The team has demonstrated* that the particles – essentially sugar-coated bits of iron oxide, about 100 nanometers wide – are potent cancer killers because they interact with one another in ways that smaller nanoparticles do not. The interactions, thought by many bioengineers to be undesirable, actually help the larger particles heat better while under the influence of an alternating magnetic field. Because this heat destroys cancer cells without potentially damaging the surrounding healthy tissue, the team’s findings may help engineers design better particles and treatment methods with fewer side effects than current chemo- and radiation therapy.

Neutron scattering probes at the NIST Center for Neutron Research revealed that the particles’ larger iron oxide cores attract one another, but that the sugar coating has fibres extending out, making it resemble a dandelion – and these fibres push against one another when two particles get too close together, making them spring apart and maintain an antibody-defying distance rather than clumping. Moreover, when the particles do get close, the iron oxide magnets all rotate together under the influence of a magnetic field, both generating more heat and depositing this heat locally. All these factors helped the nanoparticles destroy breast tumours in three out of four mice after one treatment with no regrowth.

Ultimately, the push-pull is part of a tug of war that fixes the distance between nanoparticles, suggesting interacting nanoparticles can be stabilized in ways that pay off in the clinic.

The research was funded by the U.S. Army Medical Research and Material Command, and used facilities supported by the National Science Foundation.

C.L. Dennis, A.J. Jackson, J.A. Borchers, P.J. Hoopes, R. Strawbridge, A.R. Foreman, J. van Lierop, C. Gruttner and R. Ivkov. Nearly Complete Regression of Tumors via Collective Behavior of Magnetic Nanoparticles in Hyperthermia. Nanotechnology 20 (2009) 395103. [doi:10.1088/0957-4484/20/39/395103]