Engineers at the California Institute of Technology (Caltech) have developed a synthetic analogue coating for eye implants that makes them more effective and longer-lasting.

The implant, which aims to improve the monitoring of intra-eye pressure in glaucoma patients, was coated by nanopillars that enable readings to be taken more easily from a handheld device.

These nanopillars were inspired by the structural properties of a longtail glasswing butterfly. Research by Caltech postdoctoral researcher Radwanul Hasan Siddique found that see-through sections of the wings are coated in tiny pillars, each about 100 nanometres in diameter and spaced about 150 nanometres apart.

Their size, and the way the pillars redirect the light, allows light to pass through regardless of the angle at which it hits the wings, making it clearer than if they were made of plain glass.

That redirection property, known as angle-independent antireflection, was applied to the eye implant previously developed by Caltech’s Hyuck Choo. Choo’s implant measures an increase in pressure inside the eye, which the leading theory suggests is the cause of glaucoma.

“Right now, eye pressure is typically measured just a couple times a year in a doctor’s office. Glaucoma patients need a way to measure their eye pressure easily and regularly,” said Choo, assistant professor of electrical engineering in the Division of Engineering and Applied Science.

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The drum-shaped implant, measuring the width of a few strands of hair, is inserted into an eye and flexes its surface when pressure increases. That depth can then be measured by a handheld reader.

However, to get an accurate reading the handheld reader has to be held almost perfectly perpendicular to the surface of the implant. Choo applied the angle-insensitive property of the butterflies’ nanopillars to ensure that light would always pass perpendicularly through the implant and provide an accurate reading regardless of the reader’s position.

The research team created pillars approximately the same size and shape of those on a butterflies’ wings, made from silicon nitride. After experimenting with various configurations of size and placement of the pillars, the team was able to reduce the error in the implants’ readings threefold.

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

The long-lasting, non-toxic and anti-biofouling properties of the pillars’ surfaces also make it difficult for cells to latch onto the implant and reduce their effectiveness. This longevity is possible because of the nanopillars’ hydrophilic properties, which cause the implant to become encased in a coating of water and therefore difficult for cells to gain a foothold.

“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,” said Caltech graduate Vinayak Narasimhan, who worked with Choo on the implant.

Early tests suggest that the nanopillar-equipped implant reduces such biofouling ten times more when compared to previous designs.

The team plans to explore what other medical implants could benefit from their new nanostructures, which can be mass-produced inexpensively.

The research was published in Nature Nanotechnology.