Scanning electron micrograph (SEM) image of individual nanowires and groupies of nanowires. Each wire can produce an electric current when hit by light. Credit: University of California San Diego
The nanotechnology and wireless electronics required for a new type of retinal prosthesis has been developed by engineers at the University of California San Diego and La Jolla-based startup Nanovision Biosciences Inc.
With this development, research is brought closer to re-establishing the potential of neurons present in the retina to respond to light. This response to light was demonstrated by the team in a rat retina interfacing with a prototype of the device in vitro.
Engineers have now presented their research in the latest issue of the Journal of Neural Engineering. This new technology will be able to help tens of millions of people spread all over the world suffering from neurodegenerative diseases affecting eyesight, including retinitis pigmentosa, macular degeneration and vision loss because of diabetes.
Over the past two decades, there have been major advances in the development of retinal prostheses. However, despite these advances, major limitations still exist in the performance of devices that are at currently commercially available to help the blind regain functional vision. These limitations are well under the acuity threshold of 20/200 that defines legal blindness.
We want to create a new class of devices with drastically improved capabilities to help people with impaired vision.
Gabriel A. Silva, Professor in Bioengineering and Ophthalmology, UC San Diego
Silva is also one of the original founders of Nanovision.
The new prosthesis is based on two revolutionary technologies. One comprises of arrays of silicon nanowires that sense light and electrically stimulate the retina accordingly in a simultaneous manner. The nanowires provide the prosthesis with higher resolution unlike anything that has ever been attained by other devices - closer to the dense spacing of photoreceptors present in the human retina.
The other groundbreaking technology is a wireless device capable of transmitting data and power to the nanowires over the same wireless link with energy efficiency and at record speed.
One major difference between the existing retinal prostheses and the team’s prototype is that the new system does not need a vision sensor outside of the eye in order to capture a visual scene and then change it into alternating signals that will help in sequentially stimulating retinal neurons.
Instead, the retina’s light-sensing cones and rods are imitated by the silicon nanowires in order to directly stimulate retinal cells. Nanowires are collected together into a grid of electrodes, powered by a single wireless electrical signal and directly activated by light. A much simpler, and scalable, architecture for the prosthesis can be obtained by this direct and local translation of incident light into electrical stimulation.
The light-activated electrodes are provided with high sensitivity by the power supplied to the nanowires from the single wireless electrical signal while simultaneously controlling the timing of stimulation.
To restore functional vision, it is critical that the neural interface matches the resolution and sensitivity of the human retina.
Gert Cauwenberghs, Professor of Bioengineering, UC San Diego
A team headed by Cauwenberghs developed an inductive powering telemetry system that was used to deliver power wirelessly, from outside the body to the implant.
The device is considered to be highly energy efficient as it reduces the loss of energy wireless power and data transmission and also in the stimulation process, recycling electrostatic energy flowing inside the inductive resonant tank, and also between capacitance on the electrodes and the resonant tank.
UP to 90% of the transmitted energy is in fact delivered and utilized for stimulation, which means less heating of the surrounding tissue from dissipated power, and less RF wireless power emitting radiation in the transmission.
Data and power are transmitted by the telemetry system over one pair of inductive coils, one emitting from the outer side of the body, and the other on the receiving side in the eye. The link is capable of sending and receiving one bit of data for every two cycles of the 13.56 megahertz RF signal; other two-coil systems require at least five cycles for every transmitted bit.
The wirelessly powered nanowire array was inserted by the team under a transgenic rat retina with rhodopsin P23H knock-in retinal degeneration for proof-of-concept. The degenerated retina interfaced in vitro with a microelectrode array in order to record extracellular neural action potentials, referring to electrical “spikes” from neural activity.
Action potentials were preferentially fired by the bipolar and horizontal neurons when the prosthesis was exposed to a blend of light and electrical potential - and were silent during the absence of either light or electrical bias, thus confirming the voltage-controlled and light-activated responsivity of the nanowire array.
The wireless nanowire array device is the outcome of a partnership between a multidisciplinary team headed by Cauwenberghs, Silva and William R. Freeman, director of the Jacobs Retina Center at UC San Diego, UC San Diego electrical engineering professor Yu-Hwa Lo and Nanovision Biosciences.
A Path to Clinical Translation
La Jolla-based Nanovision Biosciences, a partner in this study, was co-founded by Freeman, Silva and Scott Thorogood in order to further develop and translate the technology into clinical use, together with the aim of restoring functional vision in patients suffering from severe retinal degeneration. The device is currently used for animal tests followed by clinical trials.
We have made rapid progress with the development of the world's first nanoengineered retinal prosthesis as a result of the unique partnership we have developed with the team at UC San Diego.
Scott Thorogood, CEO of Nanovision Biosciences
Other authors include UC San Diego Jacobs School of Engineering current and former graduate and postdoctoral researchers Sohmyung Ha (currently Assistant Professor at NYU Abu Dhabi), Massoud L Khraiche (presently at Cbrite Inc.), Abraham Akinin, Yi Jing (now at Nanovision Biosciences), Samir Damle and Yanjin Kuang, as well as Sue Bauchner, Director of Engineering at Nanovision Biosciences.
Nanovision Biosciences, Qualcomm Inc. and the Institute of Engineering in Medicine and the Clinical and Translational Research Institute at UC San Diego funded this research.