Minimally invasive medical procedures offer numerous benefits to patients, including decreased tissue damage and shorter recovery periods. However, creating equipment that can pass through a small opening and function effectively on the other side calls for some innovative designing. Now, researchers have developed a cortical electrode that can be inserted through a tiny opening in the skull and still provide significant data on brain electrical activity.

Researchers at EPFL (Lausanne, Switzerland) were tasked with creating a large cortical electrode array that could be introduced through a tiny skull opening. The aim was to deploy the device in the small space of about 1mm between the skull and the brain surface, all without causing harm to the brain. The researchers invented a soft robotic electrode, capable of being inserted through a small skull opening, which unfolds a series of spiral arms, thereby allowing for electrocorticography measurements from a relatively larger brain surface area. This technology could be extremely beneficial for neurosurgeons aiming to map brain regions responsible for epileptic seizures, then surgically address these problematic areas. By minimizing the portion of the skull removed during surgery, patient recovery is faster, and trauma associated with such procedures is reduced.

The initial prototype comprises an electrode array small enough to fit through a 2 cm diameter hole, but when unfolded, it extends across a 4 cm diameter surface. It features six spiral-shaped arms designed to maximize the electrode array's surface area and, therefore, the number of electrodes interacting with the cortex. Straight arms can lead to uneven electrode distribution and reduced contact surface area with the brain. Resembling a spiraled butterfly compactly tucked within its cocoon before transformation, the electrode array, with its spiral arms, is neatly contained within a cylindrical tube, or loader, ready for insertion through the small skull opening. An averting actuation mechanism inspired by soft robotics enables the spiraled arms to be gently deployed over sensitive brain tissue, one at a time.

The electrode array looks similar to a rubber glove, with flexible electrodes patterned on one side of each spiral-shaped "finger." The "glove" is turned inside-out and housed within the cylindrical loader. For deployment, liquid is inserted into each "inverted finger" individually, causing it to revert and unfold over the brain. The electrode pattern is created by evaporating flexible gold onto highly compliant elastomer materials. The deployable electrode array has been successfully tested in a mini-pig.

“Minimally invasive neurotechnologies are essential approaches to offer efficient, patient-tailored therapies,” said Stéphanie Lacour, professor at EPFL Neuro X Institute. “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.” 

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