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The Wings of a Butterfly Lead to an Idea for an Eye Implant

Posted by Ilena Di Toro | Posted on January 29, 2019

In open angle glaucoma, fluid passes too slowly through the opening where the cornea and iris meet. This fluid build-up leads to increased pressure on the eye. Left unchecked, vision loss can occur. Wouldn’t it be great if there was an implant that could be used to monitor intra-eye pressure in glaucoma patients? Research on butterfly wings has inspired such an implant.

The Longtail Glasswing butterfly has wings that are almost transparent. The reason for this has to do with the fact that the wings are coated in tiny pillars. Each pillar is approximately 100 nanometers in diameter and spaced about 150 nanometers apart. These pillars are thinner than a human hair and they reflect the light in such a way that the rays pass through the pillars despite the angle at which the light hit the wings. That means there is no reflection of light off the wings and they are as transparent as glass.

This is known as angle-independent anti-reflection. It caught the eye of a researcher at the California Institute of Technology (Caltech), Hyuck Choo, an assistant professor of electrical engineering in the Division of Engineering and Applied Science. He has been working on implant that would improve the monitoring of intra-eye pressure in glaucoma patients. While medication helps reduce the eye pressure, it works best when it is taken at the first sign of an increase in eye pressure.

Currently, people with glaucoma have their eye pressure measured a few times a year in a doctor’s office. Yet, there can be changes in pressure in between doctor visits. So, there needs to be something that would monitor eye pressure on a more regular basis. Choo developed an implant that measures eye pressure. This implant is shaped like a drum and the surface changes with increasing eye pressure. The depth of change can be measured with a handheld reader, giving the doctor measurement of how much pressure the implant is experiencing.

Sounds great, doesn’t it? Yet, there is a problem with this and that is in order to get an accurate reading the optical reader needs to be perpendicular the surface of the lens. That’s where the butterfly wings come in. Choo feels that the angle independent optical properties of the Longtail Glasswing butterfly could be utilized to make sure that light would pass in a perpendicular fashion through the implant so that an accurate reading can be made.

Choo is working with Caltech postdoctoral researcher Radwanul Hasan Siddique who did the original research on the butterfly to see if an implant can be made of silicon nitride with pillars the same size as found on the butterfly’s wings. By tweaking the size and placement of the pillars, researchers were able to reduce the error threefold.

Another benefit is that the implant is made from a long-lasting, nontoxic anti-biofouling material. Body cells tend to attach themselves to implants and coat them over time. The nanopillars in this implant are different in that they attract water. The water causes cells to slide off instead of becoming attached to the implant.

While this implant is still in the experimental stage, Choo’s team plans to explore other implants that could benefit from nanopillars which attract water, not cells.


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