Retinal and neural stimulation with quantum dots based photovoltaic interfaces
Creators: name: Erdost Yildiz
Publisher: name: Zenodo
Year: 2021
Subjects: retinal prosthesis
neurostimulation
retinitis pigmentosa
quantum dots
biomaterials

description: Electrical stimulation of neural tissues is one of the emerging technological areas in medicine. Although several attempts from various research groups, neuro-electronic interface technologies are still in the infancy period. Especially in neurodegenerative situations, such as retinitis pigmentosa and age-related macular degeneration, neural stimulation could be effective rehabilitation method. For the retina, photovoltaic surfaces are the pioneer concepts for the recovery of sensation. The institutes, which are working on retinal prostheses, are currently exploiting various photoactive electrical surfaces to stimulate bipolar and ganglion cells in the retina. However, they fail to fulfill the functions of the retinal prosthesis due to bio-incompatibility, external energy source necessity, lack of flexibility, and mobility of the prosthesis. Therefore, there is an enormous necessity for innovative biomaterials in retinal prosthesis production.


Quantum dot-based photovoltaic devices are great candidates for nano-sized neural stimulators. Their working principle relies on the photoelectric effect, which makes them a possible replacement for the rhodopsin-based phototransduction mechanism in photoreceptor cells. For retinal implant production on flexible PET (polyethylene terephthalate) surfaces, various types of quantum dot-based photovoltaic interfaces could be used, such as Lead(II)sulfide (PbS), Aluminum antimonide (AlSb). The main concerns on these bio-interfaces are biocompatibility and effective electrical charge capacity on neurons which induce action potential activity. Compared to other photoactive polymer-based interfaces in literature, quantum dots-based materials could induce photoelectrical neurostimulation under lower light intensities due to their nanocrystal content. Also, compared to other silicon-based bio-interfaces, they do not need an external energy source or complicated processor systems, thanks to the photo-capacitive current production.


The aim of the study is to investigate various types of quantum dots-based structures to produce effective photovoltaic interfaces for neural stimulation, which could be used as a retinal prosthesis in rats with retinal degeneration. For this purpose, different types of quantum dots were examined with in vitro biocompatibility and electrophysiology experiments. Then, selected quantum dots-based neural interfaces were implanted in the subretinal spaces of the rats with and without retinal degeneration. After implantation, electrophysiology (VEP-EEG and ERG) and behavioral tests were conducted to understand biocompatibility and recovery of visual sensation. After in vivo studies, the animals were euthanized, and changes in the retina after implantations and photoelectrical stimulations were observed. In this way, both functional recovery of vision and the structural integrity of the different cell types in the retina were demonstrated.


Different types of quantum dots-based interfaces induce action potentials in primary hippocampal neurons, which enables neuromodulation with biocompatible photoactive interfaces. In in vivo step, PbS and AlSb QDs-based retinal prostheses also induce retinal stimulation with light pulses. Unfortunately, the required light levels for neural stimulation with these devices are significantly higher than ocular safety limits. Also, both AlSb and PbS QDs-based retinal prostheses induce gliosis and retinal damage in the subretinal implantation area. Because of those reasons, further investigations are required for quantum dots-based retinal stimulation systems.