Researchers have developed highly flexible and durable electrodes the size of a single neuron which could pave the way for the next generation of visual implants.
In a study, published in Advanced Healthcare Materials, the international research team said the electrodes exhibited “remarkable” stability when several billions of electrical pulses are applied in vitro.
The devices were implanted in the primary visual cortex of mice, which were trained to detect electrical microstimulation. The mice were able to detect impulses at two to 20 microamperes, which is far below the maximal currents that the electrodes can withstand.
“The long-term functionality of the devices in vivo is excellent, with stable performance for up to more than a year and little damage to the brain tissue,” the study authors said.
“These results demonstrate the potential of thin floating electrodes for the long-term restoration of lost sensory functions.”
A key challenge with visual prosthetics is deterioration of the interface. This can be caused by bio-instability of the materials, electrochemical degradation of electrodes and the brain’s foreign body response to the implant.
The implant developed by the researchers measured 40 micrometres wide and 10 micrometres thick and were made from ultra-flexible, polyimide shanks that allowed them to withstand deterioration and not damage brain tissue.
The researchers applied billions of electrical pulses to the electrodes – mimicking years of continuous use – which showed little to no degradation in performance. Moreover, the implants remained stable for up to a year after implantation due to its mild foreign body response.
“We conclude that thin film polymers with small electrodes provide a promising avenue for sensory prostheses that aim to activate neurons at a high spatial resolution over extended time periods,” the study authors said.
They said substantial work is still needed before translating this technology into medical devices that can be safely used in blind people.
“For example, there is a need to develop methods to safely implant and interconnect large numbers of electrodes in the visual brain; while, covering the entire visual field representation.”
“Nevertheless, the present work represents an important step in this direction by demonstrating a long-lasting, stable, and high-resolution interface with the visual brain.”
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