3D Printing Helps Researchers Understand How Tiny Spiders Make Rainbows

In some species, males and females are virtually indistinguishable. But in species where the sexes have different appearances, the males tend to be much more flamboyant and brightly colored, the better to attract a mate. The bright red male cardinal is a good example, and nature is full of a rainbow of colors used by different animals. But only one species is known to use an entire rainbow itself, and that’s the peacock spider. The iridescent male arachnids use a full spectrum to entice females, and a team of researchers wants to know how.

The research team was led by Bor-Kai Hsiung, a postdoctoral scholar at Scripps Institution of Oceanography at the University of California San Diego. His research started when he was a PhD student at the University of Akron, and he assembled an international team of biologists, physicists and engineers. The team began investigating the spider’s photonic structures using multiple techniques that included light and electron microscopy, hyperspectral imaging, imaging scatterometry and optical modeling. They used the results to come up with hypotheses about how the spider created its rainbows.

Those hypotheses were then tested using a nano 3D printing technique, in which several models were 3D printed. These models helped the researchers to discover that the iridescence came from specialized abdominal scales, which combine airfoil-like microscopic 3D contours with nanoscale diffraction grating structures on the surface. The interaction between the surface nano-diffraction grating and the microscopic curvature of the scales allows for the separation and isolation of light into its component wavelengths at finer angles and smaller distances than are possible with current engineering technologies.

“One of the main questions that I wanted to address in my Ph.D. dissertation was ‘how does nature modulate iridescence?'” said Hsiung. “From a biomimicry perspective, to fully understand and address a question, one has to take extremes from both ends into consideration. I purposefully chose to study these tiny spiders with intense iridescence after having investigated the non-iridescent blue tarantulas.”

The study may result in new color technology, as it introduces new ideas that weren’t possible before. As is so often the case, though, the researchers found that nature is capable of things that humans, even with our advanced technology, are not.

“As an engineer, what I found fascinating about these spider structural colors is how these long evolved complex structures can still outperform human engineering,” said Radwanul Hasan Siddique, a postdoctoral scholar at Caltech. “Even with high-end fabrication techniques, we could not replicate the exact structures. I wonder how the spiders assemble these fancy structural patterns in the first place!”

The discoveries made by the research team may be used to overcome current limitations in spectral manipulation and to reduce the size of optical spectrometers for applications where fine-scale resolution is required for something very small, such as instruments on space missions or wearable chemical detection systems.

3D printing played a vital role in the discoveries that were made, said the researchers.

“Nanoscale 3D printing allowed us to experimentally validate our models, which was really exciting,” said Matthew Shawkey of the University of Akron. “We hope that these techniques will become common in the future.”

The research was documented in a study entitled “Rainbow peacock spiders inspire miniature super-iridescent optics,” which you can access here. Authors include Bor-Kai Hsiung, Radwanul Hasan Siddique, Doekele G. Stavenga, Jürgen C. Otto, Michael C. Allen, Ying Liu, Yong-Feng Lu, Dimitri D. Deheyn, Matthew D. Shawkey and Todd A. Blackledge.

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[Source: UCSD]