Science with a Twist: Harvard Researchers Discover Helix Shape

It might be time to take a closer glance at the nearest landline phone cord. Harvard researchers recently discovered a new shape—the hemihelix—which can be found in helical-like structures such as phone cords or slinkies. Shapes like the hemihelix might shed light on the process of creating three dimensional shapes from two dimensional starting materials, researchers said.

A team of five researchers at the School of Engineering and Applied Sciences discovered the shape while studying how flexible helical springs were formed. The hemihelix, they said, is special form of helix that frequently reverses the direction in which it spirals.

“At first we were very surprised,” said Katia Bertoldi, a SEAS associate professor in applied mathematics who contributed to the discovery of the hemihelix. “This surprise motivated us to understand the reasons for such a shape to appear.”

For Bertoldi, the most exciting part of the hemihelix discovery is that it represents a step towards a greater understanding of how strained flat systems can make complex 3D shapes.

“In our daily lives, we observe many intricate and well controlled patterns in natural, slender structures, such as flowers or leaves,” Bertoldi said. “These are often the result of specific mechanical instabilities, but our understanding of how in-plane stresses generated by non-uniform growth lead to 3D complex shapes is incomplete.”

Although the synthesis of of three dimensional shapes like the hemihelix in the laboratory is currently limited, Bertoldi added that she hopes the mechanisms of hemihelix formation can help create “simple strategies to engineer flat systems that shape themselves into desired 3D configurations.”

Looking towards the future, the hemihelix researchers said they hope to compare helices and hemihelices in terms of their mechanical properties, and in particular, how they respond to light.

The team, which included a SEAS graduate student, two SEAS post-doctoral students, and two SEAS professors, continued studying the hemihelix shape and published their findings in the journal PLOS ONE on April 23.