Design And Fabrication Of Neural Microelectrode Array Based On MEMS

With the development of Biomedical Engineering and micro-electronic mechanical system (MEMS), the research on micro-device of cell-based biosensor has reached on the cellular and molecular level. Cells provide and express a series of biological information which is the research target of the biology and medicine. When stimulated, the living cell responds and takes actions in the form of generation active bio-potential. It is by implanting the microelectrode into biological tissue of interest that bio-potentials generated electrochemically by cells can be obtained.The MEMS-based microelectrode array, as a novel cell-based detecting instrument, can realize the recording of extracellular electrophysiological signals. While sites coupled with the stimulated living cells, the interface of cell-electrode can be constructed to make it feasible to extract and transfer neural signals to the amplifying units. Its small size, reproducible electrical and physical characteristics and easy fabrication make the structure a versatile tool for a variety of neurophysiological application, including pharmaceutical screening, cellular physiological analysis, toxin detecting, peripheral nerve regeneration and environment monitoring, thus they are also promising in fields of neuronal prostheses and the reconstruction of damaged sense organs.This thesis first introduced the microelectrode array designed by ourselves for extracellular action potential recording. The major contents and contributions of this thesis are given in the following aspects:First, the cell-electrode electrical model has been established based on the study of the conductance and permeability of cellular membrane, the characteristics of trans-membrane ionic current and the formation of the active bio-potential. It is the theoretical foundations of cell-based bio-potential instrument design and provides the premise to explain the experiment results. Secondly, It is shown that by optimal geometry dimensions (cross section shape, length and width of the probe shank ,along with the placement and dimensions of sites integrated on the probe shank), probe can be used to penetrate a variety of biological tissues without breakage or excessive dimpling as well as acquiring the high-quality neural signal. The constraints of minimal microprobe dimension, force withstanding capabilities, and the electrodes crosstalk are the main design issues.Thirdly, the overall structure of the 3D array consists of a silicon platform, two 2D planar probes and a spacer. The probes are inserted through slots in the platform and are held orthogonal to the platform by the spacer. All of these components are fabricated on the same silicon wafer using MEMS fabrication process. photolithographic and thin-film techniques have been used to fabricate microelectrodes with much more improved physical and electrical characteristics.Fourthly, the micro-assembly of the 3D probe arrays means dealing with the perpendicular interconnection between the probes and the platform and the connection the 3D array to the DSP system. Orthogonal lead transfer between the probes and the platform has been realized through several times of wire bonding experiments, while using a PCB circuit as an adapter between the platform and the DSP successfully solves the problem that the arranging wire, attached on the DSP system, can not be directly bonded to the platform due to its large sizes.At last, the SD rat experiment, implemented with the micro-machined 3D microelectrode array, has acquired the ideal neural signal; it is suggested that the whole system is available and successful.