Cytotoxicity of multi-walled carbon nanotubes in three skin cellular models: Effects of sonication, dispersive agents and corneous layer of reconstructed epidermis

A review of carbon nanomaterials/bacterial cellulose composites for nanomedicine applications

Carbon nanomaterials (CNMs) mainly include fullerene, carbon nanotubes, graphene, carbon quantum dots, nanodiamonds, and their derivatives. As a new type of material in the field of nanomaterials, it has outstanding physical and chemical properties, such as minor size effects, substantial specific surface area, extremely high reaction activity, biocompatibility, and chemical stability, which have attracted widespread attention in the medical community in the past decade. However, the single use of carbon nanomaterials has problems such as self-aggregation and poor water solubility. Researchers have recently combined them with bacterial cellulose to form a new intelligent composite material to improve the defects of carbon nanomaterials. This composite material has been widely synthesized and used in targeted drug delivery, biosensors, antibacterial dressings, tissue engineering scaffolds, and other nanomedicine fields. This paper mainly reviews the research progress of carbon nanomaterials based on bacterial cellulose in nanomedicine. In addition, the potential cytotoxicity of these composite materials and their components in vitro and in vivo was discussed, as well as the challenges and gaps that need to be addressed in future clinical applications.

Human and environmental impacts of nanoparticles: a scoping review of the current literature

Use of nanoparticles have established benefits in a wide range of applications, however, the effects of exposure to nanoparticles on health and the environmental risks associated with the production and use of nanoparticles are less well-established. The present study addresses this gap in knowledge by examining, through a scoping review of the current literature, the effects of nanoparticles on human health and the environment. We searched relevant databases including Medline, Web of Science, ScienceDirect, Scopus, CINAHL, Embase, and SAGE journals, as well as Google, Google Scholar, and grey literature from June 2021 to July 2021. After removing duplicate articles, the title and abstracts of 1495 articles were first screened followed by the full-texts of 249 studies, and this resulted in the inclusion of 117 studies in the presented review.In this contribution we conclude that while nanoparticles offer distinct benefits in a range of applications, they pose significant threats to humans and the environment. Using several biological models and biomarkers, the included studies revealed the toxic effects of nanoparticles (mainly zinc oxide, silicon dioxide, titanium dioxide, silver, and carbon nanotubes) to include cell death, production of oxidative stress, DNA damage, apoptosis, and induction of inflammatory responses. Most of the included studies (65.81%) investigated inorganic-based nanoparticles. In terms of biomarkers, most studies (76.9%) used immortalised cell lines, whiles 18.8% used primary cells as the biomarker for assessing human health effect of nanoparticles. Biomarkers that were used for assessing environmental impact of nanoparticles included soil samples and soybean seeds, zebrafish larvae, fish, and Daphnia magna neonates.From the studies included in this work the United States recorded the highest number of publications (n = 30, 25.64%), followed by China, India, and Saudi Arabia recording the same number of publications (n = 8 each), with 95.75% of the studies published from the year 2009. The majority of the included studies (93.16%) assessed impact of nanoparticles on human health, and 95.7% used experimental study design. This shows a clear gap exists in examining the impact of nanoparticles on the environment.

Advances in Biodegradable Electronic Skin: Material Progress and Recent Applications in Sensing, Robotics, and Human-Machine Interfaces

The rapid growth of the electronics industry and proliferation of electronic materials and telecommunications technologies has led to the release of a massive amount of untreated electronic waste (e-waste) into the environment. Consequently, catastrophic environmental damage at the microbiome level and serious human health diseases threaten the natural fate of the planet. Currently, the demand for wearable electronics for applications in personalized medicine, electronic skins (e-skins), and health monitoring is substantial and growing. Therefore, "green" characteristics such as biodegradability, self-healing, and biocompatibility ensure the future application of wearable electronics and e-skins in biomedical engineering and bioanalytical sciences. Leveraging the biodegradability, sustainability, and biocompatibility of natural materials will dramatically influence the fabrication of environmentally friendly e-skins and wearable electronics. Here, the molecular and structural characteristics of biological skins and artificial e-skins are discussed. The focus then turns to the biodegradable materials, including natural and synthetic-polymer-based materials, and their recent applications in the development of biodegradable e-skin in wearable sensors, robotics, and human-machine interfaces (HMIs). Finally, the main challenges and outlook regarding the preparation and application of biodegradable e-skins are critically discussed in a near-future scenario, which is expected to lead to the next generation of biodegradable e-skins.

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.

Physical and chemical properties of carbon nanotubes in view of mechanistic neuroscience investigations. Some outlook from condensed matter, materials science and physical chemistry

The open border between non-living and living matter, suggested by increasingly emerging fields of nanoscience interfaced to biological systems, requires a detailed knowledge of nanomaterials properties. An account of the wide spectrum of phenomena, belonging to physical chemistry of interfaces, materials science, solid state physics at the nanoscale and bioelectrochemistry, thus is acquainted for a comprehensive application of carbon nanotubes interphased with neuron cells. This review points out a number of conceptual tools to further address the ongoing advances in coupling neuronal networks with (carbon) nanotube meshworks, and to deepen the basic issues that govern a biological cell or tissue interacting with a nanomaterial. Emphasis is given here to the properties and roles of carbon nanotube systems at relevant spatiotemporal scales of individual molecules, junctions and molecular layers, as well as to the point of view of a condensed matter or materials scientist. Carbon nanotube interactions with blood-brain barrier, drug delivery, biocompatibility and functionalization issues are also regarded.

[Advantages and challenges of carbon nanotubes as bone repair materials]

With the in-depth research on bone repair process, and the progress in bone repair materials preparation and characterization, a variety of artificial bone substitutes have been fully developed in the treatment of bone related diseases such as bone defects. However, the current various natural or synthetic biomaterials are still unable to achieve the structure and properties of natural bone. Carbon nanotubes (CNTs) have provided a new direction for the development of new materials in the field of bone repair due to their excellent structural stability, mechanical properties, and functional group modifiability. Moreover, CNTs and their composites have broad prospects in the design of bone repair materials and as drug delivery carriers. This paper describes the advantages of CNTs related to bone tissue regeneration from the aspects of morphology, chemistry, mechanics, electromagnetism, and biosafety, as well as the application of CNTs in drug delivery carriers and reinforcement components of scaffold materials. In addition, the potential problems and prospects of CNTs in bone regenerative medicine are discussed.

Carbon nanomaterials against pathogens; the antimicrobial activity of carbon nanotubes, graphene/graphene oxide, fullerenes, and their nanocomposites

Recently, antibiotic resistance of pathogens has grown given the excessive and inappropriate usage of common antimicrobial agents. Hence, producing novel antimicrobial compounds is a necessity. Carbon nanomaterials (CNMs) such as carbon nanotubes, graphene/graphene oxide, and fullerenes, as an emerging class of novel materials, can exhibit a considerable antimicrobial activity, especially in the nanocomposite forms suitable for different fields including biomedical and food applications. These nanomaterials have attracted a great deal of interest due to their broad efficiency and novel features. The most important factor affecting the antimicrobial activity of CNMs is their size. Smaller particles with a higher surface to volume ratio can easily attach onto the microbial cells and affect their cell membrane integrity, metabolic procedures, and structural components. As these unique characteristics are found in CNMs, a wide range of possibilities have raised in terms of antimicrobial applications. This study aims to cover the antimicrobial activities of CNMs (both as individual forms and in nanocomposites) and comprehensively explain their mechanisms of action. The results of this review will present a broad perspective, summarizes the most remarkable findings, and provides an outlook regarding the antimicrobial properties of CNMs and their potential applications.

Improving Quality in Nanoparticle-Induced Cytotoxicity Testing by a Tiered Inter-Laboratory Comparison Study

The quality and relevance of nanosafety studies constitute major challenges to ensure their key role as a supporting tool in sustainable innovation, and subsequent competitive economic advantage. However, the number of apparently contradictory and inconclusive research results has increased in the past few years, indicating the need to introduce harmonized protocols and good practices in the nanosafety research community. Therefore, we aimed to evaluate if best-practice training and inter-laboratory comparison (ILC) of performance of the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay for the cytotoxicity assessment of nanomaterials among 15 European laboratories can improve quality in nanosafety testing. We used two well-described model nanoparticles, 40-nm carboxylated polystyrene (PS-COOH) and 50-nm amino-modified polystyrene (PS-NH2). We followed a tiered approach using well-developed standard operating procedures (SOPs) and sharing the same cells, serum and nanoparticles. We started with determination of the cell growth rate (tier 1), followed by a method transfer phase, in which all laboratories performed the first ILC on the MTS assay (tier 2). Based on the outcome of tier 2 and a survey of laboratory practices, specific training was organized, and the MTS assay SOP was refined. This led to largely improved intra- and inter-laboratory reproducibility in tier 3. In addition, we confirmed that PS-COOH and PS-NH2 are suitable negative and positive control nanoparticles, respectively, to evaluate impact of nanomaterials on cell viability using the MTS assay. Overall, we have demonstrated that the tiered process followed here, with the use of SOPs and representative control nanomaterials, is necessary and makes it possible to achieve good inter-laboratory reproducibility, and therefore high-quality nanotoxicological data.

A review of functional sorbents for adsorptive removal of arsenic ions in aqueous systems

The presence of arsenic in the water system has been a universal problem over the past several decades. Inorganic arsenic ions mainly occur in two oxidation states, As(V) and As(III), in the natural environment. These two oxidation states of arsenic ions are ubiquitous in natural waters and pose significant health hazards to humans when present at or above the allowable limits. Therefore, treatment of arsenic ions has become more stringent based on various techniques (e.g., membrane filtration, adsorption, and ion exchange). This paper aims to review the current knowledge on various functional adsorbents through comparison of removal potential for As on the basis of key performance metrics, especially the partition coefficient (PC). As a whole, novel materials exhibited far better removal performance for As(V) and As(III) than conventional materials. Of the materials reviewed, the advanced sorbent like ZrO(OH)₂/CNTs showcased superior performances such as partition coefficient values of 584.6 (As(V) and 143.8 mol kg^-1 M^-1 (As(III) with excellent regenerability (>90 % of desorption efficiency after three sorption cycles). The results of this review are expected to help researchers to establish a powerful strategy for abatement of arsenic ions in wastewater.

Toxicity of carbon-based nanomaterials: Reviewing recent reports in medical and biological systems

Application of nanomaterials in our daily life is increasing, day in day out and concerns have raised about their toxicity for human and other organisms. In this manner, carbon-based nanomaterials have been applied to different products due to their unique physicochemical, electrical, mechanical properties, and biological compatibility. But, there are several reports about the negative effects of these materials on biological systems and cellular compartments. This review article describes the various types of carbon-based nanomaterials and methods that use for determining these toxic effects that are reported recently in the papers. Then, extensively discussed the toxic effects of these materials on the human and other living organisms and also their toxicity routs including Neurotoxicity, Hepatotoxicity, Nephrotoxicity, Immunotoxicity, Cardiotoxicity, Genotoxicity and epigenetic toxicity, Dermatotoxicity, and Carcinogenicity.

Dependence of Nanoparticle Toxicity on Their Physical and Chemical Properties

Studies on the methods of nanoparticle (NP) synthesis, analysis of their characteristics, and exploration of new fields of their applications are at the forefront of modern nanotechnology. The possibility of engineering water-soluble NPs has paved the way to their use in various basic and applied biomedical researches. At present, NPs are used in diagnosis for imaging of numerous molecular markers of genetic and autoimmune diseases, malignant tumors, and many other disorders. NPs are also used for targeted delivery of drugs to tissues and organs, with controllable parameters of drug release and accumulation. In addition, there are examples of the use of NPs as active components, e.g., photosensitizers in photodynamic therapy and in hyperthermic tumor destruction through NP incorporation and heating. However, a high toxicity of NPs for living organisms is a strong limiting factor that hinders their use in vivo. Current studies on toxic effects of NPs aimed at identifying the targets and mechanisms of their harmful effects are carried out in cell culture models; studies on the patterns of NP transport, accumulation, degradation, and elimination, in animal models. This review systematizes and summarizes available data on how the mechanisms of NP toxicity for living systems are related to their physical and chemical properties.

Chemical alternatives assessment of different flame retardants - A case study including multi-walled carbon nanotubes as synergist

Flame retardants (FRs) are a diverse group of chemicals used as additives in a wide range of products to inhibit, suppress, or delay ignition and to prevent the spread of fire. Halogenated FRs (HFRs) are widely used because of their low impact on other material properties and the low loading levels necessary to meet the required flame retardancy. Health and environmental hazards associated with some halogenated FRs have driven research for identifying safer alternatives. A variety of halogen-free FRs are available on the market, including organic (phosphorus and nitrogen based chemicals) and inorganic (metals) materials. Multi-walled carbon nanotubes (MWCNT) have been demonstrated to act as an effective/synergistic co-additive in some FR applications and could thereby contribute to reducing the loading of FRs in products and improving their performance. As part of the FP7 project DEROCA we carried out a chemical alternatives assessment (CAA). This is a methodology for identifying, comparing and selecting safer alternatives to chemicals of concern based on criteria for categorising human and environmental toxicity as well as environmental fate. In the project we assessed the hazard data of different halogen-free FRs to be applied in 5 industrial and consumer products and here we present the results for MWCNT, aluminium diethylphosphinate, aluminium trihydroxide, N-alkoxy hindered amines and red phosphorus compared to the HFR decabromodiphenylether. We consulted the REACH guidance, the criteria of the U.S.-EPA Design for Environment (DfE) and the GreenScreen® Assessment to assess and compare intrinsic properties affecting the hazard potential. A comparison/ranking of exposure reference values such as Derived No Effect Levels (DNELs) showed that FRs of concern are not identified by a low DNEL. A comparison based on hazard designations according to the U.S.-EPA DfE and GreenScreen® for human health endpoints, aquatic toxicity and environmental fate showed that the major differences between FRs of concern and their proposed alternatives are the potential for bioaccumulation and CMR (carcinogenic, mutagenic or reprotoxic) effects. As most alternatives are inorganic chemicals, persistence (alone) is not a suitable criterion. From our experiences in carrying out a CAA we conclude: i) REACH registration dossiers provide a comprehensive source of hazard information for an alternative assessment. It is important to consider that the presented data is subject to changes and its quality is variable. ii) Correct identification of the chemicals is crucial to retrieve the right data. This can be challenging for mixtures, reaction products or nanomaterials or when only trade names are available. iii) The quality of the data and the practice on how to fill data gaps can have a huge impact on the results and conclusions. iv) Current assessment criteria have mainly been developed for organic chemicals and create challenges when applied to inorganic solids, including nanomaterials. It is therefore crucial to analyse and report uncertainties for each decision making step.

Differential cytotoxic effects of graphene and graphene oxide on skin keratinocytes

Impressive properties make graphene-based materials (GBMs) promising tools for nanoelectronics and biomedicine. However, safety concerns need to be cleared before mass production of GBMs starts. As skin, together with lungs, displays the highest exposure to GBMs, it is of fundamental importance to understand what happens when GBMs get in contact with skin cells. The present study was carried out on HaCaT keratinocytes, an in vitro model of skin toxicity, on which the effects of four GBMs were evaluated: a few layer graphene, prepared by ball-milling treatment (FLG), and three samples of graphene oxide (GOs, a research-grade GO1, and two commercial GOs, GO2 and GO3). Even though no significant effects were observed after 24 h, after 72 h the less oxidized compound (FLG) was the less cytotoxic, inducing mitochondrial and plasma-membrane damages with EC₅₀s of 62.8 μg/mL (WST-8 assay) and 45.5 μg/mL (propidium iodide uptake), respectively. By contrast, the largest and most oxidized compound, GO3, was the most cytotoxic, inducing mitochondrial and plasma-membrane damages with EC₅₀s of 5.4 and 2.9 μg/mL, respectively. These results suggest that only high concentrations and long exposure times to FLG and GOs could impair mitochondrial activity associated with plasma membrane damage, suggesting low cytotoxic effects at the skin level.

Self-Assembled Heterojunction Carbon Nanotubes Synergizing with Photoimmobilized IGF-1 Inhibit Cellular Senescence

Synthesis of artificial and functional structures for bone tissue engineering has been well recognized but the associated cell senescence issue remains much less concerned so far. In this work, surface-modified polycaprolactone-polylactic acid scaffolds using self-assembled heterojunction carbon nanotubes (sh-CNTs) combined with insulin-like growth factor-1 are synthesized and a series of structural and biological characterizations are carried out, with particular attention to cell senescence mechanism. It is revealed that the modified scaffolds can up-regulate the expressions of alkaline phosphates and bone morphogenetic proteins while down-regulate the expressions of senescence-related proteins in mesenchymal stem cells, demonstrating the highly preferred anti-senescence functionality of the sh-CNTs modified scaffolds in bone tissue engineering. Furthermore, it is also found that with sh-CNTs, scaffolds can accelerate bone healing with extremely low toxicity in vivo.

Physicochemical and toxicological evaluation of silica nanoparticles suitable for food and consumer products collected by following the EC recommendation

Specific information about the particle size distribution, agglomeration state, morphology, and chemical composition of four silica samples, used as additives in food and in personal care products, were achieved with a combination of analytical techniques. The combined use of differential centrifugal sedimentation (DCS), sedimentation field flow fractionation (SdFFF), and scanning and transmission electron microscopy (SEM and TEM) allows to classify the water dispersed samples as "nanomaterials" according to the EC definition. The mechanical stirring and the ultrasound treatment were compared as dispersion methods. The particle surface chemical composition, determined by particle-induced X-ray emission (PIXE) and X-ray photoelectron spectroscopy (XPS), assessed the different levels of purity between the pyrogenic and the precipitated silica and highlighted particle surface chemical composition modifications in the outer shell when dispersed by mechanical stirring. The potential toxic effects of silica on intestinal Caco-2 cells were investigated using MTS assay and by measuring lactate dehydrogenase (LDH) release and caspases 3/7 activity after 24 h of incubation. No or limited decrease of cell viability was observed for all particles regardless of dispersion procedure, suggesting a relative innocuity of these silica samples.

Chip based single cell analysis for nanotoxicity assessment

Nanomaterials, because of their tunable properties and performances, have been utilized extensively in everyday life related consumable products and technology. On exposure, beyond the physiological range, nanomaterials cause health risks via affecting the function of organisms, genomic systems, and even the central nervous system. Thus, new analytical approaches for nanotoxicity assessment to verify the feasibility of nanomaterials for future use are in demand. The conventional analytical techniques, such as spectrophotometric assay-based techniques, usually require a lengthy and time-consuming process and often produce false positives, and often cannot be implemented at a single cell level measurement for studying cell behavior without interference from its surrounding environment. Hence, there is a demand for a precise, accurate, sensitive assessment for toxicity using single cells. Recently, due to the advantages of automation of fluids and minimization of human errors, the integration of a cell-on-a-chip (CoC) with a microfluidic system is in practice for nanotoxicity assessments. This review explains nanotoxicity and its assessment approaches with advantages/limitations and new approaches to overcome the confines of traditional techniques. Recent advances in nanotoxicity assessment using a CoC integrated with a microfluidic system are also discussed in this review, which may be of use for nanotoxicity assessment and diagnostics.

Proteomic analysis of cellular response induced by multi-walled carbon nanotubes exposure in A549 cells

The wide application of multi-walled carbon nanotubes (MWCNT) has raised serious concerns about their safety on human health and the environment. However, the potential harmful effects of MWCNT remain unclear and contradictory. To clarify the potentially toxic effects of MWCNT and to elucidate the associated underlying mechanisms, the effects of MWCNT on human lung adenocarcinoma A549 cells were examined at both the cellular and the protein level. Cytotoxicity and genotoxicity were examined, followed by a proteomic analysis (2-DE coupled with LC-MS/MS) of the cellular response to MWCNT. Our results demonstrate that MWCNT induces cytotoxicity in A549 cells only at relatively high concentrations and longer exposure time. Within a relatively low dosage range (30 µg/ml) and short time period (24 h), MWCNT treatment does not induce significant cytotoxicity, cell cycle changes, apoptosis, or DNA damage. However, at these low doses and times, MWCNT treatment causes significant changes in protein expression. A total of 106 proteins show altered expression at various time points and dosages, and of these, 52 proteins were further identified by MS. Identified proteins are involved in several cellular processes including proliferation, stress, and cellular skeleton organization. In particular, MWCNT treatment causes increases in actin expression. This increase has the potential to contribute to increased migration capacity and may be mediated by reactive oxygen species (ROS).

Mechanisms of toxicity by carbon nanotubes

Carbon nanotubes (CNTs) consist of a family of carbon built nanoparticles, whose biological effects depend on their physical characteristics and other constitutive chemicals (impurities and functions attached). CNTs are considered the twenty first century material due to their unique physicochemical characteristics and applicability to industrial product. The use of these materials steadily increases worldwide and toxic outcomes need to be studied for each nanomaterial in depth to prevent adverse effects to humans and the environment. Entrance into the body is physical, and usually few nanoparticles enter the body; however, once there, they are persistent due to their limited metabolisms, so their removal is slow, and chronic cumulative health effects are studied. Oxidative stress is the main mechanism of toxicity but size, agglomeration, chirality as well as impurities and functionalization are some of the structural and chemical characteristic contributing to the CNTs toxicity outcomes. Among the many toxicity pathways, interference with cytoskeleton and fibrous mechanisms, cell signaling, membrane perturbations and the production of cytokines, chemokines and inflammation are some of the effects resulting from exposure to CNTs. The aim of this review is to offer an up-to-date scope of the effects of CNTs on biological systems with attention to mechanisms of toxicity.

Combination of small size and carboxyl functionalisation causes cytotoxicity of short carbon nanotubes

The use of carbon nanotubes (CNTs) could improve medical diagnosis and treatment provided they show no adverse effects in the organism. In this study, short CNTs with different diameters with and without carboxyl surface functionalisation were assessed. After physicochemical characterisation, cytotoxicity in phagocytic and non-phagocytic cells was determined. The role of oxidative stress was evaluated according to the intracellular glutathione levels and protection by N-acetyl cysteine (NAC). In addition to this, the mode of cell death was also investigated. CNTs <8 nm acted more cytotoxic than CNTs ≥20 nm and carboxylated CNTs more than pristine CNTs. Protection by NAC was maximal for large diameter pristine CNTs and minimal for small diameter carboxylated CNTs. Thin (<8 nm) CNTs acted mainly by disruption of membrane integrity and CNTs with larger diameter induced mainly apoptotic changes. It is concluded that cytotoxicity of small carboxylated CNTs occurs by necrosis and cannot be prevented by antioxidants.

DNA damage in human skin keratinocytes caused by multiwalled carbon nanotubes with carboxylate functionalization

Water-soluble carbon nanotubes have been found to be one of the most promising nanomaterials in biological- and biomedical-based applications. However, there have been major concerns on their ability to cause cellular and DNA damages upon exposure. In this work, we explore the toxic effects of three multiwalled carbon nanotubes (MWCNTs: nonpurified, purified and carboxylate-functionalized) on human skin keratinocytes (HaCaT). Cytotoxicity tests using the conventional thiazolyl blue tetrazolium bromide (MTT) and the water-soluble tetrazolium (WST-1) assays for 0.5 or 24 h exposure to 20 μg/mL of MWCNTs show that all three caused minimum cytotoxicity that is generally not statistically significant. Assessment of direct and oxidative DNA damages using both alkaline Comet assay and formamidopyrimidine DNA glycosylase-modified Comet assay reveals that the treatment with 20 μg/mL of MWCNTs does not cause significant direct DNA damages, but causes great amount of oxidative DNA damages in HaCaT cells. The oxidative DNA damage reaches the maximum amount at 4 h of incubation in Dulbecco's minimum essential medium, but decreases to the minimum at 8 and 24 h of incubation, indicating repair of the oxidative damages by the intrinsic DNA repair mechanism of the cells.

Carbon Nanomaterials: Efficacy and Safety for Nanomedicine

Carbon nanomaterials, including fullerenes, carbon nanohorns, and carbon nanotubes, are increasingly being used in various fields owing to these materials’ unique, size-dependent functions and physicochemical properties. Recently, because of their high variability and stability, carbon nanomaterials have been explored as a novel tool for the delivery of therapeutic molecules including peptide and nucleic acid cancer drugs. However, insufficient information is available regarding the safety of carbon nanomaterials for human health, even though such information is vital for the development of safe and effective nanomedicine technologies. In this review, we discuss currently available information regarding the safety of carbon nanomaterials in nanomedicine applications, including information obtained from our own studies; and we discuss types of carbon nanomaterials that demonstrate particular promise for safe nanomedicine technologies.

Assessing nanoparticle toxicity

Nanoparticle toxicology, an emergent field, works toward establishing the hazard of nanoparticles, and therefore their potential risk, in light of the increased use and likelihood of exposure. Analytical chemists can provide an essential tool kit for the advancement of this field by exploiting expertise in sample complexity and preparation as well as method and technology development. Herein, we discuss experimental considerations for performing in vitro nanoparticle toxicity studies, with a focus on nanoparticle characterization, relevant model cell systems, and toxicity assay choices. Additionally, we present three case studies (of silver, titanium dioxide, and carbon nanotube toxicity) to highlight the important toxicological considerations of these commonly used nanoparticles.

Differential toxicity of copper (II) oxide nanoparticles of similar hydrodynamic diameter on human differentiated intestinal Caco-2 cell monolayers is correlated in part to copper release and shape

The potential toxic effects of copper oxide (CuO) nanoparticles (NPs) were studied on differentiated Caco-2 cell monolayers, a classical in vitro model of human small intestine epithelium. Two types of CuO NPs, with different specific surface area, different sizes as raw material but the same hydrodynamic diameter in suspension, differentially disturbed the monolayer integrity, were cytotoxic and triggered an increase of the abundance of several transcripts coding for pro-inflammatory cytokines and chemokines. Specific surface area was not a major variable explaining the increased toxicity when intestinal epithelium is exposed to rod-shaped CuO NPs, compared with spherical CuO NPs. The results suggest that release of Cu(II) cations and shape of these CuO NPs are likely to be implicated in the toxicity of these CuO NPs.

Pulmonary toxicity of well-dispersed multi-wall carbon nanotubes following inhalation and intratracheal instillation

Multi-walled carbon nanotubes (MWCNTs), dispersed in suspensions consisting mainly of individual tubes, were used for intratracheal instillation and inhalation studies. Rats intratracheally received a dose of 0.2 mg, or 1 mg of MWCNTs and were sacrificed from 3 days to 6 months. MWCNTs induced a pulmonary inflammation, as evidenced by a transient neutrophil response in the low-dose groups, and presence of small granulomatous lesion and persistent neutrophil infiltration in the high-dose groups. In the inhalation study, rats were exposed to 0.37 mg/m(3) aerosols of well-dispersed MWCNTs (>70% of MWCNTs were individual fibers) for 4 weeks, and were sacrificed at 3 days, 1 month, and 3 months after the end of exposure. The inhalation exposures delivered less amounts of MWCNTs into the lungs, and therefore less pulmonary inflammation responses was observed, as compared to intratracheal instillation. The results of our study show that well-dispersed MWCNT can produce pulmonary lesions, including inflammation.

Pro-inflammatory effects of different MWCNTs dispersions in p16(INK4A)-deficient telomerase-expressing human keratinocytes but not in human SV-40 immortalized sebocytes

We tested whether multi-walled carbon nanotubes (MWCNTs) induce oxidative stress and a pro-inflammatory response in human N-hTERT telomerase-immortalized keratinocytes, in human SZ95 SV-40 immortalized sebocytes and in in vitro reconstructed epidermises. MWCNTS were tested in various dispersion states, from raw and agglomerated particles to isolated entities obtained by sonication in the presence of dispersive agents (hydroxypropylcellulose and Pluronic F108). It was observed that: (a) Contrary to individualized MWCNTs, agglomerated particles prepared by suspension into pure water increased the intracellular levels of reactive oxygen species as well as the expression and secretion of interleukin-8 in N-hTERT cells; (b) the inflammatory signature of MWCNTs in N-hTERT cells, drawn by transcriptomic analysis with low-density microfluidic cards, included various other cytokines such as interleukin-6 or C-C motif ligand 3; (c) the pro-inflammatory effects of MWCNTs, as assessed by interleukin-8 transcript level and protein release, were not observed in SZ95 cells; and (d) the secretion of interleukins-1α and -8 from in vitro reconstructed epidermal tissues, used as specific markers for skin irritation and sensitization, was unaffected in presence of MWCNTs, confirming that the cornified layer is an efficient barrier against MWCNTs.