Carbon nanotubes: promising agents against free radicals

The Stability of UV-Defluorination-Driven Crosslinked Carbon Nanotubes: A Raman Study

Carbon nanotubes (CNTs) are often regarded as semi-rigid, all-carbon polymers. However, unlike conventional polymers that can form 3D networks such as hydrogels or elastomers through crosslinking in solution, CNTs have long been considered non-crosslinkable under mild conditions. This perception changed with our recent discovery of UV-defluorination-driven direct crosslinking of CNTs in solution. In this study, we further investigate the thermal stability of UV-defluorination-driven crosslinked CNTs, revealing that they are metastable and decompose more readily than either pristine or fluorinated CNTs under Raman laser irradiation. Using Raman spectroscopy under controlled laser power, we examined both single-walled and multi-walled fluorinated CNTs. The results demonstrate that UV-defluorinated CNTs exhibit reduced thermal stability compared to their pristine or untreated fluorinated counterparts. This instability is attributed to the strain on the intertube crosslinking bonds resulting from the curved carbon lattice of the linked CNTs. The metallic CNTs in the crosslinked CNT networks decompose and revert to their pristine state more readily than the semiconducting ones. The inherent instability of crosslinked CNTs leads to combustion at temperatures approximately 100 °C lower than those required for non-crosslinked fluorinated CNTs. This property positions crosslinked CNTs as promising candidates for applications where mechanically robust, lightweight materials are needed, along with feasible post-use removal options.

Fullerenols Mitigate Radiation-Induced Myocardial Injury

Radiation-induced heart disease is a serious side effect of radiation therapy that can lead to severe consequences. However, effective and safe methods for their prevention and treatment are presently lacking. This study reports the crucial function of fullerenols in protecting cardiomyocytes from radiation injury. First, fullerenols are synthesized using a simple base-catalyzed method. Next, the as-prepared fullerenols are applied as an effective free radical scavenger and broad-spectrum antioxidant to protect against X-ray-induced cardiomyocyte injury. Their ability to reduce apoptosis via the mitochondrial signaling pathway at the cellular level is then verified. Finally, it is observed in animal models that fullerenols accumulate in the heart and alleviate myocardial damage induced by X-rays. This study represents a timely and essential analysis of the prevention and treatment of radiological myocardial injury, providing new insights into the applications of fullerenols for therapeutic strategies.

Carbon nanotubes: Structural defects as stressors inducing lung cell toxicity

Lung toxicity of carbon nanotubes (CNTs) is matter of concern since very long time. However, their mechanism of toxicity is still not yet well defined. In this work, the role of structural defects as organic stressors of CNTs able to trigger their potential toxicity is investigated. Four commercial CNTs, with different carbon purity grade, are morphologically characterized by transmission electron microscopy (TEM) and the relative amount of structural defects are estimated through Raman spectroscopy, by measuring the intensity ratio D/G (ID/IG). The oxidative potential of CNTs is evaluated with cytochrome-C assay and reactive oxygen species (ROS) detection. Data show that CNTs with larger amounts of structural defects (higher ID/IG ratio) induce an increased ROS generation and consequent cytotoxicity and cellular damage, shown by TEM images of CNTs-cells interaction. Raman analyses of cells exposed to CNTs point out that the spectra of the CNTs inside the cells show no differences with respect of the signal recorded for cell-free CNTs, evidencing their biopersistence in lung cells. Raman spectra cannot provide direct indication of the existence of metals as impurity. It follows that the intensity ratio ID/IG can be taken as a predictive marker of the toxicity of a given CNT.

Using Pegylated Graphene Oxide to Achieve High Performance Solid Polymer Electrolyte Based on Poly(ethylene oxide)/Polyvinyl Alcohol Blend (PEO/PVA)

Solid polymer electrolytes (SPEs) have emerged as a promising avenue for developing flexible lithium-ion batteries. However, the low ionic conductivity of polymers remains a primary challenge that has been the subject of intensive research efforts in recent years. In this work, polyethylene oxide (PEO), polyvinyl alcohol, lithium perchlorate (LiClO₄), and graphene functionalized with polyethylene glycol (FGO) have been used to prepare SPE/FGO electrolytes by casting solution technique. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed the reduction of SPE crystals and the increase of amorphous phases. The results demonstrated that the presence of functionalized graphene had an effective role in reducing crystallinity. Furthermore, the thermal and mechanical stability of the samples were corroborated through thermogravimetric analysis (TGA) and tensile tests, respectively. Notably, the samples exhibited adequate ionic conductivity at room temperature, with the highest ionic conductivity of 5.2 × 10^-5 S·cm^-1 observed for 2%wt of FGO in SPE (SPE/FGO(2)).

Pristine, carboxylated, and hybrid multi-walled carbon nanotubes exert potent antioxidant activities in in vitro-cell free systems

Multi-walled carbon nanotubes (MWCNTs) are tubular-shaped carbon allotropes, composed of multiple concentric graphene cylinders. The extended systems of conjugated double bonds, that MWCNTs are constituted by, provide them with high electron affinities, enabling them to act as electron donors or acceptors. Consequently, their potential biomedical applications, as synthetic antioxidant agents, are of particular interest. Based on the above, the purpose of the present study was to evaluate the intrinsic antioxidant properties of pristine and carboxylated MWCNTs, as well as of novel hybrid nanocomposites of MWCNTs and inorganic nanoparticles. To this end, after the synthesis and characterization of MWCNTs, their antiradical, reducing, and antigenotoxic properties were assessed in cell-free assays, using a methodological approach that has been recently proposed by our research group. According to our results, most of the tested MWCNTs exhibited strong antioxidant activities. More elaborately, the hybrid material of MWCNTs and ferrous oxide nanoparticles, i.e., CNTs@Fe₃O₄, showed robust scavenging capacities in all free-radical scavenging assays examined. As regards reducing properties, the pristine MWCNTs, i.e., CNTs-Ref, exhibited the greater electron donating capacity. Finally, in terms of antigenotoxic properties, the hybrid material of MWCNTs and silicon carbide nanoparticles, i.e., CNTs@SiC, exhibited potent ability to inhibit the formation of peroxyl radicals, thus preventing from the oxidative DNA damage. Conclusively, our findings suggest that the MWCNTs of the study could be considered as promising broad-spectrum antioxidants, however, further investigations are required to evaluate their toxicological profile in cell-based and in vivo systems.

Biomedical polymer scaffolds mimicking bone marrow niches to advance in vitro expansion of hematopoietic stem cells

Hematopoietic stem cell (HSC) transplantation provides an effective platform for the treatment of hematological disorders. However, the donor shortage of HSCs and immune responses severely restrict the clinical applications of HSCs. Compared to allogeneic transplantation, autogenous transplantation poses less risk to the immune system, but the problem associated with insufficient HSCs remains a substantial challenge. A significant strategy for obtaining sufficient HSCs is to promote the expansion of HSCs. In vivo, a bone marrow microenvironment supports the survival and hematopoiesis of HSCs. Therefore, it is crucial to establish a platform that mimics the features of a bone marrow microenvironment for the in vitro expansion of HSCs. Three-dimensional (3D) scaffolds have emerged as the most powerful tools to mimic cellular microenvironments for the growth and proliferation of stem cells. Biomedical polymers have been widely utilized as cell scaffolds due to their advantageous features including favorable biocompatibility, biodegradability, as well as adjustable physical and chemical properties. This review focuses on recent advances in the study of biomedical polymer scaffolds that mimic bone marrow microenvironments for the in vitro expansion of HSCs. Bone marrow transplantation and microenvironments are first introduced. Then, biomedical polymer scaffolds for the expansion of HSCs and future prospects are summarized and discussed.

Biomimetically Inspired Highly Homogeneous Hydrophilization of Graphene with Poly(l-DOPA): Toward Electroconductive Coatings from Water-Processable Paints

Water-based processing of graphene-typically considered as physicochemically incompatible with water in the macroscale-emerges as the key challenge among the central postulates of green nanotechnology. These problematic concerns are derived from the complex nature of graphene in the family of sp2-carbon nanoallotropes. Indeed, nanomaterials hidden under the common "graphene" signboard are very rich in morphological and physicochemical variants. In this work, inspired by the adhesion chemistry of mussel biomaterials, we have synthesized novel, water-processable graphene-polylevodopa (PDOPA) hybrids. Graphene and PDOPA were covalently amalgamated via the "growth-from" polymerization of l-DOPA (l-3,4-dihydroxyphenylalanine) monomer in air, yielding homogeneously PDOPA-coated (23 wt %) (of thickness 10-20 nm) hydrophilic flakes. The hybrids formed >1 year stable and water-processable aqueous dispersions and further conveniently processable paints of viscosity 0.4 Pa·s at 20 s-1 and a low yield stress τ0 up to 0.12 Pa, hence exhibiting long shelf-life stability and lacking sagging after application. Demonstrating their applicability, we have found them as surfactant-like nanoparticles stabilizing the larger, pristine graphene agglomerates in water in the optimized graphene/graphene-PDOPA weight ratio of 9:1. These characteristics enabled the manufacture of conveniently paintable coatings of low surface resistivity of 1.9 kΩ sq-1 (0.21 Ω·m) which, in turn, emerge as potentially applicable in textronics, radar-absorbing materials, or electromagnetic interference shielding.

Involvement of O2·- release in zearalenone-induced hormesis of intestinal porcine enterocytes: An electrochemical sensor-based analysis

Relationship between mycotoxin-induced hormesis and reactive oxygen species (ROS) has not been systematically investigated due to the lack of an effective analysis method. To monitor cellular release and intracellular level of O2·-, carboxymethyl cellulose-Mn3(PO4)2 nanocomposite was synthesized to fabricate an electrochemical biosensor, which selectively detects O2·- over the range of 57.50 nM ∼ 2.95 μM (R2 = 0.99) with the sensitivity of 78.67 μA μM-1 cm-2 and the detection limit of 8.47 nM. Transient exposure to zearalenone (ZEA) induces the enhancement on cell viability, immediate O2·- release from cells, and reduction of intracellular O2·- level. After post-treatment culture, intracellular O2·- initially increases to a high level and then decreases to the normal level. Concurrently, the ZEA-induced hormesis disappears. Based on the findings, we propose a mechanism, involving the ROS release, increase of succinate dehydrogenase activity and recovery of intracellular ROS, to explain the occurrence and disappearance of hormesis in intestinal porcine enterocytes.

Semi-Continuous Heterophase Polymerization to Synthesize Poly(methacrylic acid)-Based Nanocomposites for Drug Delivery

The design of nanocomposites with the potential for drug delivery is a topic of great interest. In this work, the synthesis of nanocomposites of poly(methacrylic acid) (PMAA) grafted onto carbon nanotubes (CNTs) functionalized with poly(amidoamine) (PAMAM) dendrimer by semicontinuous heterophase polymerization SHP, at three different methacrylic acid (MAA) dosing rates, is reported. SHP is a polymerization technique poorly used to prepare nanocomposites containing CNTs and has the potential to produce more ordered alkyl methacrylic polymer chains, which could favor the obtaining of a homogenous nanocomposite. For the nanocomposites synthesized, a lowest addition rate monomer-starved condition was reached. Analysis by X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) demonstrate that functionalized CNTs are grafted onto the PMAA matrix. The ability of prepared nanocomposites to deliver hydrocortisone was evaluated by ultraviolet-visible spectroscopy (UV-Vis). The hydrocortisone release profiles of pure PMAA and of their nanocomposites prepared at the lowest monomer fed rate were fitted with Higuchi and Korsmeyer–Peppas models, successfully. Functionalized CNTs have a crucial role to induce an effective release of hydrocortisone from the prepared nanocomposites.

Impact of As-Prepared and Purifıed Multi-Walled Carbon Nanotubeson the Liquid-Phase Aerobic Oxidatıon of Hydrocarbons

The article presents simple kinetic approaches to study the effect of multi-walled carbon nanotubes (MWCNTs) additives on the aerobic oxidation of hydrocarbons and to propose real acceptable mechanisms of the process. The aerobic liquid phase low-temperature oxidation of ethylbenzene conducted in the presence of multi-walled carbon nanotubes has been used as a model pattern. Kinetic analysis established the catalytic action associated with the presence of the iron compounds in inner channels of MWCNTs. These compounds are identified as ferric carbides provoking decomposition of the ethylbenzene hydroperoxide and thereby suppressing the competitive route of alky-peroxide radicals addition to the nanocarbon cage. Thus the reaction finally proceeds in the autocatalytic mode.Contradictory conclusions on the effect of CNTs on the oxidation chain processes existing in the literature are associated with the lack of control over nature and content of metal impurities in channels of nanotubes.

Recent Insights and Multifactorial Applications of Carbon Nanotubes

Nanotechnology has undergone significant development in recent years, particularly in the fabrication of sensors with a wide range of applications. The backbone of nanotechnology is nanostructures, which are determined on a nanoscale. Nanoparticles are abundant throughout the universe and are thought to be essential building components in the process of planet creation. Nanotechnology is generally concerned with structures that are between 1 and 100 nm in at least one dimension and involves the production of materials or electronics that are that small. Carbon nanotubes (CNTs) are carbon-based nanomaterials that have the structure of tubes. Carbon nanotubes are often referred to as the kings of nanomaterials. The diameter of carbon is determined in nanometers. They are formed from graphite sheets and are available in a variety of colors. Carbon nanotubes have a number of characteristics, including high flexibility, good thermal conductivity, low density, and chemical stability. Carbon nanotubes have played an important part in nanotechnology, semiconductors, optical and other branches of materials engineering owing to their remarkable features. Several of the applications addressed in this review have already been developed and used to benefit people worldwide. CNTs have been discussed in several domains, including industry, construction, adsorption, sensors, silicon chips, water purifiers, and biomedical uses, to show many treatments such as injecting CNTs into kidney cancers in rats, drug delivery, and directing a near-infrared laser at the cancers. With the orderly development of research in this field, additional therapeutic modalities will be identified, mainly for dispersion and densification techniques and targeted drug delivery systems for managing and curing posterior cortical atrophy. This review discusses the characteristics of carbon nanotubes as well as therapeutic applications such as medical diagnostics and drug delivery.

Colon targeted dosage form of Capecitabine using folic acid anchored modified carbon nanotube: in vitro cytotoxicity, apoptosis and in vivo roentgenographic study

OBJECTIVE

Development of dosage form comprising of Capecitabine loaded carbon nanotubes for its targeted delivery to the colon.

METHOD

Single walled carbon nanotubes (SWCNT) were functionalized by -COOH and Chitosan along with Folic acid. Capecitabine was loaded in these SWCNT's, and the system was analyzed by FTIR, SEM and Raman spectroscopy. Percent drug loading was assessed and the cytotoxicity (COLO320DM and HT29) was verified by using MTT and SRB assay. The apoptosis study was carried out by flowcytometry. The system was enclosed in an enteric coated capsule with pH sensitive polymers and characterized for invitro disintegration, dissolution and invivo roentgenographic studies.

RESULTS

FTIR, Raman and XRD studies indicated the confirmation of attachments, whereas SEM exhibited size range of 200-500 nm. Drug loading capacity was observed to be 94.63 ± 1.07%. Cytotoxicity studies of Capecitabine and FA-CHI-F-SWCNT-Capecitabine against COLO320DM by using MTT assay showed that FA-CHI-F-SWCNT- Capecitabine exhibited 86.45 ± 0.5788% inhibition whereas pure Capecitabine showed 50.52 ± 0.3106% inhibition. Against HT29, the % inhibition was observed to be 82.76 ± 0.4668% and 56.41 ± 0.2316% respectively for FA-CHI-F-SWCNT-Capecitabine and pure Capecitabine. In case of SRB assay of COLO320DM, the FA-CHI-F-SWCNT-Capecitabine exhibited 89.62 ± 0.4095% inhibition and Capecitabine showed 84.36 ± 0.2559% inhibition, whereas against HT29, FA-CHI-F-SWCNT-Capecitabine showed 81.36 ± 0.2958% inhibition and Capecitabine exhibited 90.62 ± 0.4196% inhibition.

CONCLUSION

FA-CHI-F-SWCNT loaded system revealed better cytotoxicity as compared with pure Capecitabine against two different cell lines. Invivo studies revealed that the prepared capsule formulation remained intact in the stomach thereby preventing drug release in the gastric milieu.

Highly Selective Multiplex Quantitative Polymerase Chain Reaction with a Nanomaterial Composite Hydrogel for Precise Diagnosis of Viral Infection

As viruses have been threatening global public health, fast diagnosis has been critical to effective disease management and control. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) is now widely used as the gold standard for detecting viruses. Although a multiplex assay is essential for identifying virus types and subtypes, the poor multiplicity of RT-qPCR makes it laborious and time-consuming. In this paper, we describe the development of a multiplex RT-qPCR platform with hydrogel microparticles acting as independent reactors in a single reaction. To build target-specific particles, target-specific primers and probes are integrated into the particles in the form of noncovalent composites with boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs). The thermal release characteristics of DNA, primer, and probe from the composites of primer-BNNT and probe-CNT allow primer and probe to be stored in particles during particle production and to be delivered into the reaction. In addition, BNNT did not absorb but preserved the fluorescent signal, while CNT protected the fluorophore of the probe from the free radicals present during particle production. Bicompartmental primer-incorporated network (bcPIN) particles were designed to harness the distinctive properties of two nanomaterials. The bcPIN particles showed a high RT-qPCR efficiency of over 90% and effective suppression of non-specific reactions. 16-plex RT-qPCR has been achieved simply by recruiting differently coded bcPIN particles for each target. As a proof of concept, multiplex one-step RT-qPCR was successfully demonstrated with a simple reaction protocol.

Changes in Surface Free Energy and Surface Conductivity of Carbon Nanotube/Polyimide Nanocomposite Films Induced by UV Irradiation

Changes in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films. Changes in contact angles and surface electrical conductivity at the surface of CNT/PI nanocomposite films after UV exposure were measured. The unpaired electron intensity of free radicals generated by UV exposure was monitored by electron paramagnetic resonance. Our study indicates that the covalent interactions between CNTs and radicals generated by UV irradiation on the PI surfaces tailor the surface energy and surface conductivity through anchoring radicals on CNTs. Surprisingly, adding CNTs into PI films exposed to UV leads to antagonistic contributions of dispersion and polar components to the surface energy. The surface electrical conductivity of the CNT/PI nanocomposite films has been improved due to an enhanced hopping behavior with dense π-conjugated CNT sites. To explain the observed changes in surface energy and surface conductivity of CNT/PI nanocomposite films induced by UV exposure, a qualitative model was put forward describing the covalent interactions between UV-induced PI free radicals and CNTs, which govern the chemical nature of surface components. This study is helpful for characterizing and optimizing nanocomposite surface properties by tuning the covalent interactions between components at the nanoscale.

Characterization of Betulinic Acid-Multiwalled Carbon Nanotubes Modified with Hydrophilic Biopolymer for Improved Biocompatibility on NIH/3T3 Cell Line

The biocompatibility of carbon nanotubes (CNT) is fairly a challenging task for their applications in nanomedicine. Therefore, the objective of this research was to formulate four types of highly biocompatible betulinic acid-loaded biopolymer nanocomposites, namely chitosan-multiwalled carbon nanotubes (MWBA-CS), polyethylene glycol-multiwalled carbon nanotubes (MWBA-PG), Tween 20-multiwalled carbon nanotubes (MWBA-T2) and Tween 80-multiwalled carbon nanotubes (MWBA-T8). The physico-chemical properties of the modified nanocomposites were determined by Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA) and Raman spectroscopy, while the surface morphology of the resulting nanocomposites was studied using field emission scanning electron microscopy (FESEM). All data revealed that the external surface of MWBA nanocomposites was successfully coated with the respective polymer molecules through hydrophobic and electrostatic interactions with improved thermal profiles. The cell viability assay, which was performed on cultured normal embryonic mouse fibroblast cells, confirmed their excellent biocompatibility in phosphate-buffered saline aqueous media. Overall, our findings herein suggest that the synthesized biopolymer-coated MWBA nanocomposites are promising nanomaterials for drug delivery applications as they enhance the solubility and dispersibility of CNT with significantly reduced cytotoxic effect, especially in normal cells.

Antimicrobial and anti-adhesive properties of carbon nanotube-based surfaces for medical applications: a systematic review

Although high-performance carbon materials are widely used in surface engineering, with emphasis on carbon nanotubes (CNTs), the application of CNT nanocomposites on medical surfaces is poorly documented. In this study, we aimed to evaluate the antimicrobial and anti-adhesive properties of CNT-based surfaces. For this purpose, a PRISMA-oriented systematic review was conducted based on predefined criteria and 59 studies were selected for the qualitative analysis. Results from the analyzed studies suggest that surfaces containing modified CNTs, and specially CNTs conjugated with different polymers, exhibited strong antimicrobial and anti-adhesive activities. These composites seem to preserve the CNT toxicity to microorganisms and promote CNT-cell interactions, as well as to protect them from nonspecific protein adsorption. However, CNTs cannot yet compete with the conventional strategies to fight biofilms as their toxicity profile on the human body has not been thoroughly addressed. This review can be helpful for the development of new engineered medical surfaces.

Alkylborane-Initiated Thiol-Ene Networks for the Synthesis of Thick and Highly Loaded Nanocomposites

Thiol-ene nanocomposites were synthesized for the first time using an alkylborane-ligand initiator complex under bulk and ambient conditions without external light or thermal stimuli. Initiation was triggered by the in situ decomplexation of an air-stable trialkylborane-amine complex to liberate trialkylborane, which rapidly autoxidizes with atmospheric oxygen and generates free radicals to drive thiol-ene polymerization. This chemically activated mode of initiation uniquely affords thiol-ene nanocomposites with an unrivaled carbon nanotube (CNT) loading of 1.3 wt % and thicknesses of ∼6.7 mm by circumventing restrictions imposed by long pathlengths and light-impeding fillers during photoinitiation. Alkylborane initiation also exhibited advantageous polymerization rates, equivalent to photoinitiation, resulting in network formation and gelation within minutes. Systematic studies were conducted to evaluate comparable alkylborane- and photo-initiated nanocomposites under progressively higher loadings and larger specimen thicknesses, revealing an enhancement or better retainment of mechanical performance in alkylborane-initiated nanocomposites.

Carbonaceous Nanomaterials-Mediated Defense Against Oxidative Stress

The concept of nanoscale materials and their applications in industrial technologies, consumer goods, as well as in novel medical therapies has rapidly escalated in the last several years. Consequently, there is a critical need to understand the mechanisms that drive nanomaterials biocompatibility or toxicity to human cells and tissues. The ability of nanomaterials to initiate cellular pathways resulting in oxidative stress has emerged as a leading hypothesis in nanotoxicology. Nevertheless, there are a few examples revealing another face of nanomaterials - they can alleviate oxidative stress via decreasing the level of reactive oxygen species. The fundamental structural and physicochemical properties of carbonaceous nanomaterials that govern these anti-oxidative effects are discussed in this article. The signaling pathways influenced by these unique nanomaterials, as well as examples of their applications in the biomedical field, e.g. cell culture, cell-based therapies or drug delivery, are presented. We anticipate this emerging knowledge of intrinsic anti-oxidative properties of carbon nanomaterials to facilitate the use of tailored nanoparticles in vivo.

Clinically Approved Carbon Nanoparticles with Oral Administration for Intestinal Radioprotection via Protecting the Small Intestinal Crypt Stem Cells and Maintaining the Balance of Intestinal Flora

The exploration of an old drug for new biomedical applications has an absolute predominance in shortening the clinical conversion time of drugs for clinical application. In this work, carbon nanoparticles suspension injection (CNSI), the first clinically approved carbon nanoparticles in China, is explored as a new nano-radioprotective agent for potent intestinal radioprotection. CNSI shows powerful radioprotective performance in the intestine under oral administration, including efficient free radical scavenging ability, good biosafety, high chemical stability, and relatively long retention time. For example, CNSI shows high reactive oxygen species (ROS) scavenging activities, which effectively alleviates the mitochondrial dysfunction and DNA double-strand breaks to protect the cells against radiation-induced damage. Most importantly, this efficient ROS scavenging ability greatly helps restrain the apoptosis of the small intestinal epithelial and crypt stem cells, which decreases the damage of the mechanical barrier and thus relieves radiation enteritis. Moreover, CNSI helps remove the free radicals in the intestinal microenvironment and thus maintain the balance of intestinal flora so as to mitigate the radiation enteritis. The finding suggests a new application of clinically approved carbon nanoparticles, which not only promotes the development of new intestinal radioprotector, but also has a great potential for clinical transformation.

Potential Role of Soluble Metal Impurities in the Acute Lung Inflammogenicity of Multi-Walled Carbon Nanotubes

Multi-walled carbon nanotubes (MWCNTs) have variable metal impurities, but little is known about the impact of soluble metal impurities on the toxicity of MWCNTs. Here, we evaluated the role of soluble metal impurities to the acute inflammogenic potential of MWCNTs, using five types of high purity MWCNTs (>95%). MWCNTs and their soluble fractions collected at 24 h after incubation in phosphate-buffered saline showed diverse metal impurities with variable concentrations. The fiber-free soluble fractions produced variable levels of reactive oxygen species (ROS), and the iron level was the key determinant for ROS production. The acute inflammation at 24 h after intratracheal instillation of MWCNTs to rats at 0.19, 0.63, and 1.91 mg MWCNT/kg body weight (bw) or fiber-free supernatants from MWCNT suspensions at 1.91 and 7.64 mg MWCNT/kg bw showed that the number of granulocytes, a marker for acute inflammation, was significantly increased with a good dose-dependency. The correlation study showed that neither the levels of iron nor the ROS generation potential of the soluble fractions showed any correlations with the inflammogenic potential. However, the total concentration of transition metals in the soluble fractions showed a good correlation with the acute lung inflammogenic potential. These results implied that metal impurities, especially transitional metals, can contribute to the acute inflammogenic potential of MWCNTs, although the major parameter for the toxicity of MWCNTs is size and shape.

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.

Antioxidants and Nanotechnology: Promises and Limits of Potentially Disruptive Approaches in the Treatment of Central Nervous System Diseases

Many central nervous system (CNS) diseases are still incurable and only symptomatic treatments are available. Oxidative stress is suggested to be a common hallmark, being able to cause and exacerbate the neuronal cell dysfunctions at the basis of these pathologies, such as mitochondrial impairments, accumulation of misfolded proteins, cell membrane damages, and apoptosis induction. Several antioxidant compounds are tested as potential countermeasures for CNS disorders, but their efficacy is often hindered by the loss of antioxidant properties due to enzymatic degradation, low bioavailability, poor water solubility, and insufficient blood-brain barrier crossing efficiency. To overcome the limitations of antioxidant molecules, exploitation of nanostructures, either for their delivery or with inherent antioxidant properties, is proposed. In this review, after a brief discussion concerning the role of the blood-brain barrier in the CNS and the involvement of oxidative stress in some neurodegenerative diseases, the most interesting research concerning the use of nano-antioxidants is introduced and discussed, focusing on the synthesis procedures, functionalization strategies, in vitro and in vivo tests, and on recent clinical trials.

Carbon Nanotubes in Biomedicine

Nowadays, biomaterials have become a crucial element in numerous biomedical, preclinical, and clinical applications. The use of nanoparticles entails a great potential in these fields mainly because of the high ratio of surface atoms that modify the physicochemical properties and increases the chemical reactivity. Among them, carbon nanotubes (CNTs) have emerged as a powerful tool to improve biomedical approaches in the management of numerous diseases. CNTs have an excellent ability to penetrate cell membranes, and the sp² hybridization of all carbons enables their functionalization with almost every biomolecule or compound, allowing them to target cells and deliver drugs under the appropriate environmental stimuli. Besides, in the new promising field of artificial biomaterial generation, nanotubes are studied as the load in nanocomposite materials, improving their mechanical and electrical properties, or even for direct use as scaffolds in body tissue manufacturing. Nevertheless, despite their beneficial contributions, some major concerns need to be solved to boost the clinical development of CNTs, including poor solubility in water, low biodegradability and dispersivity, and toxicity problems associated with CNTs' interaction with biomolecules in tissues and organs, including the possible effects in the proteome and genome. This review performs a wide literature analysis to present the main and latest advances in the optimal design and characterization of carbon nanotubes with biomedical applications, and their capacities in different areas of preclinical research.

Radical scavenging activity of carbon nanotubes: toward appropriate selection of a radical initiator

Radical scavenging activities are attractive properties not only for scientific fields e.g. biomedicine, but for the materials industry. In this study, we report that carbon nanotubes (CNTs) can scavenge radicals from organic peroxides, while radicals from azo-type radical initiators exhibit only a few effects from the presence of CNTs. In addition, experimental results suggest the possibility that captured peroxide radicals generate active radical sites on the CNT surface, from which polymerization can take place. These results indicate the importance of selecting an appropriate radical initiator.

Carbon nanotubes scavenge radicals preferentially from peroxides, and polymerization presumably takes place from generated active radical sites on the surface.

Hyaluronate Functionalized Multi-Wall Carbon Nanotubes Filled with Carboplatin as a Novel Drug Nanocarrier against Murine Lung Cancer Cells

Carbon nanotubes (CNTs) have emerged in recent years as a potential option for drug delivery, due to their high functionalization capacity. Biocompatibility and selectivity using tissue-specific biomolecules can optimize the specificity, pharmacokinetics and stability of the drug. In this study, we design, develop and characterize a drug nanovector (oxCNTs-HA-CPT) conjugating oxidated multi-wall carbon nanotubes (oxCNTs) with hyaluronate (HA) and carboplatin (CPT) as a treatment in a lung cancer model in vitro. Subsequently, we exposed TC-1 and NIH/3T3 cell lines to the nanovectors and measured cell uptake, cell viability, and oxidative stress induction. The characterization of oxCNTs-HA-CPT reveals that on their surface, they have HA. On the other hand, oxCNTs-HA-CPT were endocytosed in greater proportion by tumor cells than by fibroblasts, and likewise, the cytotoxic effect was significantly higher in tumor cells. These results show the therapeutic potential that nanovectors possess; however, future studies should be carried out to determine the death pathways involved, as well as their effect on in vivo models.

Critical Comparison of the Superoxide Dismutase-like Activity of Carbon Antioxidant Nanozymes by Direct Superoxide Consumption Kinetic Measurements

The superoxide dismutase-like activity of poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs), anthracite and bituminous graphene quantum dots (PEG-aGQDs and PEG-bGQDs, respectively), and two fullerene carbon nanozymes, tris malonyl-C₆₀ fullerene (C3) and polyhydroxylated-C₆₀ fullerene (C₆₀-OH_n), were compared using direct optical stopped-flow kinetic measurements, together with three native superoxide dismutases (SODs), CuZnSOD, MnSOD, and FeSOD, at both pH 12.7 and 8.5. Computer modeling including both SOD catalytic steps and superoxide self-dismutation enabled the best choice of catalyst concentration with minimal contribution to the observed kinetic change from the substrate self-dismutation. Biexponential fitting to the kinetic data ranks the rate constant (M^-1 s^-1) in the order of PEG-HCCs > CuZnSOD ≈ MnSOD ≈ PEG-aGQDs ≈ PEG-bGQDs > FeSOD ≫ C3 > C₆₀-OH_n at pH 12.7 and MnSOD > CuZnSOD ≈ PEG-HCCs > FeSOD > PEG-aGQDs ≈ PEG-bGQDs ≫ C3 ≈ C₆₀-OH_n at pH 8.5. Nonlinear regression of the kinetic model above yielded the same ranking as the biexponential fit, but provided better mechanistic insight. The data obtained by freeze-quench EPR direct assay at pH 12.7 also yield the same ranking as stopped-flow data. This is a necessary assessment of a panel of proclaimed carbon nano SOD mimetics using the same two direct methods, revealing a dramatic, 3-4 orders of magnitude difference in SOD activity between PEG-HCCs/PEG-GQDs from soluble fullerenes.

Pro- and anti-oxidant properties of near-infrared (NIR) light responsive carbon nanoparticles

Elemental carbon nanomaterials (ECNMs) are redox active agents that can be exploited to purposely modify the redox balance of cells. Both pro- or antioxidant properties have been reported. However, to the best of our knowledge, there are not comprehensive studies exploring both properties on the same material in view of a potential application in medicine. At the same time, the effect of the bulk structure on the pro/antioxidant properties is poorly known. Here, carbon nanoparticles (CNPs) derived by glucose with definite size and shape have been prepared, and their redox properties evaluated in cell free systems in the dark or following activation with a Near Infrared (NIR) laser beam (945 nm, 1.3 W/cm²). We found that, when irradiated with NIR, CNPs efficiently generate heat and singlet oxygen (¹O₂), a property that can be exploited for dual photo-thermal (PT)/photodynamic (PD) therapy in cancer. On the other hand, in the absence of photo-activation, CNPs react with both oxidant (hydroxyl radicals) and antioxidant (glutathione) species. When tested on a murine macrophages cell line (RAW 264.7) CNPs were clearly antioxidant. Furthermore, albeit efficiently internalized, CNPs do not exert cytotoxic effect up to 80 µg/ml and do not exacerbate TNF-α-mediated inflammation. Overall, the results reported herein suggest that CNPs may represent a new class of safe nanomaterials with potential applications in medicine.

Application of Multifunctional Nanomaterials in Radioprotection of Healthy Tissues

Radiotherapy has been extensively used in clinic for malignant tumors treatment. However, a severe challenge of it is that the ionizing radiation needed to kill tumors inevitably causes damage to surrounding normal tissues. Although some of the molecular radioprotective drugs, such as amifostine, have been used as clinical adjuvants to radio-protect healthy tissues, their shortcomings such as short systemic circulation time and fast biological clearing from the body largely hinder the sustained bioactivity. Recently, with the rapid development of nanotechnology in the biological field, the multifunctional nanomaterials not only establish powerful drug delivery systems to improve the molecular radioprotective drugs' biological availability, but also open a new route to develop neozoic radioprotective agents because some nanoparticles possess intrinsic radioprotective abilities. Therefore, considering these overwhelming superiorities, this review systematically summarizes the advances in healthy tissue radioprotection applications of multifunctional nanomaterials. Furthermore, this review also points out a perspective of nanomaterial designs for radioprotection applications and discusses the challenges and future outlooks of the nanomaterial-mediated radioprotection.

DYNAMIC PROPERTIES AND TIRE PERFORMANCES OF COMPOSITES FILLED WITH CARBON NANOTUBES

Carbon nanotubes (CNTs) have been widely studied in rubber goods and tire compounds to improve, for example, antistatic and thermal conductivity performances. CNTs were applied in passenger tire tread compounds to improve comprehensive tire performances, especially wet traction. High frequency dynamic properties of CNT-filled compounds were revealed for the first time. There was good correlation between compound dynamic properties and vehicle tire test results. The influence of CNTs on tire performances and their mechanisms was investigated and explained by the dynamic properties and master curve analysis in the frequency domain. Substituting 50 phr carbon black N234 by 20 phr CNTs could maintain hardness but increased static and dynamic moduli, which was beneficial for the tire handling, with 0.25 point improvement in the subjective testing. For the CNT-filled compounds, 1.5% traction improvement on a dry road and 6.5% traction improvement on a wet road can be explained successfully by the increased hysteresis loss (tan δ) and decreased storage modulus (G′) at high frequency domain (104–108 Hz). It is implied by Williams–Landel–Ferry law calculation that a strong interaction between CNTs and rubber resulted in higher temperature dependence; however, the trade-off was a 7% higher tire rolling resistance coefficient and 33% worse wear resistance for the CNT tires. CNT-filled compounds were demonstrated to have superior handling and traction performances suitable for racing and sports car tires.

Synthesis, characterization and assessment of hydrophilic oxidized carbon nanodiscs in bio-related applications

Hydrophilic oxidized carbon nanodiscs able to be used as drug delivery system and as support in nanobiocatalytic applications.

Antioxidant nanomaterials in advanced diagnoses and treatments of ischemia reperfusion injuries

Organ ischemia with inadequate oxygen supply followed by reperfusion (which initiates a complex of inflammatory responses and oxidative stress) occurs in different clinical conditions and surgical procedures including stroke, myocardial infarction, limb ischemia, renal failure, organ transplantation, free-tissue-transfer, cardiopulmonary bypass, and vascular surgery. Even though pharmacological treatments protect against experimental ischemia reperfusion (I/R) injury, there has not been enough success in their application for patient benefits. The main hurdles in the treatment of I/R injury are the lack of diagnosis tools for understanding the complicated chains of I/R-induced signaling events, especially in the acute phase after ischemia, determining the affected regions of the tissue over time, and then, targeting and safe delivery of antioxidants, drugs, peptides, genes and cells to the areas requiring treatment. Besides the innate antioxidant and free radical scavenging properties, some nanoparticles also show higher flexibility in drug delivery and imaging. This review highlights three main approaches in nanoparticle-mediated targeting of I/R injury: nanoparticles (1) as antioxidants for reducing tissue oxidative stress, (2) for targeted delivery of therapeutic agents to the ischemic regions or cells, and (3) for imaging I/R injury at the molecular, cellular or tissue level and monitoring its evolution using contrasts induced by nanoparticles. These approaches can also be combined to realize so called theranostics for providing simultaneous diagnosis of ischemic regions and treatments by targeted delivery.

Graphene oxide enhanced, radiation cross-linked, vitamin E stabilized oxidation resistant UHMWPE with high hardness and tensile properties

A method for enhancing the micro-hardness and tensile properties of cross-linked ultrahigh molecular weight polyethylene (UHMWPE) by radiation cross-linking after adding vitamin-E (VE) and graphene oxide (GO) was reported.

The potential ecological risk of multiwall carbon nanotubes was modified by the radicals resulted from peroxidase-mediated tetrabromobisphenol A reactions

Extensive studies have been conducted on the environmental degradation of multiwall carbon nanotubes (MWCNTs), but primarily focused on the extent and rate of MWCNTs mineralization. Few studies have explored possible structural changes that may occur to MWCNTs during natural or engineered processes. We systematically examined MWCNTs in oxidative coupling reactions in the presence of a common contaminant tetrabromobisphenol A (TBBPA). MWCNTs was modified by the radicals of TBBPA resulting from peroxidase-mediated coupling reaction. Interactions between TBBPA radicals and MWCNTs were definitely confirmed by analyzing the characteristic mass spectrometry response of bromine in TBBPA and the structures of MWCNTs. After reaction with TBBPA radicals for 60 min, the content of bromine contained in MWCNTs was 6.84(±0.12)%, a quantity equivalent to a 501.65(±2.19) mg loading of TBBPA per gram MWCNTs. Modified MWCNTs had better stability and smaller sizes than that of MWCNTs and TBBPA-adsorbed MWCNTs. Assessment using zebrafish embryos revealed that the modified MWCNTs passed through the chorion and entered the embryo inducing acute toxicity, while the MWCNTs/TBBPA-adsorbed MWCNTs was trapped by chorion. These findings indicated that MWCNTs was modified in peroxidase-mediated coupling reactions, and suggested that such modifications may have an influence on the ecological risks of MWCNTs.

Evaluating the mechanistic evidence and key data gaps in assessing the potential carcinogenicity of carbon nanotubes and nanofibers in humans

In an evaluation of carbon nanotubes (CNTs) for the IARC Monograph 111, the Mechanisms Subgroup was tasked with assessing the strength of evidence on the potential carcinogenicity of CNTs in humans. The mechanistic evidence was considered to be not strong enough to alter the evaluations based on the animal data. In this paper, we provide an extended, in-depth examination of the in vivo and in vitro experimental studies according to current hypotheses on the carcinogenicity of inhaled particles and fibers. We cite additional studies of CNTs that were not available at the time of the IARC meeting in October 2014, and extend our evaluation to include carbon nanofibers (CNFs). Finally, we identify key data gaps and suggest research needs to reduce uncertainty. The focus of this review is on the cancer risk to workers exposed to airborne CNT or CNF during the production and use of these materials. The findings of this review, in general, affirm those of the original evaluation on the inadequate or limited evidence of carcinogenicity for most types of CNTs and CNFs at this time, and possible carcinogenicity of one type of CNT (MWCNT-7). The key evidence gaps to be filled by research include: investigation of possible associations between in vitro and early-stage in vivo events that may be predictive of lung cancer or mesothelioma, and systematic analysis of dose-response relationships across materials, including evaluation of the influence of physico-chemical properties and experimental factors on the observation of nonmalignant and malignant endpoints.

Sulfonated graphene-induced hormesis is mediated through oxidative stress in the roots of maize seedlings

The present study investigated the impact of sulfonated graphene (SG) on the growth of maize seedlings at a concentration range of 0-500mgL^-1. Stress-related parameters including reactive oxygen species (ROS), intracellular Ca²⁺, antioxidant enzyme activities, lipid peroxidation, membrane leakage, cell death and root morphology were examined to reveal the potential mechanisms. The results indicate that SG induced a hormesis effect on plant height, i.e., low-concentration (50mgL^-1) stimulation and high-concentration (500mgL^-1) inhibition. The hormesis effect of SG on plant height was directly correlated with ROS levels in roots. A low concentration (50mgL^-1) of SG promoted ROS scavenging, alleviated oxidative stress, enhanced the soluble protein (SP) content, and decreased intracellular Ca²⁺ and cell death in the roots. At a higher concentration (500mgL^-1), SG stimulated the generation of ROS in the roots, decreased SP content in the leaves, increased antioxidant enzyme activities, intracellular Ca²⁺, electrolyte leakage and cell death in the roots, and increased the malondialdehyde (MDA) content in both roots and leaves. Different changes were observed for root morphology at SG concentrations of 50 and 500mgL^-1, and a larger amount of SG was deposited onto the root surface at a concentration of 500mgL^-1 compared with 50mgL^-1.

Electrochemical Methods to Study Photoluminescent Carbon Nanodots: Preparation, Photoluminescence Mechanism and Sensing

With unique and tunable photoluminescence (PL) properties, carbon nanodots (CNDs) as a new class of optical tags have been extensively studied. Because of their merits of controllability and sensitivity to the surface of nanomaterials, electrochemical methods have already been adopted to study the intrinsic electronic structures of CNDs. In this review, we mainly deal with the electrochemical researches of CNDs, including preparation, PL mechanism, and biosensing.