Scientists from Chalmers University of Technology in Sweden, University of Freiburg and the Netherlands Institute for Neuroscience have come together to create an exceptionally small implant, with electrodes the size of a single neuron.
These electrodes can remain intact in the body over time – a combination that holds promise for future vision implants for the blind.
Often when a person is blind, some or part of the eye is damaged, but the visual cortex in the brain is still functioning and waiting for input. When considering brain stimulation for sight restoration, there needs to be thousands of electrodes going into an implant to build up enough information for an image. By sending electrical impulses via an implant to the visual cortex of the brain, an image can be created, and each electrode would represent one pixel.
The vision implant created in this study can be described as a ‘thread’ with many electrodes placed in a row, one after the other. In the long term you would need several threads with thousands of electrodes connected to each one, and the results of this study are a key step towards such an implant.
The future of vision implants
An electrical implant to improve vision in people with blindness is not a new concept. However, the implant technology currently being explored in human patients is from the 1990s and there are several factors that need to be improved, for example the bulky size, scarring in the brain due to their large size, materials corroding over time and materials being too rigid.
By creating a really small electrode the size of a single neuron, the researchers have the potential to fit lots of electrodes onto a single implant and build up a more detailed image for the user. The mix of flexible, non-corrosive materials make this a long-term solution for vision implants.
The smaller the size, the worse the corrosion
To create an electrical implant on such a small scale comes with challenges. The major obstacle is not to make the electrodes small, but to make such small electrodes last a long time in a moist, humid environment. Corrosion of metals in surgical implants is a huge problem, and because the metal is the functional part, as well as the corroding part, the amount of metal is key. The electrical implant created measures in at a miniscule 40 micrometers wide and 10 micrometers thick, like a split hair, with the metal parts being only a few hundred nanometers in thickness.
The electrode includes a conducting polymer to transduce the electrical stimulation required for the implant to work, to electrical responses in the neurons. The polymer forms a protective layer on the metal and makes the electrode much more resilient to corrosion, a protective layer of plastic covering the metal.
More about: the study method
The method has been examined using an animal model, where mice were trained to respond to an electrical impulse to the visual cortex of the brain. The study showed that not only could the mice learn to react to the stimulation applied via the electrodes in just a few sessions, but the minimal current threshold for which mice reported a perception was lower than standard metal-based implants. The research team further reported that the functionality of the implant stayed stable over time, for one mouse even until the end of its natural lifespan.
The research has been published in the article: “Flexible Polymer Electrodes for Stable Prosthetic Visual Perception in Mice” in the journal Advanced Healthcare Materials.
