In order to mitigate the effccts of neurological disability, new neural interfaces are actively being developed. We present several new neural interfaces which can be used in both implantable and on-chip devices.
The silicon-on-insulator-based implantable multielectrodearray with integrated fluidic channels can record responses from cells in the visual cortex. It has fluidic outlets arranged in a sprinkler design, so that a neurotransmitter can he perfused into a large area of tissue. This fabrication process requires only reactive ion etching to define the probe outline and will be compatible with the eventual addition of on-board electronics.
A polymer coating can greatly improve the biocombatility of a biosensor. Here, the lift-off method of patterning a fluoropolymer film is presented. The film is very hydrophobic, with a contact angle greater than 110". Features ranging in size from 4 um to 1 mm are patterned in a single, easy step. This method is also compatible with standard semiconductor fabrication processes. A hydrophilic substrate patterned with this polymer can direct cell and protein attachment. The NG108-15 and SHSY5Y cell lines were used in cell adhesion studies. When the patterned features are greater than 50% of the average cell diameter, the cells prefer to grow on the hydrophilic area, where they can attach. In addition, hydrophilic substrates with polymer features can be used to pattern other materials, such as aqueous solutions of proteins. Fluorescently labeled polylysine was easily patterned onto hydrophilic grid lines in between hydrophobic areas
A novel planar patch clamp array is presented which can replace the traditional glass pipette used in electrophysiology. The substrate, which can be used for parallel analysis of cells or tethered lipid bilayers, has three-dimensional ring-shaped nozzles which are each connected to individual fluidic channels. Since this new design is vertically oriented, it allows the simultaneous recording of electrophysiology and optical/scanning probe data from each patch site, which was riot, previously feasible. The ideal microelectrode has maximum selectivity and minimum impedance. This can be achieved through the addition of nanostructures on the electrode surface, which increase the effective surface area. In order to maintain long-term survival of cells cultured on these electrodes, a new package was made to keep both the cells and electrodes viable. Pillar-shaped structures are created in a highly selective reactive ion etch arid are less than 100 nm in diameter. These structures increase the surface area more than 10 times, and decrease the impedance by an order of magnitude.
All of these neural interfaces have applications in a wide range of biosensor technologies; the polymer patterning and nanostructure modification methods presented here are applicable to a variety of materials and substrates. Optimization of the neural interface will help to enable the next generation of biomedical microdevices.
May 31, 2002
Cheung, K. C. (2002). Microscale and Nanoscale Neural Interfaces. United States: University of California, Berkeley, with University of California, San Francisco.