Fabrics made from silkworm fibers have long been treasured for their beautiful luster and refreshing coolness. Columbia Engineering researchers have discovered that fibers produced by the caterpillars of a wild silk moth, the Madagascar comet moth (Argema mittrei), are far superior in terms of brilliance and cooling ability. Not only do the comet moth’s cocoon fibers have outstanding cooling properties, they also have exceptional capabilities for transmitting light signals and images.

Led by Nanfang Yu, associate professor of applied physics, the team characterized the optical properties associated with one-dimensional nanostructures they found in comet moth cocoon fibers. They were so fascinated by the unusual properties of these fibers that they developed a technique to spin artificial fibers that mimic the nanostructures and optical properties of the natural fibers.

Madagascar comet moth cocoon fibers

“The comet moth fibers are the best natural fibrous material to block sunlight we’ve ever seen. Synthesizing fibers possessing similar optical properties could have important implications for the synthetic fiber industry,” said Yu, an expert in nanophotonics. “Another amazing property of these fibers is that they can guide light signals or even transport simple images from one end to the other end of the fiber. This means we might be able to use them as a biocompatible and bioresorbable material for optical signal and image transport in biomedical applications.”

While individual fibers produced by our domesticated silkworms look like solid, transparent cylinders under an optical microscope, the individual thread spun by the comet moth caterpillars has a highly metallic sheen. The comet moth fibers contain a high density of nanoscale filamentary air voids that run along the fibers and cause strong specular (mirror-like) reflection of light. A single fiber with the thickness of a human hair, about 50 microns in diameter, reflects more than 70% of visible light. In contrast, for common textiles, including silk fabrics, to reach such level of reflectivity, one has to put together many layers of transparent fibers for a total thickness of about 10 times that of a single comet moth fiber. In addition, the high reflectivity of comet moth fibers extends well beyond the visible range into the infrared spectrum — invisible to the human eye but containing about half of the solar power. This, together with the fibers’ ability to absorb ultra violet (UV) light, makes them ideal for blocking sunlight, which contains UV, visible, and infrared components.

Yu is currently working on increasing the throughput of producing such bioinspired nanostructured fibers. His lab wants to achieve this with minimal modifications to the common practice of industrial fiber pulling.

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