02 September 2016

Flexible electrodes will help monitor neurons for years to come

Roman Fishman, N+1

Harvard University researchers have proposed a biocompatible system of flexible microelectrodes for long-term monitoring of neuronal activity in a living brain. Tests of the device on mice have shown that it does not cause inflammatory reactions and will work effectively for many months, and possibly years. An article describing the new method was published by the journal Nature Methods (Fu et al., Stable long-term chronic brain mapping at the single-neuron level).

Implantation of microelectrodes in brain tissue is by far the most accurate method of monitoring the activity of neurons and their artificial stimulation. However, the installation of such implants requires unsafe surgical intervention and causes an inflammatory response. Inflammation not only reduces the effectiveness of their work, but sooner or later leads to the need to completely remove the electrode or at least move it to another place nearby.

All this limits the time during which it is possible to carry out such observations. Therefore, for all its accuracy, this method does not allow us to trace long-term changes in the connections and the nature of the activity of neurons that participate in the processes of maturation and learning of the brain, the development of neurodegenerative processes, etc. The system of flexible microelectrodes proposed by the team of Charles Lieber is devoid of these disadvantages: it has worked without any consequences in the body of living mice are more than eight months old, and, according to scientists, this is far from the limit.

The flexible system is produced by photolithography and consists of 16 thinnest metal electrodes embedded in a soft tape of a biocompatible polymer with a thickness of 800 nm and a width of 20 microns. The coefficient of elasticity of such a device is comparable to the corresponding indicator of ordinary living tissue (about 0.1 nN / m), and with the help of a thin needle it can be inserted into the target area of the brain with an accuracy of about 20 microns.

A snapshot from an article in Nature Methods: immunohistochemical staining of a brain slice.
Blue shows the areas of the microchip from which the activity is recorded.

The authors demonstrated the capabilities of the device by introducing it into the hippocampus, as well as into the somatosensory areas of the cerebral cortex of laboratory mice and receiving a clear signal from its electrodes. By checking the operation of the system month after month, the scientists confirmed the stability of the signal and the ability to continuously monitor the activity of individual cells without the development of inflammatory processes.

Charles Lieber and his colleagues are confident that such flexible devices will find wide application not only in brain research, but also in medicine, and possibly in the electronics of the future, offering a more "soft" option for integrating electronic components with the human nervous system. The use of electrodes promises huge opportunities to restore lost brain functions, including memory, and if implants do not cause inflammation and other negative reactions, projects to "supplement" the nervous system with electronics will be able to reach a new level. "This is exactly what we will have to do if we want to take full advantage of both," Charles Lieber added, commenting on the work of the Harvard University press service (A new window to understanding the brain).

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