These Shapeshifting DNA Nanostructures Move Like Tiny Machines

The cells that make up your body are filled with amazing molecular machinery, honed by evolution to perform the tiny biological tasks that keep you alive. There are motor molecules that scoot along the protein skeletons that give your cells their shape—like nanometre-sized monorail cars, distributing the essential components of life to where they're needed most—and there are proteins that unwind coiled-up DNA to allow for the necessary expression of your genes.

Scientists have also been building their own molecular machines—and one day, they may rival what nature has crafted in both efficiency and effectiveness. According to a paper published in the March 27 issue of the journal Science, researchers in Germany have invented a new technique for creating movable structures just a few millionths of a metre long out of DNA. With potential implications for fields as diverse as materials science and medicine, these tiny constructs could be the first step towards creating minuscule robots that live in our cells to repair damage—or even extend the length of our lives.

DNA, the molecule that stores your genetic information, consists of two strands that snap together to form a double helix. However, pieces of DNA can also glom together at their ends, and this interaction can be engineered to be very specific, such that researchers can form coherent structures. This ability was used by researchers at Technische Universitaet Muenchen, in Munich, Germany to create a whole new class of tiny machines that can spontaneously self-assemble.

But not only do they form by themselves, these machines can change their shape if certain factors are altered, such as the concentration of salt in the solution the structures are dissolved in, or the temperature. When these structures change their shape, they can be put to work—the true definition of a machine.

"The beauty about the system is that it's really simple," Professor Hendrik Dietz, the lead author of the study, told Motherboard. "You have blunt-ended DNA that serves as a glue. You don't have to design sequences anymore. You only have to design shape complementarity."

Using this molecular glue, Dietz's team put bits of DNA together and built some astonishing structures on a very small scale. They built a nano-robot with moveable arms only a few millions of a centimetre long, assembled from three components like a pint-sized Voltron; a "book" that opens and closes; and even a switchable gear that changes its configuration when its environmental conditions are altered.

The process of designing the tiny machines relies heavily on prediction. "We had to use our own imagination to figure out how to stick the pieces together," said Dietz. "We have a 3D printer here. We printed the objects to see if they fit together. We just tried manually to fit them together in the right way."

When Dietz and his team looked at their nanostructures under an electron microscope, they appeared exactly as predicted.

One of the problems with past nano-machines is that, because they relied on traditional DNA base-pairing to assemble, they required lots of thermal energy to get them to unstick and thus change shape. Relying on the forces that stick the two strands of DNA together to build machines requires high temperatures—and thus high energies—to induce them to move. But high temperatures can also cause damage, and this meant the structures were often "worn out" after just a few configurational changes and came apart.

Because these new nano-shapes require much less heat for them to make them move, the structures last a long time. A scissor-like assembly built by Dietz's team was able to open and close more than a thousand times during a four-day period—an achievement Dietz called "the precursor to an encapsulation device," or a vector for drug delivery.

One of medicine's holy grails is a drug carrier that could deliver a specific compound to a certain location, and only that location, such as a tumour—and then have the medicine released at a specific time. A three-dimensional, hollow structure could be designed to self-assemble and contain a quantity of a chemotherapeutic agent, for example. The complex could then be administered to a tumour.

When a doctor decides the time is right, he or she would then be able to shift the "nano-cage" to its open position, thus releasing the drug. Or, if the clinician wanted to regulate the flow of medication, the tiny cages could be closed again after a certain amount of time has elapsed, ceasing the flow of drugs into the body. Because the machines are reusable, this process could be repeated as many times as necessary.

Outside of medicine, Dietz suggested these tiny structures could also be coated with nano-materials, like tiny gold particles. Changing the shape of the structures would cause the bits of gold move closer together or further apart, thus changing the colour of the solution they're contained in.

"You can develop a display based on this technology," said Dietz. "You can build much more complex objects than you could ever build before."