Blue Tarantulas Inspire 3D-Printed Color That Never Fades

The spiders' blue hue is created not from pigment but by nanostructures in their hairs.

Tarantulas aren't usually known for having a striking blue color, but the ones that do recently inspired new technology that can produce vibrant, 3D-printed color that will never fade.

Back in 2015, a team of researchers led by the University of Akron marveled at the spiders' blue hue and concluded that it was created not from pigment but from nanostructures in their hairs. In other words, these tarantulas are blue because of structural color, which is produced through light scattering caused by structures of sub-micrometer size features made by translucent materials. They also realized that many species of the spider have nearly the very same color, but evolved the color independently.

"Different types of nanostructures all evolved to produce the same 'blue' across distant branches of the tarantula family tree," Bor-Kai (Bill) Hsiung, lead author and a Biomimicry Fellow in the Integrated Bioscience Ph.D. program at The University of Akron, said in a statement. "In other words, natural selection has led to convergent evolution."

The researchers were also intrigued by the fact that the spider's color doesn't change when looked at from another angle. This differs from the structural colors of other creatures like peacocks and butterflies, whose iridescent color shifts to another shade when looked at from a different viewpoint.

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Their finding overturned the assumption that vibrant, structural colors in nature are almost always iridescent. Because the tarantulas' non-iridescent structural color was produced by highly symmetrical structures, the researchers then set out to try to mimic their vibrant blue color with the help of a 3D nano printer.

They observed that the hairs of some species of blue tarantulas show a special flower-like shape that they hypothesized reduced the iridescent effect. With some crowdfunding help, they recently tested this hypothesis using a series of computer simulations and physical prototypes built using nano-3D printing technology.

"The iridescence is the key obstacle to use structural colors in our daily life," Hsiung recently told Seeker, explaining that shifting color makes hues inconsistent. "This observation inspired us to look into the mechanisms behind it and try to recreate this phenomenon."

The result: color produced by 3D-printed structures that has a viewing angle of 160 degrees. In other words, when viewed from nearly all angles, the color appears the same. This is the largest viewing angle to date, surpassing the viewing angle of any non-iridescent color that has been produced by self-assembly methods.

This non-iridescent structural colorants have many potential applications, such as replacements for synthetic pigments - many of which are expensive and not enviromentally-friendly - in materials such as plastics, metal, textiles and paper. They could also be used for wide-angle viewing systems such as phones and televisions, Hsiung explained.

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Hsiung envisions a future where the color of clothing is made of non-iridescent structural colored fibers that will remain new and pristine no matter how many times washed, since the color never fades. These colored fibers will also require no dyes, which pollute water. In addition, white and colored clothes could be washed together because there won't be any contamination caused by bleaching.

These structural colors can also be used "in any place where we see colors, including an energy efficient electronic display that can be viewed directly under the sun without any glare and reflection from the background," Hsiung explained.

Structural colors also provide an advantage over pigmentary color when it comes to variety. One pigment can only produce one color, but with structural colors, any color in the rainbow can be produced easily by a structure just by tweaking the spacing or size of the sub-micrometer scale features.

"Our next step is to prove that it can be mass produced in an economically viable way, and bring it one step closer to the market," said Hsiung.

Top photo: Haplopelma lividum, Cobalt blue tarantula. Credit: Kaeng Krachan District, Phetchaburi, Thailand WATCH: How Do Your Eyes See Color?