Implementation of medical grade materials in Soft Neural Implants for Clinical Use

n the context of implantable subdural electrodes, the project aims to facilitate the translation towards clinical use of a new type of neural implants, SOFT ElectroCorticoGraphic (ECoG) electrodes. These soft subdural electrodes present the advantage of being more compliant and less damaging to neural tissue than most of the previous models. The main focus of this project is the silicone material, the substrate of the device, and its interaction with gold layers, which form the interconnects and electrodes and that allow the devices to be stretchable and still conductive after an elastic deformation, thanks to the formation of microcracks. Through electromechanical characterization we tested multiple medical grade materials, and found that two biocompatible silicones, the Silbione® M130 from Elkem and the Nusil™ 4211, meet our expectations, such as electrical resistance stability over stretching cycles. Another aspect of the soft ECoG is its hermeticity towards body fluids. Thus experiments detailed in the report were dedicated to understanding the limits and effects of such body fluids on the bonding of silicone-silicone interfaces through T-peel tests. A final experiment, an adjacent tracks insulation verification on soaking samples, was very promising as samples didn’t show signs of failure for a soaking period of 31 days. Finally, to set the project in the context of the translation towards the clinic, one should be given the administrative and management elements that allow such translation. Hence, a part of this report is dedicated to the synthesis of such requirements, specific to medical grade devices regulation.