WASHINGTON, April 30 (Xinhua) -- American engineers have developed an effective, long-lasting synthetic analogue for eye implants inspired by tiny nanostructures on transparent butterfly wings.
A study published on Monday in the journal Nature Nanotechnology has reported the tiny-drum-shaped eye implant that could monitor the intra-eye pressure in glaucoma patients, with an angle-independent optical property.
Researchers with the California Institute of Technology (Caltech) previously developed an eye implant with the width of a few strands of hair and when inserted into an eye, its surface flexes with increasing eye pressure, narrowing the depth of the cavity inside the drum.
Then, that depth can be measured by a handheld reader, giving a direct measurement of how much pressure the implant is under.
The sudden spikes in the pressure inside the eye damages the optic nerve, causing glaucoma and medication can reduce the increased eye pressure, but ideally it must be taken at the first signs of a spike in eye pressure.
One weakness of the previous implant has been that in order to get an accurate measurement, the optical reader has to be held almost perfectly perpendicular with respect to the surface of the implant.
Then, a longtail glasswing butterfly with transparent wings lent an inspiration. The see-through sections of the wings are found being coated in tiny pillars, each about 100 nanometers in diameter and spaced about 150 nanometers apart.
According to the researchers, these pillars, 50 to 100 times smaller than the width of a human hair, can redirect the light that strikes the wings so that the rays pass through regardless of the original angle at which they hit the wings, so there is almost no reflection of the light from the wing's surface.
Choo, assistant professor of electrical engineering at Caltech, reasoned that the angle-independent optical property of the butterflies' nanopillars could be used to ensure that light would always pass perpendicularly through the implant, making the implant angle-insensitive and providing an accurate reading regardless of how the reader is held.
Choo's team 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.
After experimenting with various configurations of the size and placement of the pillars, the researchers were ultimately able to reduce the error in the eye 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.
Also, the improved surface lent the implants a long-lasting, nontoxic anti-biofouling property.
In the body, cells tend to latch on to the surface of medical implants and, over time, gum them up. One way to avoid this bio-fouling phenomenon is to coat medical implants with a chemical that discourages the cells from attaching, but such coatings eventually wear off.
Choo's nanopillars, however, are extremely hydrophilic, meaning that they attract water. Because of this, the implant, once in the eye, is soon encased in a coating of water, forcing cells sliding off instead of gaining a foothold.
Early testing suggested that the nanopillar-equipped implant reduced biofouling tenfold compared to previous designs.
