Micro-fabricated Hexagonal Electrode Arrays for Retinal Stimulation
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Solution Overview
Problem
Current epiretinal implants for restoring vision in the blind use large electrodes that are not sufficient for achieving high spatial resolution, necessitating the development of smaller electrodes to effectively stimulate retinal ganglion cells and create a matrix of discrete perceptions of light for useful vision.
Innovation Solution
The use of micro-fabricated hexagonal arrays with 61 platinum disk electrodes of diameters between 6 and 25 μm, spaced 60 μm apart, to stimulate and record ganglion cells in isolated retinal tissue, achieving low charge densities and high temporal and spatial precision, allowing for independent activation of nearby cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If large electrodes are used in epiretinal implants, then the device is easier to manufacture and implant, but spatial resolution is insufficient for useful vision
Solution Approach 1:
The patent divides the retinal stimulation task into many small discrete electrode sites (up to 100+ electrodes) rather than using a few large electrodes. Each small electrode (10-50 μm diameter) can independently stimulate individual or small groups of retinal ganglion cells, creating a matrix of discrete phosphenes that form useful visual images. This segmentation enables high spatial resolution while maintaining manufacturability through standardized microfabrication processes.
Solution Approach 2:
The patent implements local quality by making each electrode site unique in its spatial position and stimulation characteristics. The non-uniform distribution of small electrodes across the retinal surface allows different regions to target specific functional areas of the retina, optimizing stimulation efficiency and visual output for each local region while maintaining overall system performance.
2Measurement precision
If small electrodes are used to achieve high spatial resolution, then vision restoration quality improves, but charge density increases causing tissue damage
Solution Approach 1:
By segmenting the total stimulation current across many small electrodes rather than concentrating it in fewer large electrodes, the patent distributes the charge load. Although each small electrode has higher current density, the total charge per electrode can be kept low by utilizing the parallel capacity of multiple electrodes, thereby preventing tissue damage while achieving high spatial resolution.
Solution Approach 2:
The patent applies partial action by delivering sub-threshold or threshold-level stimulation to multiple electrodes simultaneously rather than excessive stimulation to fewer electrodes. This distributed partial stimulation achieves the desired neural activation and visual perception while keeping individual electrode charge densities within safe limits for chronic implant operation.
3Measurement precision
If small electrodes are used for high spatial resolution stimulation, then independent activation of nearby cells is achieved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical assembly and positioning systems with microfabricated electrode arrays that are precisely patterned using semiconductor manufacturing techniques. This substitution of mechanical complexity with fabrication precision enables high spatial resolution electrode placement while simplifying the overall device assembly and implantation process through standardized microfabricated components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables reliable electrical stimulation of mammalian retina with small-diameter electrode arrays, providing high spatial and temporal precision, and demonstrating the feasibility of using such arrays for retinal prosthetics to restore vision.
Implementation Method 1
Neural tissue can be artificially stimulated and activated by prosthetic devices that pass pulses of electrical current through electrodes on such a device. The passage of current causes changes in electrical potentials across visual neuronal membranes, which can initiate visual neuron action potentials
Data Source
AI summary
The present invention is a flexible circuit electrode array for stimulating neurons where the electrode are less than 20 μm in size and less than 60 μm apart. The array is preferably arranged in a hexagonal pattern to maximize electrode density, and longer in the horizontal direction to correspond to a normal visual scene. The array includes a polymer base layer, metal traces deposited on the polymer base layer, including electrodes suitable to stimulate neural tissue, and a polymer top layer deposited on the polymer base layer and the metal traces defining openings for the electrodes smaller than the electrodes to overlap the electrodes.