Computer models how nanoparticles harm cells

PORTLAND, Ore. — Despite mounting evidence of toxicity for almost every shape and size nanoparticle--from long-thin nanotubes to spherical buckyballs--nanoparticles are nevertheless being mass produced for a variety of applications, from transparent sunscreen that is opaque in the ultraviolet to performance-enhancing dopants for solar cells.

For half a decade, scientists have warned that nanoparticles have a strong affinity for animal DNA, attaching to it in a manner that prevents immune responses and even self-repair of cells. Experimental evidence has confirmed that buckyballs in our rivers can clog the gills of fish and damage their brains; that nanoparticles in groundwater can stunt the growth of plant roots; and, just last week, that inhaling nanotubes can result in the same kind of maladies that are caused by asbestos.

Until now, the mechanism that causes living cells to malfunction in the presence of buckyballs has been misunderstood, according to the creators of perhaps the world's most accurate computer model for living-cell membranes. These scientists now claim to have attained an understanding of the probable mechanism for how buckyballs can invade cells and cause a wide variety of damage. (Buckyballs--tiny nanoparticles officially called carbon-60 since they are composed of just 60 carbon atoms--are also called Buckminsterfullerenes, or just fullerenes, for the likeness of their atomic lattice to the geodesic dome invented by Buckminster Fuller.)

"Buckyballs are extremely insoluble, in any solvent, so they tend to stick together into clumps of a few hundred--which is too large to move through a cell membrane without damaging it," said the leader of the research group, Professor Peter Tieleman, who performed the work with post-doctoral fellow Luca Monticelli, both at the University of Calgary.

Because of the size of these buckyball clumps, scientists had hypothesized that the mechanism of brain damage in fish was rips in cell membranes as they forced their way through it. Buckyballs can cross the blood-brain barrier, so they could potentially enter through the skin, penetrate blood cells, travel to the brain and clump together. Unfortunately, it is very difficult to perform cellular-level experiments with buckyballs, according to this University of Calgary team. In lieu of experiments, Tieleman's group programmed a simulation so accurate that it could confirm the hypothesis that buckyballs damaged cell walls.

To create a simulation detailed enough, it took the combined power of Canada's fastest grid-supercomputer, the WestGrid--a high performance computing (HPC) grid that spans Western Canada connecting resources at 14 institutions for large-scale simulations and scientific visualization. Fully simulating the cell membrane in the presence of buckyballs took several months on more than 1,000 processors spanning three computer centers on the WestGrid. The computer model was developed in cooperation with the University of Groningen (The Netherlands).