Enhanced Vision Restoration for Blind People: High-Density Electrodes with Ultrasensitive Graphene Photodetectors to Realize Novel Biomimetic Neuroretinal Stimulation Paradigms

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Background: Electrical retinal implants can aid vision of blind people suffering from diseases leading to retinal degeneration. Despite the pioneering success in clinical trials, the technology still faces two main bottleneck challenges: 1) poor spatial and temporal resolution due to the use of macroelectrodes activating too many cells at once and the lower technical pixel density in comparison to retinal neuron density, and 2) the low sensitivity and limited dynamic range of the photodetectors in comparison to retinal photoreceptors. Vision: To realize artificial vision suited for daily vision tasks, the two project partners have been collaborating since 2020 by synergizing advanced technical and neuro-biological solutions towards a new retinal implant type with an unprecedented spatial and temporal resolution. The core feature of this project is a nature-inspired and high-density flower pixel architecture allowing neuronal stimulation in biomimetic fashion: a central photodetector surrounded by six electrodes. An image unit collects, adapts and enriches the light information obtained from the photodetectors and provides it to the stimulation unit, which translates it into image-encoded electrical stimuli. Specifically, for the next generation of retinal implants the following objectives are targeted: Objective 1 – Sensor: Enhanced 2D-material Based Photodetector Arrays: Enhancements for currently studied biomimetic 2D-material-based photodetectors will be developed with the aim to extend the sensitivity and the dynamic range of the photodetectors to at least 1 to 104 lux, which is the typical retinal illuminance range in a single visual scene. The upscaling will provide a 256-pixel photodetector array acting as the image sensor. Objective 2 – Image Unit: Transforming Sensor Images into Electronic Signals: An image unit consisting of a dedicated parallelized readout circuit for the novel photodetectors and an emulated real-time signal processing unit will be developed, enabling the adaptation of the image information to the requirements of the neural stimulation and pixel enrichment techniques. Objective 3 – Stimulation Unit: Image-Feature Based Electrical Stimulation: The stimulation unit acts as the driver for a custom-fabricated high-density 1536-electrode (10 µm) array chip to achieve high spatial resolution (resolving two <60 µm apart phosphenes). To evoke advanced neuronal responses, image-features will be utilized to modulate the electrical pulses. Moreover, to enhance the temporal and spatial resolution further, electrodes will be activated in biomimetic fashion reducing vision-fading and promoting sustained cell responses. Objective 4 – Semi-Assembled e-Retina: The four independent units – the photodetector array, image unit, stimulation unit and the electrode array – will be connected functionally, forming the complete e-Retina demonstrator.