Last updated May 3, 2018 at 11:46 am
Finding new uses for unique structures found in nature.
The unique structure of a butterfly’s wings could help create a new generation of eye implants.
Engineers at the California Institute of Technology have found a way to use a redirection property known as angle-independent antireflection to overcome one of the initial problems with a new implant designed to improve the monitoring of intra-eye pressure in glaucoma patients.
The implant, shaped like a drum, is no wider than a few strands of hair. When inserted into an eye, its surface flexes with increasing eye pressure, narrowing the depth of the cavity inside the drum. That depth can be measured by a handheld reader, giving a direct measurement of how much pressure the implant is under.
However, to get an accurate measurement the first iterations of the optical reader had to be held almost perfectly perpendicular, which is limiting.
While pondering this problem, Associate Professor Hyuck Choo read about work in Germany on a species of longtail glasswing butterfly that is so named because sections of its wings are perfectly transparent.
Radwanul Hasan Siddique had discovered that these sections are coated in pillars just 100 nanometres in diameter and 150 nanometres apart.
The pillars redirect light, so the rays pass through regardless of the original angle at which they hit the wings. As a result, there is almost no reflection from the wing’s surface.
Choo reasoned this same optical property could be used to ensure light would always pass perpendicularly through his implant, making it angle-insensitive and providing an accurate reading regardless of how the reader is held.
He enlisted Siddique to work in his lab, and with graduate student Vinayak Narasimhan they figured out a way to stud the eye implant with pillars approximately the same size and shape of those on the butterfly’s wings but made from silicon nitride, an inert compound often used in medical implants.
Over time they were 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,” Choo said.
The new surface also lends the implants a long-lasting, nontoxic anti-biofouling property. Unlike the butterfly’s nanopillars, the lab-made nanopillars are extremely hydrophilic, meaning they attract water. Because of this, the implant, once in the eye, is soon encased in a coating of water. Cells slide off instead of gaining a foothold.
“Cells attach to an implant by binding with proteins that are adhered to the implant’s surface,” Narasimhan said. “The water, however, prevents those proteins from establishing a strong connection on this surface.”
Early testing suggests the nanopillar-equipped implant reduces biofouling tenfold compared to previous designs.
Being able to avoid biofouling is useful for any implant regardless of its location in the body. The team plans to explore what other medical implants could benefit from their new nanostructures, which can be inexpensively mass produced.
The paper published in Nature Nanotechnology.