The Blanket Effect: How Turning the World Upside Down Reveals the Nature of Graphene Oxide Cytocompatibility

Extensive cytocompatibility testing of 2D nanocarbon materials including graphene oxide (GO) has been performed, but results remain contradictory. Literature has yet to account for settling-although sedimentation is visible to the eye and physics suggests that even individual graphenic flakes will settle. To investigate settling, a series of functional graphenic materials (FGMs) with differing oxidation levels, functionalities, and physical dimensions are synthesized. Though zeta potential indicates colloidal stability, significant gravitational settling of the FGMs is theoretically and experimentally demonstrated. By creating a setup to culture cells in traditional and inverted orientations in the same well, a "blanket effect" is demonstrated in which FGMs settle out of solution and cover cells at the bottom of the well, ultimately reducing viability. Inverted cells protected from the blanket effect are unaffected. Therefore, these results demonstrate that settling is a crucial factor that must be considered for FGM cytocompatibility experiments.