Soft Robotic Electrode Enables Minimally Invasive Placement

Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed a soft robotic electrode, that can be advanced through a small hole in the skull and then opened into a series of spiral arms, to provide electrocorticography measurements from a relatively large area of the brain surface. The technology could prove very useful for brain surgeons who wish to map regions of the brain that may be triggering epileptic seizures and then target these lesions surgically. Reducing the area of the skull that is removed during surgery helps to speed patient recovery and reduce the trauma associated with such procedures. The low profile, flexible nature, and spiral arm design of this device mean that it is well suited for minimally invasive delivery through a 2 cm hole in the skull.

Minimally invasive delivery of medical technologies inside the body has a host of benefits for patients, including reduced tissue trauma and recovery times. However, designing equipment that can pass through a tiny hole and then still function effectively on the other side requires some ingenuity. The researchers behind this latest technology were asked by a neurosurgeon to design a cortical electrode that could pass through a small hole in the skull, but which could still provide data on electrical activity for a much larger area of the brain.

“Minimally invasive neurotechnologies are essential approaches to offer efficient, patient-tailored therapies,” said Stéphanie Lacour, a researcher involved in the study. “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.”

The hole through which the electrode must pass was approximately 2 cm in diameter and then once inside the skull, the electrode had to be deployable in the space between the brain and skull, a tight 1 mm squeeze. The resulting design includes six spiral arms that are designed to maximize contact between the electrode and the brain. The device can stretch to a diameter of 4 cm across the surface of the brain when fully extended, and is delivered through a cylindrical tube in a folded state.

The technology also exploits an eversion actuation mechanism to gently open each arm over the surface of the brain, one at a time. “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,” said Suhko Song, another researcher involved in 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.”