ABSTRACT

The behavior of human monocytes exposed to diamond particles was investigated by Nordsletten et al. (1996); they noted inert behavior with regard to interleukin-1b production and cell morphology following phagocytosis [16]. When silicon carbide and hydroxyapatite particles were phagocytosed by monocytes, IL-1b production and release was observed. Also, the cells were elongated

and spindle-shaped. When diamond particles were phagocytosed by monocytes, monocyte morphology was identical to that of unexposed cells; cells were round and small. No IL-1b production was noted.Cytotoxicity of diamond nanoparticles has also been examined by Schrand et al. (2007), who showed the cytotoxicity of 2-10 nm nanodiamonds created by detonation of carbon-containing explosives in an inert atmosphere [17]. Cell viability such as mitochondrial function (MTT) and metabolic activity (adenosine 5¢ triphosphate production) studies revealed that nanodiamonds were not toxic to neuroblastoma, macrophage, keratinocyte, and PC-12 cells. Nanodiamonds did not induce generation of reactive oxygen species within the cell.On the other hand, recent work by Marcon et al. (2010) indicated that nanodiamond may exhibit toxicity under certain conditions [18]. They examined the interaction of nanodiamond with human embryonic kidney 293 (HEK293) cells and Xenopus laevis embryos. Nanodiamond particles were not cytotoxic to HEK293 cells at concentrations below 50 µg mL-1; however, a dose-dependent decrease in cell viability beyond 50 mg mL-1 was noted. Cytotoxicity of chemical surface functionalities was shown to be –NH2 >> –OH > –CO2H. In addition, potential embryotoxicity and teratogenicity were noted for carboxylated nanodiamond. In particular, abnormalities and high mortality during gastrulation (stage 10+) and neurulation (stages 14-20) stages of the embryo were observed.In addition, bone cell activity on nanocrystalline diamond has been evaluated by several investigators. Bacakova et al. (2007) examined human osteoblast-like MG 63 cell growth on nanostructured as well as hierarchically micro-and nanostructured diamond coatings grown on silicon substrates, which showed good support of cells [19]. The number of initially adhered cells was greater on the nanostructured diamond coatings. Proliferation was accelerated on hierarchically micro-and nanostructured diamond coatings. It is believed that this morphology most closely resembles the natural tissue architecture.