The EC-Eye has a similar structure and size to a human eyeball, and it has similar capabilities. (Image Credit: Yaying Xu, (c) oFantastic Color Animation Technology Co.)


Researchers from the Honk Kong University of Science and Technology have developed an electrochemical artificial eye, called EC-Eye, which closely resembles a human eyeball’s size and structure with similar capabilities.  EC-Eye could one day provide vision for humanoid robots or function as a bionic eye for those who suffer from a visual impairment. The researchers published their findings in the journal Nature on May 20th, 2020.


The EC-Eye is created with an aluminum-lined tungsten shell, functions as the round casing, which is filled with an ionic liquid. It contains an iris and lens in the front, along with a retina in the back. The retina has an aluminum oxide base dotted with pores, each of which houses a photosensor. There are thin, flexible wires in the back of the retina, which are made of a liquid metal (eutectic gallium-indium alloy) enclosed in soft rubber tubes. The wires, which mimic the nerve fibers that connect the human eye to the brain, transmit signals from the nanowire photosensors to external circuitry for processing.


A layer of indium helps to improve the electrical contact between the perovskite nanowires and liquid-metal wires at the back.  The artificial eye is held in place by a silicone polymer socket, which ensures proper alignment between the wires and nanowires.


The artificial eye is capable of detecting various light intensities that are close to what a human eye can see. It can also respond to changes in light intensity faster than human eyes, which is approximately 30 to 40 milliseconds compared to 40 to 150 milliseconds for a human. Even though the 100-degree field of vision isn’t as wide as the 150 degrees human eye, it’s still an improvement over the 70-degrees view that flat imaging sensors can see.


The artificial retina has a 100 degrees field of vision, which is less than a human eye. (Image Credit: H. Jiang/Nature 2020)


Since the artificial retina consists of 460 million light sensors per square centimeter, theoretically, the EC-Eye could observe a higher resolution than a human eye. Human retinas have around 10 million light-sensing cells per square centimeter. However, this would need separate readings from each sensor.


Currently, each wire connected to the artificial retina is only one millimeter thick, which is big enough to simultaneously come in contact with more than one sensor. One hundred wires can fit across the back of the retina, producing images that contain 100 pixels.


To demonstrate that thinner wires could be connected to the EC-Eye for higher resolution, the researchers used a magnetic field to attach 20 to 100 micrometer thick metal needles to the nanosensors on the retina. 


Additional testing will need to be conducted to determine the operational lifetime of the artificial retina. After about nine hours of use, there is no noticeable reduction in its performance, but the functionality of other electrochemical devices could worsen over time. The team also says that the response and recovery time of the EC-Eye is reduced at higher concentrations of the ionic liquid, but at the cost of light transmission through the liquid. To solve this issue, the team will need to further optimize the ionic-liquid composition.


Aside from helping humans enhance their vision, experts say this work can also help develop additional biomimetic photo-sensing devices that could be used in a wide range of technological applications.


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