Making Silk Optical Devices With Photolithography | Chemical & Engineering News
  • Correction: The captions for this story were updated on April 27, 2015, to credit the images to the correct journal. The story was also updated on May 19, 2015, to correct the spelling of researcher Vamsi K. Yadavalli’s name.
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Web Date: April 24, 2015

Making Silk Optical Devices With Photolithography

Materials: A manufacturing method taken from the semiconductor industry could help scale up production of high-tech silk devices
Department: Science & Technology | Collection: Green Chemistry, Life Sciences
News Channels: Materials SCENE, Biological SCENE
Keywords: silk, optics, photolithography
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IRIDESCENT SILK
A microstructured pattern of silk proteins diffracts sunlight to produce a rainbow of colors. The design is about 1 cm2 in size.
Credit: ACS Appl. Mater. Interfaces
Photo of iridescent micropattern made out of silk proteins with photolithography.
 
IRIDESCENT SILK
A microstructured pattern of silk proteins diffracts sunlight to produce a rainbow of colors. The design is about 1 cm2 in size.
Credit: ACS Appl. Mater. Interfaces

Researchers have demonstrated the use of photolithography to pattern simple optical devices out of silk proteins (ACS Appl. Mater. Interfaces 2015, DOI: 10.1021/acsami.5b01380).

Fibers from the cocoon of the silkworm Bombyx mori have long been fashioned into lustrous textiles and medical sutures. Lately, researchers have shown silk’s potential as a material for making optical devices, such as lenses, that are flexible and biodegradable. Such devices could be used in implants for delivering light-triggered therapies, or in environmentally friendly sensors. “If you want to make green photonics and electronics, those are overwhelming reasons to use silk,” rather than the typical plastic or glass, says Vamsi K. Yadavalli of Virginia Commonwealth University.

Researchers at Tufts University pioneered the field of making silk optical devices by molding and other methods. In 2013, Yadavalli’s group demonstrated a potentially faster and less expensive way to build with silk: photolithography (Adv. Mater., DOI: 10.1002/adma.201302823). This high-volume manufacturing method is used to make computer chips but isn’t typically used to build with biological materials such as proteins.

Yadavalli and colleagues make silk proteins compatible with photolithography by decorating them with photoreactive acrylate groups. The researchers then coat the photoreactive proteins onto a surface and expose them to a flash of ultraviolet light through a patterned mask. The illuminated acrylates cross-link, and the unexposed parts can be rinsed away.

In the current study, Yadavalli’s team used photolithography to make two simple optical devices: a flat lens called a Fresnel zone plate and an iridescent pattern. When making optical devices, it’s best to be able to pattern features hundreds of nanometers in size, comparable to the wavelength of visible light. Currently this technique can create features 1 μm in size; therefore, Yadavalli is working on improving the resolution.

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SILK OPTICS
Scanning electron micrographs show an array of 5-μm-diameter posts (left) and a Fresnel lens (right) made out of silk proteins using photolithograpy.
Credit: ACS Appl. Mater. Interfaces
Scanning electron micrographs of micropatterns made out of silk proteins.
 
SILK OPTICS
Scanning electron micrographs show an array of 5-μm-diameter posts (left) and a Fresnel lens (right) made out of silk proteins using photolithograpy.
Credit: ACS Appl. Mater. Interfaces
 
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Comments
DAK (May 4, 2015 8:47 AM)
Why do you think this is Green Chemistry? It takes considerable resources to raise silk worms and harvest their cocoons. These resources must be larger than that for plastics otherwise silk would be less expensive. Also, adding acrylate groups is unlikely to be benign chemistry. Better to use BSA as a protein as at least that protein is discarded from cow slaughter.

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