New shape using rubber bands

While setting out to fabricate new springs to support a cephalopod-inspired imaging project, a group of Harvard researchers stumbled upon a surprising discovery: the hemihelix, a shape rarely seen in nature. This made the researchers wonder: Were the three-dimensional structures they observed randomly occurring, or are there specific factors that control their formation? The scientists answered that question by performing experiments in which they stretched, joined, and then released rubber strips. Complemented by numerical simulations and analysis of the process, the results appear in a paper published in the journal PLOS ONE . Knowing precisely how to make the structures, predictably and consistently, may enable scientists to mimic the geometrical features in new molecules that could lead to possible advances in modern nanodevices, including sensors, resonators, and electromagnetic wave absorbers. "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," says Katia Bertoldi , associate professor of applied mechanics at the Harvard School of Engineering and Applied Sciences (SEAS). The shape that Bertoldi and colleagues at SEAS unexpectedly encountered is a hemihelix with multiple "perversions." Helices are three-dimensional structures; think of a corkscrew or a Slinky toy. Hemihelices form when the direction in which the spiral turns-known as the chirality-changes periodically along the length.