Simultaneously enhanced tenacity, rupture work, and thermal conductivity of carbon nanotube fibers by raising effective tube portion

Although individual carbon nanotubes (CNTs) are superior to polymer chains, the mechanical and thermal properties of CNT fibers (CNTFs) remain inferior to synthetic fibers because of the failure of embedding CNTs effectively in superstructures. Conventional techniques resulted in a mild improvement of target properties while degrading others. Here, a double-drawing technique is developed to rearrange the constituent CNTs. Consequently, the mechanical and thermal properties of the resulting CNTFs can simultaneously reach their highest performances with specific strength ~3.30 N tex-1 (4.60 GPa), work of rupture ~70 J g-1, and thermal conductivity ~354 W m-1 K-1 despite starting from low-crystallinity materials (IG:ID ~ 5). The processed CNTFs are more versatile than comparable carbon fiber, Zylon and Dyneema. On the basis of evidence of load transfer efficiency on individual CNTs measured with in situ stretching Raman, we find that the main contributors to property enhancements are the increasing of the effective tube contribution.

Highly Oriented Direct-Spun Carbon Nanotube Textiles Aligned by In Situ Radio-Frequency Fields

Carbon nanotubes (CNTs) individually exhibit exceptional physical properties, surpassing state-of-the-art bulk materials, but are used commercially primarily as additives rather than as a standalone macroscopic product. This limited use of bulk CNT materials results from the inability to harness the superb nanoscale properties of individual CNTs into macroscopic materials. CNT alignment within a textile has been proven as a critical contributor to narrow this gap. Here, we report the development of an altered direct CNT spinning method based on the floating catalyst chemical vapor deposition process, which directly interacts with the self-assembly of the CNT bundles in the gas phase. The setup is designed to apply an AC electric field to continuously align the CNTs in situ during the formation of CNT bundles and subsequent aerogel. A mesoscale CNT model developed to simulate the alignment process has shed light on the need to employ AC rather than DC fields based on a CNT stiffening effect (z-pinch) induced by a Lorentz force. The AC-aligned synthesis enables a means to control CNT bundle diameters, which broadened from 16 to 25 nm. The resulting bulk CNT textiles demonstrated an increase in the specific electrical and tensile properties (up to 90 and 460%, respectively) without modifying the quantity or quality of the CNTs, as verified by thermogravimetric analysis and Raman spectroscopy, respectively. The enhanced properties were correlated to the degree of CNT alignment within the textile as quantified by small-angle X-ray scattering and scanning electron microscopy image analysis. Clear alignment (orientational order parameter = 0.5) was achieved relative to the pristine material (orientational order parameter = 0.19) at applied field intensities in the range of 0.5-1 kV cm^-1 at a frequency of 13.56 MHz.

Effects of Low- and High-Dose Chemotherapy Agents on Thrombogenic Properties of Extracellular Vesicles Derived from Breast Cancer Cell Lines

BACKGROUND

The involvement of extracellular vesicles (EVs) in cancer-associated thrombosis (CT) is unclear. This study aimed to explore the properties of EVs derived from breast cancer (BC) cells following exposure to high- or low-dose chemotherapeutic agents and evaluate thrombogenic effects of these EVs on endothelial cells (ECs).

METHODS

EVs were isolated from BC cell lines (non-metastatic MCF7, high-metastatic MDA-MB-231), pre-exposed to serum-free medium (control), with or without increasing doses of doxorubicin or paclitaxel. EV structure and size were studied using electron microscopy and Nano-sight. Antigen levels were measured by fluorescence-activated cell sorting (FACS). EV effects on EC thrombogenicity were assessed using FACS, factor Xa chromogenic assay and RT-PCR.

RESULTS

Serum-free medium BC cell resulted in EV shedding that additionally increased when MDA-MB-231 cells were exposed to high doses of both agents. Tissue factor (TF) levels were similarly low (9-13%) in all EVs compared with the high expression on their parental MDA-MB-231 cells (76-83%). EVs derived from MDA-MB-231 cells stimulated with high-dose doxorubicin demonstrated significantly (fivefold; p < 0.001) elevated levels of negatively charged phospholipids, a 97% decrease in TF pathway inhibitor (TFPI) levels and a sixfold increase (p < 0.001) in procoagulant activity. These EVs also enhanced EC thrombogenicity. Effects of EVs originating from MCF7 cells were less pronounced.

CONCLUSION

These findings suggest that thrombogenic properties of BC-derived EVs may depend on the type and dose of the applied chemotherapy agent and may also be affected by the cell metastatic nature.

Plant cell piercing by a predatory mite: evidence and implications

Omnivorous arthropods can play an important role as beneficial natural enemies because they can sustain their populations on plants when prey is scarce, thereby providing prophylactic protection against an array of herbivores. Although some omnivorous mite species of the family Phytoseiidae consume plant cell-sap, the feeding mechanism and its influence on the plant are not known. Using scanning electron microscopy we demonstrated that the omnivorous predatory mite Euseius scutalis penetrates epidermal cells of pepper foliage and wax membranes. Penetration holes were teardrop shape to oval, of 2-5 µm diameter. The similarities between penetration holes in pollen grains and in epidermal cells implied that the same penetration mechanism is used for pollen feeding and plant cell-sap uptake. Variation in shape and size of penetration holes in leaves and a wax membrane were attributed to different mite life stages, depth of penetration or the number of chelicerae puncturing (one or both). Punctured stomata, epidermal and vein cells appeared flat and lacking turgor. When the mite penetrated and damaged a single cell, neighboring cells were most often intact. In a growth chamber experiment very large numbers of E. scutalis negatively affected the growth of young pepper plants. Consequently caution should be taken when applying cell-piercing predators to young plants. Further studies are needed to take advantage of the potential sustainability of plant cell-sap feeding predators.

Cryogenic transmission electron microscopy nanostructural study of shed microparticles

Microparticles (MPs) are sub-micron membrane vesicles (100–1000 nm) shed from normal and pathologic cells due to stimulation or apoptosis. MPs can be found in the peripheral blood circulation of healthy individuals, whereas elevated concentrations are found in pregnancy and in a variety of diseases. Also, MPs participate in physiological processes, e.g., coagulation, inflammation, and angiogenesis. Since their clinical properties are important, we have developed a new methodology based on nano-imaging that provides significant new data on MPs nanostructure, their composition and function. We are among the first to characterize by direct-imaging cryogenic transmitting electron microscopy (cryo-TEM) the near-to-native nanostructure of MP systems isolated from different cell types and stimulation procedures. We found that there are no major differences between the MP systems we have studied, as most particles were spherical, with diameters from 200 to 400 nm. However, each MP population is very heterogeneous, showing diverse morphologies. We investigated by cryo-TEM the effects of standard techniques used to isolate and store MPs, and found that either high-g centrifugation of MPs for isolation purposes, or slow freezing to –80°C for storage introduce morphological artifacts, which can influence MP nanostructure, and thus affect the efficiency of these particles as future diagnostic tools.

Cryo-SEM specimen preparation under controlled temperature and concentration conditions

Cryogenic temperature scanning electron microscopy (cryo-SEM) is an excellent technique for imaging liquid and semi-liquid materials of high vapour pressure, which are highly viscous or contain large (>0.5 μm) aggregates, in which nanometric details are to be studied. However, so far there have been no adequate tools for controlled cryo-specimen preparation. The specimen preparation stage is critical, because most of those samples are very sensitive to concentration and temperature changes, leading to nanostructural artefacts in the specimens. We designed and built a system for easy and reliable cryo-SEM specimen preparation under controlled conditions of fixed temperature and humidity. We describe this new methodology, and demonstrate its applicability, by showing imaging data of three liquid material systems. We have studied carbon nanotubes (CNTs) dispersions in superacid. We also characterized a number of systems made of water/isooctane/nonionic and cationic surfactant that showed different microemulsion phases as function of the system composition and temperature. In all of the examples given, we demonstrate artefact- and contamination-free specimens, which have preserved their native nanostructure. Our new system paves the way for a new methodology for the newly emerging field of cryo-SEM.