The process of folding DNA on a nanoscale into small two- and three-dimensional shapes isn’t new. It’s known as DNA origami and it has already been used to create tiny prototypes to deliver drugs. Though these shapes are pretty impressive, the brick-like structures tend to be rigid and designing them can be costly and time-consuming. Now researchers have streamlined the process and created a new technique for building these structures. They were able to fold DNA into the shape of a teeny-tiny bunny by turning to the famous mathematical question known as “the seven bridges of Königsberg.”

Königsberg, now known as Kaliningrad in Russia, has seven bridges. The Königsberg bridge problem asks whether it’s possible to wander around the city, ending the trip in the same place it began, while crossing all seven bridges once – and only once. Leonhard Euler, a Swiss mathematician, proved the walking route was not possible, but did discover what is now known as Eulerian circuits. These circuits start and end at the same vertex, using every edge of a graph exactly once.

How does this relate to DNA folding? Researchers were essentially trying to solve the same problem in the new study published in Nature.

“We wanted to put the DNA strand on every edge of the polygonal shape once – and if possible only once – and then bring it back to its starting point, since it’s a circular molecule,” lead researcher Björn Högberg of the Karolinska Institute, Sweden, told the Washington Post.

They were able to develop a new algorithm to build a single strand of DNA along the structure, going through every edge once – if possible – and returning to the same spot. Researchers even added “helper” edges when Eulerian circuits weren't possible. This meant that DNA could be folded into complex shapes – like an adorable bunny – with a greater amount of flexibility and ease.

Researchers suggest this is an important step to 3D printing structures that could interact with human cells. These structures could eventually be engineered to better deliver drugs or nutrients to specific parts of the body.  

“For biological applications, the most crucial difference is that we can now create structures that can be folded in, and remain viable in, physiological salt concentrations that are more suitable for biological applications of DNA nanostructures,” Högberg explained in a statement.