Stephanie Lacour has developed adaptable electrodes that have the potential to adjust to a moving body. The electrodes were developed following a request from a neuroscientist to develop minimally invasive electrodes for inserting through a human skull
The difficulty? To insert a huge cortical electrode array via a small hole in the skull, deploying the device in a space that quantifies around 1 mm between the skull and the surface of the brain—in the absence of damaging the brain.
Minimally invasive neurotechnologies are essential approaches to offer efficient, patient-tailored therapies. 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.
Stéphanie Lacour, Professor, Neuro X Institute, Ecole Polytechnique Fédérale de Lausanne
Right from the shape of its spiraled arms to the deployment of every arm on top of highly sensitive brain tissue, every aspect of this electrode is clever engineering.
The prototype developed comprises an electrode array that matches via a hole 2 cm in diameter, but when deployed, extends throughout a surface that is almost 4 cm in diameter. It consists of six spiraled-shaped arms, to optimize the surface area of the electrode array, and thus several electrodes in contact with the cortex. Straight arms lead to irregular electrode distribution and less surface area in contact with the brain.
Slightly like a spiraled butterfly elaborately squeezed within its cocoon before metamorphosis, the electrode array, complete with its spiraled arms, has been neatly folded up within a cylindrical tube, that is, the loader, all set for deployment via the small hole in the skull.
As a result of an everting actuation mechanism motivated by soft robotics, every spiraled arm is softly deployed one by one over sensitive brain tissue.
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. 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.
Suhko Song, Study Lead Author, Ecole Polytechnique Fédérale de Lausanne
The electrode array looks like a type of rubber glove, with adaptable electrodes patterned on one side of each spiral-shaped finger. The glove has been inverted, turned inside-out and folded within the cylindrical loader. For deployment, liquid has been inserted into every inverted finger, one at a time, turning the inverted finger right side out as it develops over the brain.
Also, Song explored the concept of rolling up the arm of the electrode as a plan for deployment. However, the longer the arm, the thicker it turns out to be when rolled up. If the rolled-up electrode becomes highly thick, then it would unavoidably take up much space between the skull and the brain, thereby placing risky amounts of pressure on the brain tissue.
The electrode pattern has been produced by the evaporation of flexible gold onto highly flexible elastomer materials.
Up to now, the deployable electrode array has been tested successfully in a mini-pig. Currently, the soft neurotechnology will be scaled by Neurosoft Bioelectronics, an EPFL spin-off from the Laboratory for Soft Bioelectronic Interfaces, which will result in its clinical translation. Recently, the spin-off was granted 2.5 million CHF Swiss Accelerator by Innosuisse.
Song, S., et al. (2023) Deployment of an electrocorticography system with a soft robotic actuator. Science Robotics. doi.org/10.1126/scirobotics.add1002.