Harvard Group Finds Hemihelix Structure

A group of Harvard researchers has found the hemihelix structure, which is rarely seen in nature.

The team at Harvard School of Engineering and Applied Sciences conducted several experiments using rubber bands to understand the novel shape. Their research could help scientists twist and turn biological molecules and advance nanodevices such as sensors and resonators.

"Once you are able to fabricate these complex shapes and control them, the next step will be to see if they have unusual properties; for example, to look at their effect on the propagation of light," said Katia Bertoldi, associate professor of applied mechanics at the Harvard School of Engineering and Applied Sciences (SEAS).

Researchers call the new shape hemihelix with multiple "perversions."

Helices are 3D structures such as a slinky toy. Hemihelices are what you get when you twist the telephone cord the other way ,nbcnews reports.

 Twisting the cord causes a change in direction of the spiral. The reversal of chirality, the direction of the spiral, is called a perversion.

The team was actually trying to make new springs using two strips of rubber material. The rubber pieces were of different lengths. Researchers stretched the shorter strip to reach the length of the longer piece and stick them together.

"We expected that these strips of material would just bend-maybe into a scroll. But what we discovered is that when we did that experiment we got a hemihelix and that it has a chirality that changes, constantly alternating from one side to another," explained David R. Clarke, Extended Tarr Family Professor of Materials at SEAS, according to a news release.

Researchers then tested whether the aspect ratio or the width-to-height ratio of the polymer had any effect on the resultant structure. Jia Liu, a graduate student in Bertoldi's group conducted the research. The team found that when the rubber strip is wider, it produces a helix. They found that at a critical value of the aspect ratio, the material forms a hemihelix.

 "There are a variety of complex shapes in nature that arise as a result of different growth rates. We stumbled quite by accident on a way to achieve fully deterministic manufacture of some three-dimensional objects," Clarke said.

The study is published in the journal PLOS One and was funded by Harvard Materials Research Science and Engineering Center, which is supported by the National Science Foundation.