The Enhancement Of A Chronically Implanted Microwire Electrode Array Performance And The Investigation Of Evaluation Method

The brain is the most complicated systems. Each process of the brain response to external events and information processing needs combined action of many neurons. To reveal the complicated mechanism of brain information processing, must obtain a sufficient number neurons of electrical activity information in the living brain environment. Microelectrode array recording technique provides an ideal electrophysiological detection means, and obtains a large number of neurons of electrical activity information at the same time. It lays the foundation for the working mechanism of study of brain neurons and its networks and the development of new neural restoration technology. Microwire electrode fabrication is relatively uncomplicated, and homemade microwire electrode has the advantages of small volume, multiple recording points, stable and reliable performance.Electrodes are expensive consumables of electrophysiological experiments. Cheap and homemade microwire electrodes have been widely applied, at present, the size of the electrode tip surface is bad and its recording longevity is short. To fabricate low cost and acceptable performance of microwire electrode, first, the key factors were analyzed, and these factors affect the long-term recording performance. Then, the orientation of the enhancement of electrode was determined. The electrode performance was improved through electrode fabrication process and the electrode tip surface modification, and systematically evaluated its electrochemical impedance properties, signal acquisition ability and biocompatibility. The main task is as follows:(1) The electrode performance was improved through electrode fabrication and the electrode tip surface modification. On one hand, electrode fabrication and electrode tip cutting method were enhanced. Using enhanced modified fabrication process, its size becomes smaller, its surface electrode tip is smooth, and the injury to the animal brain tissue decreased after implantation; on the other hand, using the method of constructing a layer of conductive polymer on the electrode tip was modified on the electrode tip.(2)The equivalent model of impedance of electrode-conducting polymer -electrolyte was built, and the validity of the equivalent model was proved by electrochemical impedance spectroscopy in vitro, and compared with the undecorated electrode, the modified electrode impedance is reduced by an average of56.1%.(3) To do the chronic implantation experiment, regularly acquired the signal of chronically implanted rats. From signal-to-noise ratio(SNR), neuron output and recording longevity, long-term recording signal ability of the electrode was evaluated. The results show that, compared with the undecorated electrode, the SNR of modified electrode is higher, and its neuron output is more and its recording longevity is longer.(4)Monitored physiological indexes of chronically implanted rats and fabricated the fluorescence immunohistochemistry sections. As a result, modified electrodes were embedded into rat brain regions, and each physiological index of rats remained at normal levels, while the unmodified electrodes were implanted into rat brain regions, every physiological index of rats were abnormal. The degree of astrocyte aggregation surrounding modified electrode site is less than the degree of astrocyte aggregation around unmodified electrode site. Combined physiological indexes and fluorescence immunohistochemistry sections reveals that the biocompatibility of the modified electrode is good, and its biocompatibility is better than the unmodified electrode’s.The results show that the electrode by this improved process and the tip surface modified has good electrochemical impedance properties and biocompatibility. The manufacturing cost of the electrode is low, and its recording longevity is longer, and meets the general requirements of neural electrophysiological experiments.