Implanted artificial touch sensors – always at your fingertips!

The sense of touch in our fingertips is indispensable for many everyday activities. Securely grasping a delicate object, palpating a fruit to determine its ripeness, or typing away at your keyboard – all these capacities rely on our amazingly sensitive sense of touch. Injuries can result in a permanent loss of peripheral nerves that mediate the local sense of touch. As a result, patients become severely disabled and are at a high risk for further injuries, because they fail to detect potentially harmful touches. Attempts at restoring peripheral nerves are difficult and often not successful.

Artificial touch sensors so small, thin and biocompatible that they can be implanted under the fingertips could be a new approach towards solving this problem. To that end, Israeli engineers have invented a novel “triboelectric nanogenerator”, consisting of two thin sheets of biocompatible materials. When pressed together by an external force, an electric voltage is induced in the sensor. This voltage can be used to induce electric currents, which, in turn, can activate electrosensitive biological tissue, such as cultivated nerve cells or nerve fibers.

In a series of experiments, the Israeli team first characterized their novel sensor. They found that increasing amounts of physical pressure reliably resulted in increasing levels of voltage. Electric currents, generated by the sensor, were potent enough to stimulate neuronal tissue in cell cultures.

Next, the authors took their device to an animal test. In a first step, they cut out a section of the nerve that mediates the sense of touch on the rat’s hind paws.  As a result, the animals could not detect moderate pressure anymore, so they failed to withdraw their paws in reaction to that stimulus. To see if they could restore touch, the researchers implanted their novel device in the hind paws of these rats and used a CorTec cuff electrode to electrically connect it to the sensory nerve stump. Indeed, the rats could feel again! They reliably retracted their feet in response to gentle pressure on their feet, just like normal rats would do.  In addition, the implant did not seem to disturb the rats, so it did not interfere with the rats’ movement abilities.

Further work is of course necessary before the technology could be taken to humans. Besides technical adaptations like further miniaturization, the long-term functionality and biocompatibility will need to be investigated. However, first steps are made towards a new implant technology that could one day restore the sense of touch also in human patients.

 

Citation:

 Shlomy I, Divald S, Tadmor K, Leichtmann-Bardoogo Y, Arami A, Maoz BM. Restoring Tactile Sensation Using a Triboelectric Nanogenerator. ACS Nano. 2021 Jun 17. doi: 10.1021/acsnano.0c10141. Epub ahead of print. PMID: 34137606.

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