Pioneering work with polymer-based microfabrication methods at Lawrence Livermore National Laboratory (LLNL) is feeding into the primary component of the Artificial Retina Project—namely, development of a flexible, biocompatible microelectrode array.

A key LLNL technique for making thin metal lines “allows us to pack many more electrodes into a much smaller device than previous models,” says Satinderpall Pannu, who is leading the LLNL effort. This technique, coupled with integrated-circuit and wireless technologies, drives the Department of Energy’s advanced retina prosthesis. The current goal is to develop an array with hundreds of electrodes.

Micrometer Sizing
As part of LLNL’s Center for Micro- and Nano-Technology, Pannu and his team are applying their expertise to microelectromechanical systems (called MEMS) that integrate micrometer-sized mechanical elements, sensors, actuators, and electronics through microfabrication technology.

The metal traces forming the electrodes and electronics in the array are less than a micrometer thick, less than 1% the thickness of a human hair. Embedded in such soft, moldable substrates as silicone, the array conforms easily to the curved shape of the retina.

Pannu’s group also is developing methods for integrating complementary metal oxide silicon (called CMOS) electronics into the retinal prosthesis to reduce its overall size and complexity.

These electronics send electrical signals to microelectrodes to stimulate the retina, a function normally generated by the eye’s photoreceptor cells. In blind people suffering from retinitis pigmentosa and age-related macular degeneration, however, this process has broken down. The microelectrode array mimics the function of the photoreceptor cells by electrically stimulating the remaining healthy bipolar and ganglion cell layers.

Additionally, LLNL’s expertise is being tapped to develop advanced ocular surgical tools that will allow surgeons to place the microelectrode array precisely on the retina with minimal tissue damage.

Dual-Use Technology
Many of the technological advances forming the basis of this research stem from LLNL’s role as a national security laboratory.

“This project is a great example of LLNL’s multidisciplinary approach to science,” says Cherry Murray, LLNL’s deputy director of Science and Technology.

Previously, LLNL researchers used silicone as a substrate for microfluidic devices such as biosensors to detect and identify chemical and biological pathogens in waterways.

Since silicone is a biocompatible material, more recent work has focused on developing processes for embedding metal microelectrodes and electronics within silicone for use in biomedical devices.

“We’re leveraging a lot of the technologies we’ve developed for biodetection systems onto the retinal prosthesis, and vice versa,” Pannu explains.

Future applications for the flexible electrode array go beyond the artificial retina. LLNL researchers are working to integrate this technology into next-generation devices such as the cochlear implant for hearing. The array also might be used one day to stimulate the deep brain for treating such diseases as Parkinson’s and chronic depression, and the spinal cord to relieve chronic pain.

“Our hope is that this technology will evolve into a general-purpose neural electrode array,” Pannu says, “helping to restore eyesight in blind people and revolutionizing treatment for all kinds of neurologically based diseases.”

LLNL is managed by the University of California for the U.S. Department of Energy’s National Nuclear Security Administration.