An improved dispersion method of multi-wall carbon nanotube for inhalation toxicity studies of experimental animals

• Published in: Journal of toxicological sciences Vol. 38; no. 4; pp. 619 - 628
• Main Authors: Taquahashi, Yuhji, Ogawa, Yukio, Takagi, Atsuya, Tsuji, Masaki, Morita, Koichi, Kanno, Jun
• Format: Journal Article
• Language: English
• Published: Japan The Japanese Society of Toxicology 2013; Japan Science and Technology Agency
• Subjects: Administration, Inhalation; Aerosols; Agglutination; Animals; Atmosphere Exposure Chambers; Critical point drying; Dispersion; Filtration; Freeze Drying; Humans; Inhalation Exposure; Metallic sieve; Mice; Multi-wall carbon nanotube; Nanotechnology - methods; Nanotubes, Carbon - toxicity; Particle Size; Sublimation; Tert-butyl alcohol
• ISSN: 0388-1350; 1880-3989
• DOI: 10.2131/jts.38.619

A multi-wall carbon nanotube (MWCNT) product Mitsui MWNT-7 is a mixture of dispersed single fibers and their agglomerates/aggregates. In rodents, installation of such mixture induces inflammatory lesions triggered predominantly by the aggregates/agglomerates at the level of terminal bronchiole of the lungs. In human, however, pulmonary toxicity induced by dispersed single fibers that reached the lung alveoli is most important to assess. Therefore, a method to generate aerosol predominantly consisting of dispersed single fibers without changing their length and width is needed for inhalation studies. Here, we report a method (designated as Taquann method) to effectively remove the aggregate/agglomerates and enrich the well-dispersed singler fibers in dry state without dispersant and without changing the length and width distribution of the single fibers. This method is base on two major concept; liquid-phase fine filtration and critical point drying to avoid re-aggregation by surface tension. MWNT-7 was suspended in Tert-butyl alcohol, freeze-and-thawed, filtered by a vibrating 25 µm mesh Metallic Sieve, snap-frozen by liquid nitrogen, and vacuum-sublimated (an alternative method to carbon dioxide critical point drying). A newly designed direct injection system generated well-dispersed aerosol in an inhalation chamber. The lung of mice exposed to the aerosol contained single fibers with a length distribution similar to the original and the Taquann-treated sample. Taquann method utilizes inexpensive materials and equipments mostly found in common biological laboratories, and prepares dry powder ready to make well-dispersed aerosol. This method and the chamber with direct injection system would facilitate the inhalation toxicity studies more relevant to human exposure.