Conference on Cell Interfacing Technology and Applications edition:1 location:Leuven date:4-5 October 2012
The development of high resolution, long lasting neural electronic interfaces is essential both for basic neurophysiological research as well as for the development of advanced sensory and motor prostheses based on retinal, cortical or sensory nerve implants.
In this article, we present a prototype of a novel type of microelectrocortographic (µECoG) electrode array, intended to be placed directly on the cortex.
The electrode arrays differ on two points from state of the art thin film electrode arrays: first, the insulating layers are finely patterned into spring-like structures, increasing the flexibility of the electrode, allowing stretch and conform better to a quasi spherical cavity surface.
Second, the thin film structure of the electrode array is reinforced with a porous layer of resorbable chitosan which ensures it is stiff enough for practical handling during the implantation procedure and adds haemostatic and antiseptic properties to the implant.
In this work, it is shown to be possible to fabricate thin (2-10 µm), lithographically structured neural electrode arrays reinforced with a porous 100 µm thick matrix of the resorbable material chitosan (Figure: fabrication process). It is shown possible to reliably fabricate 10 µm wide, mm-long freestanding ‘antenna shaped’ electrodes with this process, consisting of a platinum conductive layer surrounded by polyimide or Parylene C dielectric.
Finite element analysis of the tested design shows a 40% lower energy needed to bend the designed array in a spherical shape, compared with an unpatterned sheet-like design.
In vitro testing in saline shows acceptable electrode impedances.
In vivo testing on four Wistar rats is going on. On a regular schedule, the rat is sedated and the forepaw is electrically stimulated using a 1 ms wide bipolar pulse.
Both the stimulus artifact as well as a physiological reaction of certain regions of the sensorimotor cortex can be detected with the electrode arrays, up to at least six months after surgery in case the electrode is placed on the meninges. When it is placed directly on the brain, with meninges removed, long term recording is more problematic due to increased tissue reaction, and physiological reaction could only be detected in 25% of channels.