| Vision is one of the most important five senses of human beings.Having a perfect visual pathway is a necessary condition for obtaining normal vision.Studies have shown that among the blind,most of the blind's visual pathways are not completely destroyed and the use of electrical stimulation of their optic nerve can also produce illusion of light.Among these blind people,implanting artificial retinal prostheses can help them restore a certain degree of vision,so that blind people can see the light again.The MEMS flexible electrode as a neural interface realizes the connection between the artificial retinal prosthesis and the patient,and is one of the most critical parts of the artificial retinal prosthesis applied to bionic medicine.The premise that artificial retinal prosthesis implants need good artificial vision is that the artificial retinal prosthesis must have an ultra-high resolution,and correspondingly there must be enough stimulation channels on the MEMS flexible electrode of a certain size.Taking the electrode-electrolyte interface to simplify the basic theory of equivalent circuit,five-point design requirements,electrode material selection,etc.as the design basis,the design scheme based on 126-channel MEMS flexible electrode is proposed.A 126-channel MEMS flexible electrode was designed.The stimulation points were arranged in a matrix of 9×14.The diameter of the stimulation point was 170 ?m.The electrode line width and the minimum line spacing were both 5 ?m,respectively.The edge of the stimulation area was creatively designed.The hole improves the sealing of the electrode silicone injection molding.Polyimide(PI)is used as the flexible substrate layer of the electrode,platinum(Pt)is used as the electrode conductive layer,and titanium(Ti)as an adhesive layer is added between the flexible substrate(PI)and the conductive metal layer(Pt)in order to increase adhesion.According to the design layout of the 126-channel MEMS flexible electrode,based on the MEMS micro-machining technology,a 126-channel flexible electrode with a novel structure(double-layer metal clip PI thin layer structure)with high adhesion was processed,which was tested to meet the design requirements.According to research,it is necessary to integrate at least 1000 stimulation channel electrodes in a limited retinal area to help the blind person to perform good face recognition.Therefore,based on the 126-channel MEMS flexible electrode,a design scheme of 1500-channel MEMS flexible electrode is proposed.In order to be able to arrange 1500 stimulation points in a limited area of the retina,the size,spacing,and width and arrangement of the 1500 channel MEMS flexible electrode stimulation points are strictly controlled.The design of the 1500-channel MEMS flexible electrode divides the electrode into two rows of electrodes,which makes full use of the limited area of the stimulating electrode array to ensure that the stimulating electrode array is densely arranged in the retina area,and the electrode stimulation point is 33×44.+3 × 16 matrix arrangement,each stimulation point has a diameter of 100 ?m,and the minimum line width and spacing are both 2 ?m.According to the design layout of the 1500-channel MEMS electrode,based on MEMS micro-machining technology,the flexible electrode of 1500 stimulation points with many channels and ultra-high density is realized,and finally the MEMS flexibility is tested.After surface topography,tensile,bending torsion,electrochemical conductivity tests,the results show that the surface morphology of MEMS flexible electrodes has not obvious scratches,defects,broken wires,stimulating points or solder joints falling off;After the tensile test,the fracture load of the MEMS sample is basically more than 4N,and the maximum is 8N.After the bending torsion test,the conductivity of the MEMS flexible electrode is hardly reduced,the shape is not changed before and after the test,and the metal wire is still firmly adhered and firm;The electrochemical test MEMS flexible electrode conductance is above 80%.The successful fabrication of 126-channel MEMS flexible electrodes and 1500-channel MEMS flexible electrodes has laid a solid foundation for the realization of ultra-high resolution of artificial retinal prostheses,and is expected to achieve ultrahigh resolution artificial vision. |
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