Even though nanomaterials are used as constituents of many manufactured articles, there are no unified criteria for evaluating their safety or toxicity. Even the same nanomaterial can cause different sensitivities in different cell types. In addition, differences in physiological conditions can cause varied sensitivity of the same cell type to a specific nanomaterial. Generally, nanomaterials form aggregates or agglomerates in the culture medium, resulting in a range of size variations. Therefore, the response of each cell differs depending on the amount of nanomaterial it absorbs. Furthermore, it is also necessary to consider the effects when a nanomaterial releases metal ions. The most complicated scenario for the in vitro evaluation of a nanomaterial is that it affects growth, apoptosis and necrosis collectively. Nanomaterial toxicity arises from generation of reactive oxygen species (ROS) inside the cell. However, many types of cells possess ROS elimination systems. In cells that have the ability to completely remove ROS, cytotoxicity is normally not observed even after exposure to a toxic nanomaterial. However, for cells that are not able to cope with ROS, cytotoxicity occurs. A number of factors determine which specific molecular species of intracellular ROS quenchers or scavengers act inside cells, including cell type, cellular physiological state and the type and amount of nanomaterial present. In this review, we discuss the biological interpretation of nanomaterial toxicity evaluation data.

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Amorphous hydrogenated carbon (a-C:H) and amorphous deuterated carbon (a-C:D) films were prepared using radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) from CH₄ and CD₄ gas sources, respectively. Both films were prepared by adjusting the process pressure between 1 and 300 Pa. The films were characterized using Raman spectroscopy, and the concentrations of hydrogen (H) and deuterium (D) relative to carbon (C) in the films were determined by elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS).Contact angle and blood clot formation on the films were observed to evaluate the antithrombogenicity of the a-C:H and the a-C:D films. The a-C:D film contact angles were lower than the a-C:H film contact angles. These lower contact angles were correlated to lower antithrombogenicity of the a-C:D films compared with the a-C:H films.

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We investigated the phytotoxicity of multiwalled carbon nanotubes (MWNTs) on lettuce regarding inhibition effect on plant growth development as well as cell damage on root and leaves. We have cultured the plant seedling of lettuce using Hoagland's Media treated with MWNTs hydroponically. After two weeks, we observed the toxic symptoms in the presence of MWNTs in a dose-dependent manner as compared to carbon black (CB). Statistically, MWNTs could inhibit the seed germination, plant growth and plant biomass. Microscopic analysis showed the attachment of MWNTs on the root surface area, deterioration of root tip and an image of penetration of MWNTs into plant cell wall. We also showed that MWNTs caused cell death on root and leaves. In situ detection of hydrogen peroxide has proposed the reactive oxygen species (ROS) for mechanism of toxic effect of MWNTs on lettuce.

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The wear behavior of a femoral head made of CoCrMo against an acetabular cup made of CoCrMo (CoCrMo/CoCrMo coupling) was compared with that of a femoral head made of CoCrMo against an acetabular cup made of cross link (CL) – ultra high molecular weight polyethylene (UHMWPE) (CoCrMo/CL-UHMWPE coupling) using a hip joint simulator. The wear amount of CoCrMo/CoCrMo coupling was much lower than that of CoCrMo/CL-UHMWPE coupling. However, the wear debris generated from CoCrMo/CoCrMo coupling was consisted of a large number of wear particles with 100 nm size, resulted in increasing the total surface area of the metal. Therefore, Co and Cr ions drastically dissolved from CoCrMo/CoCrMo coupling in the serum after 50 × 10⁴ cycles. Therefore, it is necessary for further research of metal on metal total replacement joints to improve materials and design carefully.

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Making orthodontic adhesives visible is important for their safer and complete removal after orthodontic treatments. In this paper, we report our research on doping trivalent europium ions into lattices of zinc oxides to make orthodontic adhesives visible under purple or near ultraviolet light irradiation. The primary crystals of the synthesized products were on the nanoscale, although their size and crystallinity varied with the annealing temperatures. The X-ray diffraction (XRD) patterns were in good agreement with that of hexagonal wurtzite ZnO with the exception of patterns acquired from the products obtained by annealing at 200°C. However, with regard to the photoluminescence, the polymer adhesives containing ZnO:Eu³⁺ particles indicated characteristic excitation and emission peaks corresponding to the intra-4f transitions of Eu³⁺, although these peaks were not intense and sharp. We think that the phonon resonance can be considered as the most acceptable cause for the insufficient photoluminescence observed in this study bearing in mind that the phonon resonance is originated from the Zn interstitials. At the current moment, we conclude that the nanocrystalline ZnO could have numerous defects. By controlling the formation of defects during synthesis, we believe that the ZnO:Eu³⁺ nanocrystals will become much more useful toward developing new fluorescent orthodontic adhesives.

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To examine the embryotoxicity of the multi-walled carbon nanotubes (MWCNTs), the effects of three-dimensional culture with a collagen gel scaffold containing MWCNTs on the differentiation level of ES-D3 cells were examined and compared with those of conventional two-dimensional culture.In the present study, the rate of contraction of the pulsating myocardial cells decreased as the MWCNTs concentration increased, with no contraction observed at >25 μg. The contraction of the pulsating myocardial cells in teratomas showed uniform and rhythmic movements in the control group and non-uniform and non-rhythmic movements in the 2.5-10-μg groups.Thus, the non-rhythmic contraction of the pulsating myocardial cells, and not the rate of contraction determined by the EST method, may serve as a novel cell differentiation indicator.

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