"Controlling tissue response is particularly important for implants, which tend to work for a while, then lose electrical sensitivity," said Bruce Wheeler, a UI professor of electrical and computer engineering and a researcher at the university's Beckman Institute for Advanced Science and Technology. "If we can better understand and control the interface between electronic components and nerve cells, we could build more sophisticated and longer-lasting implants."
Wheeler's microstamping technique uses lithographic methods, borrowed from the microelectronics industry, to precisely reproduce a master pattern with biologically relevant materials. "The microstamp works the same as a conventional rubber stamp except that the ink is polylysine (an artificial polymer commonly used for cell culture) and the patterns produced are measured in micrometers, or the same size as the cells themselves," Wheeler said.
To culture nerve cells in a dish, Wheeler works with graduate students John Chang and Johnny Nam, as well as colleague Gregory Brewer, a professor of medical microbiology at the Southern Illinois University School of Medicine in Springfield, who first removes brain cells from developing rat embryos. The cells are chemically and mechanically separated, then poured onto the patterned polylysine where they selectively attach to the surface.
"Within a few days, the cells send out processes that explore the environment, preferring areas that have intact polylysine," Wheeler said. "The cells soon mature and begin sending electrical signals." Microlithographic techniques also can be used to fabricate planar microelectrode arrays. Confining the neurons to narrow tracks that intersect electrodes creates a technological basis for robust, designable neural networks useful for studying basic neuroscience or for constructing elaborate neural biosensors. "One problem with biomaterials growing on a micropatterned array, however, is the long-term stability and retention of biological activity," Wheeler said. "Also, because the brain has ordered layers of cells, we believe that orderly growth will lead to greater insight to brain activity, and we have had to develop techniques for maintaining the orderly growth of the neurons in culture."
Working with UI professor Deborah Leckband, the researchers have placed a layer of polyethylene glycol to successfully reduce unwanted protein adhesion and cell growth in portions of the array.
"The nerve cells maintained compliance to the microstamped patterns and remained viable for up to one month," said Wheeler, who presented the team's latest findings at an international workshop on cells on solid substrates, held in Tegernsee, Germany, June 27-30.