Shown here is a cross section of the capsule formed around the lead section of a Peterson type electrode. Here I show you higher magnification of the space occupied by the Teflon coated stainless steel wire and a high magnification of the connective tissue formed in the space between successive coils of the lead wire. The loose collection of collagen fibers mechanically locks the lead in place while permitting relative movement of the wire coils as the lead is flexed. The mechanical locking eliminates relative movement, sliding, between the lead wire and the tissues adjacent to the implant. Eliminating this sliding motion is believed to be a key factor behind the long term, years, functionality observed with this lead. I want to call your attention to the compact layer of cells forming a tight layer adjacent to the Teflon insulation. This layer is formed by fibroblasts, grouped tightly around each other, pulling together, to effectively constrict the capsule around the insulated wire. This tight layer forms a barrier for pathogen invasion into the interior space. This is a transmission electron micrograph of the tight cell layer, from a different experiment, adjacent to a silicone rubber implant. The dense areas at the boundaries between cells are structures identified as desmosomes, which mechanically hold adjacent cells in close proximity and are important in forming the tightness of this layer of cells adjacent to a biocompatible material.
Corey, J. M. (1990) Tissue Response and Corrosion Studies of the Peterson Type Intramuscular Electrode, Master of Science, Case Western Reserve University.
Grill, WM, (1992) Electrical Properties of Electrode Encapsulation Tissue, Master of Science, Case Western Reserve University.