Small neuron-sized vision implants with electrodes were developed by a team of researchers from Sweden’s Chalmers University, Freiburg University, and the Netherlands Institute for Neuroscience. They developed a combination that could have the potential for vision implants to restore lost sensory functions of blind people in the future, and the most fascinating thing is that it may remain in the body for a long time.
Blindness is a medical condition in which a person has a lack of vision, i.e., is unable to see anything. It is caused when the optic nerves fail to send visual information from the eyes to the brain.
Generally, in blind people, some of the parts of their eyes have been damaged while the brain's visual cortex remains active to get the information. With brain stimulation, sight can be restored by implanting thousands of electrodes. Keeping this in mind, researchers developed implants that can help the brain create images by sending electrical impulses. According to the researchers, each electrode shows one pixel.
Scientists explain that previous research proved that the use of rigid electrodes made with silicon material requires high currents of about tens of microamperes to activate the nerve impulses, and these rigid silicon electrodes can also affect the brain badly by damaging its tissues. They concluded that flexible and non-corrosive electrodes may solve the problems by causing less damage because they will move with the brain and can remain intact for a longer period.
Instead of silicon electrodes, scientists used electrodes made with sputtered iridium oxide with a coating of PEDOT poly(3,4-ethylene-dioxythiophene) and polystyrene sulfonate, as they provide efficient movement with the brain and can maximize the stimulation currents in neurons by allowing higher currents.
After the testing of these electrodes in mice, it was found that SIROF and PEDOT electrodes can handle continuous electrical stimulation without showing any deterioration. This proved that they can also be suitable for handling electrical stimulations of 42.5 coulombs over 10 billion pulses and can be used for a long time.
Researchers used five mice to implant probes in their V1 area (primary visual cortex) and trained them to lick a spout in response to micro-stimulation throughout seven sessions. The thresholds of 23 electrodes were detected three times and showed no significant change over time; however, some of the electrodes lost their functions. Scanning electron microscopy revealed cracks in some explanted probes just like in in-vitro probes; these cracks might have been formed due to implantation, preparation of explanation, and cleaning but were still functioning for up to 55 weeks. Both stimulated and non-stimulated electrodes were studied, but cracks did not affect their functioning.
Researchers found the 75 µm lesions across the cortical depth after investigating the tissue responses at three depths and probe integration by ex vivo staining histological protocol. They found a lesser number of neurons in the deep cortex with little damage to brain tissue. This study demonstrates the long-term vision restoration potential of thin and flexible electrodes.
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(Rehash/Akashita Panjla/SB)