Abstract
Purpose :
Retinal electrical stimulation (stim) evokes visual sensations in blind patients. However, the experienced temporal and spatial resolution is limited, e.g. due to a response outage of retinal cells at stim frequencies higher than 3 Hz. To evoke enhanced retinal activity, we took a multidisciplinary biomimetic approach: (1) developing a stim paradigm mimicking saccadic eye movements (bio-act); (2) to realize stim in bio-act mode, electrode arrays with several six-petal flower-like structures were fabricated (fEA). Thereby, a flower is defined as a group of six contiguous circularly arranged electrodes (petal electrode (p-el)).
Methods :
FEAs with nine flowers were fabricated with a multi-layer approach on a silicon substrate with electron- beam evaporated gold films, and silicon dioxide insulation (p-el: 10 µm, spacing: 10 µm, flower pitch: 30 µm). Stim was applied subretinally (outer retina contacting p-el), and the ganglion cell (GC) activity was recorded via Ca2+-imaging (Ca2+-indicator OGB-1). The bio-act paradigm activated sequentially the p-el of a flower in a zig-zag pattern. We applied stim pulses in biphasic (cathodic-first) configuration, varying duration (0.5 – 1 ms/phase), strength (0.5 – 2.5 V) and frequency (0.5 – 50 Hz). Experiments were conducted on retinal explants of the blind rd1 mouse (day 22-35).
Results :
The fEA was tested successfully, eliciting stim correlated GC responses (n = 5 fEA, m = 5 retinae). Individual activation of p-el in bio-act mode resulted in a narrower cell activation radius (60 ± 15 µm), in comparison to simultaneous all six p-el activation (~120 µm), mimicking a large single electrode. Bio-act allowed to evoke robust GC responses at higher stim frequencies (10 Hz) throughout sustained stim (90 s). Modulation of stim voltage and pulse duration allowed for activation of different GC adjacent to same stim p-el (n = 10 cells).
Conclusions :
We elaborated a novel approach to evoke improved retinal responses within a flower’s spatial domain:
p-el allowing narrow cell activation radius and differential activation of GC channels, and bio-act generating sustained responses. Overall, enhanced retinal activity generated by our biomimetic approach has a great potential to generate fading free visual pixels in the cortex and enable visual sensations with advanced temporal and spatial resolution in blind patients.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.