Honeycomb-shaped electro-neural interface for retinal prosthesis

Abstract

We provide a 3-dimensional configuration of an electrode array for neural cell stimulation designed to leverage migration of retinal cells into voids in the subretinal space. Walls surrounding each pixel align the electric field vertically, matching the orientation of bipolar cells in the retina, and thereby reduce the stimulation threshold. These walls also decouple the field penetration depth from the pixel width, enabling a decrease of the pixel size down to cellular dimensions. Inner retinal cells migrate into the electrode cavities, which enables very efficient stimulation. Due to 1-dimensional alignment of electric field along the cavities, stimulation threshold current density does not increase significantly with the reduced pixel size, unlike the quadratic increase seen with planar arrays.

1 . Apparatus for electrical stimulation of neural cells, the apparatus comprising:
 an array of cavities configured to allow migration of neural cells inside the cavities;   wherein each cavity has a floor and electrically conductive walls;   wherein each cavity has a first electrode disposed on its floor;   wherein each cavity has a second electrode disposed on top of its walls and vertically separated from its corresponding floor electrode;   wherein during operation of the apparatus, an ionic current flows through contents of the cavities;   wherein a second electrode capacitance is greater than a conductive wall capacitance in each cavity, whereby the second electrodes preferentially collect the ionic current relative to sides of the conductive walls.   
     
     
         2 . The apparatus of  claim 1 , wherein a depth of the cavities is between 10 μm and 100 μm. 
     
     
         3 . The apparatus of  claim 1 , wherein a width of the cavities is between 5 μm and 100 μm. 
     
     
         4 . The apparatus of  claim 1  wherein a depth of the cavities is greater than a width of the cavities. 
     
     
         5 . The apparatus of  claim 1 , wherein the array of cavities is periodic. 
     
     
         6 . The apparatus of  claim 5 , wherein the cavities are hexagonal. 
     
     
         7 . The apparatus of  claim 1 , wherein the neural cells are retinal cells. 
     
     
         8 . The apparatus of  claim 1 , wherein an injected charge density at first electrodes of the cavities is between 0.1 mC/cm 2  and 10 mC/cm 2  in operation. 
     
     
         9 . The apparatus of  claim 1 , wherein a capacitance per unit area of the second electrodes is at least 100× greater than a capacitance per unit area of the conductive walls. 
     
     
         10 . Apparatus for electrical stimulation of neural cells, the apparatus comprising:
 an array of cavities configured to allow migration of neural cells inside the cavities;   wherein each cavity has a floor and electrically insulating walls;   wherein each cavity has a first electrode disposed on its floor;   wherein the apparatus has a common return electrode disposed outside the array of cavities;   wherein during operation of the apparatus, an ionic current flows through contents of the cavities;   whereby the electrically insulating walls improve stimulation efficiency and reduce cross-talk between neighboring cavities of the apparatus by forcing the ionic current to travel vertically within the cavities.   
     
     
         11 . The apparatus of  claim 10 , wherein a depth of the cavities is between 10 μm and 100 μm. 
     
     
         12 . The apparatus of  claim 10 , wherein a width of the cavities is between 5 μm and 100 μm. 
     
     
         13 . The apparatus of  claim 10  wherein a depth of the cavities is greater than a width of the cavities. 
     
     
         14 . The apparatus of  claim 10 , wherein the array of cavities is periodic. 
     
     
         15 . The apparatus of  claim 14 , wherein the cavities are hexagonal. 
     
     
         16 . The apparatus of  claim 10 , wherein the neural cells are retinal cells. 
     
     
         17 . The apparatus of  claim 10 , wherein an injected charge density at first electrodes of the cavities is between 0.1 mC/cm 2  and 10 mC/cm 2  in operation.