Retinal Prosthesis with Three-Dimensional Soft Bioelectrodes

Retinal degenerative diseases, such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD), can cause permanent damage or even loss of photoreceptors, which leads to disability of vision. Recently, electronic retinal prosthesis, which stimulates the preserved retinal neurons electrically, has emerged as a promising way to restore vision. However, conventional retinal devices with planar stimulation electrodes have been limited with poor proximity to the target cells in the degenerative retina, resulting in a low selectivity. To overcome these challenges, retinal prosthesis with three-dimensional (3D) electrodes have been developed. The enhanced proximity to the target neurons can be effective for the degenerative surfaces because penetrated 3D electrodes are surrounded conformally by the neighboring retinal tissues. Also, the 3D electrodes effectively inject charges to the target cells, thereby providing greater spatial resolution, and excellent selectivity by focusing the electric fields. Yet, conventional penetrating neural electrodes utilize materials with high modulus, inducing undesired space between the surface of the target tissue and the electrode array causing inflammation and hemorrhage.<br/>Herein, we demonstrate a highly-integrated, flexible retinal prosthesis, based on phototransistor arrays and 3D soft stimulation electrodes, for the restoration of vision. First, we utilized eutectic gallium-indium alloy (EGaIn), as a soft material for 3D stimulation electrodes. This soft 3D electrode can minimize the undesired tissue damages induced by modulus mismatch between the electrode and the biological tissues. Second, we fabricated stimulation electrodes in a 3D pillar structure by a high-resolution direct printing method. Third, an in-vitro experiment was conducted for the morphology optimization of pillar-shaped 3D electrodes. Lastly, we implanted the retinal prosthesis into the rd1 mouse for vision restoration. We confirmed that the incident light induces the increment of the neural responses in the retinal neurons in real-time for a live rd1 mouse.