| Nerve electrodes are a kind of micro-devices for the functional electrical stimulation of neurons or the detection of neuronal firing signals.They are widely used in neuroelectrophysiology and behavioral physiology.However,microelectrode devices based on inert metals such as gold and platinum have limited charge transfer capabilities at the nerve-electrode interface.Therefore,the development of new materials and electrode modification technologies is very important to improve the long-term stability of implantable nerve electrodes.In this paper,we choose indole derivatives and poly-3,4-ethylenedioxythiophene(PEDOT)as materials,and then use electrochemical polymerization to modify the surface of nerve electrodes.We studied the effect of conductive polymer modification on the performance of neural electrode.At the same time,we also study the preparation process of flexible neural microelectrode devices to improve the long-term usability of neural electrode.It mainly includes the following contents:The electrochemical polymerization behavior and electrode modification effect of aminoindole,nitroindole and carboxyindole were studied.The experimental results showed that the the modification of the electrode surface by poly-5-nitroindole can improve the performance of the electrode.After modification,the impedance of the electrode at 1 k Hz decreased to 137±12?,and the cathode charge storage capacity(CSCc)increased to1.39±0.19 m C/cm~2.Besides,after the modification of poly-5-aminoindole,poly-6-aminoindole,poly-7-aminoindole,poly-6-nitroindole and poly-7-nitroindole,the impedance values of gold electrode increased in different magnitudes.However,because the binding force between polycarboxyindole and gold film is very weak,the polycarboxyindole is not suitable for the modification of gold electrodes.Further research on the modification behavior of poly-5-nitroindole and PEDOT on gold electrodes showed that although the impedance of the electrode at 1k Hz after PEDOT modification dropped to 78.5±11?and the CSCc increased to 16.41±1.90 m C/cm~2,poly-5-nitroindole modified electrode showed more stable electrochemical performance than PEDOT,and poly-5-nitroindole had stronger interfacial binding force with the gold film.Cell death and live staining experiments showed that the growth of SH-SY5Y cells on the surface of the poly-5-nitroindole film was better than that of the PEDOT group,indicating that poly-5-nitroindole had better biocompatibility.Therefore,for medium-term and long-term implantation applications,poly-5-nitroindole has a larger potential than PEDOT.The structure of flexible neural microelectrode device was designed using Cle Win5software.The microelectrode included a three-layer structure:a bottom insulating support layer,a middle conductive layer,and a top insulating encapsulation layer.The implanted part was designed as a triangular mesh structure,the microelectrode was designed as a circle with a diameter of 30?m,and the interface part was designed as a FPC gold finger structure.The flexible neural microelectrodes were prepared by further micromachining methods such as photolithography,metal deposition and etching,and the micromachining process flow based on photoresist SU-8 2000.5 and AZ5214E was optimized to solve the problem of degumming and defects.The obtained microelectrode has good morphology and structure,and exhibits good flexibility after releasing from the silicon wafer by etching the sacrificial layer.The surface modification of the microelectrode and the electrochemical performance test were performed.The results showed that the interfacial charge transfer ability of the microelectrode was also significantly improved after the modification of poly-5-nitroindole.Further research was made on the implantation method of flexible electrode devices.And a platform of microwire and PEG assisted implantation was set up,then we realized the combination of the flexible electrode device with copper wires and the re-release of the device in PBS solution. |
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