Deployable Soft Microelectrode Arrays for the Brain

Electrocorticography (ECoG) is an invasive approach to map cortical activity of the exposed cerebral cortex. Electrodes in form of a linear strip or two-dimensional grid embedded in a silicone membrane are surgically positioned on the cortex, epi- or subdurally. This neurotechnology is extensively used to identify epileptic foci of drug-resistant epilepsy and increasingly explored in brain-machine interfaces. However, the size of the craniotomy i.e. the exposed cortical surface area and its aesthetic and risk consequences, limits the use of the mapping technology in the operating room.<br/>We report on a novel class of ECoG technology that leverages complementary fields of soft robotics and soft bioelectronics. Soft microelectrode arrays embedded in sub-millimetre thick elastomeric membrane are deployed subdurally at the very surface of the cortex via pressure-drive eversion. The deployable system consists of a small pedestal locked on the peripheral cranium of a small circular (centimetric) craniotomy, pre-folded soft arrays mounted in the pedestal and an aqueous solution used to gently push the array in the subdural space. Soft prototypes include up to 24 channels distributed over 6 deployable legs and strain sensors informing in real-time of the status of deployment. In a proof-of-concept acute surgery, the soft ECoG was successfully deployed through a small burr hole on the cortex of a mini-pig and recorded reliably cortical activity. Further refinements are needed, especially in the multi-strip designs and system securing on the cranium but this soft neurotechnology opens promising avenues for minimally invasive cortical surgery.