Polyimide-based intracortical neural implant with improved structural stiffness

A novel structure for chronically implantable cortical electrodes using polyimide bio-polymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and the skull and at the brain/implant interface and stiffness for better surgical handling. A 5-10 mum thick silicon backbone layer was attached to the tip of the electrode to enhance the structural stiffness. This stiff segment was then followed by a I mm flexible segment without a silicon backbone layer. The fabricated implants have tri-shanks with five recording sites (20 mum x 20 mum) and two vias of 40 mum x 40 mum on each shank. In vitro cytotoxicity tests of prototype implants revealed no adverse toxic effects on cells. Bench test impedance values were assessed, resulting in an average impedance value of similar to2 MOmega at 1 KHz. For a 5 mum thick silicon backbone electrode, the stiffness of polyimide-based electrodes was increased ten times over that of electrodes without the silicon backbone layer. Furthermore, polyimide-based electrodes with 5 mum and 10 mum thick silicon backbone layer penetrated pia of rat brain without buckling that has been observed in implants without silicon reinforcement.