Nano-implant to restore sight

Editorial

Rebecca Pool

Tuesday, March 14, 2017 - 12:45
SEM image of primary cortical neurons cultured on the surface of an array of optoelectronic nanowires. [UC San Diego]
 
US-based researchers have developed the nanotechnology and wireless electronics for a retinal prosthesis set to restore the ability of retinal neurons to respond to light.
 
Professor Gabriel Silva from the University of California San Diego and colleagues from the university and Nanovision Biosciences have demonstrated response to light in a rat retina interfacing with a device prototype, in vitro.
 
Despite tremendous advances in the development of retinal prostheses over the past two decades, the performance of devices on the market is severely limited, and well under the acuity threshold of 20/200 that defines legal blindness.
 
Given this, Silva and colleagues have developed what they describe as a 'new class of device with drastically improved capabilities to help people with impaired vision'.
 
Stunning images reveal how the new prosthesis consists of arrays of silicon nanowires that simultaneously sense light and electrically stimulate the retina accordingly.
 
Nanowires; each wire can produce an electric current when hit by light. [UC San Diego]
 
The nanowires give the prosthesis higher resolution than anything achieved by other devices, and closer to the dense spacing of photoreceptors in the human retina.
 
At the same time the researchers have developed a wireless device that transmits power and data to the nanowires at record speed and energy efficiency.
 
Crucially, unlike today's devices, this retinal prostheses does not require a vision sensor outside of the eye to capture a visual scene and then transform it into alternating signals to sequentially stimulate retinal neurons.
 
Instead, the silicon nanowires mimic the retina’s light-sensing cones and rods to directly stimulate retinal cells.
 
As Silva explains, the nanowires are bundled into a grid of electrodes, directly activated by light and powered by a single wireless electrical signal.
 
He reckons this direct and local translation of incident light into electrical stimulation delivers a simpler, and more scalable architecture for the prosthesis.
 
What's more, power is delivered wirelessly from outside the body to the implant via an inductive powering telemetry system developed by Professor Gert Cauwenberghs also from the Jacobs School of Engineering at UC San Diego.
 
Primary cortical neurons cultured on the surface of an array of optoelectronic nanowires; a neuron is pulling the nanowires, indicating the cell is doing well on this material. [UC San Diego]
 
For proof-of-concept, the researchers inserted the wirelessly powered nanowire array beneath a transgenic rat retina with rhodopsin P23H knock-in retinal degeneration.
 
The degenerated retina interfaced in vitro with a microelectrode array for recording extracellular neural action potentials.
 
The horizontal and bipolar neurons fired action potentials preferentially when the prosthesis was exposed to a combination of light and electrical potential.
 
The neurons fell silent when either light or electrical bias was absent, confirming the light-activated and voltage-controlled responsivity of the nanowire array.
 
Animal tests with the device are now in progress, with clinical trials following.
 
The technology could help tens of millions of people worldwide suffering from neurodegenerative diseases that affect eyesight, including macular degeneration, retinitis pigmentosa and loss of vision due to diabetes.
 
Research is published in Journal of Neural Engineering.
 
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