Surface Modification Of Neural Electrodes For Electrical Stimulation And The Effects On Behaviors Of Neural Cells

Neural electrical stimulation provides a new treatment for neurological diseases such as Parkinson’s and epilepsy.With the global population gradually aging and the increasing of neurodegenerative diseases,there is a growing demand for neuroprosthesis with neural electrical stimulation.As the most critical component of the neural prosthesis,neural electrode directly contacts the tissue and injects the stimulating charge into the targeted tissue.The biocompatibility of the electrodes and the electrochemical performance of the electrodes are important problems need to be resolved urgently.In our study,Iridium Oxide(IrOx)coating was constructed on the surface of the electrode to improve the electrochemical performance of the electrode.Polydopamine(PDA)was modified on the surface of IrOx by self-polymerization of dopamine.Then,laminin(LN)was grafted for secondary functionalization to improve the biocompatibility of the coating and promote the adhesion and proliferation of neural cells(PC 12 and NSCs).Besides,the effects of electrical stimulation on neural cell behavior were investigated through a self-made electrical stimulation device.The details are as follows:1.Preparation and characterization of IrOx coating.Ir film was prepared by RF magnetron sputtering and then activated to IrOx coating in 0.1 M H2SO4 or 0.5 M Na2HPO4 by cyclic voltammetry.The FE-SEM images show that the IrOx coating has a regular porous structure compared with Ir,and the structure of the IrOx coating activated in 0.1 M H2SO4 is more uniform.Cyclic voltammetry tests show that the IrOx coating has excellent charge storage capacity(CSC),mechanical stability and electrochemical stability.The EIS results demonstrate that the IrOx coating has a lower impedance under 1 kHz.These results indicate that IrOx has excellent electrochemical properties and IrOx is a suitable surface modification material for neural electrodes.2.Preparation and characterization of IrOx/PDA/LN coating.PDA was immobilized on the surface of IrOx by oxidative self-polymerization of dopamine.Then,LN was grafted on PDA for secondary functionalization.The results show that the thickness of PDA gradually increased with the increase of oxidation self-polymerization time of dopamine,and the thickness of PDA reached 37.18+0.94 nm after 24 hours.IrOx/PDA only released a small amount of dopamine in PBS,which indicates the coating is very stable.Elemental analysis by XPS and protein quantitative analysis show that the protein content on PDA surface is gradually increased with the increase of LN concentration,indicating that PDA can effectively immobilize LN to the subtrates.The water contact angles of IrOx,IrOx/PDA and IrOx/PDA/LN coatings were 122.43 ± 5.70°,75.31 ± 3.93°,and 68.60 ± 3.30°,respectively.It demonstrates that modification of PDA and LN can significantly improve the hydrophilicity of the material.The above results show that IrOx/PDA/LN coating has excellent stability and hydrophilicity.3.The biocompatibility of the IrOx/PDA/LN coating was further evaluated by the indirect cytotoxicity of the extract medium and the adhesion and proliferation assay of neural cells on the coatings.The results show that IrOx has no cytotoxicity to PC 12 cells and NSCs,and IrOx/PDA/LN coating can promote the adhesion and proliferation of PC 12 cells and NSCs.When NSCs were cultured on the surface of the IrOx/PDA/LN coating,it was found that under the influence of the surface pattern of the coating,with the increase of culture time,the neurites of NSCs began to align and gradually parallel to the direction of the surface pattern.Due to the excellent electrical conductivity of the IrOx/PDA/LN coating,the extension of NSCs on the IrOx/PDA/LN samples increased.These results further demonstrate that the IrOx/PDA/LN coating has good biocompatibility and can be applied for surface modification of implantable neural electrodes.4.The effects of electrical stimulation on the behavior of neural cells.We applied electrical stimulation to the PC 12 cells on the IrOx/PDA/LN coating,the electrical stimulation direction is perpendicular or parallel to the surface texture.We found that the neurite outgrowth of PC 12 on the IrOx/PDA/LN coating increased after electrical stimulation,and the arrangement of neurites reoriented towards the direction of electrical stimulation.After electrical stimulation with specific parameters of NSCs on the IrOx/PDA/LN coating,the proportion of NSCs differentiated into neurons increased.These results indicate that when the IrOx/PDA/LN coating is applied as a surface coating for neural stimulation electrodes,it can regulate the behavior of neural cells under specific electrical stimulation conditions,and promote the differentiation of NSCs into neurons to repair neural networks,which is of great significance for the treatment of nervous system diseases.