Submicron Scale Research Articles

Arbuscular Mycorrhizal Fungi Drive Organo-Mineral Association in Iron Ore Tailings: Unravelling Microstructure at the Submicron Scale by Synchrotron-Based FTIR and STXM-NEXAFS.

Arbuscular mycorrhizal (AM) fungi play an important role in organic matter (OM) stabilization in Fe ore tailings for eco-engineered soil formation. However, little has been understood about the AM fungi-derived organic signature and organo-mineral interactions in situ at the submicron scale. In this study, a compartmentalized cultivation system was used to investigate the role of AM fungi in OM formation and stabilization in tailings. Particularly, microspectroscopic analyses including synchrotron-based transmission Fourier transform infrared (FTIR) and scanning transmission X-ray microspectroscopy combined with near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS) were employed to characterize the chemical signatures at the AM fungal-mineral and mineral-OM interfaces at the submicron scale. The results indicated that AM fungal mycelia developed well in the tailings and entangled mineral particles for aggregation. AM fungal colonization enhanced N-rich OM stabilization through organo-mineral association. Bulk spectroscopic analysis together with FTIR mapping revealed that fungi-derived lipids, proteins, and carbohydrates were associated with Fe/Si minerals. Furthermore, STXM-NEXAFS analysis revealed that AM fungi-derived aromatic, aliphatic, and carboxylic/amide compounds were heterogeneously distributed and trapped by Fe(II)/Fe(III)-bearing minerals originating from biotite-like minerals weathering. These findings imply that AM fungi can stimulate mineral weathering and provide organic substances to associate with minerals, contributing to OM stabilization and aggregate formation as key processes for eco-engineered soil formation in tailings.

Ag2O-Containing Biocidal Interpolyelectrolyte Complexes on Glass Surfaces-Adhesive Properties of the Coatings.

Biocidal coatings are of great interest to the healthcare system. In this work, the biocidal activity of coatings based on a complex biocide containing polymer and inorganic active antibacterial components was studied. Silver oxide was distributed in a matrix of a positively charged interpolyelectrolyte complex (IPEC) of polydiallyldimethylammonium chloride (PDADMAC) and sodium polystyrene sulfonate (PSS) using ultrasonic dispersion, forming nanoparticles with an average size of 5-6 nm. The formed nanoparticles in the matrix are not subject to agglomeration and changes in morphology during storage. It was found that the inclusion of silver oxide in a positively charged IPEC allows a more than 4-fold increase in the effectiveness of the complex biocide against E. coli K12 in comparison with the biocidal effect of PDADMAC and IPEC. Polycation, IPEC, and the IPEC/Ag2O ternary complex form coatings on the glass surface due to electrostatic adsorption. Adhesive and cohesive forces in the resulting coatings were studied with micron-scale coatings using dynamometry. It was found that the stability of the coating is determined primarily by adhesive interactions. At the macro level, it is not possible to reliably identify the role of IPEC formation in adhesion. On the other hand, use of the optical tweezers method makes it possible to analyze macromolecules at the submicron scale and to evaluate the multiple increase in adhesive forces when forming a coating from IPEC compared to coatings from PDADMAC. Thus, the application of ternary IPEC/Ag2O complexes makes it possible to obtain coatings with increased antibacterial action and improved adhesive characteristics.

Bayesian optimization of periodic multilayered slabs for passive absorptivity control

A vanadium dioxide (VO2) film grown on a titanium oxide crystal shows a metal–insulator transition at room temperature with drastically changed optical properties. A multilayered slab with a sub-micron scale VO2 film was proposed to utilize its unique properties for passive intensity control of sunlight absorption and radiative cooling. Its optimal geometries were numerically explored using the Bayesian optimization (BO) method. BO was applied for three types of multilayered slabs, those having one, two, or three isolated slabs of different widths. For each type of multilayered slab, BO could optimize geometric variables with practical calculation times considering the total number of possible combinations of variables, which is subsequently referred to as the total number of candidates. Optimization results revealed that two isolated slabs had the most suitable spectral absorptivity in both hot and cold environments. The infrared absorptivity of the double slab was kept low in cold conditions to suppress radiative cooling. However, the double slab exhibited good radiative cooling performance under hot conditions. Electromagnetic energy density surrounding the slab illustrated that metallic VO2 and gold placed in a parallel manner excited the coupled mode of surface plasmon polaritons to enhance absorptivity. Radiative cooling faded for the triple slab because each slab could couple with radiation propagating only across a portion of the cross-sectional area. Through three BO trials, improvement of the VO2 visible reflectivity was recognized as a future issue for further development of passive sunlight absorption control.

Multiscale analysis of Klf10's impact on the passive mechanical properties of murine skeletal muscle

Skeletal muscle is a hierarchical structure composed of multiple organizational scales. A major challenge in the biomechanical evaluation of muscle relates to the difficulty in evaluating the experimental mechanical properties at the different organizational levels of the same tissue. Indeed, the ability to integrate mechanical properties evaluated at various levels will allow for improved assessment of the entire tissue, leading to a better understanding of how changes at each level evolve over time and/or impact tissue function, especially in the case of muscle diseases.Therefore, the purpose of this study was to analyze a genetically engineered mouse model (Klf10 KO: Krüppel-Like Factor 10 knockout) with known skeletal muscle defects to compare the mechanical properties with wild-type (WT) controls at the three main muscle scales: the macroscopic (whole muscle), microscopic (fiber) and submicron (myofibril) levels. Passive mechanical tests (ramp, relaxation) were performed on two types of skeletal muscle (soleus and extensor digitorum longus (EDL)).Results of the present study revealed muscle-type specific behaviors in both genotypes only at the microscopic scale. Interestingly, loss of Klf10 expression resulted in increased passive properties in the soleus but decreased passive properties in the EDL compared to WT controls.At the submicron scale, no changes were observed between WT and Klf10 KO myofibrils for either muscle; these results demonstrate that the passive property differences observed at the microscopic scale (fiber) are not caused by sarcomere intrinsic alterations but instead must originate outside the sarcomeres, likely in the collagen-based extracellular matrix. The macroscopic scale revealed similar passive mechanical properties between WT and Klf10 KO hindlimb muscles.The present study has allowed for a better understanding of the role of Klf10 on the passive mechanical properties of skeletal muscle and has provided reference data to the literature which could be used by the community for muscle multiscale modeling.

Ultra-Large Compressive Plasticity of E-Ga2O3 Thin Films at the Submicron Scale.

Gallium oxide (Ga2O3) usually fractures in the brittle form, and achieving large plastic deformability to avoid catastrophic failure is in high demand. Here, ε-Ga2O3 thin films with columnar crystals and partial unoccupied Ga sites are synthesized, and it is demonstrated that the ε-Ga2O3 at the submicron scale can be compressed to an ultra-large plastic strain of 48.5% without cracking. The compressive behavior and related mechanisms are investigated by in situ transmission electron microscope nanomechanical testing combined with atomic-resolution characterizations. The serrated plastic flow and large strain burst are two major deformation forms of ε-Ga2O3 during compression, which are attributed to the dislocation nucleation and avalanches, formation of new grains, and amorphization. The ultra-large compressive plasticity of ε-Ga2O3 thin films at the submicron scale can inspire new applications of Ga2O3 in micro- or nano- electronic and optoelectronic devices, especially those that require impact resistance during processing or service.

Ultrahigh Strength and Plasticity Mechanisms of Si and SiC Nanoparticles Revealed by First-Principles Molecular Dynamics.

It is now well established that materials are stronger when their dimensions are reduced to the submicron scale. However, what happens at dimensions such as a few tens of nanometers or lower remains largely unknown, with conflicting reports on strength or plasticity mechanisms. Here, we combined first-principles molecular dynamics and classical force fields to investigate the mechanical properties of 1-2nm Si and SiC nanoparticles. These compression simulations unambiguously reveal that the strength continues to increase down to such sizes, and that in these systems the theoretical bulk strength can be reached or even exceeded in some cases. Most of the nanoparticles yield by amorphization at strains greater than 20%, with no evidence of the β-tin phase for Si. Original and unexpected mechanisms are also identified, such as the homogeneous formation of a dislocation loop embryo for the ⟨111⟩ compression of SiC nanoparticles, and an elastic softening for the ⟨001⟩ compression of Si nanoparticles.

The Effect of Conductive Additive Morphology and Crystallinity on the Electrochemical Performance of Ni-Rich Cathodes for Sulfide All-Solid-State Lithium-Ion Batteries

Sulfide electrolyte all-solid-state lithium-ion batteries (ASSLBs) that have inherently nonflammable properties have improved greatly over the past decade. However, determining both the stable and functional electrode components to pair with these solid electrolytes requires significant investigation. Solid electrolyte comprises 20–40% of the composite cathode electrode, which improves the ionic conductivity. However, this results in thick electrolyte that blocks the electron pathways in the electrode, significantly lowering the electrochemical performance. The application of conductive carbon material is required to overcome this issue, and, hence, determining the carbon properties that result in the most stable performance in the sulfide solid electrolyte is vital. This study analyzes the effect of the cathode conductive additive’s morphology on the electrochemical performance of sulfide electrolyte-based ASSLBs. Carbon black (CB) and carbon nanotubes (CNTs), which provide electron pathways at the nanoscale and sub-micron scale, and carbon nanofiber (CNF), which provides electron pathways at the tens-of-microns scale, are all tested individually as potential conductive additives. When the CNF, with its high crystallinity, is used as a conductive material, the electrochemical performance shows an excellent initial discharge capacity of 191.78 mAh/g and a 50-cycle capacity retention of 83.9%. Conversely, the CB and the CNTs, with their shorter pathways and significantly increased surface area, show a relatively low electrochemical performance. By using the CNF to provide excellent electrical conductivity to the electrode, the polarization is suppressed. Furthermore, the interfacial impedance across the charge transfer region is also reduced over 50 cycles compared with the CB and CNT composite cells. These findings stringently analyze and emphasize the importance of the morphology of the carbon conductive additives in the ASSLB cathode electrodes, with improvements in the electrochemical performance being realized through the application of long-form two-dimensional crystalline CNFs.

Communication—Monoatomic Amorphous Metals via Electrochemical Discharge Reduction

Monoatomic amorphous metals (MAM) are highly desirable for gaining fundamental understandings of amorphous metals. To date, only a handful of metals have been successfully made into MAMs, which, however, are either limited to very small yields/sample sizes (e.g., 10 nm) or highly unstable at ambient conditions. Here we report a simple and effective solution-based anodization method for synthesizing MAMs by rapidly reducing the corresponding metal ions during the discharge approach. MAMs are conveniently produced at a large quantity with a diameter up to the sub-micron scale, representing a drastically enhanced sample volume, opening new possibilities for the research of amorphous metals.

Bandgap and its defect band analysis of flexoelectric effect in phononic crystal plates

The wave equations of a novel model for the electro-elastic Kirchhoff plate containing the flexoelectric effect are constructed using a variational formulation. Through an Improved Plane Wave Expansion (IPWE) approach, the proposed wave equations are then applied to examine the elastic wave bandgap and defect band in a phononic crystal plate structure without or with a defect. The results demonstrate that the flexoelectric effect on the bandgap is apparent when the structure is at the submicron scale and fades as the scale increases. Moreover, at all length scales, the magnitude of the bandgap varies dramatically with lattice length and inclusion volume ratio. This suggests that the frequency and broadness of the bandgap can be tuned by modifying the volume percentage of inclusion, plate size parameters and lattice length. The dispersion curves of the defect model and corresponding mode shape at the defect band are also studied, which can indicate the applicability of the current model incorporating flexoelectric effect in energy harvesting and wave focusing. The novel model and these findings would help the design of MEMS/NEMS devices for enhanced wave guiding when flexoelectric-based electro-elastic fields are involved.

Multiple shearing induced in one-step deformation fabricating gradient-structured aluminium disks

Repeated deformation or extended time is generally required in producing ultrafine grained structures, while this applies equally to forming gradient structures with ultrafine grains, which have been developed to evade the strength-ductility trade-off in recent years. This paper reports multiple shearing assisted fabrication of gradient-structured (GS) aluminium disks involving ultrafine grain formation in one step through a new process, called radial extrusion machining (REM). Finite element analysis and microstructural observations revealed that REM introduced multiple shearing, which provided hierarchical combinations of shear effects of different origins, intensities, and ranges of influence, resulting in a structural gradient across the disk thickness. The fabricated GS disks exhibited significant refinement of grains from ∼100 µm to submicron scale in the large-strained layers, which is attributable to the promoted multiple shearing. It was demonstrated that the grain refinement process is accelerated with the evolution of mutually crossing deformation or microshear bands introduced by multiple shearing. The operating structural mechanisms responsible for the dynamic formation of new grains were discussed in detail. This study provides a feasible method to fabricate GS disks with ultrafine grains formed in a straightforward and time-efficient way, and offers insights and guidance to develop new processes by introducing multiple shearing.

New thermometer measures cryogenic temperatures at submicron scales

New thermometer measures cryogenic temperatures at submicron scales

Multimodal Three-Dimensional Printing for Micro-Modulation of Scaffold Stiffness Through Machine Learning.

The ability to precisely control a scaffold's microstructure and geometry with light-based three-dimensional (3D) printing has been widely demonstrated. However, the modulation of scaffold's mechanical properties through prescribed printing parameters is still underexplored. This study demonstrates a novel 3D-printing workflow to create a complex, elastomeric scaffold with precision-engineered stiffness control by utilizing machine learning. Various printing parameters, including the exposure time, light intensity, printing infill, laser pump current, and printing speed were modulated to print poly (glycerol sebacate) acrylate (PGSA) scaffolds with mechanical properties ranging from 49.3 ± 3.3 kPa to 2.8 ± 0.3 MPa. This enables flexibility in spatial stiffness modulation in addition to high-resolution scaffold fabrication. Then, a neural network-based machine learning model was developed and validated to optimize printing parameters to yield scaffolds with user-defined stiffness modulation for two different vat photopolymerization methods: a digital light processing (DLP)-based 3D printer was utilized to rapidly fabricate stiffness-modulated scaffolds with features on the hundreds of micron scale and a two-photon polymerization (2PP) 3D printer was utilized to print fine structures on the submicron scale. A novel 3D-printing workflow was designed to utilize both DLP-based and 2PP 3D printers to create multiscale scaffolds with precision-tuned stiffness control over both gross and fine geometric features. The described workflow can be used to fabricate scaffolds for a variety of tissue engineering applications, specifically for interfacial tissue engineering for which adjacent tissues possess heterogeneous mechanical properties (e.g., muscle-tendon).

Effect of a novel controlled thermomechanical treatment on the microstructure and mechanical properties of a high-carbon nanobainitic steel

The effect of the novel controlled thermomechanical treatment, including torsion components in the elastic strain range during the isothermal holding on the microstructure and mechanical properties of the high-carbon nanobainitic steel, was investigated. TEM observations of the thermo-mechanically treated steel revealed bainitic ferrite laths with an average size of 68 ± 40 nm and films of retained austenite with an average size of 34 ± 17 nm, along with the blocky morphology of retained austenite in sub-micron scale. The XRD synchrotron diffraction allows estimating the amount of retained austenite at 43.1 ± 1.2% volume fraction with a carbon concentration of 1.17 ± 0.09 wt.%. Furthermore, the deconvolution of (200) Fe-γ reflections corresponding to two different low-carbon and high-carbon retained austenite peaks and, simultaneously, the blocky and film-like retained austenite was performed. In addition, the Nishiyama–Wassermann (N–W) crystallographic orientation relationship between bainitic ferrite and retained austenite was described as dominant using the misorientation distribution function (MDF). The crystallographic texture results indicated that the main growth of bainitic ferrite plates occurred after removing external stress during isothermal holding. The tensile tests and hardness measurements showed a high tensile strength achieved mainly by nano-metric bainitic ferrite plates and a high dislocation density. The high level of elongation is most likely attained due to a high amount of retained austenite in steel and both TRIP and TWIP effects during tensile deformation.

Genesis of Devonian volcanic-associated Lahn-Dill-type iron ores — part I: iron mobilisation and mineralisation style

Fe-oxide deposits of the Lahn-Dill-type in the eastern Rhenish Massif comprise haematite and quartz with minor siderite, magnetite, and calcite. The deposits are located in the hanging wall of thick volcaniclastic rock sequences and mark the Middle to Late Devonian boundary. Varying ore types with accompanying footwall rocks were sampled from two formerly important ore deposits, the Fortuna mine (Lahn syncline) and the Briloner Eisenberg mine (East Sauerland anticline), in order to elucidate the interplay of processes leading to ore formation. Deposit geology, petrography, and whole-rock geochemistry suggest that the ores formed by iron mobilisation from deeply altered footwall volcaniclastic rocks, subsequent venting of a modified H2O-CO2-Fe-rich and H2S-poor fluid, and precipitation on the seafloor (sedimentary-type), or locally by metasomatic replacement of wall rocks (replacement-type). Petrographic analysis to the sub-micron scale revealed that the sedimentary-type ores most likely formed from a Fe-Si-rich gel and accompanying maturation. Early gel textures include the presence of spherules, aggregates, tubes, and filamentous stalks consisting of nanocrystalline haematite dispersed in a matrix of microcrystalline quartz. Local diagenetic Fe3+ reduction within the gel is indicated by siderite replacement of haematite. Replacement-type ores formed due to a two-step process including coprecipitation of (precursor) haematite and carbonates and subsequent metasomatic replacement by haematite. These ore-forming processes took place during a time when several restricted shallow marine basins in the north-eastern Rheic Ocean were influenced by extensive volcanism and associated hydrothermal fluid flux. Examples of similar volcanic-associated Fe-oxide occurrences of Silurian to Carboniferous age can be categorised as being of Lahn-Dill-type ores as well.

A Review On Electrospun Short Fiber Production

Nanotechnology has become the interest of researchers in recent years for their unique properties of submicron scale materials. Nanotechnology also consists of nanofibers made from natural or synthetic polymers which can be electrospun into ultra-thin continuous fibers. These nanofibers are versatile as it can be found in various applications such as in filtration, affinity membranes, tissue engineering, biosensors, scaffolds, drug delivery and fiber reinforcement. Over the years, many researchers have reported various methods used to produce short electrospun fiber by means of ultrasonication, mechanical cutting, UV cutting, precipitation method, microtome cutting, cryo-microcutting, cryogenic milling, ball milling, and razor blade cutting under liquid nitrogen. The aim of this paper is to provide a review on electrospun short fiber production which elaborates more on the scission methods of the continuous as-spun fibers. The literature shows that several methods have been proposed and utilized, with varying degrees of success. Overall, it can be concluded that further research is needed to fully understand the complexities of this area and to develop a more effective approach.

Shadow imaging for panoptical visualization of brain tissue in vivo

Progress in neuroscience research hinges on technical advances in visualizing living brain tissue with high fidelity and facility. Current neuroanatomical imaging approaches either require tissue fixation (electron microscopy), do not have cellular resolution (magnetic resonance imaging) or only give a fragmented view (fluorescence microscopy). Here, we show how regular light microscopy together with fluorescence labeling of the interstitial fluid in the extracellular space provide comprehensive optical access in real-time to the anatomical complexity and dynamics of living brain tissue at submicron scale. Using several common fluorescence microscopy modalities (confocal, light-sheet and 2-photon microscopy) in mouse organotypic and acute brain slices and the intact mouse brain in vivo, we demonstrate the value of this straightforward ‘shadow imaging’ approach by revealing neurons, microglia, tumor cells and blood capillaries together with their complete anatomical tissue contexts. In addition, we provide quantifications of perivascular spaces and the volume fraction of the extracellular space of brain tissue in vivo.

X-ray multi-scale microfabrication system and x-ray imaging evaluation system all in one beamline

We have completed a system that can achieve both deep x-ray lithography and submicron x-ray lithography with a single beamline by introducing the combination of x-ray plane and cylindrical mirrors. This x-ray lithography system can provide a large-scale microfabrication processing with 210 × 300 mm2 (A4 size). To exploit multiscale lithography, the beamline has a beam transport vacuum duct with a two-stage stacked structure and a 5-axis stage. This two-stage stacked structure allows us to fabricate both micron scale structures with high aspect ratios and submicron scale structures using the same beamline. In addition, x-ray imaging and computer tomography (CT) system are connected to the x-ray lithography system for nondestructive inspection and evaluation of the fabricated microstructures. The x-ray imaging system constructed this study has a relatively low energy range of x-ray energy in the beamline, which is in the range of 2–15 keV or less. Therefore, relatively good absorption contrast can be obtained for plastic materials, biomaterials, and the like. Since nondestructive imaging of the processed shape by x-ray lithography is possible, it is a very useful system in processing and evaluation can be performed simultaneously. This system also enables us to obtain the live images with keeping the creature alive in liquid using an indirect x-ray imaging system which converts x-ray images to visible light images through the fluorescent plate.

Application of Optical Photothermal Infrared (O-PTIR) Spectroscopy for Assessment of Bone Composition at the Submicron Scale.

The molecular basis of bone structure and strength is mineralized collagen fibrils at the submicron scale (∼500 nm). Recent advances in optical photothermal infrared (O-PTIR) spectroscopy allow the investigation of bone composition with unprecedented submicron spatial resolution, which may provide new insights into factors contributing to underlying bone function. Here, we investigated (i) whether O-PTIR-derived spectral parameters correlated to standard attenuated total reflection (ATR) Fourier transform infrared spectroscopy spectral data and (ii) whether O-PTIR-derived spectral parameters, including heterogeneity of tissue, contribute to the prediction of proximal femoral bone stiffness. Analysis of serially demineralized bone powders showed a significant correlation (r = 0.96) between mineral content quantified using ATR and O-PTIR spectroscopy, indicating the validity of this technique in assessing bone mineralization. Using femoral neck sections, the principal component analysis showed that differences between O-PTIR and ATR spectra were primarily attributable to the phosphate ion (PO4) absorbance band, which was typically shifter toward higher wavenumbers in O-PTIR spectra. Additionally, significant correlations were found between hydrogen phosphate (HPO4) content (r = 0.75) and carbonate (CO3) content (r = 0.66) quantified using ATR and O-PTIR spectroscopy, strengthening the validity of this method to assess bone mineral composition. O-PTIR imaging of individual trabeculae at 500 nm pixel resolution illustrated differences in submicron composition in the femoral neck from bones with different stiffness. O-PTIR analysis showed a significant negative correlation (r = -0.71) between bone stiffness and mineral maturity, reflective of newly formed bone being an important contributor to bone function. Finally, partial least squares regression analysis showed that combining multiple O-PTIR parameters (HPO4 content and heterogeneity, collagen integrity, and CO3 content) could significantly predict proximal femoral stiffness (R2 = 0.74, error = 9.7%) more accurately than using ATR parameters. Additionally, we describe new findings in the effects of bone tissue orientation in the O-PTIR spectra. Overall, this study highlights a new application of O-PTIR spectroscopy that may provide new insights into molecular-level factors underlying bone mechanical competence.

Non-Local Q-Tensor Approach for Description of Elastic Deformations of Nematic Liquid Crystals at Sub-Micron Scale

Within the framework of phenomenological approach, a generalized concept of a non-local order parameter, that have the form of a traceless correlation tensor function or a tensor integral operator, is introduced. The main relationships, which determine the equilibrium orientational states and the phase transitions of a deformed nematic liquid crystal, are described. The resulting expression for the free energy is quadratic with respect to the gradients of the order parameter tensor. The limiting transition of the non-local order parameter to the local one leads to an expression that complements the classical Oseen–Frank theory of elasticity. The considered model includes eight independent elastic constants. Three of them relate to "bulk" constants analogous to Frank constants, another three ones relate to "surface" constants, and the remaining two constants determine the anisotropic effect of the gradient of the scalar order parameter on the director field. The constants are necessary for the consideration of a liquid crystal state near defects, as well as for the description of orientation effects caused by the inhomogeneity of order parameter. It is shown that in the free energy expression, the "surface" terms contribute to the director orientation in the case of a non-constant scalar order parameter, even in the approximation of rigid boundary conditions.

Difference in carcinogenicities of two different vapor grown carbon fibers with different physicochemical characteristics induced by intratracheal instillation in rats

BackgroundCarbon fibers are high aspect ratio structures with diameters on the submicron scale. Vapor grown carbon fibers are contained within multi-walled carbon tubes, with VGCF™-H commonly applied as a conductive additive in lithium-ion batteries. However, several multi-walled carbon fibers, including MWNT-7, have been reported to induce lung carcinogenicity in rats. This study investigated the carcinogenic potential of VGCF™-H fibers in F344 rats of both sexes with the vapor grown carbon fibers VGCF™-H and MWNT-7 over 2 years. The carbon fibers were administered to rats by intratracheal instillation at doses of 0, 0.016, 0.08, and 0.4 mg/kg (total doses of 0, 0.128, 0.64, and 3.2 mg/kg) once per week for eight weeks and the rats were observed for up to 2 years after the first instillation.ResultsHistopathological examination showed the induction of malignant mesothelioma on the pleural cavity with dose-dependent increases observed at 0, 0.128, 0.64, and 3.2 mg/kg in rats of both sexes that were exposed to MWNT-7. On the other hand, only two cases of pleural malignant mesothelioma were observed in the VGCF™-H groups; both rats that received 3.2 mg/kg in male. The animals in the MWNT-7 groups either died or became moribund earlier than those in the VGCF™-H groups, which is thought related to the development of malignant mesothelioma. The survival rates were higher in the VGCF™-H group, and more carbon fibers were observed in the pleural lavage fluid (PLF) of the MWNT-7 groups. These results suggest that malignant mesothelioma is related to the transfer of carbon fibers into the pleural cavity.ConclusionsThe intratracheal instillation of MWNT-7 clearly led to carcinogenicity in both male and female rats at all doses. The equivocal evidence for carcinogenic potential that was observed in male rats exposed to VGCF™-H was not seen in the females. The differences in the carcinogenicities of the two types of carbon fibers are thought due to differences in the number of carbon fibers reaching the pleural cavity. The results indicate that the carcinogenic activity of VGCF™-H is lower than that of MWNT-7.