Evidencing the mask effect of graphene oxide: a comparative study on primary human and murine phagocytic cells

Graphene oxide (GO) is attracting an ever-growing interest in different fields and applications. Not much is known about the possible impact of GO sheet lateral dimensions on their effects in vitro, especially on human primary cells. In an attempt to address this issue, we present a study to evaluate, how highly soluble 2-dimensional GO constituted of large or small flakes affects human monocyte derived macrophages (hMDM). For this purpose, the lateral size of GO was tuned using sonication and three samples were obtained. The non sonicated one presented large flakes (similar to 1.32 mu m) while sonication for 2 and 26 hours generated small (similar to 0.27 mu m) and very small (similar to 0.13 mu m) sheets of GO, respectively. Cell studies were then conducted to evaluate the cytotoxicity, the oxidative stress induction, the activation potential and the pro-inflammatory effects of these different types of GO at increasing concentrations. In comparison, the same experiments were run on murine intraperitoneal macrophages (mIPM). The interaction between GO and cells was further examined by TEM and Raman spectroscopy. Our data revealed that the GO sheet size had a significant impact on different cellular parameters (i.e. cellular viability, ROS generation, and cellular activation). Indeed, the more the lateral dimensions of GO were reduced, the higher were the cellular internalization and the effects on cellular functionality. Our data also revealed a particular interaction of GO flakes with the cellular membrane. In fact, a GO mask due to the parallel arrangement of the graphene sheets on the cellular surface was observed. Considering the mask effect, we have hypothesized that this particular contact between GO sheets and the cell membrane could either promote their internalization or isolate cells from their environment, thus possibly accounting for the following impact on cellular parameters.