Scientists at the University of California at Los Angeles, together with researchers at Second Sight, a Valencia, Calif.-based company working on artificial sense organs, presented their work at the Microelectromechanical Systems or MEMS 2002 conference Wednesday.
Jack Judy, an assistant professor of electrical engineering at UCLA, told United Press International researchers already know the strength of electrical current needed to stimulate the retina even if the eye's light-sensitive cells have stopped working. The problem the group focused on, Judy said, is finding ways to transfer that current without damaging the electrodes involved.
"As you reduce the size of the electrode, because you want a higher density of electrodes in a given area ... for higher-definition images, it starts hitting some barriers," Judy said. "Eventually the charge through the (smaller) electrode can cause hydrolysis -- gas bubbles -- or corrode the metal."
To reach the highest possible density while avoiding the barriers, the group used computer chip-making processes to create a field of platinum posts about 20 microns high and 30 microns across -- a human hair is about 100 microns wide. These posts performed better than a flat surface, but even better results were in store, Judy said.
One step in chipmaking involves rinsing chemicals off a surface before a layer of metal is applied. Judy said the team discovered incomplete rinsing led to the creation of hollow posts, which perform about four times better than the original flat surface.
"When my student showed me this, I said, 'I bet you couldn't do that again,'" Judy said. "He went back and duplicated it not only for platinum, but also gold and nickel."
Today's electrodes can create a very coarse image five blocks square, Judy told UPI, so the hollow-post technology could provide a much more detailed 20-by-20 block image. It might also be possible to alter the current to create shades of grey in each block, therefore providing more detail, he said.
Second Sight already is testing electrodes at the five-by-five level, he said, so the team hopes those results can easily be transferred to the hollow-post electrode model.
But obstacles still remain, said John Foster, chief executive of Innovative Micro Technology, a Santa Barbara, Calif.-based company specializing in complex chipmaking and MEMS techniques. Essentially, electricity seeks out sharp corners to travel from, Foster told UPI, so the hollow-post configuration might simply transfer corrosion and hydrolysis problems to the outer lip of the post.
Another problem lies in figuring out how to create separate electrical contacts for electrodes of that size, Foster said. The best today's technology can do is create a contact a few hundred microns wide, he said, so several hollow posts would have to go into a single electrode. That approach, however, might mitigate the "sharp corner" problem on individual posts, he said.
Judy said the group is creating computer models of different hollow-post designs to deal with the "sharp corner" issue. Foster said it's quite possible those models will show a simple rounded bump is preferable to a post for this application.
There's also much more in the way of systems design to be worked out for creating a practical retinal stimulation device, Judy said. This includes finding an optimal stimulation point, since experiments have shown a single electrode can elicit points, lines or even shapes, depending on the retinal area affected, he said. Another issue involves creating a wireless interface between the electrodes and whatever camera system is used outside the body.
Co-sponsored by the Institute of Electrical and Electronics Engineers and the Robotics and Automation Society, the MEMS 2002 conference displayed the latest research into devices ranging from a small computer chip down to a few molecules in size. Scientists expect the technology to provide breakthroughs in several areas, including medicine, computers and robotics, in the next few years.
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