I want to turn your attention to tissue encapsulation of electrodes and leads. When we build a neural prosthesis, our objective is to place an electrode, in a stable location, and close to the target tissue. The electrode location is most likely some distance from the electrical current source, requiring a conduction lead, probably a metal. For these purposes I’m going to assume that the materials use in the electrode are “biocompatible”, meaning that they do not elude something that produces at chronic inflammatory response that would compromise the functionality of the implanted device. Teflon, silicone rubber, platinum, and stainless steel are commonly use materials and are believed to qualify as biocompatible.
The cells that develop around our implant, encapsulate the device. This encapsulation provides two very important functions: First it mechanically stabilizes the position of the electrode relative to the target tissue, and second, it provides a barrier to pathogens that could compromise the life-time of the device.
Shown here is a cuff type electrode fabricated from silicone rubber, having a platinum contact, and a Teflon insulated stranded stainless steel lead for connection to a stimulator either inside the body or, outside, making it a percutaneous lead in that case. The lead is shown here in a scanning electron micrograph. The tissue layer encapsulating the lead section is shown here and the encapsulation surrounding the silicone rubber cuff is shown here. In my judgement, the ideal encapsulation is a thin sheet of tightly connected cells; thin to minimize the current scattering barrier and tight to maximize the efficacy as a pathogen barrier.