Bionic Eyes

Scientists at Johns Hopkins University, MIT, and elsewhere have tried to build artificial rods and cones before, notes Ignatiev. Most of those earlier efforts involved silicon-based photodetectors. But silicon is toxic to the human body and reacts unfavourably with fluids in the eye - problems that SVEC's ceramic detectors do not share.

"We are conducting preliminary tests on the ceramic detectors for biocompatibility, and they appear to be totally stable" he says. "In other words, the detector does not deteriorate and [neither does] the eye."

[More] In 1996, during shuttle mission STS-80, astronauts use Columbia's robotic arm to deploy the Space Vacuum Epitaxy Centre's Wake Shield Facility.

"These detectors are thin films, grown atom-by-atom and layer-by-layer on a background substrate - a technique called epitaxy," continues Ignatiev. "Well-ordered, 'epitaxally-grown' films have [the best] optical properties."

Crafting such films is a skill SVEC scientists learned from experiments conducted using the Wake Shield Facility (WSF) - a 12-foot diameter disk-shaped platform launched from the space shuttle. The WSF was designed by SVEC engineers to study epitaxial film growth in the ultra-vacuum of space. "We grew thin oxide films using atomic oxygen in low-Earth orbit as a natural oxidising agent," says Ignatiev. "Those experiments helped us develop the oxide (ceramic) detectors we're using now for the Bionic Eye project."

The ceramic detectors are much like ultra-thin films found in modern computer chips, "so we can use our semiconductor expertise and make them in arrays - like chips in a computer factory," he added. The arrays are stacked in a hexagonal structure mimicking the arrangement of rods and cones they are designed to replace.

The natural layout of the detectors solves another problem that plagued earlier silicon research: blockage of nutrient flow to the eye.

"All of the nutrients feeding the eye flow from the back to the front," says Ignatiev. "If you implant a large, impervious structure [like the silicon detectors] in the eye, nutrients can't flow" and the eye will atrophy. The ceramic detectors are individual, five-micron-size units (the exact size of cones) that allow nutrients to flow around them.