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Six-Legged Robot Electrode Can Be Gently Deployed Across the Brain’s Surface

A spiral shaped electrode is seen on a hand.
Credit: EPFL/Alain Herzog
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A new robotic brain electrode system developed by researchers at École Polytechnique Fédérale de Lausanne (EPFL) can be deployed onto the brain’s surface after being delivered through a tiny hole in the skull. The six “legs” of the electrodes are used to monitor regions of the brain affected by epileptic seizures and the new device could offer a less invasive solution for patients.

The study is published in Science Robotics.

The challenge of recording seizure activity

Medical professionals treating epilepsy patients face a difficult process in trying to understand the source of their seizures, which are driven by aberrant brain activity that can be tracked using electrodes. To achieve a clear picture of brain activity, these electrocorticography (ECoG) devices need to be in contact with the brain’s outer surface, the cortex. In order to deliver a device that covers enough of the cortex in enough detail to provide a useful reading, ECoG devices are often limited to use in the operating room.

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But a six-legged robot might change all this. The device was developed by a team at EPFL in Switzerland. Senior study author and EPFL Neuro X Institute professor Stéphanie Lacour specializes in developing flexible electrode systems that can respond to the harsh and dynamic environment inside the human body to make reliable and informative contact with our nervous system.

“Minimally invasive neurotechnologies are essential approaches to offer efficient, patient-tailored therapies,” says Lacour. “We needed to design a miniaturized electrode array capable of folding, passing through a small hole in the skull and then deploying in a flat surface resting over the cortex. We then combined concepts from soft bioelectronics and soft robotics.”

Ingenious engineering

The robot, which remains in a prototype stage, features several engineering innovations that help it capture data from the brain. The array is soft, meaning it can be fit through a 2 cm-diameter hole in the skull and is stored in a cylindrical tube prior to deployment. When released, it then expands to cover a 4 cm-diameter area of cortex. The device is also thin, as the space between the skull and the brain’s surface is around a millimeter in depth.

The device has six spiral-shaped “legs” that are designed to maximize the area the device can record from and the number of electrodes in contact with that area. Straight arms, in comparison, cover less surface area and can contain fewer electrodes.  The legs are released sequentially to minimize the risk of any damage to the brain’s surface. The technique used to achieve this gentle deployment is called an eversion mechanism. “The beauty of the eversion mechanism is that we can deploy an arbitrary size of electrode with a constant and minimal compression on the brain,” says Sukho Song, lead author of the study. “The soft robotics community has been very much interested in this eversion mechanism because it has been bio-inspired. This eversion mechanism can emulate the growth of tree roots, and there are no limitations in terms of how much tree roots can grow.”

Inside the tube, the electrode is both folded and turned inside-out. When it is ready to be released, liquid fills each finger-like process of the electrode, unfolding it over the brain and turning it right-side out, exposing the electrode pattern, tattooed onto the electrode’s surface by a process involving the evaporation of gold onto the electrode’s elastomer surface.

The electrode has only been tested in a mini-pig thus far, but a spin-off company aiming to translate the technology into humans has been granted 2.5 million CHF Swiss Accelerator by Innosuisse.

Reference: Song S, Fallegger F, Trouillet A, Kim K, Lacour SP. Deployment of an electrocorticography system with a soft robotic actuator. Science Robotics. 2023;8(78):eadd1002. doi:10.1126/scirobotics.add1002

This article is a rework of a press release issued by EPFL. Material has been edited for length and content.