Long-term retention of pristine multi-walled carbon nanotubes in rat lungs after intratracheal instillation.

As a result of the growing potential industrial and medical applications of multi-walled carbon nanotubes (MWCNTs), people working in or residing near facilities that manufacture them may be exposed to airborne MWCNTs in the future. Because of concerns regarding their toxicity, quantitative data on the long-term clearance of pristine MWCNTs from the lungs are required. We administered pristine MWCNTs well dispersed in 0.5 mg ml(-1) Triton-X solution to rats at doses of 0.20 or 0.55 mg via intratracheal instillation and investigated clearance over a 12-month observation period. The pristine MWCNTs pulmonary burden was determined 1, 3, 7, 28, 91, 175 and 364 days after instillation using a method involving combustive oxidation and infrared analysis, combined with acid digestion and heat pretreatment. As 0.15- and 0.38-mg MWCNTs were detected 1 day after administration of 0.20 and 0.55 mg MWCNTs, respectively, approximately 30% of administrated MWCNTs may have been cleared by bronchial ciliary motion within 24 h of administration. After that, the pulmonary MWCNT burden did not decrease significantly over time for up to 364 days after instillation, suggesting that MWCNTs were not readily cleared from the lung. Transmission electron microscopy (TEM) showed that alveolar macrophages internalized the MWCNTs and retained in the lung for at least 364 days after instillation. MWCNTs were not detected in the liver or brain within the 364-day study period (<0.04 mg per liver, < 0.006 mg per brain).

A determination method of pristine multiwall carbon nanotubes in rat lungs after intratracheal instillation exposure by combustive oxidation-nondispersive infrared analysis.

This paper describes a method for determination of multiwall carbon nanotubes (MWCNTs) in rat lungs after intratracheal instillation exposure. The MWCNTs were quantitatively decomposed to CO(2) by combustive oxidation and were then determined by non-dispersive infrared analysis. Samples were pretreated by acid digestion, muffle ashing and in situ preheating to remove interferences due to coexisting biological carbon from the lung tissue sample, while preserving the MWCNTs as in its their original form. The preservation was confirmed by transmission electron microscopic observation of the pretreated samples of exposed lung tissues and by the fact that the recoveries of MWCNTs spiked to the lung tissues were close to 100%. The detection limit for MWCNTs obtained by the proposed method was 0.30 µg and the repeatability as expressed by the relative standard deviation was 5.6% (n=4). The method was sufficiently sensitive and precise to apply to real samples of rat lung to investigate the in vivo persistence of intratracheally instilled MWCNTs. To our knowledge, this is the first report of this type of sample pretreatment and direct determination of pristine MWCNTs without modification or tagging. Conventional indirect methods use tagging with other compounds or metal impurities in the CNTs for detection, and the detachment of these tags can increase uncertainties in the determination of the CNTs. The tags can also change how the CNTs persist in vivo, which can lead to an incorrect understanding of the persistence of pristine CNTs in vivo.

Clearance kinetics of fullerene C60 nanoparticles from rat lungs after intratracheal C60 instillation and inhalation C60 exposure.

Fullerene (carbon sixty [C(60)]) has potential industrial and medical applications. In the future, people working in or residing near manufacturing facilities may be exposed to C(60). Therefore, quantitative data on long-term C(60) clearance from the lungs are required. To estimate the clearance rate and deposition fraction of C(60) from inhalation exposure, the C(60) burden in the lungs, liver, and brain of rats was determined after intratracheal instillation and inhalation. Male Wistar rats were intratracheally instilled with different concentrations of a C(60) suspension prepared with Tween 80 (geometric mean [GM] of particle diameter based on number, 18-29 nm; geometric standard deviation [GSD] of particle diameter, 1.5; and doses, 100, 200, and 1000 micrograms per body) or exposed to a C(60) aerosol prepared with nebulizer (GM of particle diameter based on number, 96 nm; GSD of particle diameter, 2.0; and exposure level, 120 µg/m(3)). C(60) burden in the lungs, liver, and brain was determined at various time points (1 h to 6 months) by a newly developed sensitive high-performance liquid chromatography-ultraviolet absorptiometry combined with extraction and concentration of C(60) from the organs. C(60) clearance was evaluated using a 2-compartment model: fast clearance after deposition on lung surface and slow clearance after retention in the epithelium. The detection limit of our analysis method was 8.9 ng/g tissue. Pulmonary C(60) burden decreased with time and depended on the C(60) concentration administered. The concentration of C(60) in the liver and brain was below the detection limit: 8.9 ng/g tissue. The half-life of intratracheally instilled C(60) was 15-28 days. The deposition mass fraction of inhaled C(60) was 0.14. Mode evaluation revealed that most instilled particles could be eliminated by the fast clearance pathway. This finding is consistent with the transmission electron microscopy finding that many particles were present in alveolar macrophages.

Magnetic alignment of the chiral nematic phase of a cellulose microfibril suspension.

Stable suspensions of tunicate cellulose microfibrils were prepared by acid hydrolysis of the cellulosic mantles of tunicin. They formed a chiral nematic phase above a critical concentration. External magnetic fields were applied to the chiral nematic phase in two different manners to control its phase structure. (i) Static magnetic fields ranging 1-28 T were used to align the chiral nematic axis (helical axis) in the field direction. (ii) A rotating magnetic field (5 T, 10 rpm) was applied to unwind the helices and to form a nematic phase. These phenomena were interpreted in terms of the anisotropic diamagnetic susceptibility of the cellulose microfibril. The diamagnetic susceptibility of the microfibril is smaller in the direction parallel (chi( parallel)) to the fiber axis than in the direction perpendicular (chi( perpendicular)) to the fiber axis, that is, chi( parallel) < chi( perpendicular) < 0. Because the helical axis coincides with the direction normal ( perpendicular) to the fiber axis, the helical axis aligned parallel to the applied field. On the other hand, the rotating magnetic field induced the uniaxial alignment of the smallest susceptibility axis, that is, chi( parallel) in the present case, and brought about unwinding of the helices.