Nanomaterials can have drastically different characteristics compared to the bulk material. Although nanomaterials are already being used in nanomedical applications, they can be highly toxic. It is therefore important for scientists to better understand how nanomaterials interact with biological systems, such as cell membranes, so that we can take full advantage of the unique properties of these compounds while minimizing their adverse effects.

Fullerenes (C60 and C70 molecules) and their derivatives have many potential applications in medicine, for example, as anti-HIV drugs, X-ray contrast agents and transporters for delivering drugs. However, recent research found that pristine C60 is toxic because it creates pores in cell membranes through which substances in the cells can then leak out. This work also found that changing the surface properties of these molecules significantly lowered their toxicity so that there was no membrane leakage.

To investigate this further, Qiao and colleagues decided to model the way in which pristine C60 molecules adsorb onto and travel across cell membranes compared to functionalized C60 containing hydroxyl groups (C60(OH)20). The researchers did this using standard molecular dynamics simulations.

Qiao's team found that the pristine C60 molecules can readily "jump" into the cell membrane and diffuse across it easily in a matter of milliseconds. In contrast, C60(OH)20 molecules cannot easily penetrate the cell membrane and take much longer to diffuse across it. Moreover, the researchers found that the two molecules affect the structure of the membrane in different ways. The C60 molecules help create micropores in the membrane, which cause the cell membrane leakage mentioned earlier, while C60(OH)20 molecules adsorbed on the membrane surface decrease the spacing between lipid groups present there.

"Our results could facilitate the rational modification of surface properties of nanomaterials to achieve minimal toxicity," Qiao told "They could also help design nanoparticle-based drug-delivery systems, where translocation through a cell membrane is actually beneficial."

The team now plans to investigate how other properties of nanomaterials, apart form surface modification, affect the interactions with cell membranes. "Also of interest is how nanomaterials interact with proteins embedded in the membrane," says Qiao.

The researchers reported their work in Nano Letters.