29-12-2009, 02:58 PM
The design, fabrication and testing of a novel neurochip structure for extracellular stimulation and recording of cultured neural networks are presented. The neurochip has 16 neuron wells, spaced 100 Ã‚Âµm apart, in a 4 x 4 array, which are fabricated on a 9 mm by 3 mm silicon membrane, 20-Ã‚Âµm-thick. The fabrication of the chips involves photolithography and micromachining on both sides of the membrane, which is located at the bottom of a 500-Ã‚Âµm-deep cavity. Experimentally, the biocompatibility has been demonstrated by culturing live neuron networks in the neurochips.
INTRODUCTION The dynamics of long-term synaptic interactions is thought to be a key problem in understanding brain function. The study of synaptic plasticity is now possible in vitro, due to advances in cell culture, which allow specific neuron types to be removed from an animal and grown in a biochemical environment similar to their original habitat for periods of months. As a result, studies of synapse formation and neurite outgrowth are much easier to perform on cultured neurons. In general, it is not easy to achieve long-term, two-way electrical connection with the cells . Moreover, difficulties may arise if one would like to perform experiments on cultured neural networks, where simultaneous electrical connection with many neurons is required. As for establishing electrical connection with cells, one way is to impale a neuron by a glass electrode filled with electrolyte. Another similar technique, so called patch-clamp technique, is using a thin glass pipette of the proper shape to tightly seal against a cell membrane . Both techniques are extremely sensitive to voltage changes and highly specific in spatial resolution, but they can damage the cell during experiments. Also, it is extremely difficult to use more than two electrodes simultaneously, because of the bulky manipulators required to maneuver the electrodes into the correct position. Another category of methods is to use extracellular electrodes that capacitatively measure the cell potential. Silicon micromachining has been used to make such microdevices. For example, Najafi and Wise  have laid a valuable foundation for silicon multielectrode probes. Regehr, Pine and Rutledge  have demonstrated novel diving board electrodes for cultured neuron study. The major advantages of these silicon electrodes are their small sizes and biocompatibility. However, using these microdevices requires physical movement of the devices to, or near to, target neurons in order to form neuronmicrodevice connections. There are major drawbacks such as a lack of reliable and precise potential measurement due to a small signal-tonoise ratio and a poor spatial resolution.