Graphene oxide and titanium: synergistic effects on the biomineralization ability of osteoblast cultures.

Graphene oxide (GO) has attracted remarkable attention in recent years due to properties such as extremely large surface area, biocompatibility, biostability, and easy chemical functionalization. Osteoblasts underlie the deposition of hydroxyapatite crystals in the bone protein matrix during biomineralization; hydroxyapatite deposition involves extracellular matrix vesicles that are rich in alkaline phosphatase (ALP). Here, we have investigated how GO affects osteoblast viability, ALP activity, and mineralized matrix formation in osteoblast cultures in three different phases of cell growth, in the presence and in the absence of titanium (Ti). Scanning electron microscopy (SEM), Raman spectra, and energy dispersive spectroscopy aided GO characterization. The presence of GO increased the viability of osteoblast cells grown on a plastic surface. However, osteoblast viability on Ti discs was lower in the presence than in the absence of GO. ALP activity emerged at 14 days for the cell culture incubated with GO. The total protein concentration also increased at 21 days on both the Ti discs and plastic surface. Osteoblasts grown on Ti discs had increased mineralized matrix formation in the presence of GO as compared to the cells grown in the absence of GO. SEM images of the cell cultures on plastic surfaces in the presence of GO suggested delayed mineralized matrix formation. In conclusion, applications requiring the presence of Ti, such as prostheses and implants, should benefit from the use of GO, which may increase mineralized nodule formation, stimulate biomineralization, and accelerate bone regeneration.

Cyto- and genotoxic effects of metallic nanoparticles in untransformed human fibroblast.

Metallic nanoparticles such as silver (Ag), cerium dioxide (CeO2) and titanium dioxide (TiO2) are produced at a large scale and included in many consumer products. It is well known that most metallic NPs are toxic to humans which raise concerns about these engineered particles. Various studies have already been published on the subject, however, almost all of these studies have been conducted in cancer or transformed cell lines. In this work we performed a comparative evaluation of these metallic NPs on normal untransformed human fibroblasts (GM07492) detecting cyto- and geno-toxic responses after exposure to these NPs. Our results showed that all three metallic NPs were able to cross the plasma membrane and were mainly found in endocytic vesicles. The Ag and TiO2 NPs affected mitochondrial enzymatic activity (XTT), increased DNA fragmentation, oxidative damage (Comet assay) and induced cell death mainly by the apoptotic pathway. Ag NPs increased GADD45α transcript levels and the phosphorylation of proteins γH2AX. Transient genotoxicity was also observed from exposure to CeO2 NPs while TiO2 NPs showed no increase in DNA damage at sub-cytotoxic concentrations. In comparison, Ag NPs were found to be the most cyto-genotoxic NPs to fibroblasts. Thus, these results support the use of normal fibroblast as a more informative tool to detect the mechanisms of action induced by metallic NPs.

Evaluation of carbon nanotubes network toxicity in zebrafish (Danio rerio) model.

This is a detailed in vivo study of the biological response to carbon nanotubes network as probed by the zebrafish model. First, we prepared pristine carbon nanotubes (CNTs) by methanol chemical vapor deposition in the presence of Mn and Co as catalysts, followed by purification in acid, which furnished curved tubes with diameters lying between 10 and 130 nm. The CNT network consisted of pristine CNTs dispersed in water in the presence of a surfactant. The CNT network pellets corresponded to agglomerated multi-walled CNTs with an average diameter of about 500 nm. Although the same pristine CNTs had been previously found to exert genotoxic effects in vitro, here we verified that the CNT network was not genotoxic in vivo. Indeed, Raman spectroscopy and microscopy conducted in the intestine of the zebrafish revealed complete clearance of the CNT network as well as minimal disturbances, such as aneurysms, hyperemia, and reversible inflammatory focus in the zebrafish gills.