A hemihelix - a strange shape, has been created by scientists using nothing more advanced than rubber bands.
Harvard University investigators were working on developing a new type of spring. Their idea was inspired by cephalopods, the group of animals that include octopuses and squids. Researchers accidentally developed a hemihelix, a shape that is almost never seen in nature.
"Nature abounds with complex, three-dimensional shapes. Of these, the helix and spiral are amongst the most ubiquitous, often emerging during growth from initially straight or flat 2-D configurations," researchers wrote in the article profiling their research.
Plant roots may start out straight, but they can twist into a helix, or corkscrew shape when they encounter dense dirt. Valves of seed pods are straight when they first form, but begin to twist as they grow.
Researchers began their study using two strips of rubber, one piece of which was longer than the other. The shorter band was stretched to the same length as the longer piece. The two strips were then glued together. At the beginning of the experiment, the investigators believed the objects would likely curl up like a scroll.
Instead, certain structures created by the researchers begin twisting in one direction, then stopped and reversed direction, in what is called a perversion. Investigators developed the term hemihelix to describe this unusual shape.
They found that when the strips were relatively wide compared to its height, the system produced a helix. At certain aspect ratios, the bands spontaneously formed a hemihelix.
"We see deterministic growth from a two-dimensional state - two strips bonded together - to a three-dimensional state. The actual number of perversions, the diameter, everything else about it is entirely prescribed. There is no randomness; it's fully deterministic. So if you make one hundred of these, they'll always perform exactly the same way," Jia Liu, a researcher on the study said.
The hemihelix could lead to advances in electronic sensors, resonators and could be the basis of a new generation of springs.
"Simply by changing geometry, you can design this whole family of springs with very different behavior with predictable results," Katia Bertoldi of Harvard stated in a press release from the University.
Most other materials would shatter if subjected to the relative forces the team applied to the elastic bands. This may have accounted for the fact that such a simple discovery could have gone unnoticed for so long, says researchers.
Investigation of the hemihelix by was detailed in the online journal Plos One.
