Graphene micro-sheets may be considerably more toxic to human cells than was previously thought, according to new research from Brown University. The new research has found that the sharp edges of graphene sheets can easily pierce cell membranes, and then after piercing the membranes, be pulled into the cell where they then disrupt normal cellular functions.
The researchers think that their work should spur further investigations into the effects that graphene may possibly have on human/animal health, and could perhaps lead to the development of means to minimize any potential toxicity.
“At a fundamental level, we want to understand the features of these materials that are responsible for how they interact with cells,” stated Agnes Kane, chair of the Department of Pathology and Laboratory Medicine at Brown, and study author. “If there’s some feature that is responsible for its toxicity, then maybe the engineers can engineer it out.”
For those that don’t know, graphene is essentially just a sheet of carbon that is only one atom think, but it possesses an incredible number of unique electronic, mechanical, and photonic properties, as well as being incredibly strong. Since it was discovered only relatively recently — about a decade ago — there remains much that is unknown about it though. But even though there are many unknowns, there is still a great deal of interest in the material, especially with regard to electronics, solar energy, batteries, medical devices, etc. The commercial application of the material is expected to be only a couple of years off — so it would be good to know about any potential toxicity. Before this new research, there wasn’t really anything known about what effect graphene might have on the human body, whether with regard to normal exposure via product wear-and-tear or exposure via a working environment — such as during the manufacturing of products containing the material.
“These materials can be inhaled unintentionally, or they may be intentionally injected or implanted as components of new biomedical technologies,” stated Robert Hurt, a professor of engineering and one of the study’s authors. “So we want to understand how they interact with cells once inside the body.”
Brown University explains the research further:
Preliminary research by Kane’s biology group had shown that graphene sheets can indeed enter cells, but it wasn’t clear how they got there. Huajian Gao, professor of engineering, tried to explain those results using powerful computer simulations, but he ran into a problem. His models, which simulate interactions between graphene and cell membranes at the molecular level, suggested that it would be quite rare for a microsheet to pierce a cell. The energy barrier required for a sheet to cut the membrane was simply too high, even when the sheet hit edge first.
The problem turned out to be that those initial simulations assumed a perfectly square piece of graphene. In reality, graphene sheets are rarely so pristine. When graphene is exfoliated, or peeled away from thicker chunks of graphite, the sheets come off in oddly shaped flakes with jagged protrusions called asperities. When Gao reran his simulations with asperities included, the sheets were able to pierce the membrane much more easily.
Annette von dem Bussche, assistant professor of pathology and laboratory medicine, was able to verify the model experimentally. She placed human lung, skin and immune cells in Petri dishes along with graphene microsheets. Electron microscope images confirmed that graphene entered the cells starting at rough edges and corners. The experiments showed that even fairly large graphene sheets of up to 10 micrometers could be completely internalized by a cell.
“The engineers and the material scientists can analyze and describe these materials in great detail,” Kane stated. “That allows us to better interpret the biological impacts of these materials. It’s really a wonderful collaboration.”
The researchers are now planning to follow this work up by investigating in further detail what happens — biologically speaking — when sheets of graphene end up inside of human cells. Kane notes, though, that the work that they have already done provides an important first step with regard to understanding the potential toxicity of graphene.
“This is about the safe design of nanomaterials,” she explained. “They’re man-made materials, so we should be able to be clever and make them safer.”
The new research was just published July 9th in the Proceedings of the National Academy of Sciences.