Polymer coating on carbon nanotubes into Durobeads is a novel strategy for human environmental safety

Our plain-English summary of Polymer coating on carbon nanotubes into Durobeads is a novel strategy for human environmental safety, by F. Ito, H. Hisashi, S. Toyokuni (Nagoya Journal of Medical Science, 2018).

The study

• Authors: F. Ito, H. Hisashi, S. Toyokuni
• Journal: Nagoya Journal of Medical Science
• Published: 2018;80(4):597-604
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Carbon nanotubes (CNTs) have attracted much business interest in industrial applications due to their high electrical and heat conductivities while being both durable and versatile. However, multiwall CNTs (MWCNTs) of ~50 nm diameter (NT50) have been shown to cause mesothelioma in rodents after direct exposure to mesothelial cells, and thus were classified as a Group 2B carcinogen to humans, which requires considerable regulations for use. In contrast, tangled MWCNTs of ~15 nm diameter (NTtngl) are not carcinogenic to rats, indicating that the physical dimension linked with mesothelial cellular uptake is an important factor for human environmental risk. In the present study, hypothesizing that dustability is another distinct risk factor, for the first time, we evaluated the toxicity of CNT granules (Durobeads) that were generated with a polymer coating to mesothelial cells. Polymer coating induced prominent agglomeration and significantly suppressed the dustability of CNTs in a dose-dependent manner, with a 10% polymer coating resulting in 730 times less dustability. These CNT granules revealed significantly lower mesothelial uptake and cytotoxicity in comparison to NT50 in in vitro assays. Similarly, in in vivo analyses, CNT granules induced limited peritoneal inflammation 4 weeks after intraperitoneal injection, whereas NT50 caused severe fibrosing inflammation. Previously, we demonstrated that the severity of inflammation by intraperitoneal injection in the subacute studies are in agreement with the mesothelial carcinogenicity by CNTs. Therefore, we suggest that adding a polymer coating to CNTs provides another smart strategy for the safe use of CNTs.

In plain English

This laboratory and animal study examined carbon nanotubes, not asbestos. Asbestos appears only as background. From multiwall carbon nanotubes (K-Nanos 100P, 7 to 23 nm in diameter), the authors made millimeter-sized granules called Durobeads, coated with 6%, 10% or 20% of an olefin-based polymer, and also granules made with no polymer (0%). In dust tests, the 10% polymer granules gave 0.0124 mg of respirable particles against 9.053 mg for the uncoated powder, which the authors described as more than 730 times lower. After sonication, the granules were tested on Met5A human mesothelial cells and injected (10 mg) into the abdomen of male rats, three per group. They were compared with NT50, a nanotube that earlier studies found causes mesothelioma in rodents. The coated nanotubes were taken up less by the cells and killed fewer cells than NT50. After 4 weeks they caused only local, mild inflammation in rats, whereas NT50 caused severe fibrosis throughout the abdominal cavity. Cancer was not an outcome, and no people were studied. The authors concluded that Durobeads are safer to humans. Mitsubishi Corporation supplied the Durobeads and partly funded the study.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study combining dust measurements, cell-culture (in vitro) experiments and a 4-week (subacute) animal experiment in rats
• Who was studied: Met5A human mesothelial cell line, and male Fischer-344 rats (6 weeks old), three rats per group in six groups (0%, 6%, 10% and 20% polymer-coated K-Nanos 100P, NT50 and NTtngl)
• Exposure: Multiwall carbon nanotubes: K-Nanos 100P (7 to 23 nm diameter), made into granules with 6%, 10% or 20% of an olefin-based polymer, or with no polymer (0%). NT50 (about 50 nm diameter) was the positive control and tangled NTtngl (about 15 nm) the negative control. Rats received 10 mg of each type by intraperitoneal injection. Granules were sonicated before the cell and animal experiments.
• Main results:
  • Respirable dust (dustability) was 9.053 mg for uncoated K-Nanos 100P, 1.756 mg for K-Nanos 100T, 0.134 mg for 0% polymer granules, 0.059 mg for 6% granules and 0.0124 mg for 10% granules. The authors described the 10% granules as more than 730 times lower than the original nanotubes.
  • In mesothelial cells, NT50 was readily taken up, while polymer-coated nanotubes stayed mainly outside the cells, as NTtngl did
  • Mesothelial cell death (necrosis, measured by LDH assay) was significantly lower with polymer-coated nanotubes than with NT50
  • Neither cell uptake nor cell death showed a significant trend with the amount of polymer used
  • In rats 4 weeks after injection, NT50 caused severe fibrosing inflammation throughout the peritoneal cavity. Fibrosis from polymer-coated nanotubes stayed confined to the areas they touched.
• The authors' conclusion: The authors concluded that Durobeads are safer to humans than uncoated nanotubes because of much lower dustability and mesothelial cytotoxicity. They proposed that dustability be treated as an independent risk factor for carbon nanotubes.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Mesothelial Cells, Carcinogenic, Inflammation.

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