Study Of Electrochemical Modification Of Implantable Cortical Electrodes For Rats

Neural electrode and its devices play an important role in neural therapies and neuromodulations, because it contacts with neural tissue directly and injects the stimulation charge into target neural tissue. Currently, neural stimulation in vivo and brain research are in a key stage of operating animal study and preclinical trials. Development of high performance electrodes would promote these studies towards clinical application.Considering the requirments of the rat cortical stimulation, a fully implantable electrical stimulator and a low cost flexible electrode array were developed, different electrochemical modification technologies for the implantable neural electrodes were investigated. The detailed contents are as follows.The section 1 including chapter 2, is a study of the fully implantable electrical stimulator and its electrode. To meet the needs of fully implantable electrical stimulator for rats, nanostructured porous platinum (Pt-p) electrode was prepared by electrochemical modification. The experimental results showed that, after the surface modification, the electrochemical performance of the electrodes in the phosphate buffered solution (PBS) was improved remarkably. The impedance of Pt-p electrode at 1 kHz decreased by 62.3%, compared to the smooth platinum electrode. The voltage transient experiment on rats revealed Pt-p electrodes could help reducing the energy consumption, and thus prolong the duration of electrical stimulator implants. Morever, the neuronal nuclei (NeuN) staining revealed that the electrode material was biocompatible under stimulation after 16 days implantation in rats.The section 2 including chapter 3, is a study of flexible electrode array and its application for brain mapping. Based on the flexible printed circuit (FPC) technology, the flexible can be easily prepared. The main ingredient of the electrode material are polyimide and plated gold. They are know as biocompatible. With the electrochemical and morphology study in vitro, the electrode site of the array are good processing reprodycubility. The safe charge injection (Qinj) limit was 0.23 mC/cm2 for anodic-first stimulation, which are comparable to the platinum electrode. Then, brain mapping experiment was conducted after the electrode array was implanted to the rat motor cotex. The behavior response can be successfully recorded, when the delivered electrical pulse reached the stimulation threshold.The section 3 including chapter 4,5 is the section of electrochemical modification for the flexible electrode arrays. In chapter 4, the Grephene and the polystyrene sulfonate doped Poly(3,4-ethylenedioxythiophene) (PEDOT) was used to modified the electrode array. Three different modes of electrodeposition were performed, including the potentiostatic method, galvanostatic method, and the galvanostatic method combined with the potentiostatic method, and the electrochemical performance were compared. The results showed the FPC electrode arrays modified by the galvanostatic method combined with the potentiostatic method (FPC-GP) exhibited the best electrochemical characteristics. The impedance of FPC-GP electrode at 1 kHz decreased by 94%, compared to the electrode sites without coating. The Qinj limit reached 3.2 mC/cm2 for cathodic-first pulses. Based on the superior characteristic above, we consider the flexible electrode arrays deposited with the conducting polymer is suitable for the acute animal experiments.The chapter 5, we studied the electrodeposition of iridium oxide (IrOx) to modify the flexible electrode arrays. The different parameter of potential square wave depositon and CV deposition method were investigated. The results showed that the FPC electrode array deposited with IrOx by 400 potention square waves possessed the best electrochemical performance and stability. The impedance of FPC-GP electrode at 1 kHz decreased by 89.3%, compared to the FPC electrode site without coating. The Qinj limit reached 2.2 mC/cm2 for anodic-first pulses. Morever, after the ultrasonic accelerate testing and 500 CV cycles experiments, the reduction of CSCc was only 4% and 4.3%, respectively. Based on the superior characteristic above, we consider the IrOx films deposited in the optimized condition can meets more requirement of electrical stimulation application in animal experiments.