Butterfly wings inspire a better eye implant
The transparent sections of the glasswing butterfly's wings barely reflect any light, which is why we've previously heard about them inspiring glare-free device screens. Now, their antireflective quality has led to an improvement in a glaucoma-monitoring eye implant.
Glaucoma is thought to cause blindness when pressure within the eye damages the optic nerve. That damage can be minimized via pressure-reducing medication, but that medication should be taken at the first sign of a spike in eye pressure – and unfortunately, most glaucoma patients only get their eye pressure checked about twice a year, at a doctor's office.
To that end, Caltech's assistant professor Hyuck Choo has developed a tiny drum-shaped implant designed to stay in the eye full-time. Its surface flexes in response to eye pressure, reducing the depth of a cavity within the implant. A handheld external device is used to visually read that depth, and by doing so can determine the current amount of pressure. The idea is that patients could use it at home, to frequently check their eyes.
Unfortunately, the reader device has to be held at almost exactly 90 degrees relative to the surface of the implant, otherwise light emitted by the reader won't illuminate the implant at the proper angle, and an accurate reading won't be obtained. That's where the butterfly wings come in.
Exhibiting a quality known as angle-independent antireflection, the clear sections of the wings remain antireflective from any viewing angle. This is because they're coated with tiny pillars that are approximately 100 nanometers in diameter and spaced about 150 nanometers apart. These pillars direct incoming light rays to pass straight through the wing, regardless of the angle at which they strike it.
Choo's team replicated this structure on the surface of the implant, by studding it with pillars that were approximately the same shape and size as those on the butterfly wings. The pillars were composed of silicon nitride, which is an inert material. After some experimenting, the scientists were ultimately able to achieve a threefold error reduction when reading the implant.
As a side benefit, it was found that the nanopillars are very hydrophilic, meaning that they attract water. This keeps the implant encased in water, stopping cells from adhering to it and gumming it up (a process known as biofouling).
"The nanostructures unlock the potential of this implant, making it practical for glaucoma patients to test their own eye pressure every day," says Choo.
A paper on the research was recently published in the journal Nature Nanotechnology.