biocompatible bone replacements. The three essential components of BTE, i.e., Scaffold material and Cells and Growth factors altogether, facilitate support and guide for bone formation, differentiation of the bone tissues, and enhancement in the cellular activities and bone regeneration. However, there is a scarcity of the appropriate materials that can match the mechanical property as well as functional similarity to native tissue, considering the bone as hard tissue. In such scenarios, nanotechnology can be leveraged upon to achieve the desired aspects of BTE, and that is the key point of this review article. This review article examines the significant areas of nanotechnology research that have an impact on regeneration of bone: (a) scaffold with nanomaterials helps to enhance physicochemical interactions, biocompatibility, mechanical stability, and attachment; (b) nanoparticle-based approaches for delivering bioactive chemicals, growth factors, and genetic material. The article begins with the introduction of components and healing mechanisms of bone and the factors associated with them. The focus of this article is on the various nanotopographies that are now being used in scaffold formation, by describing how they are made, and how these nanotopographies affect the immune system and potential underlying mechanisms. The advantages of 4D bioprinting in BTE by using nanoink have also been mentioned. Additionally, we have investigated the importance of an in silico approach for finding the interaction between drugs and their related receptors, which can help to formulate suitable systems for delivery. This review emphasizes the role of nanoscale approach and how it helps to increase the efficacy of parameters of scaffold as well as drug delivery system for tissue engineering and bone regeneration.

The attenuating ability of deep eutectic solvents towards the carboxylated multiwalled carbon nanotubes induced denatured β-lactoglobulin structure

The stabilization of proteins has been a major challenge for their practical utilization in industrial applications. Proteins can easily lose their native conformation in the presence of denaturants, which unfolds the protein structure. Since the introduction of deep eutectic solvents (DESs), there are numerous studies in which DESs act as promising co-solvents that are biocompatible with biomolecules. DESs have emerged as sustainable biocatalytic media and an alternative to conventional organic solvents and ionic liquids (ILs). However, the superiority of DESs over the deleterious influence of denaturants on proteins is often neglected. To address this, we present the counteracting ability of biocompatible DESs, namely, choline chloride-glycerol (DES-1) and choline chloride-urea (DES-2), against the structural changes induced in β-lactoglobulin (Blg) by carboxylated multiwalled carbon nanotubes (CA-MWCNTs). The work is substantiated with various spectroscopic and thermal studies. The spectroscopic results revealed that the fluorescence emission intensity enhances for the protein in DESs. Contrary to this, the emission intensity extremely quenches in the presence of CA-MWCNTs. However, in the mixture of DESs and CA-MWCNTs, there was a slight increase in the fluorescence intensity. Circular dichroism spectral studies reflect the reappearance of the native band that was lost in the presence of CA-MWCNTs, which is a good indicator of the counteraction ability of DESs. Further, thermal fluorescence studies showed that the protein exhibited extremely great thermal stability in both DESs as well as in the mixture of DES-CA-MWCNTs compared to the protein in buffer. This study is also supported by dynamic light scattering and zeta potential measurements; the results reveal that DESs were successfully able to maintain the protein structure. The addition of CA-MWCNTs results in complex formation with the protein, which is indicated by the increased hydrodynamic size of the protein. The presence of DESs in the mixture of CA-MWCNTs and DESs was quite successful in eliminating the negative impact of CA-MWCNTs on protein structural alteration. DES-1 proved to be superior to DES-2 over counteraction against CA-MWCNTs and maintained the native conformation of the protein. Overall, both DESs act as recoiling media for both native and unfolded (denatured by CA-MWCNTs) Blg structures. Both the DESs can be described as potential co-solvents for Blg with increased structural and thermal stability of the protein. To the best of our knowledge, this study for the first time has demonstrated the role of choline-based DESs in the mixture with CA-MWCNTs in the structural transition of Blg. The DESs in the mixture successfully enhance the stability of the protein by reducing the perturbation caused by CA-MWCNTs and then amplifying the advantages of the DESs present in the mixture. Overall, these results might find implications for understanding the role of DES-CA-MWCNT mixtures in protein folding/unfolding and pave a new direction for the development of eco-friendly protein-protective solvents.

Application of Inorganic Nanomaterials in Cultural Heritage Conservation, Risk of Toxicity, and Preventive Measures

Nanotechnology has allowed for significant progress in architectural, artistic, archaeological, or museum heritage conservation for repairing and preventing damages produced by deterioration agents (weathering, contaminants, or biological actions). This review analyzes the current treatments using nanomaterials, including consolidants, biocides, hydrophobic protectives, mechanical resistance improvers, flame-retardants, and multifunctional nanocomposites. Unfortunately, nanomaterials can affect human and animal health, altering the environment. Right now, it is a priority to stop to analyze its advantages and disadvantages. Therefore, the aims are to raise awareness about the nanotoxicity risks during handling and the subsequent environmental exposure to all those directly or indirectly involved in conservation processes. It reports the human-body interaction mechanisms and provides guidelines for preventing or controlling its toxicity, mentioning the current toxicity research of main compounds and emphasizing the need to provide more information about morphological, structural, and specific features that ultimately contribute to understanding their toxicity. It provides information about the current documents of international organizations (European Commission, NIOSH, OECD, Countries Normative) about worker protection, isolation, laboratory ventilation control, and debris management. Furthermore, it reports the qualitative risk assessment methods, management strategies, dose control, and focus/receptor relationship, besides the latest trends of using nanomaterials in masks and gas emissions control devices, discussing their risk of toxicity.

Bioaccumulation of functionalized polystyrene nanoplastics in sea cucumber Apostichopus japonicus (Selenka, 1867) and their toxic effects on oxidative stress, energy metabolism and mitochondrial pathway

Micro/nano-plastics (M/NPs) are emerging contaminants in aquatic environment, however, little knowledge regarding the adverse effects of functionalized NPs has been documented so far. This study investigated the accumulation of different polystyrene nanoplastics (PS-NPs, i.e., plain PS, carboxyl-functional PS-COOH and amino-functional PS-NH₂) at two particle sizes of 100 nm and 200 nm, and evaluated the impacts on oxidative stress, energy metabolism and mitochondrial pathway responses in intestine and respiratory tree of Apostichopus japonicus during the 20-d exposure experiment. The results showed that there were significant interactions of particle size and nanoplastic type on the accumulation of different PS-NPs. Exposure to NPs significantly increased the production of malondialdehyde, glutathione and reactive oxygen species, as well as the activities of antioxidant enzymes including glutathione reductase, superoxide dismutase and catalase, resulting in various degrees of oxidative damage in sea cucumber. The significant decrease in adenosine triphosphate content and increases in alkaline phosphatase and lactate dehydrogenase activities suggested that NPs impaired energy metabolism and modified their energy allocation. After 20-d exposure, the complex I, II and III activities in mitochondrial respiratory chain were significantly inhibited. Meanwhile, the Bax and Caspase-3 gene expression were significantly up-regulated, and Bacl-2 was down-regulated, indicating the toxicity on mitochondrial pathway of A. japonicus. The calculated IBR values elucidated the greater detriment to mitochondrial pathway than oxidative stress and energy metabolism. For 100 nm particle size, plain PS has stronger influence on all the biomarkers compared to PS-COOH/NH₂, however, the opposite trends were observed in 200 nm PS-NPs. Furthermore, 100 nm PS-NPs were recognized to be more hazardous to sea cucumber than 200 nm microbeads. These findings provide new insights for understanding the differentiated toxic effects of functionalized NPs in marine invertebrates.

Oxidative Stress in Long-Term Exposure to Multi-Walled Carbon Nanotubes in Male Rats

Multi-walled carbon nanotubes (MWCNTs) serve as nanoparticles due to their size, and for that reason, when in contact with the biological system, they can have toxic effects. One of the main mechanisms responsible for nanotoxicity is oxidative stress resulting from the production of intracellular reactive oxygen species (ROS). Therefore, oxidative stress biomarkers are important tools for assessing MWCNTs toxicity. The aim of this study was to evaluate the oxidative stress of multi-walled carbon nanotubes in male rats. Our animal model studies of MWCNTs (diameter ~15-30 nm, length ~15-20 μm) include measurement of oxidative stress parameters in the body fluid and tissues of animals after long-term exposure. Rattus Norvegicus/Wistar male rats were administrated a single injection to the knee joint at three concentrations: 0.03 mg/mL, 0.25 mg/mL, and 0.5 mg/mL. The rats were euthanized 12 and 18 months post-exposure by drawing blood from the heart, and their liver and kidney tissues were removed. To evaluate toxicity, the enzymatic activity of total protein (TP), reduced glutathione (GSH), glutathione S-transferase (GST), thiobarbituric acid reactive substances (TBARS), Trolox equivalent antioxidant capacity (TEAC), nitric oxide (NO), and catalase (CAT) was measured and histopathological examination was conducted. Results in rat livers showed that TEAC level was decreased in rats receiving nanotubes at higher concentrations. Results in kidneys report that the level of NO showed higher concentration after long exposure, and results in animal serums showed lower levels of GSH in rats exposed to nanotubes at higher concentrations. The 18-month exposure also resulted in a statistically significant increase in GST activity in the group of rats exposed to nanotubes at higher concentrations compared to animals receiving MWCNTs at lower concentrations and compared to the control group. Therefore, an analysis of oxidative stress parameters can be a key indicator of the toxic potential of multi-walled carbon nanotubes.

Microwave-Assisted Functionalization of Multi-Walled Carbon Nanotubes for Biosensor and Drug Delivery Applications

Microwave-assisted synthetic methods have emerged as a popular technique for surface modification and the functionalization of multi-walled carbon nanotubes (MWCNTs) for diverse drug delivery applications. Microwave-induced functionalization of MWCNTs provides a high functionalization and requires less time than conventional techniques. Microwave methods are simple, fast, and effective for the covalent and noncovalent conjugation of MWCNTs with various biomolecules and polymers. The present review focuses on the synthetic and drug delivery applications of microwave irradiation techniques (MITs) for the functionalization of MWCNTs, using amino acids and other molecular frameworks containing amino groups, vitamins, proteins, epoxy moieties, metal nanoparticles, and polymers.

Assessment of Pristine Carbon Nanotubes Toxicity in Rodent Models

Carbon nanotubes are increasingly used in nanomedicine and material chemistry research, mostly because of their small size over a large surface area. Due to their properties, they are very attractive candidates for use in medicine and as drug carriers, contrast agents, biological platforms, and so forth. Carbon nanotubes (CNTs) may affect many organs, directly or indirectly, so there is a need for toxic effects evaluation. The main mechanisms of toxicity include oxidative stress, inflammation, the ability to damage DNA and cell membrane, as well as necrosis and apoptosis. The research concerning CNTs focuses on different animal models, functionalization, ways of administration, concentrations, times of exposure, and a variety of properties, which have a significant effect on toxicity. The impact of pristine CNTs on toxicity in rodent models is being increasingly studied. However, it is immensely difficult to compare obtained results since there are no standardized tests. This review summarizes the toxicity issues of pristine CNTs in rodent models, as they are often the preferred model for human disease studies, in different organ systems, while considering the various factors that affect them. Regardless, the results showed that the majority of toxicological studies using rodent models revealed some toxic effects. Even with different properties, carbon nanotubes were able to generate inflammation, fibrosis, or biochemical changes in different organs. The problem is that there are only a small amount of long-term toxicity studies, which makes it impossible to obtain a good understanding of later effects. This article will give a greater overview of the situation on toxicity in many organs. It will allow researchers to look at the toxicity of carbon nanotubes in a broader context and help to identify studies that are missing to properly assess toxicity.

Enhanced anti-biofilm and biocompatibility of Zn and Mg substituted β-tricalcium phosphate/functionalized multiwalled carbon nanotube composites towards A. baumannii and Methicillin-Resistant Staphylococcus aureus, and MG-63 cells

In this work, Zn and Mg substituted β-tricalcium phosphate/functionalized multiwalled carbon nanotube (f-MWCNT) nanocomposites were prepared by the co-precipitation method. The structural, vibrational, morphological and biological properties of the prepared nanocomposites were studied. The structural study revealed that the increase of Zn concentration shifts the β-tricalcium phosphate planes towards higher angle. Morphological analysis confirmed the formation of hexagonal-shaped particles after substitution of Zn. The particle size of the nanoparticles decreased with the increase of Zn concentration. XPS analysis clearly showed the presence of Zn, Mg, P, Ca, O and C. The Zn (5%) rich nanocomposites have better antibiofilm activity compared to 2% of zinc substituted composite. Also, it has been proven that the prepared nanocomposites have the ability to enhance the bioactivity of commercial antibiotics by means of a decrease in drug resistance. Finally, this study acted as a pioneer to improve drug efficiency and reduced the biofilm formation of certain medically important bacteria. The in-vitro cell viability and anti-biofilm results of zinc (5%) rich nanocomposite confirmed that prepared nanocomposite has biocompatible and enhanced anti-biofilm property, which will be beneficial candidate for biomedical applications.

Robust antibacterial activity of functionalized carbon nanotube- levofloxacine conjugate based on in vitro and in vivo studies

A new nano-antibiotic was synthesized from the conjugation of multi-walled carbon nanotubes with levofloxacin (MWCNT-LVX) through covalent grafting of drug with surface-modified carbon nanotubes in order to achieve an effective, safe, fast-acting nano-drug with the minimal side effects. This study is the first report on the evaluation of in vitro cell viability and antibacterial activity of nano-antibiotic along in addition to the in vivo antibacterial activity in a burn wound model. The drug-loading and release profile at different pH levels was determined using an ultraviolet–visible spectrometer. MWCNT-LVX was synthesized by a simple, reproducible and cost-effective method for the first time and characterized using various techniques, such as scanning electron microscope, transmission electron microscopy, and Brunauer–Emmett–Teller analysis, and so forth. The noncytotoxic nano-antibiotic showed more satisfactory in vitro antibacterial activity against Staphylococcus aureus compared to Pseudomona aeruginosa. The novel synthetic nano-drug possessed high loading capacity and pH-sensitive release profile; resultantly, it exhibited very potent bactericidal activity in a mouse S. aureus wound infection model compared to LVX. Based on the results, the antibacterial properties of the drug enhanced after conjugating with surface-modified MWCNTs. The nano-antibiotic has great industrialization potential for the simple route of synthesis, no toxicity, proper drug loading and release, low effective dose, and strong activity against wound infections. In virtue of unique properties, MWCNTs can serve as a controlled release and delivery system for drugs. The easy penetration to biological membranes and barriers can also increase the drug delivery at lower doses compared to the main drug alone, which can lead to the reduction of its side effects. Hence, MWCNTs can be considered a promising nano-carrier of LVX in the treatment of skin infections.

Aromatic Dipeptide Homologue-Based Hydrogels for Photocontrolled Drug Release

Peptide-based hydrogels are considered of special importance due to their biocompatibility and biodegradability. They have a wide range of applications in the biomedical field, such as drug delivery, tissue engineering, wound healing, cell culture media, and biosensing. Nevertheless, peptide-based hydrogels composed of natural α-amino acids are limited for in vivo applications because of the possible degradation by proteolytic enzymes. To circumvent this issue, the incorporation of extra methylene groups within the peptide sequence and the protection of the terminal amino group can increase the enzymatic stability. In this context, we investigated the self-assembly capacity of aromatic dipeptides (Boc-α-diphenylalanine and Boc-α-dityrosine) and their β- and γ-homologues and developed stable hydrogels. Surprisingly, only the Boc-diphenylalanine analogues were able to self-assemble and form hydrogels. A model drug, l-ascorbic acid, and oxidized carbon nanotubes (CNTs) or graphene oxide were then incorporated into the hydrogels. Under near-infrared light irradiation, the photothermal effect of the carbon nanomaterials induced the destabilization of the gel structure, which caused the release of a high amount of drug, thus providing opportunities for photocontrolled on-demand drug release.

Superior operational stability of immobilized L-asparaginase over surface-modified carbon nanotubes

L-asparaginase (ASNase, EC 3.5.1.1) is an enzyme that catalyzes the L-asparagine hydrolysis into L-aspartic acid and ammonia, being mainly applied in pharmaceutical and food industries. However, some disadvantages are associated with its free form, such as the ASNase short half-life, which may be overcome by enzyme immobilization. In this work, the immobilization of ASNase by adsorption over pristine and modified multi-walled carbon nanotubes (MWCNTs) was investigated, the latter corresponding to functionalized MWCNTs through a hydrothermal oxidation treatment. Different operating conditions, including pH, contact time and ASNase/MWCNT mass ratio, as well as the operational stability of the immobilized ASNase, were evaluated. For comparison purposes, data regarding the ASNase immobilization with pristine MWCNT was detailed. The characterization of the ASNase-MWCNT bioconjugate was addressed using different techniques, namely Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and Raman spectroscopy. Functionalized MWCNTs showed promising results, with an immobilization yield and a relative recovered activity of commercial ASNase above 95% under the optimized adsorption conditions (pH 8, 60 min of contact and 1.5 × 10-3 g mL-1 of ASNase). The ASNase-MWCNT bioconjugate also showed improved enzyme operational stability (6 consecutive reaction cycles without activity loss), paving the way for its use in industrial processes.

Understanding the close encounter of heme proteins with carboxylated multiwalled carbon nanotubes: a case study of contradictory stability trend for hemoglobin and myoglobin

Carbon nanotubes (CNTs) are one of the unique and promising nanomaterials that possess plenty of applications, such as biosensors, advanced drug delivery systems and biotechnology. CNTs bind rapidly with proteins, which result in the formation of a protein coating layer known as a "protein corona" around the surface of the nanomaterial. This hinders their applications as a drug carrier and influences the properties of biological macromolecules. The present work focuses on studying the thermal stability and molecular level interactions of two heme proteins, hemoglobin (Hb) and myoglobin (Mb), in the presence of carboxylated functionalized multi-walled CNTs (CA-MWCNTs). Through the current study, the following steps have been taken to distinguish the biocompatibility of the hydrophilic surface CA-MWCNTs for heme proteins via a series of spectroscopic techniques and differential scanning calorimetry (DSC). UV-Visible and steady-state fluorescence spectroscopy were used to reveal changes in the aromatic amino acid residues of heme proteins upon the addition of CA-MWCNTs. Circular dichroism spectroscopy (CD) shows the alteration in the native structure of proteins in the presence of the nanomaterial. A tremendous increase in the size of the protein CA-MWCNTs system is observed in dynamic light scattering (DLS), which clearly manifests the protein corona formation. Unexpectedly, both proteins interact differently with CA-MWCNTs, which is observed in CD spectroscopy and DSC. In the presence of CA-MWCNTs, an increase in the transition temperature (T_m) was observed for Hb, while the T_m value decreases for Mb. Different interactions with proteins at the molecular scale may be the reason for this unexpected behavior. Henceforth, the present results can help in the design of the next-generation drug carrier nanomaterials with the idea of the heme protein corona formation prior to development.

Respiratory and systemic impacts following MWCNT inhalation in B6C3F1/N mice

Background

A very pure multi-walled carbon nanotube (MWCNT) that was shown to have very low toxicity in vitro, was evaluated for lung and systemic effects and distribution following inhalation exposure.

Methods

B6C3F1/N mice were exposed to varying doses (0, 0.06, 0.2, and 0.6 mg/m³) of the (99.1% carbon) MWCNT by inhalation for 30 days (excluding weekends). Ten days following the last exposure, the lungs and spleen were harvested and processed for histology and immune cell population assessment. In addition, lung lavage cells and fluid were analyzed. Stimulated Raman scattering (SRS) was used to identify particles in the lungs, spleen, kidneys, liver, mediastinal and brachial lymph nodes, and olfactory bulb. Splenic tissue sections were stained with hematoxylin and eosin (H&E) for light microscopic histopathology assessment. Blood plasma was analyzed for cytokines and cathepsins. A section of the spleen was processed for RNA isolation and relative gene expression for 84 inflammation-related cytokines/chemokines.

Results

Following MWCNT exposure, particles were clearly evident in the lungs, spleens, lymph nodes and olfactory bulbs, (but not livers or kidneys) of exposed mice in a dose-dependent manner. Examination of the lavaged lung cells was unremarkable with no significant inflammation indicated at all particle doses. In contrast, histological examination of the spleen indicated the presence of apoptotic bodies within T cells regions of the white pulp area. Isolated splenic leukocytes had significant changes in various cells including an increased number of proinflammatory CD11b⁺Ly6C⁺ splenic cells. The gene expression studies confirmed this observation as several inflammation-related genes were upregulated particularly in the high dose exposure (0.6 mg/m³). Blood plasma evaluations showed a systemic down-regulation of inflammatory cytokines and a dose-dependent up-regulation of lysosomal cathepsins.

Conclusions

The findings in the lungs were consistent with our hypothesis that this MWCNT exposure would result in minimal lung inflammation and injury. However, the low toxicity of the MWCNT to lung macrophages may have contributed to enhanced migration of the MWCNT to the spleen through the lymph nodes, resulting in splenic toxicity and systemic changes in inflammatory mediators.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00408-z.

Kolaviron ameliorates hepatic and renal dysfunction associated with multiwalled carbon nanotubes in rats

The increase in the exposure to carbon nanotubes (CNTs) and their incorporation into industrial, electronic, and biomedical products have required several scientific investigations into the toxicity associated with CNTs. Studies have shown that the metabolism and clearance of multiwalled CNTs (MWCNTs) from the body involve biotransformation in the liver and its excretion via the kidney. Since oxidative stress and inflammation underlines the toxicity of MWCNT, we investigated the ameliorative effect of kolaviron (KV), a natural antioxidant and anti-inflammatory agent, on hepatorenal damage in rats. Exposure to MWCNTs for 15 days significantly increased serum activities of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and lactate dehydrogenase thereby suggesting hepatic dysfunction. Kidney function, which was monitored by urea and creatinine levels, was also impaired by MWCNTs. Additionally, MWCNTs markedly increased myeloperoxidase activity, nitric oxide level, reactive oxygen and nitrogen species, and tumor necrosis factor level in both tissues. However, KV in a dose-dependent manner markedly attenuated MWCNT-induced markers of hepatorenal function in the serum and MWCNT-associated inflammation in the liver and kidney. Also, MWCNTs elicited significant inhibition of superoxide dismutase, catalase, glutathione peroxidase, and glutathione-S-transferase activities. There was a significant diminution in glutathione level (GSH) and enhanced production of malondialdehyde (MDA) in MWCNTs-exposed rats. KV treatment was able to significantly increase the antioxidant enzymes and enhance the GSH level with a subsequent reduction in the MDA level. Taken together, KV elicited ameliorative effects against hepatorenal damage via its anti-inflammatory and antioxidant properties. Thus, KV could be an important intervention strategy for the hepatorenal damage associated with MWCNTs exposure.

Modification of multiwalled carbon nanotubes with a ruthenium drug candidate-indazolium[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019 )

Functionalized carbon nanotubes are interesting, promising and unique delivery systems for anticancer drugs, which are now in the spotlight of nanomedicine. Connecting nanotubes with anticancer drugs or new compounds with anticancer properties aims at improving their stability, efficiency and reduces the toxic side effects of cancer treatment. In our research, we are interested in connecting functionalized MWCNTs-NH2 with [InH][trans-RuCl4(In)2], (KP1019) which is one of the most promising anticancer ruthenium(iii) drug candidates, known mainly as a cytotoxic agent for the treatment of platinum-resistant colorectal cancers. As a result of the amidation of MWCNTs (1), MWCNTs-NH2 (2) were obtained. Then, they were modified with [InH][RuCl4(In)2] (4) and the nanosystem [MWCNT-NH3+][RuCl4(In)2-] (3) was obtained. The characterization of the resulting products was performed using IR, Raman spectroscopy, thermal gravimetric, XRD, STEM-EDX, ESI-MS, ICP-MS, and XPS analyses. The cytotoxic activity has been tested on human lung carcinoma (A549), chronic myelogenous leukemia (K562) and human cervix carcinoma (HeLa) cells which showed the higher toxicity of the nanosystem than the ruthenium complex.

Multiwall Carbon Nanotube Composites as Artificial Joint Materials

Because ultrahigh-molecular-weight polyethylene (UHMWPE) is susceptible to frictional wear when used in sliding members of artificial joints, it is common practice to use cross-linked UHMWPE instead. However, cross-linked UHMWPE has low impact resistance; implant breakage has been reported in some cases. Hence, sliding members of artificial joints pose a major trade-off between wear resistance and impact resistance, which has not been resolved by any UHMWPE. On the other hand, multiwall carbon nanotubes (MWCNTs) are used in industrial products for reinforcement of polymeric materials but not used as biomaterials because of their unclear safety. In the present study, we attempted to solve this trade-off issue by complexing UHMWPE with MWCNTs. In addition, we assessed the safety of these composites for use in sliding members of artificial joints. The results showed the equivalence of MWCNT/UHMWPE composites to cross-linked UHMWPE in terms of wear resistance and to non-cross-linked UHMWPE in terms of impact resistance. In addition, all MWCNT/UHMWPE composites examined complied with the requirements of biosafety testing in accordance with the ISO10993-series specifications for implantable medical devices. Furthermore, because MWCNTs can occur alone in wear dust, MWCNTs in an amount of about 1.5 times that contained in the dust produced from 50 years of wear (in the worst case) were injected into rat knees, which were monitored for 26 weeks. Although mild inflammatory reactions occurred in the joints, the reactions soon became quiescent. In addition, the MWCNTs did not migrate to other organs. Furthermore, MWCNTs did not exhibit carcinogenicity when injected into the knees of mice genetically modified to spontaneously develop cancer. The MWCNT/UHMWPE composite is a new biomaterial expected to be safe for clinical applications in both total hip arthroplasty and total knee arthroplasty as the first sliding member of artificial joints to have both high wear resistance and high impact resistance.

Carbon nanotubes and their polymeric composites: the applications in tissue engineering

Carbon nanotubes (CNTs), with unique graphitic structure, superior mechanical, electrical, optical and biological properties, has attracted more and more interests in biomedical applications, including gene/drug delivery, bioimaging, biosensor and tissue engineering. In this review, we focus on the role of CNTs and their polymeric composites in tissue engineering applications, with emphasis on their usages in the nerve, cardiac and bone tissue regenerations. The intrinsic natures of CNTs including their physical and chemical properties are first introduced, explaining the structure effects on CNTs electrical conductivity and various functionalization of CNTs to improve their hydrophobic characteristics. Biosafety issues of CNTs are also discussed in detail including the potential reasons to induce the toxicity and their potential strategies to minimise the toxicity effects. Several processing strategies including solution-based processing, polymerization, melt-based processing and grafting methods are presented to show the 2D/3D construct formations using the polymeric composite containing CNTs. For the sake of improving mechanical, electrical and biological properties and minimising the potential toxicity effects, recent advances using polymer/CNT composite the tissue engineering applications are displayed and they are mainly used in the neural tissue (to improve electrical conductivity and biological properties), cardiac tissue (to improve electrical, elastic properties and biological properties) and bone tissue (to improve mechanical properties and biological properties). Current limitations of CNTs in the tissue engineering are discussed and the corresponded future prospective are also provided. Overall, this review indicates that CNTs are promising “next-generation” materials for future biomedical applications.

The Importance of Evaluating the Lot-to-Lot Batch Consistency of Commercial Multi-Walled Carbon Nanotube Products

The biological response of multi-walled carbon nanotubes (MWNTs) is related to their physicochemical properties and a thorough MWNT characterization should accompany an assessment of their biological activity, including their potential toxicity. Beyond characterizing the physicochemical properties of MWNTs from different sources or manufacturers, it is also important to characterize different production lots of the same MWNT product from the same vendor (i.e., lot-to-lot batch consistency). Herein, we present a comprehensive physicochemical characterization of two lots of commercial pristine MWNTs (pMWNTs) and carboxylated MWNTs (cMWNTs) used to study the response of mammalian macrophages to MWNTs. There were many similarities between the physicochemical properties of the two lots of cMWNTs and neither significantly diminished the 24-h proliferation of RAW 264.7 macrophages up to the highest concentration tested (200 μg cMWNTs/mL). Conversely, several physicochemical properties of the two lots of pMWNTs were different; notably, the newer lot of pMWNTs displayed less oxidative stability, a higher defect density, and a smaller amount of surface oxygen species relative to the original lot. Furthermore, a 72-h half maximal inhibitory concentration (IC-50) of ~90 µg pMWNTs/mL was determined for RAW 264.7 cells with the new lot of pMWNTs. These results demonstrate that subtle physicochemical differences can lead to significantly dissimilar cellular responses, and that production-lot consistency must be considered when assessing the toxicity of MWNTs.

Quantitative Flow Cytometric Evaluation of Oxidative Stress and Mitochondrial Impairment in RAW 264.7 Macrophages after Exposure to Pristine, Acid Functionalized, or Annealed Carbon Nanotubes

Conventional nanotoxicological assays are subjected to various interferences with nanoparticles and especially carbon nanotubes. A multiparametric flow cytometry (FCM) methodology was developed here as an alternative to quantify oxidative stress, mitochondrial impairment, and later cytotoxic and genotoxic events. The experiments were conducted on RAW264.7 macrophages, exposed for 90 min or 24 h-exposure with three types of multiwalled carbon nanotubes (MWCNTs): pristine (Nanocyl™ CNT), acid functionalized (CNTf), or annealed treatment (CNTa). An original combination of reactive oxygen species (ROS) probes allowed the simultaneous quantifications of broad-spectrum ROS, superoxide anion (O₂^•-), and hydroxyl radical (•OH). All MWCNTs types induced a slight increase of broad ROS levels regardless of earlier antioxidant catalase activity. CNTf strongly stimulated the O₂^•- production. The •OH production was downregulated for all MWCNTs due to their scavenging capacity. The latter was quantified in a cell-free system by electron paramagnetic resonance spectroscopy (EPR). Further FCM-based assessment revealed early biological damages with a mitochondrial membrane potential collapse, followed by late cytotoxicity with chromatin decondensation. The combined evaluation by FCM analysis and cell-free techniques led to a better understanding of the impacts of MWCNTs surface treatments on the oxidative stress and related biological response.

Cytotoxicity-Related Bioeffects Induced by Nanoparticles: The Role of Surface Chemistry

Nanoparticles (NPs) are widely used in a variety of fields, including those related to consumer products, architecture, energy, and biomedicine. Once they enter the human body, NPs contact proteins in the blood and interact with cells in organs, which may induce cytotoxicity. Among the various factors of NP surface chemistry, surface charges, hydrophobicity levels and combinatorial decorations are found to play key roles inregulating typical cytotoxicity-related bioeffects, including protein binding, cellular uptake, oxidative stress, autophagy, inflammation, and apoptosis. In this review, we summarize the recent progress made in directing the levels and molecular pathways of these cytotoxicity-related effects by the purposeful design of NP surface charge, hydrophobicity, and combinatorial decorations.

Organ accumulation and carcinogenicity of highly dispersed multi-walled carbon nanotubes administered intravenously in transgenic rasH2 mice

PURPOSE

Multiwalled carbon nanotubes (MWCNTs) have been known to enter the circulatory system via the lungs from inhalation exposure; however, its carcinogenicity and subsequent accumulation in other organs have not been adequately reported in the literature. Moreover, the safety of MWCNTs as a biomaterial has remained a matter of debate, particularly when the material enters the circulatory system. To address these problems, we used carcinogenic rasH2 transgenic mice to intravenously administer highly dispersed MWCNTs and to evaluate their carcinogenicity and accumulation in the organs.

METHODS

Two types of MWCNTs (thin- and thick-MWCNTs) were intravenously administered at a high dose (approximately 0.7 mg per kg body weight) and low dose (approximately 0.07 mg per kg body weight).

RESULTS

MWCNTs showed pancreatic accumulation in 3.2% of mice administered with MWCNTs, but there was no accumulation in other organs. In addition, there was no significant difference in the incidence of tumor among the four MWCNTs-administered groups compared to the vehicle group without MWCNTs administration. Blood tests revealed elevated levels in mean red blood cell volume and mean red blood cell hemoglobin level for the MWCNTs-administered group, in addition to an increase in eotaxin.

CONCLUSION

The present study demonstrated that the use of current technology to sufficiently disperse MWCNTs resulted in minimal organ accumulation with no evidence of carcinogenicity.

A holistic study on potential toxic effects of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) on zebrafish (Danio rerio) embryos/larvae

Multi-walled carbon nanotubes (MWCNTs) have widespread use in industrial and consumer products and great potential in biomedical applications. This leads to inevitably their release into the environment and the formation of their toxic effects on organisms. These effects can change depending on their physicochemical characteristics. Therefore, the toxicological findings of MWCNTs are inconsistent. Their toxicities related to surface modification have not been elucidated in a holistic manner. Hence, this study was conducted to clarify their potential toxic effects on zebrafish embryos/larvae in a comprehensive approach using morphologic, biochemical and molecular parameters. Zebrafish embryos were exposed to 5, 10, 20 mg/L doses of MWCNTs-COOH at 4 h after fertilization and grown until 96 hpf. Physiological findings demonstrated that they induced a concentration-dependent increase in the mortality rate, delayed hatching and decrease in the heartbeat rate. Moreover, it caused abnormalities including yolk sac edema, pericardial edema, head, tail malformations, and vertebral deformities. These effects may be due to the alterations in antioxidant and immune system related gene expressions after their entry into zebrafish embryo/larvae. The entry was confirmed from the evaluation of Raman spectra collected from the head, yolk sac, and tail of control and the nanotube treated groups. The gene expression analysis indicated the changes in the expression of oxidative stress (mtf-1, hsp70, and nfkb) and innate immune system (il-1β, tlr-4, tlr-22, trf, and cebp) related genes, especially an increased in the expression of the hsp70 and il-1β. These findings proved the developmental toxicities of MWCNTs-COOH on the zebrafish embryos/larvae.

Protected Amino Acid-Based Hydrogels Incorporating Carbon Nanomaterials for Near-Infrared Irradiation-Triggered Drug Release

Molecular gels formed by the self-assembly of low-molecular-weight gelators have received increasing interest because of their potential applications in drug delivery. In particular, the ability of peptides and amino acids to spontaneously self-assemble into three-dimensional fibrous network has been exploited in the development of hydrogels. In this context, we have investigated the capacity of binary mixtures of aromatic amino acid derivatives to form hydrogels. Carbon nanomaterials, namely oxidized carbon nanotubes or graphene oxide, were incorporated in the two most stable hydrogels, formed by Fmoc-Tyr-OH/Fmoc-Tyr(Bzl)-OH and Fmoc-Phe-OH/Fmoc-Tyr(Bzl)-OH, respectively. The structural and physical properties of these gels were assessed using microscopic techniques and rheology. Circular dichroism and molecular dynamics simulations demonstrated that the hydrogel formation was mainly driven by aromatic interactions. Finally, a model hydrophilic drug (l-ascorbic acid) was loaded into the hybrid hydrogels at a high concentration. Under near-infrared light irradiation, a high amount of drug was released triggered by the heat generated by the carbon nanomaterials, thus offering interesting perspectives for controlled drug delivery.

Smart nanocarrier-based drug delivery systems for cancer therapy and toxicity studies: A review

Nonspecific distribution and uncontrollable release of drugs in conventional drug delivery systems (CDDSs) have led to the development of smart nanocarrier-based drug delivery systems, which are also known as Smart Drug Delivery Systems (SDDSs). SDDSs can deliver drugs to the target sites with reduced dosage frequency and in a spatially controlled manner to mitigate the side effects experienced in CDDSs. Chemotherapy is widely used to treat cancer, which is the second leading cause of death worldwide. Site-specific drug delivery led to a keen interest in the SDDSs as an alternative to chemotherapy. Smart nanocarriers, nanoparticles used to carry drugs, are at the focus of SDDSs. A smart drug delivery system consists of smart nanocarriers, targeting mechanisms, and stimulus techniques. This review highlights the recent development of SDDSs for a number of smart nanocarriers, including liposomes, micelles, dendrimers, meso-porous silica nanoparticles, gold nanoparticles, super paramagnetic iron-oxide nanoparticles, carbon nanotubes, and quantum dots. The nanocarriers are described in terms of their structures, classification, synthesis and degree of smartness. Even though SDDSs feature a number of advantages over chemotherapy, there are major concerns about the toxicity of smart nanocarriers; therefore, a substantial study on the toxicity and biocompatibility of the nanocarriers has been reported. Finally, the challenges and future research scope in the field of SDDSs are also presented. It is expected that this review will be widely useful for those who have been seeking new research directions in this field and for those who are about to start their studies in smart nanocarrier-based drug delivery.

Toxicity of carbon nanotubes to white rot fungus Phanerochaete chrysosporium

Carbon nanotubes (CNTs) are widely used in diverse areas with increasing annual production, thus the environmental impact of CNTs needs thorough investigation. In this study, we evaluated the effect of pristine multi-walled CNTs (p-MWCNTs) and oxidized multi-walled CNTs (o-MWCNTs) on white rot fungus Phanerochaete chrysosporium, which is the decomposer in carbon cycle and also has many applications in environmental remediation. Both p-MWCNTs and o-MWCNTs had no influence on the dry weight increase of P. chrysosporium and the pH value of culture system. The fibrous structure of P. chrysosporium was disturbed by p-MWCNTs seriously, while o-MWCNTs had litter influence. The ultrastructural changes were more evident for P. chrysosporium exposed to p-MWCNTs and only p-MWCNTs could penetrate into the cell plasma. The chemical composition of P. chrysosporium was nearly unchanged according to the infrared spectra. The laccase activity was suppressed by p-MWCNTs, while o-MWCNTs showed stimulating effect. The decoloration of reactive brilliant red X-3B was not affected by both CNT samples. However, serious inhibition of wood degradation was observed in the p-MWCNTs exposed groups, suggesting the potential threat of CNTs to the decomposition of carbon cycle. The implication to the environmental risks and safe applications of carbon nanomaterials is discussed.

Proteomic investigation on bio-corona of functionalized multi-walled carbon nanotubes

BACKGROUND

The formation of bio-corona, due to adsorption of biomolecules onto carbon nanotubes (CNTs) surface in a physiological environment, may lead to a modified biological "identity" of CNTs, contributing to determination of their biocompatibility and toxicity.

METHODS

Multi-walled carbon nanotubes surfaces (f-MWCNTs) were modified attaching acid and basic chemical functions such as carboxyl (MWCNTs-COOH) and ammonium (MWCNTs-N) groups respectively. The investigation of interactions between f-MWCNTs and proteins present in biological fluids, like human plasma, was performed by electrophoretic separation (SDS-PAGE) and mass spectrometry analysis (nLC-MS/MS).

RESULTS

A total of 52 validated proteins was identified after incubation of f-MWCNTs in human plasma. 86% of them was present in bio-coronas formed on the surface of all f-MWCNTs and 29% has specifically interacted with only one type of f-MWCNTs.

CONCLUSIONS

The evaluation of proteins primary structures, present in all bio-coronas, did not highlight any correlation between the chemical functionalization on MWCNTs and the content of acid, basic and hydrophobic amino acids. Despite this, many proteins of bio-corona, formed on all f-MWCNTs, were involved in the inhibitor activity of serine- or cysteine- endopeptidases, a molecular function completely unrevealed in the human plasma as control. Finally, the interaction with immune system's proteins and apolipoproteins has suggested a possible biocompatibility and a favored bio-distribution of tested f-MWCNTs.

GENERAL SIGNIFICANCE

Considering the great potential of CNTs in the nanomedicine, a specific chemical functionalization onto MWCNTs surface could control the protein corona formation and the biocompatibility of nanomaterials.

Scanning Techniques for Nanobioconjugates of Carbon Nanotubes

Nanobioconjugates using carbon nanotubes (CNTs) are attractive and promising hybrid materials. Various biological applications using the CNT nanobioconjugates, for example, drug delivery systems and nanobiosensors, have been proposed by many authors. Scanning techniques such as scanning electron microscopy (SEM) and scanning probe microscopy (SPM) have advantages to characterize the CNT nanobioconjugates under various conditions, for example, isolated conjugates, conjugates in thin films, and conjugates in living cells. In this review article, almost 300 papers are categorized based on types of CNT applications, and various scanning data are introduced to illuminate merits of scanning techniques.

Review of techniques and studies characterizing the release of carbon nanotubes from nanocomposites: Implications for exposure and human health risk assessment

Composites made with engineered nanomaterials (nanocomposites) have a wide range of applications, from use in basic consumer goods to critical national defense technologies. Carbon nanotubes (CNTs) are a popular addition in nanocomposites because of their enhanced mechanical, thermal, and electrical properties. Concerns have been raised, though, regarding potential exposure and health risks from nanocomposites containing CNTs because of comparisons to other high aspect ratio fibers. Assessing the factors affecting CNT release from composites is therefore paramount for understanding potential exposure scenarios that may occur during product handling and manipulation. Standardized methods for detecting and quantifying released CNTs, however, have not yet been developed. We therefore evaluated experimental approaches deployed by various researchers, with an emphasis on characterizing free versus composite bound CNTs. From our analysis of published studies characterizing CNT releases from nanocomposites, we found that the qualitative and quantitative methods used across studies varied greatly, thus limiting the ability for objective comparison and evaluation of various release factors. Nonetheless, qualitative results indicated that factors such as composite type, CNT functionalization, and energy input during manipulation (i.e., grinding) may affect CNT release. Based on our findings, we offer several recommendations for future product testing and assessment of potential exposure and health risks associated with CNT nanocomposites.

Peptide Probe for Multiwalled Carbon Nanotubes: Electrophoretic Assessment of the Binding Interface and Evaluation of Surface Functionalization

Noncovalent interactions of peptides and proteins with carbon nanotubes play a key role in sensing, dispersion, and biocompatibility. Advances in these areas require that the forces which contribute to physical adsorption are understood in order that the carbon nanotubes present a degree of functionalization appropriate to the desired application. Affinity analyses of peptides are employed to evaluate the role of tryptophan and arginine residues in physical adsorption to carboxylated multiwalled carbon nanotubes. Peptides containing arginine and tryptophan, WR(W) _n, are used with affinity capillary electrophoresis to identify factors that lead to the formation of peptide-carbon nanotube complexes. The effects of changing the amino acid composition and residue length are evaluated by measuring dissociation constants. Electrostatic interactions contribute significantly to complexation, with the strongest interaction observed using the peptide WRWWWW and carboxylated carbon nanotube. Stronger interaction is observed when the tryptophan content is successively increased as follows: WR(W)₄ > WR(W)₃ > WR(W)₂ > WRW > WR. However, as observed with polytryptophan (W₅, W₄, W₃, and W₂), removing the arginine residue significantly reduces the interaction with carbon nanotubes. Increasing the arginine content to WRWWRW does not improve binding, whereas replacing the arginine residue in WRWWWW with lysine (WKWWWW) reveals that lysine also contributes to surface adsorption, but not as effectively as arginine. These observations are used to guide a search of the primary sequence of lysozyme to identify short regions in the peptide that contain a single cationic residue and two aromatic residues. One candidate peptide sequence (WMCLAKW) from this search is analyzed by capillary electrophoresis. The dissociation constant of carboxylated multiwalled carbon nanotubes is measured for the peptide, WMCLAKW, to demonstrate the utility of affinity capillary electrophoresis analysis.

Capillary electrophoresis analysis of affinity to assess carboxylation of multi-walled carbon nanotubes

Surface oxidation improves the dispersion of carbon nanotubes in aqueous solutions and plays a key role in the development of biosensors, electrochemical detectors and polymer composites. Accurate characterization of the carbon nanotube surface is important because the development of these nano-based applications depends on the degree of functionalization, in particular the amount of carboxylation. Affinity capillary electrophoresis is used to characterize the oxidation of multi-walled carbon nanotubes. A polytryptophan peptide that contains a single arginine residue (WRWWWW) serves as a receptor in affinity capillary electrophoresis to assess the degree of carboxylation. The formation of peptide-nanotube receptor-ligand complex was detected with a UV absorbance detector. Apparent dissociation constants (K_D) are obtained by observing the migration shift of the WRWWWW peptide through background electrolyte at increasing concentrations of multi-walled carbon nanotubes. A 20% relative standard deviation in method reproducibility and repeatability is determined with triplicate analysis within a single sample preparation and across multiple sample preparations for a commercially available carbon nanotube. Affinity capillary electrophoresis is applied to assess differences in degree of carboxylation across two manufacturers and to analyze acid treated carbon nanotubes. The results of these studies are compared to X-ray photoelectron spectroscopy and zeta potential. Affinity capillary electrophoresis comparisons of carbon nanotube samples prepared by varying acid treatment time from 30 min to 3 h yielded significant differences in degree of carboxylation. X-ray photoelectron spectroscopy analysis was inconclusive due to potential acid contamination, while zeta potential showed no change based on surface charge. This work is significant to research involving carbon nanotube-based applications because it provides a new metric to rapidly characterize carbon nanotubes obtained from different vendors, or synthesized in laboratories using different procedures.

The Effects of Varying Degree of MWCNT Carboxylation on Bioactivity in Various In Vivo and In Vitro Exposure Models

Functionalization has been shown to alter toxicity of multi-walled carbon nanotube (MWCNT) in several studies. This study varied the degree of functionalization (viz., amount of MWCNT surface carboxylation) to define the relationship between the extent of carboxylation and effects in a variety of in vitro cell models and short-term ex vivo/in vivo particle exposures. Studies with vitamin D₃ plus phorbol ester transformed THP-1 macrophages demonstrated that functionalization, regardless of amount, corresponded with profoundly decreased NLRP3 inflammasome activation. However, all MWCNT variants were slightly toxic in this model. Alternatively, studies with A549 epithelial cells showed some varied effects. For example, IL-33 and TNF-α release were related to varying amounts of functionalization. For in vivo particle exposures, autophagy of alveolar macrophages, measured using green fluorescent protein (GFP)- fused-LC3 transgenic mice, increased for all MWCNT tested three days after exposure, but, by Day 7, autophagy was clearly dependent on the amount of carboxylation. The instilled source MWCNT continued to produce cellular injury in alveolar macrophages over seven days. In contrast, the more functionalized MWCNT initially showed similar effects, but reduced over time. Dark-field imaging showed the more functionalized MWCNTs were distributed more uniformly throughout the lung and not isolated to macrophages. Taken together, the results indicated that in vitro and in vivo bioactivity of MWCNT decreased with increased carboxylation. Functionalization by carboxylation eliminated the bioactive potential of the MWCNT in the exposure models tested. The observation that maximally functionalized MWCNT distribute more freely throughout the lung with the absence of cellular damage, and extended deposition, may establish a practical use for these particles as a safer alternative for unmodified MWCNT.

Isolation, identification, and characterization of novel nanovesicles

Extracellular microvesicles (EVs) have been recognized for many potential clinical applications including biomarkers for disease diagnosis. In this study, we identified a major population of EVs by simply screening fluid samples with a nanosizer. Unlike other EVs, this extracellular nanovesicle (named HG-NV, HG-NV stands for HomoGenous nanovesicle as well as for Huang-Ge- nanovesicle) can be detected with a nanosizer with minimal in vitro manipulation and are much more homogenous in size (8–12 nm) than other EVs. A simple filtration platform is capable of separating HG-NVs from peripheral blood or cell culture supernatants. In comparison with corresponding exosome profiles, HG-NVs released from both mouse and human breast tumor cells are enriched with RNAs. Tumor derived HG-NVs are more potent in promoting tumor progression than exosomes. In summary, we identified a major subset of EVs as a previously unrecognized nanovesicle. Tumor cell derived HG-NVs promote tumor progression. Molecules predominantly present in breast tumor HG-NVs have been identified and characterized. This discovery may have implications in advancing both microvesicle biology research and clinical management including potential used as a biomarker.

Emergence in the functionalized carbon nanotubes as smart nanocarriers for drug delivery applications

Carbon nanotubes (CNTs) are the newer generation advanced materials for diverse applications, starting from physical, mechanical, chemical and biological sciences. However, the present era of healthcare industry is extensively using CNTs for exploring their applications in mitigating diverse needs. The considered attention in CNTs is due to their inimitable properties such as size and aspect ratio covering surface area to the length, and amenable electrical, thermal and mechanical properties. Available in diverse forms, viz. single-walled, double walled or multi-walled structures, CNTs of different forms possess multiple advantages in various healthcare segments, and especially in drug delivery for the treatment of diseases. CNTs have proven to be useful in specific drug delivery applications such as controlled and targeted drug delivery to desired sites such as lymphatic and ocular systems, brain and other cancerous tissues. Multiple research reports have been published till date, which unequivocally gives testimony to the potential applications of CNTs. The present book chapter, in this regard, endeavor to provide an overview on synthesis, characterization and drug delivery applications of CNTs. The chapter highlights on recent regulatory standards on commercial production and safety testing of the CNTs for translating them into market.

Interactions of the innate immune system with carbon nanotubes

The therapeutic application of nanomaterials requires that they are biocompatible and can reach the desired target. The innate immune system is likely to be the first defence machinery that would recognise the nanomaterials as 'non-self'. A number of studies have addressed the issue of how carbon nanotubes (CNTs) interact with phagocytic cells and their surface receptors that can impact on their intracellular processing and subsequent immune response. In addition, soluble innate immune factors also get involved in the recognition and clearance of CNTs. The interaction of CNTs with the complement system, the most potent and versatile innate immune mechanism, has shed interesting light on how complement activation on the surface of CNTs can modulate their phagocytosis and effector cytokine response. The charge or altered molecular pattern on the surface of CNTs due to functionalization and derivatization can also dictate the level of complement activation and subsequent inflammatory response. It is becoming evident that complement deposition may facilitate phagocytic uptake of CNTs through receptor routes that leads to dampening of pro-inflammatory response by complement-receptor bearing macrophages and B cells. Thus, recombinant complement regulators decorated on the CNT surface can constructively influence the therapeutic strategies involving CNTs and other nanoparticles.

Effect of surface functionalizations of multi-walled carbon nanotubes on neoplastic transformation potential in primary human lung epithelial cells

Functionalized multi-walled carbon nanotube (fMWCNT) development has been intensified to improve their surface activity for numerous applications, and potentially reduce toxic effects. Although MWCNT exposures are associated with lung tumorigenesis in vivo, adverse responses associated with exposure to different fMWCNTs in human lung epithelium are presently unknown. This study hypothesized that different plasma-coating functional groups determine MWCNT neoplastic transformation potential. Using our established model, human primary small airway epithelial cells (pSAECs) were continuously exposed for 8 and 12 weeks at 0.06 μg/cm² to three-month aged as-prepared-(pMWCNT), carboxylated-(MW-COOH), and aminated-MWCNTs (MW-NH_x). Ultrafine carbon black (UFCB) and crocidolite asbestos (ASB) served as particle controls. fMWCNTs were characterized during storage, and exposed cells were assessed for several established cancer cell hallmarks. Characterization analyses conducted at 0 and 2 months of aging detected a loss of surface functional groups over time due to atmospheric oxidation, with MW-NH_x possessing less oxygen and greater lung surfactant binding affinity. Following 8 weeks of exposure, all fMWCNT-exposed cells exhibited significant increased proliferation compared to controls at 7 d post-treatment, while UFCB- and ASB-exposed cells did not differ significantly from controls. UFCB, pMWCNT, and MW-COOH exposure stimulated significant transient invasion behavior. Conversely, aged MW-NH_x-exposed cells displayed moderate increases in soft agar colony formation and morphological transformation potential, while UFCB cells showed a minimal effect compared to all other treatments. In summary, surface properties of aged fMWCNTs can impact cell transformation events in vitro following continuous, occupationally relevant exposures.

Carbon Nanotubes as an Effective Opportunity for Cancer Diagnosis and Treatment

Despite the current progresses of modern medicine, the resistance of malignant tumors to present medical treatments points to the necessity of developing new therapeutic approaches. In recent years, numerous studies have focused their attention on the promising use of nanomaterials, like iron oxide nanowires, zinc oxide or mesoporous silica nanoparticles, for cancer and metastasis treatment with the advantage of operating directly at the bio-molecular scale. Among them, carbon nanotubes emerged as valid candidates not only for drug delivery, but also as a valuable tool in cancer imaging and physical ablation. Nevertheless, deep investigations about carbon nanotubes' potential bio-compatibility and cytotoxicity limits should be also critically addressed. In the present review, after introducing carbon nanotubes and their promising advantages and drawbacks for fighting cancer, we want to focus on the numerous and different ways in which they can assist to reach this goal. Specifically, we report on how they can be used not only for drug delivery purposes, but also as a powerful ally to develop effective contrast agents for tumors' medical or photodynamic imaging, to perform direct physical ablation of metastasis, as well as gene therapy.

Multiwalled carbon nanotubes for drug delivery: Efficiency related to length and incubation time

Batches of oxidized multiwalled carbon nanotubes differing in length were adopted to prepare two drug delivery systems (DDS) loaded with doxorubicin. The different internalization of the two batches, verified by atomic emission spectroscopy onto cell lysates, was also confirmed by the different toxicity of the same DDS loaded with doxorubicin. In vitro experiments evidenced, after 48h of incubation, the superior efficacy of the shortest nanotubes. However, upon prolonging the incubation time up to 72h the difference in efficiency was minimized due to the spontaneous release of doxorubicin by the non-internalized long nanotubes.

Enriched surface acidity for surfactant-free suspensions of carboxylated carbon nanotubes purified by centrifugation

It is well known that surfactant-suspended carbon nanotube (CNT) samples can be purified by centrifugation to decrease agglomerates and increase individually-dispersed CNTs. However, centrifugation is not always part of protocols to prepare CNT samples used in biomedical applications. Herein, using carboxylated multi-walled CNTs (cMWCNTs) suspended in water without a surfactant, we developed a Boehm titrimetric method for the analysis of centrifuged cMWCNT suspensions and used it to show that the surface acidity of oxidized carbon materials in aqueous cMWCNT suspensions was enriched by ~40% by a single low-speed centrifugation step. This significant difference in surface acidity between un-centrifuged and centrifuged cMWCNT suspensions has not been previously appreciated and is important because the degree of surface acidity is known to affect the interactions of cMWCNTs with biological systems.