Silk-Based Optical Lenses Green Enough to Eat

Aug. 20, 2008 -- Boiling a sleeping insect alive can make for a new generation of "green" optical devices, according to scientists at Tufts University.

The new silk-based lenses are a nontoxic alternative to glass and plastics and could be equipped with tiny sensors to create a new generation of biodegradable medical devices.

"Anything you can do with traditional plastics you could do with silk," said David Kaplan, one of the co-authors of the study that appeared recently in the journal Biomacromolecules.

"It is as green as you can get -- all water processing, natural proteins, etc."

To make their devices Kaplan and his colleagues boiled the pupae of the Bombyx mori silkworm alive to kill them (standard practice for silk processing) and loosen up the raw silk. They then removed the protein glue that holds the single, unbroken, and up to 3,000-foot-long single strand of silk.

The scientists then took the watery solution of silk and poured it onto a mold and let it air dry, doused it with water, and dried it again. From those films they produced optical lenses between 10 and 100 micrometers that were of roughly equal quality to plastic and glass lenses.

"It's not trivial that you can make very clear lenses and films with silk," said Kaplan. "And second, when we expose them to lasers they behave in an interesting fashion and let us diffract white light with lots of control."

The entire process takes place at normal room temperatures and without the toxic chemical solvents most industrial processes use to create many glass or plastic-based optical devices today.

The researchers say that their silk-based products could be a clean, green replacement for nearly anything made of plastic or glass that would eventually degrade naturally over time when exposed to light.