Department of Applied Physics, Stanford University, Stanford, CA, United States of America.
J Neural Eng. 2018 Jun;15(3):036011. doi: 10.1088/1741-2552/aaac39. Epub 2018 Feb 1.
High-resolution prosthetic vision requires dense stimulating arrays with small electrodes. However, such miniaturization reduces electrode capacitance and penetration of electric field into tissue. We evaluate potential solutions to these problems with subretinal implants based on utilization of pillar electrodes.
To study integration of three-dimensional (3D) implants with retinal tissue, we fabricated arrays with varying pillar diameter, pitch, and height, and implanted beneath the degenerate retina in rats (Royal College of Surgeons, RCS). Tissue integration was evaluated six weeks post-op using histology and whole-mount confocal fluorescence imaging. The electric field generated by various electrode configurations was calculated in COMSOL, and stimulation thresholds assessed using a model of network-mediated retinal response.
Retinal tissue migrated into the space between pillars with no visible gliosis in 90% of implanted arrays. Pillars with 10 μm height reached the middle of the inner nuclear layer (INL), while 22 μm pillars reached the upper portion of the INL. Electroplated pillars with dome-shaped caps increase the active electrode surface area. Selective deposition of sputtered iridium oxide onto the cap ensures localization of the current injection to the pillar top, obviating the need to insulate the pillar sidewall. According to computational model, pillars having a cathodic return electrode above the INL and active anodic ring electrode at the surface of the implant would enable six times lower stimulation threshold, compared to planar arrays with circumferential return, but suffer from greater cross-talk between the neighboring pixels.
3D electrodes in subretinal prostheses help reduce electrode-tissue separation and decrease stimulation thresholds to enable smaller pixels, and thereby improve visual acuity of prosthetic vision.
高分辨率的假体视觉需要具有小电极的密集刺激阵列。然而，这种小型化会降低电极电容和电场穿透组织的能力。我们评估了基于利用柱状电极的视网膜下植入物来解决这些问题的潜在解决方案。
为了研究与视网膜组织整合的三维（3D）植入物，我们制造了具有不同柱直径、间距和高度的阵列，并将其植入退化的大鼠视网膜下（皇家外科学院，RCS）。术后 6 周，使用组织学和全层共焦荧光成像评估组织整合情况。在 COMSOL 中计算了各种电极配置产生的电场，并使用网络介导的视网膜反应模型评估了刺激阈值。
在 90%的植入阵列中，视网膜组织迁移到柱之间的空间中，没有可见的神经胶质增生。高度为 10 μm 的柱到达内核层（INL）的中间，而 22 μm 的柱到达 INL 的上部。具有圆顶形帽的电镀柱增加了有效电极表面积。通过溅射在帽上选择性地沉积氧化铱确保了电流注入到柱顶，从而避免了需要对柱侧壁进行绝缘。根据计算模型，与具有环形阴极返回电极位于 INL 上方和表面上的有源阳极环形电极的平面阵列相比，具有柱状阴极返回电极和有源阳极环形电极的柱状阵列将使刺激阈值降低六倍，但是相邻像素之间的串扰更大。
视网膜下假体中的 3D 电极有助于减少电极-组织分离，并降低刺激阈值，从而实现更小的像素，从而提高假体视觉的视力。
