Transparent Butterfly Wings Inspire Researchers To Create Eye Implant For Glaucoma Patients

Glasswing butterflies and the unusual optical properties of their wings led to perfected eye implants that accurately measure intra-eye pressure.

According to the World Health Organization, glaucoma is the second leading cause of blindness worldwide, after cataracts. Studies suggest that the disease damages eyesight due to sudden spikes in intra-eye pressure, which affect the optic nerve.

To measure the pressure inside their eyes, glaucoma patients typically make a trip to the doctor’s office once or twice a year. This is hardly enough, opines Hyuck Choo, from the California Institute of Technology (Caltech) in Pasadena.

Choo, who is an assistant professor in the Division of Engineering and Applied Science at the institute, wanted to provide glaucoma patients with “a way to measure their eye pressure easily and regularly,” states a Caltech news release.

Therefore, he developed a drum-shaped eye implant, no wider than a few strands of hair, which keeps tabs on intra-eye pressure by flexing as the pressure goes up. This narrows the depth of the cavity inside the drum, which can be measured using a handheld optical reader that shows exactly how much pressure the implant is under.

The only problem with this eye implant was that, in order to get an accurate reading, the optical reader needed to be held in an almost perfectly perpendicular position to the surface of the implant, at an angle of 90 degrees (plus or minus five degrees).

The fix came from the unlikeliest of places and was inspired by glasswing butterflies.

This butterfly species, scientifically known as Greta oto, is famous for its transparent wings. In fact, the wings of glasswing butterflies have sections that reflect almost no light and are nearly perfectly transparent according to the laws of optics. If you’re wondering how this is possible, Radwanul Hasan Siddique, a Caltech colleague of Choo’s, figured out the answer three years ago.

Siddique studied glasswing butterflies for his dissertation and discovered that those particular sections in the butterflies’ wings are coated in microscopic pillars which hold unusual optical properties. These tiny pillars are only 100-nanometers-wide — 50 to 100 times smaller than the width of a human hair — and stand 150 nanometers from one another, notes the news release.

“The pillars redirect the light that strikes the wings so that the rays pass through regardless of the original angle at which they hit the wings,” explains the Caltech news release.

In a creative mash-up of nature and science, Choo and Siddique decided to apply the pillars’ redirection property, known as angle-independent antireflection, to correct the fault with the eye implant.

Together with Caltech graduate student Vinayak Narasimhan, the pair developed a synthetic version of the microscopic pillars, made from silicon nitride. When placed on the surface of the implant, the nanopillars reduced the error in the device’s readings threefold, notes the news release.

According to Choo, the key to their success lies in the nanoscale components inspired by nature.

“The nanostructures unlock the potential of this implant, making it practical for glaucoma patients to test their own eye pressure every day.”

The trio explained the process in the video below, noting that they also came up with an idea to counteract biofouling, a process that normally occurs with medical implants because body cells attach to their surface over time.

To prevent this from happening, the scientists made the synthetic nanopillars extremely hydrophilic, so they would attract water and coat the implant in a protective layer.

“Cells attach to an implant by binding with proteins that are adhered to the implant’s surface. The water, however, prevents those proteins from establishing a strong connection on this surface,” explains Narasimhan.

The result: a better, longer-lasting eye implant that proved 10 times more resistant to biofouling compared with its original version. The new device is described in a study published yesterday in Nature Nanotechnology.
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