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Rikizo Hatakeyama

Publications and source records attributed to Rikizo Hatakeyama.

5 recordsLinked to original sources
PubMed2005

Influence of length on cytotoxicity of multi-walled carbon nanotubes against human acute monocytic leukemia cell line THP-1 in vitro and subcutaneous tissue of rats in vivo.

Carbon nanotubes (CNTs) are single- or multi-cylindrical graphene structures that possess diameters of a few nanometers, while the length can be up to a few micrometers. These could have unusual toxicological properties, in that they share intermediate morphological characteristics of both fibers and nanoparticles. To date, no detailed study has been carried out to determine the effect of length on CNT cytotoxicity. In this paper, we investigated the activation of the human acute monocytic leukemia cell line THP-1 in vitro and the response in subcutaneous tissue in vivo to CNTs of different lengths. We used 220 nm and 825 nm-long CNT samples for testing, referred to as "220-CNTs" and "825-CNTs", respectively. 220-CNTs and 825-CNTs induced human monocytes in vitro, although the activity was significantly lower than that of microbial lipopeptide and lipopolysaccharide, and no activity appeared following variation in the length of CNTs. On the other hand, the degree of inflammatory response in subcutaneous tissue in rats around the 220-CNTs was slight in comparison with that around the 825-CNTs. These results indicated that the degree of inflammation around 825-CNTs was stronger than that around 220-CNTs since macrophages could envelop 220-CNTs more readily than 825-CNTs. However, no severe inflammatory response such as necrosis, degeneration or neutrophil infiltration in vivo was observed around both CNTs examined throughout the experimental period.

Animals↗
PubMed2005

Strict preparation and evaluation of water-soluble hat-stacked carbon nanofibers for biomedical application and their high biocompatibility: influence of nanofiber-surface functional groups on cytotoxicity.

Water-soluble H-CNFs modified with a carboxyl group possessed the ability to induce TNF-alpha, whereas CHAPS-treated H-CNFs possessed significantly greater activity and were also found to activate NF-kappaB reporter activity, to a significantly greater level than H-CNFs; furthermore the functional group modified or coated on the surface of H-CNFs was a significant cytotoxic factor that affected cell activation.

Carbon↗
PubMed2003

Plasma state transition originating from local production of massive negative ions.

A dynamic evolution of plasma structures and its associated state transition due to local production of massive negative ions are investigated by the particle-in-cell simulation which is based on an experimental configuration of an open plasma system (Q machine). Two different states, a stationary state and a dynamic state, are achieved depending on the production rate of massive negative ions. The plasma is stationary for a low production rate, while solitary pulses and fluctuations are spontaneously excited and the plasma state is unstable for a high production rate. Phenomena of a two-stream instability and a double layer formation induced by the local production are closely concerned with the excitation of the solitary pulse. The solitary pulses play a role in the rapid ejection of massive negative ions from the system. A staying time distribution of charged particles is analogically introduced for the special convenience of explanation, which corresponds with a so-called population pyramid. The staying time distribution can clearly express the feature of the state since all the phenomena occurring in the system directly reflect the distribution.

Journal Article↗
PubMed2003

Pair-ion plasma generation using fullerenes.

We have developed a novel method for generating pure pair plasma which consists of positive- and negative-charged particles with an equal mass. The pair-ion plasma without electrons is generated using fullerene as an ion source through the processes of hollow-electron-beam impact ionization, electron attachment, preferential radial diffusion of ions, and resultant electron separation in an axial magnetic field. Basic characteristics of this plasma are discussed in terms of the differences from ordinary electron-ion plasmas, such as a phenomenon in the absence of sheath and potential structure formation.

Journal Article↗