Nanomotors that are controlled, for the first time, inside living cells

February 10, 2014

Optical microscope image of a HeLa cell containing several gold-ruthenium nanomotors. Arrows indicate the trajectories of the nanomotors, and the solid white line shows propulsion. Near the center of the image, a spindle of several nanomotors is spinning. Inset: Electron micrograph of a gold-ruthenium nanomotor. The scattering of sound waves from the two ends results in propulsion. (Credit: Mallouk lab, Penn State University)

Penn State University chemists and engineers have, for the first time, placed tiny synthetic motors inside live human cells in a lab, propelled them with ultrasonic waves, and steered them magnetically.

KurzweilAI has covered a number of designs for microbots studies in laboratories (and one that uses a pill that is swallowed) that could one day be passively or actively propelled through the body, but the devices are not designed to penetrate cells.

‘Fantastic Voyage’ concept

The Penn State nanomotors are the closest so far to a “Fantastic Voyage” concept (without the miniature people).

The nanomotors, which are rocket-shaped gold rods ~300 nanometers in diameter and ~3 microns long, move around inside the cells, spinning and battering against the cell membrane.

The nanomotors are activated by resonant ultrasound operating at ~4 MHz, and show axial propulsion as well as spinning.

“As these nanomotors move around and bump into structures inside the cells, the live cells show internal mechanical responses that no one has seen before,” said Tom Mallouk, Evan Pugh Professor of Materials Chemistry and Physics at Penn State.

“It may be possible to use synthetic nanomotors to study cell biology in new ways. We might be able to use nanomotors to treat cancer and other diseases by mechanically manipulating cells from the inside.

“Nanomotors could perform intracellular surgery and deliver drugs noninvasively to living tissues.”

The researchers’ findings will be published today (Feb. 10) in Angewandte Chemie International Edition.

Chemically powered nanomotors first were developed ten years ago at Penn State by Mallouk and others. “Our first-generation motors required toxic fuels and they would not move in biological fluid, so we couldn’t study them in human cells,” Mallouk said. When Mallouk and French physicist Mauricio Hoyos discovered that nanomotors could be powered by ultrasonic waves, the door was open to studying the motors in living systems.

Ultrasonic control

For their experiments, the team uses HeLa cells, an immortal line of human cervical cancer cells that typically is used in research studies.

These cells ingest the nanomotors, which then move around within the cell tissue, powered by ultrasonic waves.

At low ultrasonic power, Mallouk explained, the nanomotors have little effect on the cells. But when the power is increased, the nanomotors spring into action, moving around and bumping into organelles — structures within a cell that perform specific functions.

The nanomotors can act as battering rams to puncture the cell membrane or as egg beaters to essentially homogenize the cell’s contents.

While ultrasound pulses control whether the nanomotors spin around or whether they move forward, the researchers can control the motors even further by steering them, using magnetic forces. Mallouk and his colleagues also found that the nanomotors can move autonomously — independently of one another — an ability that is important for future applications.

“Autonomous motion might help nanomotors selectively destroy the cells that engulf them,” Mallouk said. “If you want these motors to seek out and destroy cancer cells, for example, it’s better to have them move independently. You don’t want a whole mass of them going in one direction.”

Promise for medicine

The ability of nanomotors to affect living cells holds promise for medicine, Mallouk said. “One dream application of ours is Fantastic Voyage-style medicine, where nanomotors would cruise around inside the body, communicating with each other and performing various kinds of diagnoses and therapy. There are lots of applications for controlling particles on this small scale, and understanding how it works is what’s driving us.”

Researchers at Weinberg Medical Physics in Maryland were also involved. The research was funded by the National Science Foundation, the National Institutes of Health, the Huck Innovative and Transformative Seed Fund (HITS) and Penn State University.

Abstract of Angewandte Chemie International Edition paper

We demonstrate the ultrasonic propulsion of rod-shaped nanomotors inside living HeLa cells. These nanomotors (gold rods ~300 nm in diameter and ~3 ┬Ám long)attach strongly to the external surface of the cells, and are readily internalized by incubation withthe cells for periods longer than 24 h. Once inside the cells, the nanorod motors can be activated by resonant ultrasound operating at ~4 MHz, and show axial propulsion as well as spinning. The intracellular propulsion does not involve chemical fuels or high powerultrasound andthe HeLa cells remain viable. Ultrasonic propulsion of nanomotors may thus provide a new tool for probingthe response of living cells to internal mechanical excitation, for controllably manipulating intracellular organelles, and for biomedical applications.