Bionic Eyes

Applications of the Wake Shield research extend much further than the semiconductor and electronics industries. Ignatiev has pointed to the ability to build replacement rods and cones - which convert light into electrical impulses and transmit them along the optic nerve to the brain, constructing images and enabling us to 'see' - for insertion into the retina, possibly aiding retinitis pigmentosa and macular degeneration, both of which can lead to permanent blindness. ''If only we could replace those damaged rods and cones with artificial ones,'' said Ignatiev, ''then a person who is retinally blind might be able to regain some of their sight.''

Even as the three WSF missions were underway, SVEC researchers were busy experimenting with thin, photosensitive ceramic films, capable of responding to light in much the same way as rods and cones. Arrays of such films, it is hoped, could be implanted in human eyes to restore lost vision; in effect, creating 'bionic eyes'. Previous tests had been conducted with silicon-based photodetectors, which are toxic to the human body and react unfavourably to fluids in our eyes, whereas ceramic ones are considerably more stable.

''We grew thin oxide films using atomic oxygen in low-Earth orbit as a natural oxidising agent,'' said Ignatiev. ''Those experiments helped us to develop the oxide [ceramic] detectors we're using now for the Bionic Eye project.'' He pointed out that the ceramic detectors are much like computer chips and can be 'arrayed' in the same way; by arraying them in a hexagonal structure, mimicking the arrangement of the rods and cones they are designed to replace, it was expected that they would not block the flow of nutrients to the eye.

''All of the nutrients feeding the eye flow from the back to the front,'' Ignatiev explained. ''If you plant a large, impervious structure [like silicon detectors] in the eye, nutrients can't flow'' and the eye would atrophy. The ceramic detectors, on the other hand, are individual, five-micron-sized units - the exact size of cones - which allow nutrients to flow around them. Artificial retinas constructed at SVEC consisted of 100,000 ceramic detectors, each a twentieth the thickness of a human hair; so small, in fact, that the only way to handle them was to attach them to a one-millimetre-square piece of film.

Within two weeks of insertion into the eyeball, this polymer film simply dissolved and left only the arrays behind; even at the time of the WSF-3 mission, Ignatiev was expecting the first human trials to take place around 2002. ''An incision is made in the white portion of the eye and the retina is elevated by injecting fluid underneath,'' said Charles Garcia of the University of Texas Medical School, the surgeon-incharge of the procedure. ''Within that little 'blister', we place the artificial retina.'' However, he pointed out that such technology was still in its infancy.

Originally, four WSF missions were planned: three funded by NASA and a fourth by industry. In May 1998 the Spacehab company acquired the rights to market and manage the Wake Shield from the University of Houston. ''This is a key first step to reassemble the WSF engineering team and bring the hardware out of storage,'' Spacehab project manager Mike Chewning said at the time. ''We have set a very aggressive goal for the flight system to be ready for a mission in mid-1999 and we are all anxious to get started.''

Sadly, WSF-4 - which was to have included solar panels for additional power and a capability to produce as many as 300 semiconductor thin films - never flew and, with the focus of post-Columbia missions exclusively on the International Space Station, in all likelihood never will.

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